Professor Adel Sharif

The need for using sustainable green energy to fulfill the more and more energy demands is essential because of many problems like changes in climate, environmental pollution, and global warming and their effects on the health of humans. A process of closed-loop pressure retarded osmosis (CL-PRO) is a renewable technology producing green energy with no deleterious impacts on nature. For the first time, Ethylene-diamine tetra-acetic acid disodium (EDTA-2Na) salt is estimated for its possibility as a draw solution in the PRO process, while its performance is put to comparison with inorganic sodium chloride (NaCl) draw solution. The impact of various operational variables including the concentration of draw solution (0.1M-0.5M) and applied pressure difference (0-8bar) was estimated via laboratory-based investigation related to the CL-PRO. The impact of such operational parameters was examined on power density, reverse salt flux, water flux, and specific salt flux. Based on the experimental results, the EDTA-2Na salt is showing as an effective draw solution in CL-PRO as a result of its elevated osmotic pressure and reduced reverse salt flux. With regard to the same molar concentrations, the EDTA-2Na draw solution created high water flux and significantly less reverse salt flux in comparison with NaCl. Furthermore, the maximum power density which is reached for EDTA-2Na draw solution is 1.6 W/m2, while the corresponding water flux is 7.209 LMH at an applied pressure of 8 bars. According to the results of this work, elevated production of power and low reversal salt flux made EDTA-2Na salt as possible draw solution for future studies in CL-PRO.

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.

•Desalination power consumption of RO alone increased with increasing Re.•Power consumption was dependent on Re when pretreatment energy is added.•High pressure pump (Epp) was responsible for 57–68% of total power consumption.•Epp was higher for RO with 95% ERD efficiency followed by 80% & 65% efficiency. The energy requirements for reverse osmosis (RO) seawater desalination continue to be a major matter of debate. Previous studies have shown the dependence of optimum RO desalination energy on the RO recovery rate. However, they overlooked including the effect of Energy Recovery Device (ERD) and pretreatment on the power consumption. In this work, a computer model was used to analyze the energy requirements for RO desalination, taking into account the effect of ERD efficiencies and pretreatment. The specific power consumption (SPC) of the RO was found to increase with the increase of RO recovery rate when the ERD system was included. The optimum SPC became more dependent on the RO recovery rate when the pretreatment energy was added. The recovery for optimum desalination energy was 46%, 44%, and 40% for the RO system coupled with an ERD of 65%, 80%, and 95% efficiency, respectively. The results showed that RO process could be operated at lower recovery rate and still meet the projected desalination capacity by increasing the feed flow rate and coupling with high-efficiency ERD. A trivial decrease of the total desalination energy was achieved when the feed flow rate increased from 7m3/h to 8m3/h and recovery rate decreased from 46% to 44% by coupling the RO with an ERD of 95% efficiency. This suggests that the RO–ERD system can be operated at a high feed flow rate and low recovery rate without affecting the plant capacity.

The effect of inserting twisted tapes with various configurations and parameters inside a circular pipe on the flow field is studied. The pressure drop and turbulent heat transfer are investigated using the computational fluid dynamics (CFD) technique. Ten cases of heat exchanger pipes are considered numerically. The 3D Navier–Stokes, continuity, momentum, and energy equations are solved using Fluent software. To study the impact of the turbulent flow on the heat transfer performance, a scheme with the semi-implicit method for pressure-linked equations (SIMPLE) algorithm is adopted. Water is applied as the working liquid, with constant heat flux boundary conditions. The results show that insertion of a twisted tape has a strong effect on all the flow properties inside the pipe, such as the pressure, velocity, vorticity, and temperature. Moreover, the turning induced by the twisted tape can provide more effective mixing of the fluid and enhance the turbulent intensity, leading to a thermal boundary layer. It is reported that the maximum dynamic pressure occurs midway between the surface of the twisted tape and the pipe outlet. Such use of a twisted tape could lead to a greater pressure drop and make the flow in the pipe more unstable, due to influences of the stronger swirling flow and vortex flow as well as the effect of the increased turbulent intensity. The resulting strong swirling flow leads to an improvement in the heat transfer performance. The numerical results reveal that the introduction of a twisted tape efficiently increases the pressure drop and heat transfer, as well as improving the heat transfer performance by about 46.0%. Furthermore, the results indicate that insertion of a twisted tape can improve the thermal performance of the system.

