The Relationship of Optimum Heat Exchanger Allocation and Minimum Entropy Generation Rate for Refrigeration Cycles

1998 ◽  
Vol 120 (2) ◽  
pp. 172-178 ◽  
Author(s):  
S. A. Klein ◽  
D. T. Reindl
Keyword(s):  
Heat Exchanger ◽  
Entropy Generation ◽  
System Performance ◽  
Coefficient Of Performance ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Vapor Compression ◽  
Minimum Entropy ◽  
Vapor Compression Refrigeration Cycle ◽  
Optimum Heat

This paper investigates the effect of heat exchanger allocation on overall system performance using both reverse Carnot and vapor compression refrigeration cycle models to calculate system performance and entropy generation rate. The algebraically simple constraints applied in previous studies are shown to be justifiable. The vapor compression model considers nonideal compressor performance, compressor volumetric efficiency, refrigerant properties, and throttling, in addition to mechanistic heat exchanger models. The results support the conclusions of previous studies in that maximum performance is observed when the condenser and evaporator thermal sizes are approximately equal. For air-to-air systems, this result indicates that the areas of the heat exchangers should be approximately equal. However, it is found that minimizing the entropy generation rate does not always result in the same design as maximizing the system performance unless the refrigeration capacity is fixed. Minimizing the entropy generation rate per unit capacity is found to always correspond to maximizing the coefficient of performance of refrigeration systems.

The Role of Fin Geometry in Heat Sink Performance

2006 ◽  
Vol 128 (4) ◽  
pp. 324-330 ◽  
Author(s):  
W. A. Khan ◽  
J. R. Culham ◽  
M. M. Yovanovich
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Entropy Generation ◽  
Heat Sink ◽  
Control Volume ◽  
Generation Rate ◽  
Heat Transfer Fluid ◽  
Entropy Generation Rate ◽  
Minimum Entropy ◽  
Axis Ratio

The following study will examine the effect on overall thermal/fluid performance associated with different fin geometries, including, rectangular plate fins as well as square, circular, and elliptical pin fins. The use of entropy generation minimization, EGM, allows the combined effect of thermal resistance and pressure drop to be assessed through the simultaneous interaction with the heat sink. A general dimensionless expression for the entropy generation rate is obtained by considering a control volume around the pin fin including base plate and applying the conservations equations for mass and energy with the entropy balance. The formulation for the dimensionless entropy generation rate is developed in terms of dimensionless variables, including the aspect ratio, Reynolds number, Nusselt number, and the drag coefficient. Selected fin geometries are examined for the heat transfer, fluid friction, and the minimum entropy generation rate corresponding to different parameters including axis ratio, aspect ratio, and Reynolds number. The results clearly indicate that the preferred fin profile is very dependent on these parameters.

Second-Law Analysis on Wavy Plate Fin-and-Tube Heat Exchangers

1998 ◽  
Vol 120 (3) ◽  
pp. 797-800 ◽  
Author(s):  
W. W. Lin ◽  
D. J. Lee
Keyword(s):  
Entropy Generation ◽  
Operating Conditions ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Second Law ◽  
Spanwise Direction ◽  
Minimum Entropy ◽  
Tube Heat Exchanger ◽  
Second Law Analysis ◽  
Minimum Entropy Generation

Second-law analysis on the herringbone wavy plate fin-and-tube heat exchanger was conducted on the basis of correlations of Nusselt number and friction factor proposed by Kim et al. (1997), from which the entropy generation rate was evaluated. Optimum Reynolds number and minimum entropy generation rate were found over different operating conditions. At a fixed heat duty, the in-line layout with a large tube spacing along streamwise direction was recommended. Furthermore, within the valid range of Kim et al.’s correlation, effects of the fin spacing and the tube spacing along spanwise direction on the second-law performance are insignificant.

scholarly journals THEORETICAL AND EXPERIMENTAL ANALYSIS OF A VAPOR-COMPRESSION REFRIGERATION CYCLE WITH A HEAT EXCHANGER BETWEEN THE SUCTION AND LIQUID LINES

