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Abstract: This paper presents an experimental study on the application of hydrocarbon mixtures to replace HFC-134a in automotive air conditioners. The hydrocarbons investigated are propane (R290), butane (R600) and isobutane (R600a). The measured data are obtained from an automotive air conditioning test facility utilizing HFC-134a as the refrigerant. The air conditioner, with a capacity of 3.5kW driven by a Diesel engine, is charged and tested with four different ratios of hydrocarbon mixtures. The experiments are conducted at the same surrounding conditions. The temperature and pressure of the refrigerant at every major position in the refrigerant loop, the temperature, flow rate and humidity of air, torque and engine speed are recorded and analyzed. The parameters investigated are the refrigeration capacity, the compressor power and the coefficient of performance (COP). The results show that propane/butane/isobutane: 50%/40%/10% is the most appropriate alternative refrigerant to replace HFC-134a, having the best performance of all the hydrocarbon mixtures investigated. [Copyright &y& Elsevier]

Abstract: An experimental study is conducted to investigate the effects of a fin pitch and number of tube rows on the air side performance of fin and tube heat exchangers having herringbone wavy fin configuration at various fin thicknesses. A total of 10 samples of fin and tube heat exchanger with a tube outside diameter of 9.53mm, transverse tube pitch of 25.4mm and longitudinal tube pitch of 19.05mm, having various fin pitches, number of tube rows and fin thicknesses, are tested in a well insulated open wind tunnel. The heat exchangers are made from aluminium plate finned, copper tube. Ambient air is used as a working fluid in the air side while hot water is used for the tube side. The results are presented as the variation of the Colburn factor and the friction factor with the Reynolds number based on the fin collar outside diameter (). The experimental results reveal that the fin pitch has an insignificant effect on the heat transfer characteristic. The friction factor increases with increasing fin pitch when >2500, approximately. The Colburn factor and the friction factor decrease with increasing number of tube rows when <4000, approximately. These results remain the same when the fin thickness is changed. [Copyright &y& Elsevier]

This work presents an experimental study on the application of hydrocarbon mixtures to replace HFC-134a in a domestic refrigerator. The hydrocarbons investigated are propane (R290), butane (R600) and isobutane (R600a). A refrigerator designed to work with HFC-134a with a gross capacity of 239 l is used in the experiment. The consumed energy, compressor power and refrigerant temperature and pressure at the inlet and outlet of the compressor are recorded and analysed as well as the distributions of temperature at various positions in the refrigerator. The refrigerant mixtures used are divided into three groups: the mixture of three hydrocarbons, the mixture of two hydrocarbons and the mixture of two hydrocarbons and HFC-134a. The experiments are conducted with the refrigerants under the same no load condition at a surrounding temperature of 25 °C. The results show that propane/butane 60%/40% is the most appropriate alternative refrigerant to HFC-134a. [Copyright &y& Elsevier]

Heat transfer enhancement using the electrohydrodynamic (EHD) technique during evaporation inside horizontal smooth and micro-fin tubes is experimentally investigated. The test section is a counter-flow concentric tube-in-tube heat exchanger with R-134a flowing inside inner tube and heating water flowing in the annulus. Smooth and micro-fin inner tubes are used as test section. The outer diameter and length of inner tubes are 9.52mm and 2.50m, respectively. The outer tube is a smooth copper tube having inner diameter of 27mm. The electrode is made from stainless steel rod of 1.47mm diameter. Experiments are performed at average saturation temperatures ranging between 10 and 20°C, heat fluxes ranging between 10 and 20kW/m2 at mass flux of 400kg/m2 s and applied voltage of 2.5kV. The maximum heat transfer enhancement ratios are 1.25 and 1.15 for smooth tube and micro-fin tube, respectively. New correlations based on the data gathered during this work for predicting the evaporation heat transfer coefficient in smooth tube and micro-fin tube are proposed for practical applications. [Copyright &y& Elsevier]

The purpose of this study is to analyze the influence of the ambient temperature and humidity on the performance of a counterflow wet cooling tower according to the second law, exergy analysis, of thermodynamics. First, the properties of water and air flow through the tower were predicted and validated by the experiment. Exergy analysis then has been carried out for investigating the cooling tower performance with various inlet air conditions, relative humidity and dry bulb temperature, while the water side condition is kept constant. According to the analysis in this paper, the similar result in terms of required dry air flow rate, exergy change of water and that of air, exergy destruction and second law efficiency were obtained for the various inlet air conditions. The exergy change of water Δx w is higher than that of air Δx air, since Δx w is the available energy of water to supply to air throughout the tower while Δx air is the available energy of air to recover or utilize that supplied by water. It reveals that Δx air is dominated by the exergy change of air due to evaporative heat transfer. In addition, it gives a clearer explanation of the cooling tower performance and gives clear trends for optimization. [Copyright &y& Elsevier]

