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SUMMARY In this paper, a new design for the flow channels is presented, and a parametric study of the proton exchange membrane (PEM) fuel cell is conducted in order to investigate the effect of the new flow channels, as well as different operating parameters, on the efficiency and energy output of the cell. Design parameters are selected based on studies presented in the literature to build a physical and practical model. With the new design of the flow channels, it is noticed that the cell efficiency increases from 33.8% to 47.7% if the temperature of the cell is increased. The power output of the cell increases from 2.6 to 282.5 W when the cell temperature and the current density are increased. Moreover, decrease in the efficiency of the cell ranges from 45.5% to 28.4% with the increase in the current density and membrane thickness. Based on the analytical model, design parameters were selected to manufacture a fuel cell that has a power output of 175 W and an efficiency of 35% running at 353 K and 3 bar, with an effective membrane area of 450 cm2. Experiments are conducted to investigate the effect of newly designed flow channels on pressure distribution. It is found that when hydrogen is supplied from both inlets, pressure across the channels become symmetric and, therefore increasing the power output. This study reveals that, with the proper choice of design parameters, a PEM fuel cell is an attractive economical, efficient, and environmental solution when compared with conventional systems of power generation such as gas turbines. Copyright © 2011 John Wiley & Sons, Ltd.

Summary The performance comparison of multi‐effect absorption refrigeration systems has been conducted in the present study. The absorption cooling cycles are operated on the solar heat in order to improve the utilization of high temperature heat sources for absorption systems. The absorption refrigeration cycles of multi‐effect are modeled and designed for the identical refrigeration capacity along with the similar operating conditions. The engineering equation solver tool is deployed to analyze the coefficient of performance (COP) and exergetic efficiency of the absorption cooling cycles. Performance simulations were carried out over a range of operating conditions, including the effect of heat transfer fluids (nanofluids) used in solar parabolic trough collectors. The COP of the triple effect absorption refrigeration cycle (TEARC) is observed to be 1.752. The COP of the double effect absorption refrigeration cycle (DEARC) is perceived to be 51.9% higher as compared with single effect absorption refrigeration cycle (SEARC) which has a COP of 0.852. The exergetic efficiency of the TEARC is witnessed to be 16% higher than DEARC, and it is 31% higher than SEARC at an evaporator temperature of 7 ̊C. The effect of nanoparticle's (Al2O3) concentration and percentage of weak and strong solutions of LiBr‐H2O is also evaluated at design conditions. A high temperature heat reservoir is required to operate the TEARC, whereas, the SEARC and DEARC operate on lower temperatures than triple effect cycle.

SUMMARYThe present study has been conducted using nanofluids and molten salts for energy and exergy analyses of two types of solar collectors incorporated with the steam power plant. Parabolic dish (PD) and parabolic trough (PT) solar collectors are used to harness solar energy using four different solar absorption fluids. The absorption fluids used are aluminum oxide (Al 2 O 3 ) and ferric oxide (Fe 2 O 3 )-based nanofluids and LiCl-RbCl and NaNO 3 -KNO 3 molten salts. Parametric study is carried out to observe the effects of solar irradiation and ambient temperature on the parameters such as outlet temperature of the solar collector, heat rate produced, net power produced, energy efficiency, and exergy efficiency of the solar thermal power plant. The results obtained show that the outlet temperature of PD solar collector is higher in comparison to PT solar collector under identical operating conditions. The outlet temperature of PD and PT solar collectors is noticed to increase from 480.9 to 689.7 K and 468.9 to 624.7 K, respectively, with an increase in solar irradiation from\ 400 to 1000 W/m 2 . The overall exergy efficiency of PD-driven and PT-driven solar thermal power plant varies between 20.33 to 23.25% and 19.29 to 23.09%, respectively, with rise in ambient temperature from 275 to 320 K. It is observed that the nanofluids have higher energetic and exergetic efficiencies in comparison to molten salts for the both operating parameters. The overall performance of PD solar collector is observed to be higher upon using nanofluids as the solar absorbers.

SUMMARY In this paper, a novel integrated solar photovoltaic thermal absorption desalination system for freshwater and cooling production is proposed and analyzed thermodynamically. Ammonia–water pair is considered as a working fluid for the absorption system. Effect of average solar radiation for different months, time period of solar radiation availability in Abu Dhabi, salinity of seawater, and temperature of the seawater on energetic and exergetic COPs, production rate of freshwater, and overall performance of the system are investigated under different operating conditions. It is found that energetic and exergetic COPs, production rate of freshwater, energetic and exergetic utilization factors, and performance ratios vary greatly from one month to another because of the dynamic variation in solar radiation and its time of availability. The highest amount of freshwater is produced in the month of July as calculated to be 152 kg/h for a collector area of 100 m2 and solar power of 4.8 kW. The highest energetic and exergetic COPs and utilization factors are also obtained for the month of July. Moreover, the highest performance ratio is found to be 0.056 as obtained in the month of July when solar radiation intensity is highest as available for more than half of a day. Copyright © 2012 John Wiley & Sons, Ltd.

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The parabolic trough collector (PTC) is one of the most widely deployed concentrating solar power technology in the world. This study aims at improving the operational efficiency of the commercially available LS-2 solar collector by increasing the convective heat transfer coefficient inside the receiver tube. The two main factors affecting this parameter are the properties of the working fluid and the inner geometry of the receiver tube. An investigation was carried out on six different working fluids: pressurized water, supercritical CO2, Therminol VP-1, and the addition of CuO, Fe3O4, and Al2O3 nanoparticles to Therminol VP-1. Furthermore, the influence of a converging-diverging tube with sine geometry is investigated because this geometry increases the heat transfer surface and enhances turbulent flow within the receiver. The results showed that of all the fluids investigated, the Al2O3/Oil nanofluid provides the best improvement of 0.22% to thermal efficiency, while the modified geometry accounted for a 1.13% increase in efficiency. Other parameters investigated include the exergy efficiency, heat transfer coefficient, outlet temperatures, and pressure drop. The analysis and modeling of a parabolic trough receiver are implemented in engineering equation solver (EES).

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