Professor Rex Thorpe

Experiments have been carried out using glass ballotini and diakon spheres in water, to study the flow behaviour of solid-liquid mixtures of high solid fraction from storage vessels such as hoppers. A theoretical model has been developed to predict the discharge rates from hoppers of the solid and the liquid in the mixture. This model is modified from the theory proposed for the discharge of dry powders from hoppers which have been pressurized by a gas. The solid flow rate W was experimentally found to have a similar relationship with the pressure drop DELTA-P to that of the air-assisted flow of dry particulates, i.e. W(2) is proportional to DELTA-P. Good qualitative agreement between the experimental results and the theory has also been obtained. The introduction of a discharge coefficient C(D) in the model enabled a good correlation with the experimental results. The average value of C(D) obtained from the various experiments was found to be about 0.42. This value is disappointingly low which leads to the conclusion that some aspect of the mechanics has not been included in the model. A more practical objective of this work was to understand the factors which affect the production of a consistent homogeneous food product of high particulate content for aseptic packaging.

A force balance is derived for a hemispherical particle in the viscous boundary layer at the wall of a horizontal pipe conveying Newtonian fluid; the hemisphere, of radius much less than that of the pipe, rests on the bottom with its flat face against the wall. The drag on the hemisphere is calculated from the creeping flow field of Price (Q. J. Mech. Appl. Math. Pt. 1 (1993)). This yields a prediction of the maximum velocity gradient at the wall for equilibrium, with limiting friction between the hemisphere and the wall. It is shown that the flow field of Price predicts a zero lift force but the validity of this, for actual flows, is questioned. Use of a hemisphere formulates a relevant well-posed problem, capable of mathematical solution. However, the flow field around real particles, e.g. sand, is complex, because of their irregular shapes, but the hemisphere work gives a qualitative indication of the behaviour of irregular particles. For turbulent flow in a pipe it is pertinent to consider a particle wholly within the viscous sub-layer, because it is isolated from significant turbulence and therefore hard to move; for such flow, the theory gives Eq. (21) to predict the critical pipe velocity, v C , for incipient motion of the hemisphere. For laminar flow, the wall shear rate is readily obtained from the parabolic velocity profile leading to Eq. (26) for v C . The flow field of Price (and therefore the force acting on the hemisphere) is valid only for creeping flow (i.e. very low particle Reynolds number). Modifications to the force balance are tentatively suggested to account for inertial components to the drag force. The predictions of critical velocity are tested against our data for the incipient motion of small hemispheres at pipe walls in hydraulic conveying as well as new and previously published data for both hydraulic and pneumatic conveying. The new method of predicting incipient motion works well for both the pneumatic and hydraulic conveying of hemispheres and sand shaped particles but it overpredicts the critical velocity for more rounded particles. The dependency of critical velocity on particle shape is under-researched.

The UK is a global leader in the decarbonisation of its electricity grid to meet zero-carbon targets. However, the main renewable sources, wind, and solar are intermittent and weather dependent. Therefore, other flexible sources need to be able to rapidly increase generation when needed. In this context, electricity generation from anaerobic digestion (AD) of sewage sludge has been traditionally operated as a baseload provider (i.e. steady biogas production rate and electrical output). This work challenges such a traditional approach and aims to investigate how the sewage sludge-to-electricity generation system can provide flexible renewable power generation. Specific feeding regimes were designed following an analysis of the power grid balancing services, to increase the biogas production rate when needed. These feeding regimes were tested at incremental experimental scales. Multiple AD conditions were tested at a pilot scale (50 l) in a controlled environment, which proved the potential economic and environmental benefits. Then, the most challenging conditions were tested at a demonstration scale (18 m3), which confirmed the results obtained at the pilot scale in a relevant operational environment. This research work proved that by implementing an appropriate control of AD, the process can produce more biogas in peak periods to generate electricity when the grid’s prices and carbon emissions peak, unlocking the potential for full-scale implementation.

For many gas turbine architectures a failure modes and effects analysis identifies a potential mode in which failure of an oil transfer pipe could result in oil leakage into the secondary air system. Such an event would result in a complex two-phase interacting flow The atomisation and transport of the oil within the air system is of interest, but is difficult to predict. Available data for the droplet size resulting from jet breakup in cropflow are limited. A dimensional analysis shows jet breakup in a crossflow to involve many factors. The atomisation process has been shown experimentally to include many physical processes and is still not completely understood. Current v, the most practical method of modelling these breakup processes in sprays is by using a CFD package with a set of sub-models within an Euler-Lagrangian (discrete-droplet) approach, The strengths and weaknesses of each of these sub-models cannot reasonably, he tested when used in combination with other approximations to model a spray in crossflow. The purpose of this study was to assess various submodels for liquid breakup with a series of simple test cases.

The onset of convection in a thermal layer generated by transient heat conduction in deep fluid is examined. It is generally accepted that buoyancy driven convection predominates in deep fluids while surface tension driven convection can occur only in very thin layers of liquid. The occurrence of buoyancy convection can be predicted from conventional linear stability analysis for steady-state heat conduction. Its results are summarised in terms of critical Rayleigh numbers. The point of instability in transient heat conduction is, however, less well understood. Its onset in deep fluids is determined by the mode and rate of cooling. In this paper, the judicial application of transient heat conduction equations and a newly defined transient local Ra with the appropriate boundary conditions has allowed the tracking of the time and spatial development of local hydrodynamic equilibrium to the point of instability. The onset of convection can be predicted from the maximum transient Ra whose values are the same as those previously obtained by linear stability analysis for the same boundary conditions. The critical times and critical depths for stable diffusion in fluids (i.e. without convection) can thus be determined accurately. Agreement with observed values from the literature is very good. The mode and rate of heat conduction are confirmed to be the controlling factors in determining the time of onset of convection.

Moisture migration occurring during storage in multicomponent food systems is one of the most common problems facing the food manufacturing industry. An example for such a food system is a mass of ice cream in contact with a wafer. In this work, a dynamic moisture migration model for a confectionery food system consisting of a wafer separated by a moisture barrier from a high water activity component (e.g. ice cream) is developed. The 1D diffusion equation was solved for the barrier and wafer each having different transport properties. The developed model predicts the moisture content of the wafer in different locations throughout the product’s shelf life.

This paper presents theoretical and experimental work on the effect of interstitial air pressure on the flow of granular materials from hoppers. In the first part of the paper, a theory is developed for the case of low Reynolds number flow in a conical hopper. In subsequent sections, the theory is extended to cylindrical bunkers, to higher Reynolds numbers, (where inertia effects cannot be neglected) and to cases where the compressibility of the gas is important. In all cases, the theory agrees well with experiment.