In this work, process simulation and cost analysis of an osmotic-driven process for simultaneous clean water and power generation from seawater using the concept of solute-gradient method are developed, with the aim of determining its potential application at the industrial scale. The simulations were carried out by Aspen Plus® software, considering a plant size corresponding to 1 MW power generation, using ethanol–water as the draw solution. Different draw solution regeneration techniques are investigated with the aim of minimizing the thermal requirements while respecting the threshold purity of the extracted water. It is shown that, by optimizing the inlet draw solution flow rate and concentration, power densities of about 5 W/m2 can be obtained using hollow fine fiber membrane, with a projected cost of electricity around 152 €/MWh. Economic analysis, based on Saudi Arabia water cost, shows that the process profitability is strongly affected by the water selling price, which needs to be at least 1.7 €/m3 in order to have the cumulative cash position equal to zero at the end of the plant lifetime (25 years). Nevertheless, it is suggested that both water and power could be industrially produced in a profitable way (DPBP less than 5 years) with a drinking water selling price equal to 2 €/m3, which is about 30% higher than the current value yet a realistic one in the near future.

In cooling water systems, cooling towers play a critical role in removing heat from the water. Cooling water systems are commonly used in industry to dispose the waste heat. An upward spray cooling water systems was especially designed and investigated in this work. The effect of two nanofluids (Al2O3/ water, black carbon /water) on velocity and temperature distributions along reverse spray cooling tower at various concentrations (0.02, 0.08, 0.1, 0.15, and 0.2 wt.%) were investigated, beside the effect of the inlet water temperature (35 ,40, and 45 ͦ C) and water to air flow ratio (L/G) of 0.5, 0.75, and 1.  The best thermal performance was found when the working solution contained 0.1 wt.% for each of Al2O3 and black carbon nanoparticles, with a maximum drop in temperature drops (i, e. range) of (16 ͦ C) and (20 ͦ C), respectively. The temperature of the tower's outlet water was decreased as the inlet working fluid increased, and the thermal efficiency declined with the increasing of the L/G by about 5%. However, the drop in the outlet temperature caused by the nanofluid is more than that of pure water at every point by about 6 ͦ C.

Forward osmosis has gained tremendous attention in the field of desalination and wastewater treatment. However, membrane fouling is an inevitable issue. Membrane fouling leads to flux decline, can cause operational problems and can result in negative consequences that can damage the membrane. Hereby, we attempt to review the different types of fouling in forward osmosis, cleaning and control strategies for fouling mitigation, and the impact of membrane hydrophilicity, charge and morphology on fouling. The fundamentals of biofouling, organic, colloidal and inorganic fouling are discussed with a focus on recent studies. We also review some of the in-situ real-time online fouling monitoring technologies for real-time fouling monitoring that can be applicable to future research on forward osmosis fouling studies. A brief discussion on critical flux and the coupled effects of fouling and concentration polarization is also provided.

The aim of this study is to investigate the performance of specific organic osmotic agents, namely, Sucrose draw solution and Glucose draw solution against deionized water in a Forward Osmosis (FO) process using NF flat sheet membrane. The key parameters affecting the FO process studied were: temperature, flow rates of osmotic agent and feed water, and concentration of osmotic agent. The experimental results showed that increasing the concentration of osmotic agents yield lower water flux, recovery percentage and permeability, along with an apparent increase in the specific energy consumption. Although the findings indicated superior performance of Glucose over Sucrose as a better osmotic agent, it has to be emphasized that both organics were ineffective draw solutions against deionized water for the Nano-filtration (TFC-SR2) membrane used in this study and the given operating parameters.

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.

The objective of the present work is to investigate the behaviour of binary and ternary aqueous systems, which could be employed in the selection criteria for draw agents (DA) to be used in Forward Osmosis (FO) process applications. In this study the osmotic properties of the selected binary and ternary aqueous solutions of magnesium chloride (MgCl2), sodium chloride (NaCl), sucrose and maltose are investigated. Osmotic pressures were calculated from water activities obtained from measured relative humidity of the solutions of concentrations in the range 0.5-6.0 mol kg-1 at 298.15 K. The osmotic behaviours of the ternary systems were compared with their binary counter parts; the results showed either positive or negative osmotic synergic effects. This could be used besides transport properties for considering the selection of favourable draw agents from those that exhibited positive synergy, i.e. the osmotic pressure of a ternary solution is greater than the sum of the pressures of the corresponding binary solutions. The results showed that the ternary aqueous solutions of MgCl2 + NaCl showed significant positive synergy and therefore are possible suitable candidates as draw solutions, less so were the sugar-electrolyte systems.

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.

