Duality of Heat Exchanger Performance in Balanced Counter-Flow Systems

2003 ◽  
Vol 125 (3) ◽  
pp. 530-532 ◽  
Author(s):  
Ken Ogiso
Keyword(s):  
Heat Exchanger ◽  
Entropy Generation ◽  
Heat Exchangers ◽  
Flow System ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Heat Conductor ◽  
Counter Flow ◽  
Heat Insulator ◽  
Flow Systems

The duality of heat exchangers to act as both heat conductors and insulators when considering heat exchanger performance is studied from the viewpoint of entropy generation. By defining an appropriate index of the entropy generation rate, it is clarified that the performance paradox pointed out by Bejan can be resolved. The case of a balanced counter-flow system was examined and it has been shown that a heat exchanger can be regarded as both a heat conductor and a heat insulator in terms of entropy generation.

Entropy Analysis of a Radiating Variable Viscosity EG/Ag Nanofluid Flow in Microchannels with Buoyancy Force and Convective Cooling

2018 ◽  
Vol 387 ◽  
pp. 273-285 ◽  
Author(s):  
R.L. Monaledi ◽  
Oluwole Daniel Makinde
Keyword(s):  
Thermal Stability ◽  
Thermal Radiation ◽  
Entropy Generation ◽  
Buoyancy Force ◽  
Volume Fraction ◽  
Flow System ◽  
Variable Viscosity ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Convective Cooling

The inherent irreversibility of a variable viscosity ethylene glycol/silver (EG/Ag) nanofluid single-phase Poiseuille flow in a vertical microchannel with convective cooling under the combined influence of buoyancy force, nonlinear thermal radiation, nanoparticles shape and volume fraction is investigated. The nonlinear model equations are obtained and numerically solved via shooting method with Runge-Kutta-Fehlberg integration scheme. Pertinent results with respect to the effects of emerging thermophysical parameters on the nanofluid velocity, temperature, skin friction, Nusselt number, thermal stability criteria, entropy generation rate and Bejan number are presented graphically and discussed. It is observed that thermal radiation, Biot number and buoyancy force boost the release of heat energy thereby cooling the flow system. Meanwhile, an increase in nanoparticles volume fraction lessens the entropy generation rate which augment the exergetic effectiveness and thermal stability of the flow system.

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.

Entropy Generation in Counter Flow Gas to Gas Heat Exchangers

2005 ◽  
Vol 128 (1) ◽  
pp. 87-92 ◽  
Author(s):  
Hany Ahmed Mohamed
Keyword(s):  
New York ◽  
Heat Exchanger ◽  
Entropy Generation ◽  
Heat Exchangers ◽  
Operating Conditions ◽  
Working Fluid ◽  
Counter Flow ◽  
Thermodynamic Irreversibility ◽  
Flow Imbalance ◽  
New Equation

Analysis of heat transfer and fluid flow thermodynamic irreversibilities is realized on an example of a counter flow double pipe heat exchanger utilizing turbulent air flow as a working fluid. During the process of mathematical model creation and for different working and constructing limitations, total thermodynamic irreversibility is studied. The present work proves that the irreversibility occurred due to unequal capacity flow rates (flow imbalance irreversibility). It is concluded that the heat exchanger should be operated at effectiveness, ε, greater than 0.5 and the well operating conditions will be achieved when ε approaches one where low irreversibility is expected. A new equation is adopted to express the entropy generation numbers for imbalanced heat exchangers of similar design with smallest deviation from the exact value. The results obtained from the new equation are compared with the exact values and with those obtained by Bejan (Bejan, A., 1997, Advanced Engineering Thermodynamics, Wiley, New York).

Analysis of the Effects of Joule Heating and Viscous Dissipation on Combined Pressure-Driven and Electrokinetic Flows in a Two-Parallel Plate Channel with Unequal Constant Temperatures

2018 ◽  
Vol 233 (4) ◽  
pp. 871-879 ◽  
Author(s):  
Harshad Sanjay Gaikwad ◽  
Pranab Kumar Mondal ◽  
Dipankar Narayan Basu ◽  
Nares Chimres ◽  
Somchai Wongwises
Keyword(s):  
Viscous Dissipation ◽  
Entropy Generation ◽  
Joule Heating ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Local Entropy ◽  
Temperature Dependent ◽  
Temperature Dependent Viscosity ◽  
Dependent Viscosity ◽  
Local Entropy Generation

In this article, we perform an entropy generation analysis for the micro channel heat sink applications where the flow of fluid is actuated by combined influences of applied pressure gradient and electric field under electrical double layer phenomenon. The upper and lower walls of the channels are kept at different constant temperatures. The temperature-dependent viscosity of the fluid is considered and hence the momentum equation and energy equations are coupled in this study. Also, a hydrodynamic slip condition is employed on the viscous dissipation. For complete analysis of the entropy generation, we use a perturbation approach with lubrication approximation. In this study, we discuss the results depicting variations in the velocity and temperature distributions and their effect on local entropy generation rate and Bejan number in the system. It can be summarized from this analysis that the enhanced velocity gradients in the flow field due to combined effect of temperature-dependent viscosity and Joule heating and viscous dissipative effects, leads to an enhancement in the local entropy generation rate in the system.

Aerodynamic Optimization Design of Airfoil Shape Using Entropy Generation as an Objective

2018 ◽  
Vol 11 (2) ◽  
Author(s):  
Wei Wang ◽  
Jun Wang ◽  
Xiao-Pei Yang ◽  
Yan-Yan Ding
Keyword(s):  
Entropy Generation ◽  
Energy Cost ◽  
Optimization Design ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Aerodynamic Optimization ◽  
Analysis And Design ◽  
Constraint Model ◽  
The Impact ◽  
Drag Ratio

Abstract An entropy analysis and design optimization methodology is combined with airfoil shape optimization to demonstrate the impact of entropy generation on aerodynamics designs. In the work herein, the entropy generation rate is presented as an extra design objective along with lift-drag ratio, while the lift coefficient is the constraint. Model equation, which calculates the local entropy generation rate in turbulent flows, is derived by extending the Reynolds-averaging of entropy balance equation. The class-shape function transform (CST) parametric method is used to model the airfoil configuration and combine the radial basis functions (RBFs) based mesh deformation technique with flow solver to compute the quantities such as lift-drag ratio and entropy generation at the design condition. From the multi-objective solutions which represent the best trade-offs between the design objectives, one can select a set of airfoil shapes with a low relative energy cost and with improved aerodynamic performance. It can be concluded that the methodology of entropy generation analysis is an effective tool in the aerodynamic optimization design of airfoil shape with the capability of determining the amount of energy cost.

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.

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