The onset of convection caused by surface tension (ST) during transient cooling of a thin layer of liquid is investigated. This study shows that it can be predicted by a newly defined transient Marangoni number Ma, which incorporates the mode and rate of cooling, where a non-linear temperature profile develops continuously until instability sets in. The spatio-temporal development of local hydrodynamic equilibrium can thus be traced to the point of instability. The onset of convection for evaporative-cooling can be predicted from the maximum transient Ma whose values are the same as those previously obtained by linear stability analysis for Biot number=0. The critical times and critical depths for stable heat conduction in liquids (before convection) can thus be determined accurately. Agreement with observed values from the literature is very good. The critical transient Marangoni numbers and the sizes of convection cells have also been predicted with reasonable accuracy. A theoretical limiting depth that demarcates between surface tension and buoyancy controlled convection is proposed. There exists theoretical and laboratory evidence to support that surface tension dominates in fluid depth less than 5 mm and buoyancy predominates over 10 mm.

A model for the incipient motion of a particle resting on a bed of like particles carried by a submerged oscillating plate is presented. The model is developed by extending the theory of Stevenson et al. (Chem. Eng. Sci. 57, (2002) 4505) who gave a force balance for limiting equilibrium of a particle within the viscous sublayer at a pipe wall to the present case by including a d'Alembert type force due to the oscillatory motion of the plate. Simultaneous equations are presented that can estimate the phase and frequency of first motion as a function of system parameters. The new model is compared with the data of Bagnold (Proceedings of the Royal Society, London A 187, (1946) 1–15) and is shown to be in excellent agreement.

A novel, non-intrusive method is described for measuring the particle residence time distribution (RTD) in a system with a short mean residence time. The method uses phosphorescent tracer particles activated by a high intensity pulse of light at the inlet. Tracer is detected using a light sensitive photomultiplier unit. Appropriate boundary conditions are maintained by using an annular feeder fluidised bed at the entrance boundary and an inline jet mixer installed at the exit boundary. This well defined arrangement of experimental boundary conditions represents a significant advance in the measurement of unbiased particle RTDs in these systems. The method was developed for measuring the particle RTD in a circulating fluidised bed (CFB) riser, but is applicable to other particle–fluid systems where a fast response measurement is required.

The interstitial voidage profiles prevailing in static and flowing beds of nearly buoyant granular materials in aqueous solutions are measured directly by scanning with the use of γ-ray tomography, the contents of a mass-flow hopper and vertical stand-pipe system. In a series of ‘start-stop’ flow and ‘steady-state” flow experiments, horizontal line profiles, and radial profiles of interstitial voidage are produced at different heights within the conical hopper and vertical stand-pipe sections. The voidage profiles obtained within the static beds prior to the onset of discharge are compared with the profiles measured at the same heights during batch discharge of the hopper contents. Furthermore, the plane mean values of the flowing bed voidage are calculated at different heights using the cross-sectional profiles of voidage obtained under the steady discharge condition. The resulting vertical profiles of plane-mean voidage obtained with three different food analogues are found to reveal hitherto unavailable and highly significant new information about the transitions accompanying flow between the packed-bed and settling-suspension states as a function of the mixture discharge rates and the single particle properties, such as particle size, shape, and particle density. The experimental results presented here are subsequently incorporated into simple mean-field models (ignoring interparticle and wall frictional effects) which are used to calculate slip velocities of the particle phase, interstitial pore pressures due to the fluid phase, as well as the observed variation of the discharged solids concentration with the mixture discharge rate. The model predictions are compared with experimental measurements in Faderani et al. (1998, Chem. Engng Sci. 53, 575).

A theory of formation of transient thermals or plumes generated by unsteady-state heat conduction is proposed. Rising or falling mushroom-shaped plumes formed during transient heating or cooling, respectively, originate from the extending thermal boundary layers. The sizes of the hemispherical caps of the plumes can be predicted from the critical wave number and the corresponding Biot number from linear stability analysis, and the critical depth of transient heat conduction at the onset of convection. The rate of generation and size of the hemispherical cap of the thermal are determined by the mode and rate of transient heat conduction, which is characterised by the Biot number. The critical sizes of the plumes are found to be proportional to the square root of the critical times for onset of convection. Equations of critical sizes of plumes for various Biot numbers and a combination of free and solid surfaces are derived. Agreement with observed values for evaporating cooling from the literature is very good, while it is fair for fluids subjected to bottom heating.

The onset of convection induced by transient heat conduction in deep fluid is examined for two boundary conditions, namely: fixed surface temperature (FST) and linear rate of change of surface temperature with respect to time (LTR). Transient Rayleigh numbers ( Ra) for these boundary conditions are defined for each of the respective modes of heat transport. It is found that the onset of convection can be predicted from a maximum transient Ra if its corresponding Biot number ( Bi) is known. Hence the critical times and critical depths for stable heat conduction in fluids are obtained. However, the Biot number for an interface in an unsteady-state experiment is difficult to determine. A transient Biot number is defined to allow the evaluation of Bi between Bi=0 and ∞. The onset of convection for a FST boundary has yet to be verified experimentally, although it has been shown to be valid in analogous gas absorption experiments. The LTR model is found to have no distinct value of Biot number, which could lie between those of CHF (constant heat flux) and FST. The purported LTR experiments were difficult to verify because surface temperature profiles were generally non-linear and the Biot numbers for the system under study could not be determined with certainty. In all cases the critical magnitude of the maximum Rayleigh number for each mode of heat conduction is unique and is independent of the critical time and the depth of the fluid.

The onset of convection induced by buoyancy caused by interfacial gas diffusion in deep fluids is analysed. It was found, as in heat transfer, that transient convection during mass diffusion is dependent on a Biot number. A transient diffusive Biot number ( Bi D ) was defined such that Bi D =0 and ∞ correspond to constant mass flux (CMF) and fixed surface concentration (FSC) boundaries, which have theoretical critical Rayleigh numbers of 669 and 1100, respectively. Transient Rayleigh numbers were derived for both boundary conditions. Experiments of soluble and sparingly soluble gases diffusing in water were found to agree very well with the theory advanced in this paper for the onset of convection in accordance with CMF and FSC models. The stable diffusion times were also predicted accurately for both gases. They also represent the theoretical time limits for the gas penetration theory, which relies on Fick’s law that assumes no convection. The horizontal dimension of the plunging plumes was also predicted with reasonable accuracy. Monolayer formed by surfactant was found to produce an FSC boundary for a soluble solute and to render the liquid surface rigid and prolonged the onset of convection.