The present study assesses the application of the forward osmosis process using a thermolytic draw solution for irrigation water supply. A novel forward osmosis desalination process with thermal depression regeneration for producing high quality irrigation water is also proposed aiming to provide a reliable and cost-effective method in terms of specific energy consumption. The modified forward osmosis process proposed in this chapter has the potential to provide low-energy production of fresh water from seawater and wastewater, therefore leading to a substantial cost reduction. The specific energy consumption was calculated at the optimum operating conditions of the forward osmosis membrane system producing 1 m3/h of fresh water from seawater at a recovery rate of 50%. The estimated specific energy consumption was 2.7 kWh/m3 and could be decreased when a heat recovery process was used. Furthermore, the combination of the proposed process with a salinity gradient solar pond was evaluated, which resulted in a major reduction of the specific energy consumption to 0.25 kWh/m3. This method can provide a financially viable and sustainable cycle for seawater desalination, particularly in areas of high solar irradiance.

Closed-loop pressure retarded osmosis (CL-PRO) process has been used for generating renewable energy from osmotic power by using a semipermeable membrane. In this research, the sodium chloride NaCl solution with a specific molar concentration was employed as the draw solution DS, while feed solution FS was tap water. The laboratory-scale system was utilized for evaluating the CL-PRO process performance of a cellulose triacetate hollow fiber CTA-HF module within a broad range of the operational conditions such as draw solution concentration (0.1 - 0.5 M), applied hydraulic pressure difference (0 - 8 bar), flow rate of the draw solution (0.8 - 2.8 L/min), and the temperature of the DS and FS (20 - 35 C). The effect of these operational parameters was investigated on the power density and the flux of permeated water. According to the experimental results, the power density and the flux of the permeated water increased with increasing the draw solution concentration, the flow rate of the draw solution, and the temperature of solutions. By increasing the applied hydraulic pressure on the shell-side of hollow fiber membranes (draw solution side), the water flux decreased while the produced power density increased. The maximum power density and the flux of permeated water of 0.5 M NaCl DS were approximately 0.94 W/m2 and 4.27 LMH respectively, which occurs at 8 bar hydraulic pressure.

Membrane distillation (MD) is a recent and unique separation technology, in use in the process industry. The process of separation in MD involves the simultaneous heat and mass transfer through a hydrophobic semi permeable membrane, using thermal energy. Consequently a separation of the feed solution into two components - the permeate or product and the retentate or the return stream occurs. MD utilises low grade or alternative energy, e.g., solar energy, geothermal energy, etc., as a source and is the most cost effective separation technology. Hence the process has come to acquire the attention and interest of researchers, experimentalists and theoreticians all over the world. This article is a comprehensive review of the prominent research in the field of MD technology, including its basic principle, MD configurations, area of applications, membrane characteristics and modules, experimental studies involving the effect of main operating parameters, MD energy and economic, fouling and long-term performance. Copyright © 2013 Inderscience Enterprises Ltd.

The performance of Dual Stage Pressure Retarded Osmosis (DSPRO) was analyzed using a developed computer model. DSPRO process was evaluated on Pressure Retarded Osmosis (PRO) and Forward Osmosis (FO) operating modes for different sodium chloride (NaCl) draw and feed concentrations. Simulation results revealed that the total power generation in the DSPRO process operating on the PRO mode was 2.5-5 times more than that operating on the FO mode. For DSPRO operating on the PRO mode, the higher power generation was in the case of 2M NaCl-fresh and 32% the contribution of the second stage to the total power generation in the DSPRO. To the contrast, he total power generated in the DSPRO operating on the FO mode was in the following order 5M-0.6M > 5M-0.7M > 2M-0.01 > 2M-0.6 M. Interestingly, single stage process operating on the FO mode performed better than DSPRO process due to the severe concentration polarization effects. The results also showed that power density of the DSPRO reached a maximum amount at a hydraulic pressure less than the average osmotic pressure gradient, Delta pi/2, due to the variation of optimum operating pressure of each stage. Moreover, results showed that the effective specific energy in the PRO process was lower than the maximum specific energy. However, the effective specific energy of the DSPRO was larger than that of the single stage PRO due to the rejuvenation of the salinity gradient, emphasizing the high potential of the DSPRO process for power generation.