2019 ◽  
Vol 18 (2) ◽  
pp. 19
Author(s):  
L. S. Santana ◽  
J. Castro ◽  
L. M. Pereira
Keyword(s):  
Heat Exchanger ◽  
Experimental Analysis ◽  
Thermodynamic Cycle ◽  
Electrical Energy ◽  
Coefficient Of Performance ◽  
Refrigeration Cycle ◽  
Vapor Compression ◽  
Vapor Compression Refrigeration Cycle ◽  
Vapor Compression Refrigeration ◽  
Liquid Heat

Vapor-compression refrigeration systems require a significant amount of electrical energy. Therefore, there is a need for finding efficient ways of operating this equipment, reducing their energy consumption. The use of heat exchangers between the suction line and the liquid line can produce a better performance of the thermodynamic cycle, as well as reduce it. The present work aims at an experimental analysis of the suction/liquid heat exchanger present in a freezer running with refrigerant fluid R-134a. Three different scenarios were used in order to evaluate the thermal performance of the refrigeration cycle. The first scenario was the conventional freezer set up to collect the required data for further comparison. Moreover, the second and third scenarios were introduced with a 20 cm and 40 cm suction/liquid heat exchanger, respectively, into the system. From the experiments, it was observed that the heat exchange does not significantly affect the coefficient of performance (COP) of the freezer. It was concluded from this work that the best scenario analyzed was the 20 cm suction/liquid heat exchanger where most of the thermodynamic properties were improved, one of them being the isentropic efficiency.

Entropy Generation Minimization in a Pressure-Driven Microflow of Viscoelastic Fluid With Slippage at the Wall: Effect of Conjugate Heat Transfer

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Rajkumar Sarma ◽  
Pranab Kumar Mondal
Keyword(s):  
Heat Transfer ◽  
Viscoelastic Fluid ◽  
Entropy Generation ◽  
Conjugate Heat Transfer ◽  
Applied Pressure ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Minimum Entropy ◽  
Viscoelastic Parameter ◽  
Entropy Generation Minimization

We focus on the entropy generation minimization for the flow of a viscoelastic fluid through a parallel plate microchannel under the combined influences of applied pressure gradient, interfacial slip, and conjugate heat transfer. We use the simplified Phan–Thien–Tanner model (s-PTT) to represent the rheological behavior of the viscoelastic fluid. Using thermal boundary conditions of the third kind, we solve the transport equations analytically to obtain the velocity and temperature distributions in the flow field, which are further used to calculate the entropy generation rate in the analysis. In this study, the influential role of the following dimensionless parameters on entropy generation rate is examined: the viscoelastic parameter (εDe2), slip coefficient (k¯), channel wall thickness (δ), thermal conductivity of the wall (γ), Biot number (Bi) and Peclet number (Pe). We show that there exists a particular value of the abovementioned parameters that lead to a minimum entropy generation rate in the system. We believe the results of this analysis could be of helpful in the optimum design of microfluidic system/devices typically used in thermal management, such as micro-electronic devices, microreactors, and microheat exchangers.

Genetic Algorithm-Based Optimal Design of Plate Fins Following Minimum Entropy Generation Considerations

2005 ◽  
Vol 219 (8) ◽  
pp. 757-765 ◽  
Author(s):  
R. K. Jha ◽  
S Chakraborty
Keyword(s):  
Heat Transfer ◽  
Genetic Algorithm ◽  
Optimal Design ◽  
Forced Convection ◽  
Entropy Generation ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Minimum Entropy ◽  
Minimum Entropy Generation ◽  
Continuous Plate

This paper deals with estimation of the optimal dimensions of arrays of plate fins cooled by forced convection. The optimization is achieved by minimizing the entropy generation rate using genetic algorithm-based evolutionary computing techniques. Results are presented for staggered plate fins configuration and continuous plate fins configuration. The effects of heat transfer and fluid friction on entropy generation rate are also reported.