The effects of liquid physical properties on the hydrodynamic forces acting on pipe bends in two-phase slug flow were investigated. The two properties of interest were liquid viscosity and liquid surface tension although density was also changed. Discussion will be centred around the effects of the liquid viscosity and liquid surface tension on the maximum forces acting on a pipe bend, which is important for the design of the bend support system. Comparison between the experimental results and predictions from a one-dimensional model, the piston flow model, proposed by Tay and Thorpe will be presented.

The leakage and transport of oil within secondary air system cavities is of interest in oil and air system design, for which CFD can be used as a predictive tool. This paper focuses on the leakage of oil from cracks into a high speed crossflow, idealised as round nozzles at Weber numbers and momentum flux ratios relevant to those in an aero-engine. Simulations were performed using the Euler-Lagrangian approach implemented in a commercial CFD code (FLUENT), including sub-models for breakup, deforming droplet drag, collisions/coalescence and turbulent dispersion. CFD predictions were compared with experimental data from two independent studies. The calculated position of the centre-of-mass of the spray plume agreed well with experiment in all cases, but the penetration was found to be under-estimated. Differences in droplet sizes between experiments could not be explained by variations in the the gas Weber number alone, and a review of the literature has highlighted the importance of the liquid to gas viscosity ratio in determining droplet size trends. Experimental trends in droplet size with changing viscosity ratios were captured by CFD simulations, and droplet SMD was predicted within 20% of experiment. It is concluded that the sub-models used within an Euler-Lagrangian approach can be useful tools for the prediction of droplet size, although further improvements in breakup and coalescence modelling will be necessary if greater accuracy is required.

In this paper the experiments of Fickie (1989) on the density of a granular material flowing through a wedge-shaped hopper are discussed with respect to their impact on the theoretical modelling of the flow from a hopper or bin under the influence of gravity. It is concluded that the degree of dilation found in these experiments is most significant. Furthermore, the experiments suggest that the material is less dense at the outlet than might be expected from the current theory. This in turn suggests that no discontinuity in the stress and velocity fields is needed to model the flow. The dilation is capable of reducing the flow so much that the challenge to the theoretician is no longer to find ways of increasing the dissipation of energy in their models but to decrease it.

Thermal hydrolysis has proven to be an efficient pre-treatment process for sludge before anaerobic digestion (AD), by thermally enhancing organic matter hydrolysis. Recent research has shown that a new configuration with the existing technology can further enhance the efficiency of the system. The intermediate thermal hydrolysis process (ITHP) has been explored and tested in the Sludge and Energy Innovation Centre pilot plant located at Basingstoke sewage treatment works for a period of 15 months. The pilot facility has allowed operational considerations to be explored and understood to inform the design and construction of full scale. ITHP results showed a volatile solids destruction of 64% and an average overall specific gas production of 503 m(3)/TDS. Furthermore, techno-economic analysis was used to compare conventional thermal hydrolysis process (THP) with surplus activated sludge (SAS) only THP and ITHP. Data captured from operational sites, laboratory scale experiments and the large scale ITHP pilot plant, was used in the model. The results showed that ITHP offers an excellent solution for energy recovery having the best economic return, but overall the largest CapEx. SAS only THP is the cheapest to build but does not perform as well as conventional THP and ITHP. Conventional THP remains an excellent solution when space and AD volume is constrained.

Correlations for predicting the properties of clusters of particles travelling near the riser wall are presented. The correlations were developed from experimental data published in the literature on vertical risers ranging from laboratory to industrial scale. Expressions are presented for predicting the size, shape, density, wall film coverage and velocity of particle clusters. These expressions should prove useful in the development of heat transfer and process models for gas–solid riser flow.

This paper gives experimental measurements of the particle residence time distribution (RTD) made in the riser of a square cross section, cold model, circulating fluidised bed, using the fast response particle RTD technique developed by Harris et al. (Chem. Eng. J. 89 (2002a) 127). This technique depends upon all particles having phosphorescent properties. A small proportion of the particles become tracers when activated by a flash of light at the riser entry; the concentration of these phosphorescent particles can subsequently be detected by a photomultiplier. The influence of the solids circulation rate and superficial gas velocity on the RTD were investigated. The results presented are novel because (i) the experiments were performed in a system with closed boundaries and hence give the true residence time distribution in the riser and (ii) the measurement of the tracer concentration is exceedingly fast. The majority of previous studies have measured the RTD in risers with open boundaries, giving an erroneous measure of the RTD. Analysis of the results suggests that using pressure measurements in a riser to infer the solids inventory leads to erroneous estimates of the mean residence time. In particular, the results cast doubt on the assumption that friction and acceleration effects can be neglected when inferring the axial solids concentration profile from riser pressure measurements. An assessment of particle RTD models is also given. A stochastic particle RTD model was coupled to a riser hydrodynamic model incorporating the four main hydrodynamic regions observed in a fast-fluidised bed riser namely (i) the entrance region, (ii) a transition region, (iii) a core-annulus region and (iv) an exit region. This model successfully predicts the experimental residence time distributions.

In the present investigation, pyrolysis and gasification, two widely used thermochemical processes, are compared as potential chemical recycling methods for MWP and plastic rich MSW in terms of products of high value and their end uses. High temperature pyrolysis results in a wide spectrum of products which also contain monomers of C2-C4 range such as ethylene and 1,3-butadiene. Recovery of monomers from their isomers and other products is difficult and energy-intensive. Gasification breaks solid wastes into simple molecules (mainly CO & H2) which subsequently can be converted to value added liquid chemicals (namely alcohols) by a catalytic synthesis processes. Synthetic alcohol then can be converted to the desired petrochemical precursors. After reviewing different aspects of both pyrolysis and gasification, recycling through gasification is chosen as the preferred route for project SPORT as syngas product can be converted into several key petrochemical products in high yield.

Three different solid-liquid food analogues and one model food were used in a series of flow experiments in a model conical hopper and vertical stand-pipe system. The mixture discharge rates, the liquid fraction in the discharge and the differential pore pressures set up during flow along the hopper and stand-pipe walls were monitored. The liquid fraction in the discharge decreases from an asymptotic limit set at high mixture rates to values considerably less than 0.5 as the discharge rate is reduced. Individual solid particle properties affect both the value of the critical discharge rate, below which the discharge has a higher solid content and the limiting value of the discharge rate, above which the liquid content remains unchanged. The results obtained with near-spherical particles couple well with the tomographic observations of the corresponding flow fields presented in Part I (Faderani et al., 1998, Chem. Engng Sci. 53, 553), which indicate the onset of a settling suspension well within the conical hopper at low mixture-discharge rates but a packed-bed flow extending almost to the plane of the hopper orifice as the mixture rate is increased. With cylindrical particles, the packed-bed to settling suspension flow transition is postponed to occur within the vertical stand-pipe resulting in a high liquid content in the discharge even at small-mixture discharge rates. The profiles of pore pressure measured along the hopper and stand-pipe walls during steady discharge agree well with the observed flow regime transitions and the changes in the liquid content of the discharge. The values of pore pressures corresponding to the packed-bed flow regime are compared with the predictions based on a modified form of the Ergun equation first proposed by Mills Lamptey and Thorpe (1990, Chem. Engng Sci. 46, 2197). The interstitial fluid pressures measured in the suspension regime are also compared with the theoretical predictions corresponding to the incipient settling condition. Good agreement with experiment is reported in both regimes when the transition from packed-bed to settling suspension occurs at the vicinity of the hopper orifice. A simple, first-order theoretical treatment based on Wallis' Drift-Flux Model (1969, One-dimensional Two-phase Flow, McGraw-Hill, London) explains well the observed relationships between the mixture discharge rates, the voidage profiles within the flow field and the liquid content of the discharge.

