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A generalized methodology for pinch point design and optimization of subcritical and transcritical organic Rankine cycles (ORCs) using both wet and dry fluids is adopted in this study. The presented algorithm can predict the pinch point location in evaporator and condenser simultaneously and optimize the evaporator pressure for best performance with various heat source and sink conditions. Effects of pinch point temperature difference (PPTD), isentropic efficiency, subcooling, superheating and regenerator on the energy and economic performances are discussed for selected working fluids. System yields similar optimum design for both maximum power generation and minimum capital cost per unit power. At optimum condition, ammonia is best in terms of higher thermal efficiency and lower component size, R152a is best in terms of higher net power output and heat recovery efficiency (11.1%), and toluene is best in terms of lower capital cost and cost per unit power output (7060 $/kW). Effect of heat source and sink parameters on both energy and economic performances is significant. Contour plots are presented to select the best ORC design parameters for available heat source condition. PPTD and expander isentropic efficiency have significant effect on performances. However, the effect of subcooling, superheating and regenerator depends on working fluid. [ABSTRACT FROM AUTHOR]

In this work, parametric analysis of ejector expansion refrigeration cycles (EERC) with two different types of ejectors (constant area (CA) ejector and constant pressure (CP) ejector) is pet formed, and comparison of the results is presented. Effects of variation in operational parameters (condenser temperature, evaporator temperature, and cooling capacity) on coefficient of performance (COP), entrainment ratio (w), and pressure lift factor (Pif) are investigated. The range of variation for evaporator temperature, condenser temperature, and cooling capacity are --5 to 15 °C, 50-70 °C, and 10-80 kW, respectively. The ejector refrigeration cycle is simulated by ees software. The obtained results are validated by the experimental data available in the literature. The refrigerant RI34a is selected based on the merit of its environmental and peiformance characteristics. The results show that the effect of evaporator temperature is much higher than that of condenser temperature on Py. In contrast, the influence of condenser temperature on COP is much stronger than that of evaporator temperature. It is seen that COP and Pif of ejector expansion refrigeration cycle with constant pressure ejector (CP-EERC) are higher than those of refrigeration cycle with constant area ejector. [ABSTRACT FROM AUTHOR]

In this study, first and second law analyses of a new combined power cycle based on wet ethanol fuelled homogeneous charge compression ignition (HCC1) engine and an organic Rankine cycle are presented. A computational analysis is performed to evaluate first and second law efficiencies, with the latter providing good guidance for performance improvement. The effect of changing turbocharger pressure ratio, organic Rankine cycle (ORC) evaporator pinch point temperature, turbocharger compressor efficiency, and ambient temperature have been observed on cycle's first law efficiency, second law efficiency, and exergy destruction in each of its component. A first law efficiency of 41.5% and second law efficiency of 36.9% were obtained for the operating conditions (T0 = 300 K, rp = 3, ηT= 80%). The first law efficiency and second law efficiency of the combined power cycle significantly val~y with the change in the turbocharger pressure ratio, but the change in pinch point temperature, turbocharger efficiency, and ambient temperature shows small variations in these efficiencies. Second law analysis demonstrates well how the fuel exergy is used, lost, and reused in all of the cycle components. It was found that 78.9% of the total input exergy is lost: 2.0% to the environment in the flue and 76.9% due to irreversibilities in the components. The biggest exergy loss occurs in the HCCI engine which is 68.7%, and the second largest exergy loss occurs in catalytic converter, i.e., nearly 3.13%. Results clearly show that performance evaluation based on first law analysis alone is not adequate, and hence more meaningful evaluation must include second law analysis. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate how the heat exchanger inventory allocation plays a role in maximizing the thermal performance of a two-stage refrigeration system with two evaporators. First, the system is modeled as a Carnot refrigerator and a particular heat transfer parameter is kept constant as the heat exchanger allocation parameter is allowed to vary. The value of the heat exchanger allocation parameter corresponding to the maximum coefficient of performance (COP) is noted. The results are compared to those of a non-Carnot refrigerator with isentropic and nonisentropic compression. It is found that the Carnot refrigerator can be used to predict the value of the heat exchanger allocation parameter where the maximum COP occurs for a non-Carnot refrigerator. In order to improve the accuracy of that prediction, the predicted value of the heat exchanger allocation parameter has to be inputted into the set of equations used for the non-Carnot refrigerator. This study is useful in designing a low-cost, high-performance refrigeration system. [ABSTRACT FROM AUTHOR]

An optimization for the geometrical parameters of continuous fins on an array of tubes of a refrigeration evaporator is developed in this paper using the exergy method. The method is based on exergy, economic analysis, and optimization theory. As there are humid air and refrigerant single- and two-phase streams involved in the heat transfer process, then there are irreversibilities or exergy destruction, due to pressure losses İΔP, due to temperature difference İΔT and due to specific humidity gradient İΔω. These principal components of total irreversibility are not independent, and their relative contribution to total irreversibility of a cross-flow refrigeration evaporator is investigated. A change in geometry was obtained by varying the evaporator tube diameter for a selected evaporator capacity, and hence the evaporator tube length and total heat transfer area are calculated for a fixed evaporator face length. In this way, the effect of changes in the geometry on the total number of exergy destruction units of the heat exchange process is investigated. The optimum balance between the three components of irreversibility (İΔP, İΔT, and İΔω) is also determined, thereby giving the optimum solution for the heat exchanger area. The total cost function, which provides a measure of the contribution of the evaporator to the total cost of the refrigeration system, is expressed on the basis of annual capital and electrical energy costs. The total cost function is minimized with respect to the total heat transfer area and the total number of exergy destruction units (NI). The relationship between the operational variables, heat transfer area, refrigerant and air irreversibilities, and the total annual cost for this type of evaporator are developed, presented, and discussed. The pressure, temperature, and specific humidity irreversibilities are found to be 30.34%, 33.78%, and 35.88%, respectively, of the total irreversibility, which is 8.5% of the evaporator capacity. [ABSTRACT FROM AUTHOR]

Discusses the development and use of a transient model for evaluating frost formation on a parallel-plate heat pump evaporator. Background on the frost formation model; Heat pump model; Characteristics of the heat pump and evaporator.