   Pressure retarded osmosis (PRO) can be considered as one of the methods for utilizing osmotic power, which is a membrane-based technology. Mathematical modeling plays an essential part in the development and optimization of PRO energy-generating systems. In this research, a mathematical model was developed for the hollow fiber module to predict the power density and the permeate water flux theoretically. Sodium chloride solution was employed as the feed and draw solution. Different operating parameters, draw solution concentration (1 and 2 M), the flow rate of draw solution (2, 3, and 4 L/min), and applied hydraulic pressure difference (0 - 90 bar) was used to evaluate the performance of PRO process of a hollow fiber module. The effect of these operational parameters was investigated on the theoretical permeate water flux and power density. According to the theoretical results, the permeate water flux and the power density increased with increasing the concentration of draw solution and the flow rate of the draw solution. While decreased with increasing the feed solution concentration. By increasing the applied hydraulic pressure on the draw solution, the water flux decreased and the produced power density increased. The maximum power density and the corresponding permeate water flux of 2 M NaCl draw solution was approximately 16.414 W/m2 and 11.818 LMH respectively, which occurs at an applied hydraulic pressure of 50 bar.

A novel design of an air injection zigzag system was developed to enhance the tubular membrane distillation module's performance for desalination of water, unlike the basic design that works without an air injection system. Designed in a zigzag mode, the membrane distillation module is set to yield a high turbulence flow. Operating parameter effects, for example, the feed temperature (40 degrees C, 50 degrees C, 60 degrees C, and 70 degrees C), feed concentration (1, 3, and 5 g/L), and airflow rate (30-90 L/h), on process performance were investigated. The system proved its capability to enhance the heat and mass transfer coefficients. The basic and developed modules' performances were compared in terms of permeate flux (J(m)) and thermal efficiency (eta). The Reynolds number increased threefold, which consequently, increased the mass transfer coefficient by 25% and the heat transfer coefficient twofold compared to the basic module at airflow rate of 90 L/h. Moreover, the thermal efficiency and permeate flux were higher than the basic module's by roughly 1.4 and 1.5-fold, respectively, for a 5 g/L feed concentration.

Enhancing the effectiveness of solar power, including daytime storage for overnight use, is essential to reduce fossil fuel usage. This work explores the melting behaviour of paraffin wax in shell and tube latent heat thermal storage unit (LHSU) in different configurations and orientations. Numerical simulation were carried out and compared with experimental measurements for non-finned and finned configurations arranged vertically during the melting (charging) process. A commercial paraffin wax was used as a phase change material (PCM). The temperature and liquid fraction of the PCM during the course of the melting process in both configurations were used for model validation. When considering the liquid fraction, the numerical results showed excellent qualitative agreement with the experimental images for all the cases being studied. Specifically, the shape and progress of the melting front showed good agreement between the experiments and numerical results. Furthermore, the model predicted well the experimentally measured temperature in the melting PCM, with a maximum average discrepancy of 3.6%. The validated model was then used to investigate different process configurations. The results indicated that the addition of fins enhanced the melting process by an average of 50%. The non-finned tubes had a superior melting rate in the horizontal orientation over the vertical orientation, while orientation was found to have only a minor impact on the melting process with finned tubes.

When primary oil production decreases in a field because of reduction in original pressure, water is usually injected to increase oil production. Injected water in special wells (injection wells) forces the oil remaining in certain layers to emerge from other wells (production wells) surrounding the injector. This technique, commonly called secondary recovery, contributes in extracting up to 50% of the original oil in place. Although this technique was first used in old reservoirs where oil production had decreased, it is today a common practice to begin the exploitation of new wells with fluid injection as a way to optimize oil recovery. For this reason, the name secondary recovery is being replaced by the more general term water flooding. Efficiency of the water flooding process is highly dependent on the rock and fluid characteristics. In general, it will be less efficient if heterogeneity is present in the reservoir, such as permeability barriers or high permeability channels that impede a good oil displacement by the injected water [1]. On the other hand Most of the scales found in oil fields forms either by direct precipitation from the water that occurs naturally in reservoir rocks, or as a result of produced water becoming oversaturated with scale components when two incompatible waters meet downhole. The present study attempts to establish the tracer technology as a reliable source of information in scaling experiments and reservoir evaluation such as reservoir heterogeneity. In a series of calcite scaling experiments in sand, Ca2+ was used as a tracer to monitor the CaCO3 precipitation. The results show that the introduction of tracer technology, for the first time in scaling experiments in porous media, has been successful [3]. Copyright 2006, Society of Petroleum Engineers.