The dispersion of bubbles into down-flowing liquids is often encountered in a number of industrial applications involving pipe flow, bubble columns and loop reactors. Usually a gas horizontal sparging device is used to generate bubbles that are carried downward with the bulk liquid flow. At low gas flowrates discrete bubbles are formed. However, at higher gas flowrates a ventilated cavity attached to the sparger is formed. For downward pipe flow the liquid forms an annular jet, which entrains gas into the recirculation region immediately beneath the ventilated cavity. The rate of gas entrainment and the size of the bubbles produced is determined by the pipe diameter, liquid and gas volumetric flowrates and the strength of the recirculation region below the base of the ventilated cavity. In this study a model was developed to predict the liquid velocity field and bubble breakup in the recirculation region. The velocity profile was modelled using the potential flow solution of the Hill's vortex, where the strength of the vortex was assumed to be directly proportional to the velocity of the annular wall jet. The proportionality constant was found to be 0.38, based on predictions obtained using the commercial code CFX. The CFX velocity profile predictions for the central part of the recirculation region were very similar to the Hill's vortex velocity profile. Bubble breakup was modelled using a critical Weber number concept, based on the predicted velocity profile within the recirculation region. It was found that the prediction of bubble size was in general agreement with experimental observations when a critical Weber number of 4.7 was assumed. A digital high-speed video was used to observe the liquid and bubble motion at the base of the ventilated cavity. The video was used to obtain estimates of the recirculating liquid flow velocity, which compared reasonably well with predictions based on the Hill's vortex model. The video evidence also highlighted the unsteady nature of the flow, particularly the actual gas entrainment process, and possible reasons for this behaviour are presented.

The transient temperature distribution and volumetric heat transfer coefficient during the inception of flooding in a three-phase bubble type direct contact condenser have been experimentally investigated. The flooding mechanism and the factors affecting the onset of flooding of the three-phase direct contact column are not considered. A short Perspex column of 70 cm total height and 4 cm internal diameter utilising two immiscible fluids was studied. Pentane vapour with initial temperatures of 40 degree C, 43.5 degree C and 47.5 degree C was the dispersed phase and tap water at a constant temperature (19 degree C) was the continuous phase. Only 48 cm of the column was used as the active height and different mass flow rates of both phases were used. The experimental results showed that the instantaneous temperature distribution along the direct contact column tends to be uniform when the direct contact column is working under flooding conditions. Furthermore, the volumetric heat transfer coefficient increases as the dispersed mass flow rate is increased towards the flooding limit and remains constant along the column height. In addition, the dispersed phase mass flow rate that leads to flooding increased with increasing mass flow rate of the continuous phase. The initial temperature of the dispersed phase did not have a considerable effect on the flooding inception limit under the present experimental conditions.

The onset of instability induced by transient momentum diffusion in a boundary layer over an impulsively started rotating cylinder is examined. Kirchner and Chen (J. Fluid Mech. 40 (1970) 39) have conducted experiments and reported anomalously large Taylor numbers of up to 20×10 6, far exceeding the well-known value of 1708 for Taylor vortices in steady flow. In this paper, we argue that it is inappropriate to treat the phenomenon as a steady-state wide-gap Couette flow, because the unstable boundary layer in their experiments was very thin. The instability in the fluid induced by momentum diffusion is an unsteady-state phenomenon analogous to transient thermal instability, whose mathematical equivalence for the steady-state cases have been established by Taylor (Philos. Trans. R. Soc. London A 223 (1923) 289). We find that the onset of instability can be predicted from a transient Taylor number defined as Ta= y 5( ∂u/ ∂y) 2/ ν 2 R i . The maximum transient Taylor number is found to occur at a critical depth y max = 5νt c , where Ta max=1.461 U i 2( νt) 1.5/ ν 2 R i . Ta max bears a theoretical critical value of 1100 from linear stability analysis. The experimental data of Kirchner and Chen (J. Fluid Mech. 40 (1970) 39) agree remarkably well with this value. The critical time can thus be predicted with good accuracy from a critical value of the maximum transient Taylor number of 1100. The theoretical critical dimension of the toroidal plume formed after the boundary layer becomes unstable is found to be λ c=5.24 νt c , which agrees well with measurements. The average critical dimensionless wavenumber of the experiments of Kirchner and Chen (J. Fluid Mech. 40 (1970) 39) is found to be 3.05, which is very close to the theoretical value of 2.9.

The testing of granular materials for silo design is most commonly carried out using a Jenike shear cell. The alternative instrument is an annular shear cell, which is used less widely. In this paper we draw attention to the many merits of the annular shear cell. During the operation of an annular shear cell a peak shear stress is observed on the consolidation of loosely filled samples of coarse (above 1 mm diameter) granular materials. By the use of a power balance on the vertical displacement of the shear cell lid, we show experimentally that the peak is a consequence of the extra work expended in lifting the lid when the granular material dilates to accommodate shear. If not properly accounted for, this peak shear stress could erroneously be attributed to cohesion. This observation has consequences for the Jenike flow function and effective angle of internal friction of coarse granular materials. We further demonstrate that our observations made on an annular shear cell are compatible with similar observations previously made on sand in a simple shear box, at higher stress levels.

A set of stochastic mathematical models have been developed to simulate the residence time distribution of solids in the riser of a circulating fluidised bed. The models simulate the motion of single particles moving up and down the riser using a Markov chain. Two models are presented in detail: (i) a core-annulus solids interchange model, and (ii) a four zone model that follows from the fast fluidised bed hydrodynamic profile. Both discrete and continuous time versions are presented. Each model incorporates different sections to account for the different flow regimes that exist within a riser. Simulations are linked to actual experimental conditions using local particle transfer rates between each model section. Simulations are able to predict the influence of changes in the solids flux, riser height and riser exit geometry. The influence of core-annulus solids transfer is also investigated. Comparison with a range of experimental data is presented.

