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Number of results: 4
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Abstract

This paper presents mathematical modelling and numerical analysis to evaluate entropy generation analysis (EGA) by considering pressure drop and second law efficiency based on thermodynamics for forced convection heat transfer in rectangular duct of a solar air heater with wire as artificial roughness in the form of arc shape geometry on the absorber plate. The investigation includes evaluations of entropy generation, entropy generation number, Bejan number and irreversibilities of roughened as well as smooth absorber plate solar air heaters to compare the relative performances. Furthermore, effects of various roughness parameters and operating parameters on entropy generation have also been investigated. Entropy generation and irreversibilities (exergy destroyed) has its minimum value at relative roughness height of 0.0422 and relative angle of attack of 0.33, which leads to the maximum exergetic efficiency. Entropy generation and exergy based analyses can be adopted for the evaluation of the overall performance of solar air heaters.
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Abstract

The engine simulations have become an integral part of engine design and development. They are based on approximations and assumptions. The precision of the results depends on the accuracy of these hypotheses. The simplified models of frozen composition, chemical equilibrium and chemical kinetics provide the compositions of combustion products for engine cycle simulations. This paper evaluates the effects of different operating conditions and hypotheses on the exergetic analysis of a spark-ignition engine. The Brazilian automotive market has the highest number of flex-fuel vehicles. Therefore, a flex-fuel engine is considered for simulations in order to demonstrate the effects of these different hypotheses. The stroke length and bore diameter have the same value of 80 mm. The in-cylinder irreversibility is calculated for each case at the closed part of the engine cycle. A comparative analysis of these hypotheses provides a comprehensive evaluation of their effects on exergetic analysis. Higher values of accumulated irreversibility are observed for the oversimplified hypothesis.
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Abstract

In this study a cooling ejector cycle coupled to a compression heat pump is analyzed for simultaneous cooling and heating applications. In this work, the influence of the thermodynamic parameters and fluid nature on the performances of the hybrid system is studied. The results obtained show that this system presents interesting performances. The comparison of the system performances with hydrofluorocarbons (HFC) and natural fluids is made. The theoretical results show that the a low temperature refrigerant R32 gives the best performance.
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Abstract

Irreversibility analysis was investigated by using refrigerants R22, R407A, and R407C in window type air conditioner system. The experimental study was conducted at various ambient temperatures and air volumetric flow rates to determine the parameters that cause the energy degradation of the system. The irreversibility was compared with respect to volumetric flow rates of the air passing through evaporator (14.15, 12.74, and 10.618 m3/min) and different ambient temperatures (ranging from 28 ◦C to 39 ◦C dry bulb. Results show that the total irreversibility increases with refrigerant mass flow rate and ambient temperature for the three refrigerants. Additionally, R22 shows the highest irreversibility in low ambient temperature (28 ◦C to 30 ◦C) while R407A shows the lowest one with ambient temperature ranging from 30 ◦C to 36 ◦C. Both tested refrigerants are very good replacement for R22 in terms of irreversibility and energy analysis and these results are more remarkable with R407A.
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