The Equivalence of Maximum Power and Minimum Entropy Generation Rate in the Optimization of Power Plants

1996 ◽  
Vol 118 (2) ◽  
pp. 98-101 ◽  
Author(s):  
Adrian Bejan
Keyword(s):  
Heat Transfer ◽  
Power Plant ◽  
Entropy Generation ◽  
Heat Input ◽  
Power Plants ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Total Entropy ◽  
Minimum Entropy ◽  
Minimum Entropy Generation

It is shown that to maximize the power output of a power plant is equivalent to minimizing the total entropy generation rate associated with the power plant. This equivalence is illustrated by using two of the oldest and simplest models of power plants with heat transfer irreversibilities. To calculate the total entropy generation rate correctly, one must recognize that the optimization process (e.g., the variability of the heat input) requires “room to move,” i.e., an additional, usually overlooked, contribution to the total entropy generation rate.

Specific Entropy Generation in a Gas Turbine Power Cycle

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Y. Haseli
Keyword(s):  
Gas Turbine ◽  
Entropy Generation ◽  
Thermal Efficiency ◽  
Operating Conditions ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Minimum Entropy ◽  
Power Cycle ◽  
Specific Entropy ◽  
Energy Conversion Systems

Numerous studies have shown that the minimization of entropy generation does not always lead to an optimum performance in energy conversion systems. The equivalence between minimum entropy generation and maximum power output or maximum thermal efficiency in an irreversible power cycle occurs subject to certain design constraints. This article introduces specific entropy generation defined as the rate of total entropy generated due to the operation of a power cycle per unit flowrate of fuel. Through a detailed thermodynamic modeling of a gas turbine cycle, it is shown that the specific entropy generation correlates unconditionally with the thermal efficiency of the cycle. A design at maximum thermal efficiency is found to be identical to that at minimum specific entropy generation. The results are presented for five different fuels including methane, hydrogen, propane, methanol, and ethanol. Under identical operating conditions, the thermal efficiency is approximately the same for all five fuels. However, a power cycle that burns a fuel with a higher heating value produces a higher specific entropy generation. An emphasis is placed to distinguish between the specific entropy generation (with the unit of J/K mol fuel) and the entropy generation rate (W/K). A reduction in entropy generation rate does not necessarily lead to an increase in thermal efficiency.

scholarly journals Effect of Using Extra Fins on the Pin Fin Classic Geometry for Enhancement Heat Sink Performance using EGM Method

2018 ◽  
Vol 24 (4) ◽  
pp. 1 ◽  
Author(s):  
Kadhum Audaa Jehhef
Keyword(s):  
Reynolds Number ◽  
Nusselt Number ◽  
Cross Section ◽  
Entropy Generation ◽  
Heat Sink ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Minimum Entropy ◽  
Pin Fin ◽  
Pin Fins

In the present study, the effect of new cross-section fin geometries on overall thermal/fluid performance had been investigated. The cross-section included the base original geometry of (triangular, square, circular, and elliptical pin fins) by adding exterior extra fins along the sides of the origin fins. The present extra fins include rectangular extra fin of 2 mm (height) and 4 mm (width) and triangular extra fin of 2 mm (base) 4 mm (height). The use of entropy generation minimization method (EGM) allows the combined effect of thermal resistance and pressure drop to be assessed through the simultaneous interaction with the heat sink. A general dimensionless expression for the entropy generation rate is obtained by considering a control volume around the pin fin including a base plate and applying the conservations equations of mass and energy with the entropy balance. The dimensionless numbers used includes the aspect ratio (ε), Reynolds number (Re), Nusselt number (Nu), and the drag coefficients (CD). Fourteen different cross-section fin geometries are examined for the heat transfer, fluid friction, and the minimum entropy generation rate. The results showed that the Nusselt number increases with increasing the Reynolds number for all employed models. The ellipse models (ET and ER-models) give the highest value in the Nusselt number as compared with the classical pin fins. The fin of the square geometry with four rectangular extra fins (SR-models) gives an agreement in Nusselt number as compared with the previous study.  

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