This paper reports measurements of the influence of riser exit geometry upon the particle residence time distribution in the riser of a square cross section, cold model, circulating fluidised bed. The bed is operated within the fast fluidisation regime. The fast response particle RTD technique developed by Harris et al. (Chem. Eng. J. 89 (2002) 127–142) was used to measure the residence time distribution. The geometry of the riser exit is shown to have a modest but consistent influence upon the particle RTD; the influence of operating conditions, i.e. superficial gas velocity and solids flux is more significant. Increasing the refluxing effect of the riser exit increases the mean, variance and breakthrough time and decreases the coefficient of variation of the residence time distribution. Changes in reflux do not have a systematic effect upon the skewness of the RTD.

Dissolved air flotation (DAF) is often used after a primary gravity separator to enhance the quality of wastewater, so it can be released to streams, rivers or the sea. The main aim of the DAF experiments reported here was to measure the oil droplet removal efficiency, (η) mostly in the range 15-80 μm from oil-in-water mixtures. The DAF tank used in this investigation was a scale model of real DAF unit. Two kinds of oil, vegetable and mineral and two types of water, fresh and salty were used, and four other operating parameters were varied. A droplet counting and oil-in-water measuring methods were used to estimate the η. Dimensional analysis concluded that the η in this experiment is a function of eight other dimensionless groups and the experimental data has been subjected to multivariable linear regression. The resulting correlation was found to have a root mean square error of 6.0%, but predict η outside the range zero and one. An alternative mathematical formulation was devised that cannot predict η outside the range. Regression of the data by this formulation, which had the same number of adjustable parameters as the linear regression, was successful with a lower root mean square error of 5.5%.

The performance of a particular type of horizontal three phase separator (bucket & weir) was evaluated on the Alba Field, situated offshore of the coast of Equatorial Guinea, by coding a set of equations for the design of the separators. Output parameters such as the oil and water residence times, liquid droplet settling/rising times, minimum lengths for gas-liquid disengagement, and holdup and surge times for the oil bucket and the water compartment, were checked regularly against max/min values for good operation. Thus it was possible to assess the likely behavior of the four Alba field separators to changes in operating variables while also comparing the results obtained from the equations with real field data for performance. The performance of the separators was fairly consistent, even though oils of varying viscosity and temperature were processed. The values of parameters at which performance deteriorated was somewhat different from those usually quoted in the literature for good operation. © BHR Group 2007 Multiphase Production Technology 13.

•Five sludge to energy configurations were compared environmentally and economically.•Advanced AD (THP) has advantages over conventional AD.•CHP is environmentally superior to bio-methane injection in the UK.•The UK financial incentives support bio-methane and advanced energy recovery.•Drying post AD creates very attractive energy recovery solutions. The UK Water Industry currently generates approximately 800GWh pa of electrical energy from sewage sludge. Traditionally energy recovery from sewage sludge features Anaerobic Digestion (AD) with biogas utilisation in combined heat and power (CHP) systems. However, the industry is evolving and a number of developments that extract more energy from sludge are either being implemented or are nearing full scale demonstration. This study compared five technology configurations: 1 – conventional AD with CHP, 2 – Thermal Hydrolysis Process (THP) AD with CHP, 3 – THP AD with bio-methane grid injection, 4 – THP AD with CHP followed by drying of digested sludge for solid fuel production, 5 – THP AD followed by drying, pyrolysis of the digested sludge and use of the both the biogas and the pyrolysis gas in a CHP. The economic and environmental Life Cycle Assessment (LCA) found that both the post AD drying options performed well but the option used to create a solid fuel to displace coal (configuration 4) was the most sustainable solution economically and environmentally, closely followed by the pyrolysis configuration (5). Application of THP improves the financial and environmental performance compared with conventional AD. Producing bio-methane for grid injection (configuration 3) is attractive financially but has the worst environmental impact of all the scenarios, suggesting that the current UK financial incentive policy for bio-methane is not driving best environmental practice. It is clear that new and improving processes and technologies are enabling significant opportunities for further energy recovery from sludge; LCA provides tools for determining the best overall options for particular situations and allows innovation resources and investment to be focused accordingly.

Low-grade energy cycles for power generation require efficient heat transfer equipment. Using a three-phase direct contact heat exchanger instead of a surface type exchanger, such as a shell and tube heat exchanger, potentially makes the process more efficient and economic. This is because of its ability to work with a very low temperature driving force, as well as its low cost of construction. In this study, an experimental investigation of the heat transfer efficiency, and hence cost, of a three-phase direct contact condenser has been carried out utilising a short Perspex tube of 70 cm total height and 4 cm internal diameter. Only 48 cm was used for the direct contact condensation. Pentane vapour with three different initial temperatures (40℃, 43.5℃ and 47.5℃) was contacted with water with an inlet temperature of 19℃. In line with previous studies, the ratio of the fluid flow rates was shown to have a controlling effect on the exchanger. Specifically, the heat transfer efficiency increased virtually linearly with this ratio, with higher efficiencies also being observed with higher flow 2 rates of the continuous phase. The effect of the initial temperature of the dispersed phase was shown to have a lower order impact than flow rate ratio. The capital cost of the direct contact condenser was estimated and it was found to be less than the corresponding surface condenser (shell and tube condenser) by 30 times. An optimum value of the continuous phase flow rate was observed at which the cost of the condenser is at a minimum. Keywords: Three-phase direct contact condenser, heat transfer efficiency, costing

A semi-analytical model for the drag coefficient of a swarm of two-phase bubbles, condensing in direct contact with an immiscible sub-cooled liquid, has been developed. The analysis used a cellular model configuration, assuming potential (but not inviscid) flow around the reference two-phase bubble in the cell. The effect of the condensation ratio within the two-phase bubbles was included using an approximate relation. The drag coefficient for a wide range of Reynolds numbers (0.1. ≤. Re. ≤. 1000) has been found using the viscous dissipation integral method, and the effect of the liquid content within the two-phase bubble or the half opening angle (β), and the system void fraction (α) were examined. The drag coefficient has been found to increase with the condensation ratio and with the void fraction of the system. The present model agrees well with previously available experimental data and theoretical predictions for single bubbles or particles.

An experimental investigation of the volumetric heat transfer coefficient in a three-phase direct contact condenser was carried out. A 75-cm long cylindrical Perspex column with a 4 cm diameter was used. Only 48 cm of the column was utilised as the active direct contact condensation height. Pentane vapour at three different initial temperatures (40°C, 43.5°C and 47.5°C), with differing mass flow rates, and tap water at a constant initial temperature (19°C) with five different mass flow rates were employed as the dispersed phase and the continuous phases, respectively. The results showed that the volumetric heat transfer coefficient increased with increasing mass flow rate ratio (variable dispersed phase mass flow rate per constant continuous phase mass flow rate), the continuous phase mass flow rate and holdup ratio. An optimal value of the continuous phase mass flow rate is shown for an individual dispersed phase mass flow rates. This value increases with increasing vapour (dispersed) phase mass flow rate. Furthermore, it was observed that the initial driving temperature difference had no effect on the volumetric heat transfer coefficient. While, the temperature gained by the continuous phase has a considerable effect.