• Multiports act as internal fins and enhances evaporation rate of working fluid. • Reservoirs at the ends supply required quantity of fluid & reduce fluid entrainment. • Reduction in heat transfer and pressure drop irreversibilities of 17 & 48% observed. • Multiport design showed good stability by withstanding 2.7 bar pressure at 90 W. Thermal performance of an air cooled minichannel thermosyphon having multiports (10 ports) with hydraulic diameter of 1.18 mm is investigated. Experiments conducted at different heat loads (10 to 90 W), filling ratios (40, 50 and 60 %), inclination angles (30, 45, 60 and 90°), confluence lengths (0, 5 and 10 mm) and cooling air velocities (0.8, 1, 1.2 and 1.5 m/s) using acetone as working fluid. Results showed a maximum heat dissipation of 90 W with evaporator wall temperature of 72.2 °C at 5 mm confluence length. Multiports act as internal fins and enhance the surface area of the thermosyphon. This improves the boiling and evaporation rate, leading to reduced thermal resistance and wall temperature. An average reduction of 17.1 and 48.2 % are respectively noted in the irreversibilities of heat transfer and pressure drop at optimum condition. Liquid reservoirs at both ends of the thermosyphon overcomes the entrainment problem and supply the required quantity of working fluid and prevents it from reaching dry out condition. Analysis revealed that, the internal flow pattern transition is between Slug and Geyser flow for the tested heat loads. The present experimental findings can be a useful guide for engineering design to satisfy the requirement of cooling in miniaturized electronic devices. [ABSTRACT FROM AUTHOR]

In this paper, an analytical analysis has been performed to evaluate the performance of a minichannel-based solar collector using four different nanofluids including Cu/water, Al 2 O 3 /water, TiO 2 /water, and SiO 2 /water. The analysis of first and second laws is conducted for turbulent flow by considering the constant mass flow rate of nanofluid. The results are presented for volume fractions up to 4% and nanoparticle size of 25 nm where the inner diameter of the risers of flat plate collector is assumed to be 2 mm. Analysis of the first law of thermodynamics reveals that Al 2 O 3 /water nanofluids show the highest heat transfer coefficient in the tubes while the lowest value belongs to SiO 2 /water nanofluids. The highest outlet temperature is provided by Cu/water nanofluids, and after that TiO 2 /water, Al 2 O 3 /water, and SiO 2 /water nanofluids are in ranks of second to fourth. The results of second law analysis elucidate that Cu/water nanofluid produces the lowest entropy generation among the nanofluids. It is found that although the effective thermal conductivity of TiO 2 /water nanofluids is less than Al 2 O 3 /water nanofluids, but the entropy generation of TiO 2 /water is lower than Al 2 O 3 /water. Finally, some recommendations are given for future studies on the applications of nanofluids in solar collectors. [ABSTRACT FROM AUTHOR]

• To propose a novel integrated system based on geothermal and solar energy. • To apply energy, exergy, and exergo-economic analysis of the system. • To apply a multi-objective genetic algorithm optimization to the proposed system. • To produce hydrogen using PEM electrolysis. • To form a Perto curve to show cost and exergy efficiency objective functions. In this paper, a multi-generation system based on geothermal energy and parabolic trough solar collectors is proposed for the simultaneous generation of power, cooling, freshwater, hydrogen, and heat. Power is generated by a combined steam Rankine cycle and an organic Rankine cycle. Ten different refrigerants are used for the organic Rankine cycle, among which R123 has the best performance. In addition, four fluids are used as the geothermal fluid, among which Therminol 59 has recorded the best performance. Solar intensity, geothermal mass flow rate, geothermal fluid temperature, and steam turbine inlet pressure have proven to be the most prominent parameters affecting the exergy efficiency and cost. After analyzing the proposed system from the energy, exergy and exergoeconomic points of view, a multi-objective-optimization-genetic-algorithm is applied for improving the performance of the system. In order to apply the multi-objective optimization, Engineering Equation Solver and MATLAB software are linked together by the Dynamic Data Exchange method. According to the obtained results. The results show that the exergy efficiency of the system and the total unit cost respectively reach to 29.95% and 129.7 $/GJ at the optimum point. [ABSTRACT FROM AUTHOR]