An energy and exergy thermodynamic analysis using EES program was done for a domestic refrigerator working with R-134a using vapor compression refrigeration cycle. The analysis deals with the system component, i.e. compressor, condenser, evaporator and the expansion device. The analysis depends on the entropy generation minimization approach to improve the refrigerator performance by exploring the optimum design points. These design points were derived from three different theories governing the entropy generation minimization using exergy analyzing method. These theories were first applied to find the optimum balance between the hot inner condenser area and the cold inner evaporator area of the refrigerator and between its hot and cold thermal conductances. Nine types of condensers were used according to its internal surface area and thermal conductance, in order to reach the minimum entropy generation in the refrigerator. The results showed that the compressor has the lowest exergy efficiency of 25%. The expansion device was the second component after the compressor with exergy efficiency of 92%, followed by the condenser with an efficiency of 93%. The evaporator was found to have an exergy efficiency of 98 %. The experimental tests were repeated for the nine condensers sizes with three different ambient temperatures 25℃, 30℃ and 35℃.  The exergy analysis showed that the design of the refrigerator mainly depends on thermal conductance calculations rather than the surface inner area estimation.

Because of the complexity involved, most researchers avoid studying the entropy generation due to both convection and radiation. In this study, the heat transfers from the horizontal heated cylinder by natural convection and radiation and the entropy generation is the case study and the ability to combine of these two heat transfer methods depending on the thermodynamic principles. Three heating horizontal cylinders were used during this study. The results indicated that the natural convection is effective parameter to produce the entropy generation when the ratio of Ra/Ra, opt lower than 1 and the Ns increased slightly to 3 at Ra/Ra, opt=0.001, but when the radiation is the effective parameter to produce the entropy generation that is done when Ra/Ra, opt higher than 1 and the Ns increases to 200 at Ra/Ra, opt=1000.

No abstract

Recently, most of the researchers focused on provide lower greenhouse gas emissions that emitted from diesel engines by using renewable fuels to be good alternative to the conventional diesel fuel. Ethanol can be derived from renewable sources such as sugar cane, corn, timber and dates. In the current study, the ethanol fuel used in the tests was derived from the dates. The effects of using exhaust gas recirculation (EGR) diesel-ethanol blend (E10) with on engine performance and emissions characteristics have been studied in diesel engine under various engine loads. This study focused the use of oxygen in the bio-ethanol composition to compensate for the decrease occurred by the addition of EGR, which improves the engine performance and reduces its emissions. In this experiment, the ratios of EGR were 10%, 20% and 30% as well as 10% ratio of ethanol was blended into the diesel fuel blend under fixed engine speed. A traditional (without additional systems to reduce emissions) four cylinders direct injection (DI) diesel engine was used for all tests. The brake specific fuel consumption (BSFC) increased with increasing the EGR ratio by 10%, 20% and 30% by 18.7%, 22.4% and 37.4%, respectively. The thermal efficiency decreased under variable conditions of engine load for different ethanol blends. Furthermore, the emissions of NOX decreased when fuelled B10 into the engine in comparison with diesel under low engine load. Significant reduction in the NOx emissions were found when applied EGR in the tests than to the absence EGR for E10 blend and diesel. The NOx reduction rate was 12.3%, 30.6% and 43.4% when EGR rate was 10%, 20% and 30%, respectively. In addition, the concentrations of HC and CO emissions decreased more by 8.23% and 6.4%, respectively, when using E10 in comparison with the diesel for various engine loads. It is indicated that the oxygen reduction by EGR effect was compensated from ethanol blend combustion. The results showed that the combination use of E10 and EGR leads to significant reduction in engine emissions accompanied with partial reduction in the engine performance.

A semi-empirical model has been investigated to represent household compressors. The model based on calorimeter data for two distinguished brand (Danfoss and Electrolux CUBIGEL) and compared with eight brands consisting of ninety compressors model. The calorimeter data are correlated (according to ARI standard 540-90 [1] and working refrigeration temperature cycle for ASHRAE Technical Committee 8.9[2]) as a function of refrigerant saturated evaporating temperatures from (-35 to 10) °C and swept volume range (2.24-11.15) cm3 keeping of the refrigerant saturated condensing temperature constant at 54.5 °C. The correlations were found with ten-coefficient polynomial by using Matlab software – surface fitting method for cooling capacity, power consumption, and refrigerant mass flow rate.In addition, other equations for cooling capacity, power consumption, and refrigerant mass flow rate at-23.3 °C evaporator temperature, 54.4 °C condenser temperature, and 32 °C temperature for liquid line which is the base points of the refrigerator cycle according to ASHRAE[2] , cover the range (2.42-11.15) cm3 swept volume which are created to quick choose the proper compressor.The result indicated that the surface fitting models are accurate within ± 15% deviation of compressors data of seventy-two models for cooling capacity, fifty models for power, and twenty-five models for refrigerant mass flow rate.