In a net-zero emissions scenario, a secure supply of electricity involves renewable generators that can flexibly increase their production when needed. Currently, electricity generation from biogas in the water industry is most commonly at a steady level, given Anaerobic Digestion (AD) is traditionally operated in steady state. This research demonstrated at different scales that demand-driven biogas production from AD of sewage sludge is feasible. Performance parameters are not negatively affected by a flexible feeding schedule and stability parameters show transitional imbalances that do not threaten the overall process. This paper presents the trial implementation in digesters of volume 3800 m3, which became permanent. Economic and environmental benefits exist; however, in order to unlock the full potential of flexible electricity generation from sewage sludge, synergies between technical, operational and political factors in the water and energy sectors need to be developed.

The process operations and management (POM) module offered by the University of Surrey’s Chemical and Process Engineering Department, in which students take charge of pilot-scale industrial equipment, is thought to create a learning environment which challenges undergraduates to develop their transferable skills. This study aimed to assess how effective the POM module is at improving student perceptions of their transferable skills by using questionnaires. The students reported high learning in the areas assessed, and an increased appreciation for transferable skills. The results indicate that the interest in UK Chemical Engineering departments for using pilot plants as a tool for effective teaching is justified, although care must be taken to make the most of the opportunities they provide when designing the modules that use them.

An experimental investigation of heat exchange in a three-phase direct contact condenser was carried out using a 70-cm-high Perspex tube with a 4-cm inner diameter. The active direct contact condenser comprised 48 cm. Pentane vapour at three initial temperatures (40℃,43.5℃, and 47.5℃) and water at a constant temperature (19℃) were used as the dispersed and continuous phases, respectively, with different mass flow rate ratios. The results showed that the continuous phase outlet temperature increased with increasing mass flow rate ratio. On the contrary, the continuous phase temperature decreased with increases in the continuous mass flow rate. The initial temperature of the dispersed phase slightly affected the direct contact condenser output, which confirms a latent phase effect in this type of heat exchanger.

Experiments are described on the pneumatic conveying of 2.7mm alumina particles up a vertical riser of internal diameter 46.4mm or 71.4mm. The particles entered the riser from a fluidised bed, via a short horizontal pipe and a bend of radius 75mm. Measured variables included solids flow rates, air flow rates, inlet and outlet air pressures P 1 and P 2, and the pressure profile in the riser. The solids flow rate was consistent with some earlier models of similar systems, in which the plugs of packed solids move up at a velocity of about U-U mf, where U=superficial air velocity and U mf=incipient fluidising velocity. Solids-wall friction is significant and suppresses fluidisation. To model the system approximately, a conveying efficiency=(power for air compression)/(rate of gain of potential energy of solids) is defined and correlated against solids flux. It was found that the conveying efficiency tended to an asymptote just above 20%. The correlation led to a tentative design formula, Eq. (6), for predicting P 1-P 2 at a given solids flow rate. P 1-P 2 is typically between 50% and 100% of the pressure drop needed to support a column of solids of height equal to that of the riser.It was concluded that plug flow pneumatic conveying is a satisfactory technology for transporting coarse particles which cannot be conveyed in leaner regimes due to the possibility of pipeline erosion or solids attrition. © 2012 Elsevier B.V.

A SULPHUS™ biotrickling filter (BTF) and an ACTUS™ polishing activated carbon filter (ACF) were used at a wastewater treatment plant to treat 2,432 m3·h–1 of air extracted from sewage sludge processes. The project is part of Thames Water’s strategy to reduce customer odour impact and, in this case, is designed to achieve a maximum discharge concentration of 1,000 ouE·m–3. The odour and hydrogen sulphide concentration in the input air was more influenced by the operation of the sludge holding tank mixers than by ambient temperature. Phosphorous was found to be limiting the performance of the BTF during peak conditions, hence requiring additional nutrient supply. Olfactometry and pollutant measurements demonstrated that during the high rate of change of intermittent odour concentrations the ACF was required to reach compliant stack values. The two stage unit outperformed design criteria, with 139 ouE·m–3 measured after 11 months of operation. At peak conditions and even at very low temperatures, the nutrient addition increased considerably the performance of the BTF extending the time before activated carbon replacement over the one year design time. During baseline operation the BTF achieved values between 266-1,647 ouE·m–3 even during a 6 days irrigation failure of the biofilm.

Trials performed by Thames Water on a Sludge Powered Generator (SPG) have used sludge from a Thermal Hydrolysis Process (THP) as feed. Data from the trials with THP product sludge at Thames Water's Crossness SPGs was subject to data analysis by converting the trial data into flows of operating cost. Sludge is a mixture of many chemicals and these would be very time consuming to analyse for combustion performance in full detail. Therefore sludge has been simplified to a mixture of water and a single combustible chemical component (coniferyl alcohol) with the same heat of combustion as water-free sludge and roughly the right elemental analysis. This simplification enables the thermal behaviour of the combustion, including its tendency to extinguish without support fuel, to be captured. Both the simplified model and the data analysis from the trial show the THP product sludge is a viable fuel which produces a net financial benefit to the SPG’s operation.

This paper outlines the industrial problem of air current segregation in alumina storage silos which occurs with the handling of the feedstock alumina in aluminium plants. One significant parameter, the air extraction rate, was studied in an experimental silo which was manufactured for this purpose. The experiments conducted in small scale devices displayed the interaction between the particle flow and air current segregation. Results from these experiments show that the increase of the silo air extraction rate reduces air current segregation. The dimensional analysis method has been applied to form dimensionless groups out of the significant parameters. Five dimensionless groups were obtained which is unwieldy. To reduce the number of dimensionless groups the physical properties were lumped into the terminal velocity. This simplified approach gives three dimensionless groups. Initial experiments justify further research to establish weather the simplified approach can scale the dynamic of the flow and the degree of segregation from a small scale silo to industrial equipment.