Thermal performance of a Latent Heat helical coil Thermal Energy Storage (LHTS) was investigated experimentally for both phases; melting and solidification processes. Paraffin wax (type P56-58) and tap water were used as a Phase Change Material (PCM), and a Heat Transfer Fluid (HTF), respectively. The paraffin wax (PCM) thermos-physical properties were determined experimentally. To simulate the solar energy conditions, three different initial temperatures (70 °C, 75 °C and 80 °C) and flow rates (1 L/min, 3 L/min and 5 L/min) of the HTF were tested throughout the PCM melting experiments, while the temperature of HTF was only 30 °C with the same flow rates for solidification process. The storage was completely insulated to reduce the heat losses. The PCM temperature during the melting and solidification processes was measured with time using 16 K-type calibrated thermocouples distributed along the PCM axially and radially. The experimental results showed that contrary to the solidification process, the melting was a superior in the helical coil LHTS under different operational conditions. Axial and radial melting fronts were noticed during the PCM melting process which considerably shortened the melting time under the effect of convection and a shape like a pyramid is formed at the core of the storage. Initial temperature of heat transfer fluid (HTF) was significantly affected the melting process and the increased of it from 70 °C to 75 °C and from 75 °C to 80 °C resulted in shortening the total melting time by about 34.5% and 27.2% respectively. An optimum HTF flow rate was observed during the melting process and it was found to be 3 L/min under the operational conditions of the present experiments. Contrary, the flow rate of HTF was insignificant during the solidification process. The initial temperature of HTF was slightly affected the effectiveness of the melting process. In spite of the efficiency of the melting process, enhancement of the solidification in the coiled LHTS is necessary in order to use the process in the thermal applications of solar energy.

The current study highlights the advancement in Pressure Retarded Osmosis (PRO) process and covers most recent development in the process applications. The first application of PRO process goes back to 1973 by Sidney Loeb who suggested using the concept of osmotic energy for power generation. In principle, two solutions of different concentrations are separated by semipermeable membrane of, relatively, high water permeability and solute rejection rate. The high-concentration solution is usually known as the draw solution while the low-concentration solution is called the feed solution. The draw solution is pressurized before entering the membrane. Due to the osmotic pressure gradient across the membrane, fresh water transports in the direction of the osmotic pressure gradients resulting in the dilution of the high-concentration solution. After leaving the membrane, the diluted draw solution is depressurized in a turbine system for power generation. Different types of membrane materials and solute gradient resources were proposed and their impact on the performance of PRO process was investigated. In addition to power generation, the hybridization of PRO process with membrane and thermal processes for power generation and seawater desalination is not unusual nowadays. The current study provides a critical review about the recent advancements in the PRO process and research outcomes.

This work investigates the effectiveness of sodium chloride and sucrose binary draw solutions in a forward osmosis pilot plant unit with either deionised or salt water feeds. Specifically, the effects of draw solution concentration on water flux through the membrane, the overall water recovery and the specific energy consumption of the unit are considered. For both feed types, sodium chloride draw solution exhibited a relatively high effectiveness in terms of all the measured performance indicators. Further, improvements in flux and recovery were also achievable with an increase in the sodium chloride (draw solution) concentration. In contrast, a sucrose-based draw solution led to a severe deterioration of the membrane performance that could not be effectively overcome by an increase in the draw solution concentration. This observation was attributed to the relatively large increase in the viscosity of the draw solution with increase in sucrose concentration. Interestingly, in the case of a salt water feed, an increase in the sucrose draw solution concentration led to a relatively small increase in flux and recovery, suggesting some complex but favourable interaction between the salt and sucrose due to the reverse diffusion of the salt into the draw solution.

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 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

This study is a combination of experimental and theoretical works in an attempt to produce a new useful empirical model for the mass transfer in pressure-driven membrane separation processes. Following on from our previous work in Part I, this part II paper introduces three new permeability models when using aqueous solutions as feed. The Solution-Diffusion Pore-Flow Concentration-Polarization (SDPFCP) model, which is a combination between the Solution-Diffusion Pore-Flow (SDPF) model [1] and the Concentration Polarization (CP) model, is presented. The SDPFCP model examines the CP model to represent the transfer phenomena outside the membrane by merging its effect within the water permeability coefficient. A further development for this model, the SDPFCP+, is obtained by adding an additional resistance to the system in series with the membrane resistance and the CP. The second model shows fair representation of the experimental results. The Solution-Diffusion Pore-Flow Fluid-Resistance (SDPFFR) model is then proposed to provide better representation for the system. The feed solution resistance to water flux, the Fluid Resistance (FR), is suggested to replace the CP and the additional resistance. The latter model shows excellent fitting to the experimental results; it may be useful for development and design applications, when based on experimental data. Crown Copyright (C) 2010 Published by Elsevier By. All rights reserved.