In this paper, the resultant hydrodynamic force ( FR , where 2 2 FR  Fx  Fy ) acting on pipe bends will be discussed. A hypothesis that the peak (resultant) forces, FR, peak acting on pipe bends can be described by the normal distribution function will be tested, with the purpose of predicting the mean of the FR, peak ( FR, mean ) and the standard deviations of the FR, peak ( FR, standard deviation ) generated. This in turn allows prediction of the probability of the largest forces that occasionally occur at various flow rates. This information is vital in designing an appropriate support for the piping system, to cater the maximum force over a long period of operation. Besides, this information is also important in selecting a pipe material or material for connections suitable to withstand fatigue failure, by reference to the S-N curves of materials. In many cases, large numbers of response cycles may accumulate over the life of the structure. By knowing the force distribution, ‘cumulative damage’ can also be determined; ‘cumulative damage’ is another phenomenon that can cause fatigue, apart from the reversal maximum force.

To avoid structural changes within nanofiltration membranes during operation, pre-compaction of filtration membranes is usually performed. However, even after pre-compaction, the NF270 membrane has previously been shown to display a level of pressure susceptibility in pure water systems, particularly evident at low pressures. For the first time, this study provides experimental evidence for the effect of salinity on the pressure susceptibility of the NF270 membrane. Permeability was shown to decrease with increasing salinity up to 189 mM MgSO4, with the largest reduction (22 %) observed at the lowest MgSO4 concentration (31.49 mM MgSO4). A significant reduction (35 %) in the membrane susceptibility was also observed following the introduction of MgSO4 to a concentration of 31.49 mM. A mathematical expression, developed for pure water systems, was modified to account for salinity effects and fitted the experimental data well for concentrations up to 0.2 M. These results are explained by compaction of the membrane polymer, due to either charge neutralisation at the membrane surface, or electric double layer compression, or both. However, further increases in salinity had no significant effect on membrane susceptibility, suggesting that salt induced membrane compaction occurs at very low concentrations.

The power system needs flexible electricity generators. Whilst electricity generation from anaerobic digestion (AD) of sewage sludge has traditionally been baseload, transforming the generation capacity into a modern flexible operator is an opportunity to further valorise the resource. This work aims to demonstrate that AD of sewage sludge can support flexible generation and be operated dynamically in a relevant operational environment, to promote full scale implementation. A demonstration scale plant (20 m3 conventional AD reactors) was used to test several feeding regimes designed to return a biogas production rate that matches the demand. Two demand profiles are defined, either by common corporate power purchase agreements or by the main balancing mechanism used by the grid operator in UK. Demand-driven biogas production is demonstrated in this relevant operational environment, and the flexibilisation performance is positive in all scenarios. The value of the biogas increases by up to 2%, which outperforms the results obtained at pilot scale. Additionally, an increase in biogas yield is observed. Whilst transitional imbalances are recorded, they last for few hours and the overall stability is not affected. In conclusion, these trials demonstrate demand-driven biogas production is a feasible operational solution and full-scale implementation is possible.

The earlier in the development of a process a design change is made, the lower the cost and the higher the impact on the final performance. This applies equally to environmental and technical performance, but in practice the environmental aspects often receive less attention. To maximise sustainability, it is important to review all of these aspects through each stage, not just after the design. Tools that integrate environmental goals into the design process would enable the design of more environmentally friendly processes at a lower cost. This paper brings together approaches based on Life Cycle Assessment (LCA) including comparisons of design changes, hotspot analysis, identification of key impact categories, environmental break-even analysis, and decision analysis using ternary diagrams that give detailed guidance for design while not requiring high quality data. The tools include hotspot analysis to reveal which unit operations dominate the impacts and therefore should be the focus of further detailed process development. This approach enables the best variants to be identified so that the basic design can be improved to reduce all significant environmental impacts. The tools are illustrated by a case study on the development of a novel process with several variants: thermal cracking of mixed plastic waste to produce a heavy hydrocarbon product that can displace crude oil, naphtha, or refinery wax or be used as a fuel. The results justified continuing with the development by confirming that the novel process is likely to be a better environmental option than landfill or incineration. The general approach embodied in the toolkit should be applicable in the development of any new process, particularly one producing multiple products.

In this paper, data is published on the removal of H2S and VOCs by a Biotrickling Filter (BTF) demonstration plant, namely a SULPHUS™, which was installed by Thames Water in late 2015. These data, along with some data already published by Sempere et al. (2018), were compared to the predictions of a number of existing and novel models for the removal of a single pollutant by a biofilm. The two widely used models of Ottengraf and van den Over (1983) were found to be inadequate with sum of squares of errors of 11 and 41 mg2m-6 respectively. These models are based on zero-order kinetics in the biofilm which according to the M-M kinetic model, are likely to be inaccurate at low pollutant concentration. The odour control unit was designed to produce low emission levels of less than 1 ppmv of H2S, rendering the zero-order assumption unlikely to be accurate. A model based on first-order kinetics, which also has some support in the literature, was found to be a better, but not a good, fit to the data with a sum of squares of errors of 4.7 mg2m-6. A novel model for the BTF based on M-M kinetics was found to be a good fit to the shape of the data with the lowest sum of squares of errors of 2.5 mg2m-6. This novel M-M model was also identified as the best fit for VOC data from the same unit. Other publications support the M-M approach with a product of saturation constant and Henry’s Law constant of about 50 mg m-3, which is equivalent to an H2S level in the gas phase of about 40 ppmv. Broad agreement was found between the SULPHUS™, experiments and data in the literature for other BTFs destroying H2S under the zero-order regime, at V_max value of about 0.3 g/m3/s. This paper represents an attempt to harmonise a literature that was previously disparate, which has not previously been attempted.

Computational fluid dynamics (CFD) is a simulation technique widely used in chemical and process engineering applications. However, computation has become a bottleneck when calibration of CFD models with experimental data (also known as model parameter estimation) is needed. In this research, the kriging meta-modelling approach (also termed Gaussian process) was coupled with expected improvement (EI) to address this challenge. A new EI measure was developed for the sum of squared errors (SSE) which conforms to a generalised chi-square distribution and hence existing normal distribution-based EI measures are not applicable. The new EI measure is to suggest the CFD model parameter to simulate with, hence minimising SSE and improving match between simulation and experiments. The usefulness of the developed method was demonstrated through a case study of a single-phase flow in both a straight-type and a convergent-divergent-type annular jet pump, where a single model parameter was calibrated with experimental data.

This study investigates the long-term performance of the mesophilic (35 °C) anaerobic mono-digestion of process waters (PW) from the hydrothermal carbonisation (HTC) of spent coffee grounds. At an organic loading rate (OLR) of 0.4 gCOD L−1 d−1, initial instability was seen, but after 40 days and supplementary alkalinity, the digestion stabilised with the chemical oxygen demand (COD) in the untreated PW degraded with 37.8–64.6% efficiency and the yield of methane at 0.16 L gCOD−1. An increase in OLR to 0.8 gCOD L−1 d−1 caused a collapse in biogas production, and resulted in severe instability in the reactor, characterised by falling pH and an increasing volatile fatty acid concentration. Comparatively, the digestion of a treated PW (concentrated in nanofiltration and reverse osmosis after removal of the fouling fraction), at OLR between 0.4 and 0.8 gCOD L−1 d−1, was stable over the entire 117 days of treated PW addition, yielded methane at 0.21 L gCOD−1 and the COD was degraded with an average efficiency of 93.5% - the highest efficiency the authors have seen for HTC PW. Further anaerobic digestion of untreated PW at an average OLR of 0.95 gCOD L−1 d−1 was stable for 38 days, with an average COD degradation of 69.6%, and methane production between 0.15 and 0.19 L gCOD−1. The digestion of treated PW produced significantly higher COD degradation and methane yield than untreated PW, which is likely to be related to the removal of refractory and inhibitory organic material in the post-HTC treatment by adsorption of hydrophobic material.

This study investigates the recovery of phosphorus from the process water obtained through hydrothermal carbonisation (HTC) of a ‘wet’ biomass waste, namely spent coffee grounds. HTC was shown to liberate more than 82% of the total phosphorus in the grounds in the form of dissolved ortho-phosphate. Nanofiltration was used to concentrate the inorganic nutrients of the HTC process water, achieving a mass concentration factor of 3.9 times. The natural stoichiometry of phosphorus, magnesium and ammoniacal nitrogen in the nanofiltration retentate was favourable for struvite precipitation. 92.8% of aqueous phosphorus was recovered as struvite through simple pH adjustment, yielding a total phosphorus recovery of 75% from the feedstock spent coffee grounds.

The aim of this work was to study the potentials and benefits of dynamic biogas production from Anaerobic Digestion (AD) of sewage sludge. The biogas production rate was aimed to match the flexible demand for electricity generation and so appropriate feeding regimes were calculated and tested in both pilot and demonstration scale. The results demonstrate that flexibilization capability exists for both conventional AD and advanced AD using Thermal Hydrolysis Process (THP) as pre-treatment. Whilst the former provides lower capability, flexible biogas production was achieved by the latter, as it provides a quick response. In all scenarios, the value of the biogas converted into electricity is higher than with a steady operational regime, increasing by 3.6% on average (up to 5.0%) in conventional and by 4.8% on average (up to 7.1%) with THP. The process has proven scalable up to 18m3 digester capacity in operational conditions like those in full scale.

Energy usage is increasing around the world due to the continued development of technology, and population growth. Solar energy is a promising low-grade energy resource that can be harvested and utilised in different applications, such solar heater systems, which are used in both domestic and industrial settings. However, the implementation of an efficient energy conversion system or heat exchanger would enhance such low-grade energy processes. The direct contact heat exchanger could be the right choice due to its ability to efficiently transfer significant amounts of heat, simple design, and low cost. In this work, the heat transfer associated with the direct contact condensation of pentane vapour bubbles in a three-phase direct contact condenser is investigated experimentally. Such a condenser could be used in a cycle with a solar water heater and heat recovery systems. The experiments on the steady state operation of the three-phase direct contact condenser were carried out using a short Perspex tube of 70 cm in total height and an internal diameter of 4 cm. Only a height of 48 cm was active as the direct contact condenser. Pentane vapour, (the dispersed phase) with three different initial temperatures (40℃,43.5℃ and 47.5℃) was directly contacted with water (the continuous phase) at 19℃. The experimental results showed that the total heat transfer rate per unit volume along the direct contact condenser gradually decreased upon moving higher up the condenser. Additionally, the heat transfer rate increases with increasing mass flow rate ratio, but no significant effect on the heat transfer rate of varying the initial temperature of the dispersed phase was seen. Furthermore, both the outlet temperature of the continuous phase and the void fraction were positively correlated with the total heat transfer rate per unit volume, with no considerable effect of the initial temperature difference between the dispersed and continuous phases.

The measurement of kinetic parameters in the pyrolysis of polyolefins requires the use of a lumped kinetic model for predicting the product distribution of wax, oil and gas yields. A non-isothermal method was established, in which a sample is heated in a tube reactor to a desired temperature at a constant rate of temperature rise. This method avoided the error present in the heating up stage which is inherent in any practical isothermal method in which reaction proceeds to a significant extent before the operating temperatures of polyolefin pyrolysis are reached, which results in challenges when defining the reaction time. The non-isothermal measurements were conducted between 450 and 550°C for polypropylene (PP) and polyethylene (HDPE and LDPE) and the temperature and lump yields are non-linearly regressed to achieve the kinetic parameters. The measured kinetic rate constants have the same trend as those reported in the literature using the isothermal method, but are higher than the values reported above 450°C and similar to the values for lower temperatures of 350°C and 370°C. The kinetic parameters derived are then validated by using isothermal experimental data. The calculated data using the measured kinetic parameters are generally in agreement with the experimental data. The non-isothermal method established in this work proves to be a much faster method for the measurement of intrinsic rate constants at high temperatures.

The transient temperature distribution and volumetric heat transfer coefficient during the 16 inception of flooding in a three-phase bubble type direct contact condenser have been 17 experimentally investigated. The flooding mechanism and the factors affecting the onset of 18 flooding of the three-phase direct contact column are not considered. A short Perspex column 19 of 70 cm total height and 4 cm internal diameter utilising two immiscible fluids was studied. 20 Pentane vapour with initial temperatures of 40°C, 43.5°C and 47.5℃ was the dispersed phase 21 and tap water at a constant temperature (19℃) was the continuous phase. Only 48 cm of the 22 column was used as the active height and different mass flow rates of both phases were used. 23 The experimental results showed that the instantaneous temperature distribution along the 24 direct contact column tends to be uniform when the direct contact column is working under 25 flooding conditions. Furthermore, the volumetric heat transfer coefficient increases as the 26 dispersed mass flow rate is increased towards the flooding limit and remains constant along 27 the column height. In addition, the dispersed phase mass flow rate that leads to flooding 28 increased with increasing mass flow rate of the continuous phase. The initial temperature of 29 the dispersed phase did not have a considerable effect on the flooding inception limit under 30 the present experimental conditions

Calibration and sensitivity studies in the computational fluid dynamics (CFD) simulation of process equipment such as the annular jet pump are useful for design, analysis and optimisation. The use of CFD for such purposes is computationally intensive. Hence, in this study, an alternative approach using kriging-based meta-models was utilised. Calibration via the adjustment of two turbulent model parameters, C_μ and C_2ε, and likewise two parameters in the simulation correlation for C_μ was considered; while sensitivity studies were based on C_μ as input. The meta-model based calibration aids exploration of different parameter combinations. Computational time was also reduced with kriging-assisted sensitivity studies which explored effect of different C_μ values on pressure distribution.