The Role of Entropy Generation in Momentum and Heat Transfer

2010 ◽  
Author(s):  
Heinz Herwig
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
Entropy Generation ◽  
Second Law ◽  
Transfer Processes ◽  
Second Law Analysis ◽  
Momentum And Heat Transfer ◽  
Transfer Problems

Entropy generation in a velocity and temperature field is shown to be very significant in momentum and heat transfer problems. After the determination of this post-processing quantity many details about the physics of a problem are available. This second law analysis (SLA) is a tool for conceptual considerations, for the determination of losses, both in the velocity and the temperature field, and it helps to assess complex convective heat transfer processes. These three aspects in conjunction with entropy generation are discussed in detail and illustrated by several examples.

The Role of Entropy Generation in Momentum and Heat Transfer

2012 ◽  
Vol 134 (3) ◽  
Author(s):  
Heinz Herwig
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
Entropy Generation ◽  
Second Law ◽  
Transfer Processes ◽  
Second Law Analysis ◽  
Momentum And Heat Transfer ◽  
Transfer Problems

Entropy generation in a velocity and temperature field is shown to be very significant in momentum and heat transfer problems. After the determination of this postprocessing quantity, many details about the physics of a problem are available. This second law analysis (SLA) is a tool for conceptual considerations, for the determination of losses, both in the velocity and the temperature field, and it helps to assess complex convective heat transfer processes. These three aspects in conjunction with entropy generation are discussed in detail and illustrated by several examples.

scholarly journals Analytical Assessment of (Al2O3–Ag/H2O) Hybrid Nanofluid Influenced by Induced Magnetic Field for Second Law Analysis with Mixed Convection, Viscous Dissipation and Heat Generation

Coatings ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 498
Author(s):  
Wasim Ullah Khan ◽  
Muhammad Awais ◽  
Nabeela Parveen ◽  
Aamir Ali ◽  
Saeed Ehsan Awan ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Viscous Dissipation ◽  
Entropy Generation ◽  
Heat Generation ◽  
Transfer Rate ◽  
Second Law ◽  
Hybrid Nanofluid ◽  
Entropy Generation Number ◽  
Generation Number ◽  
Second Law Analysis

The current study is an attempt to analytically characterize the second law analysis and mixed convective rheology of the (Al2O3–Ag/H2O) hybrid nanofluid flow influenced by magnetic induction effects towards a stretching sheet. Viscous dissipation and internal heat generation effects are encountered in the analysis as well. The mathematical model of partial differential equations is fabricated by employing boundary-layer approximation. The transformed system of nonlinear ordinary differential equations is solved using the homotopy analysis method. The entropy generation number is formulated in terms of fluid friction, heat transfer and Joule heating. The effects of dimensionless parameters on flow variables and entropy generation number are examined using graphs and tables. Further, the convergence of HAM solutions is examined in terms of defined physical quantities up to 20th iterations, and confirmed. It is observed that large λ1 upgrades velocity, entropy generation and heat transfer rate, and drops the temperature. High values of δ enlarge velocity and temperature while reducing heat transport and entropy generation number. Viscous dissipation strongly influences an increase in flow and heat transfer rate caused by a no-slip condition on the sheet.

Second Law Analysis of Spray Evaporation

1990 ◽  
Vol 112 (2) ◽  
pp. 130-135 ◽  
Author(s):  
S. K. Som ◽  
A. K. Mitra ◽  
S. P. Sengupta
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Entropy Generation ◽  
Exergy Analysis ◽  
Droplet Evaporation ◽  
Second Law ◽  
Hot Gas ◽  
Second Law Analysis ◽  
Initial Drop ◽  
Parallel Stream

A second law analysis has been developed for an evaporative atomized spray in a uniform parallel stream of hot gas. Using a discrete droplet evaporation model, an equation for entropy balance of a drop has been formulated to determine numerically the entropy generation histories of the evaporative spray. For the exergy analysis of the process, the rate of heat transfer and that of associated irreversibilities for complete evaporation of the spray have been calculated. A second law efficiency (ηII), defined as the ratio of the total exergy transferred to the sum of the total exergy transferred and exergy destroyed, is finally evaluated for various values of pertinent input parameters, namely, the initial Reynolds number (Rei = 2ρgVixi/μg) and the ratio of ambient to initial drop temperature (Θ∞′/Θi′).

Entropy generation and second law analysis of pulsed impinging jet

2015 ◽  
Vol 25 (5) ◽  
pp. 1089-1106 ◽  
Author(s):  
Kazem Esmailpour ◽  
Behnam Bozorgmehr ◽  
Seyed Mostafa Hosseinalipour ◽  
Arun S. Mujumdar
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
Entropy Generation ◽  
Impinging Jet ◽  
Entropy Generation Rate ◽  
Second Law ◽  
Pulsation Frequency ◽  
Content Type ◽  
Thermal Entropy ◽  
Plate Distance

Purpose – The purpose of this paper is to examine entropy generation rate in the flow and temperature field due pulsed impinging jet on to a flat plate. Heat transfer of pulsed impinging jets has been investigated by many researchers. Entropy generation is one of the parameters related to the second law of thermodynamics which must be analyzed in processes with heat transfer and fluid flow in order to design efficient systems. Effect of velocity profile parameters and various nozzle to plate distances on viscous and thermal entropy generation are investigated. Design/methodology/approach – In this study, the flow and temperature field of a pulsed turbulent impinging jet are simulated numerically by the finite volume method with appropriate boundary conditions. Then, flow and temperature results are used to calculate the rate of entropy generation due to heat transfer and viscous dissipation. Findings – Results show that maximum viscous and thermal entropy generation occurs in the lowest nozzle to plate distance and entropy generation decreases as the nozzle to plate distance increases. Entropy generation in the two early phase of a period in the most frequencies is more than steady state whereas a completely opposite behavior happens in the two latter phase. Increase in the pulsation frequency and amplitude leads to enhancement in entropy generation because of larger temperature and velocity gradients. This phenomenon appears second and even third peaks in entropy generation plots in higher pulsation frequency and amplitude. Research limitations/implications – The predictions may be extended to include various pulsation signal shape, multiple jet configuration, the radiation effect and phase difference between jets. Practical implications – The results of this paper are a valuable source of information for active control of transport phenomena in impinging jet configurations which is used in different industrial applications such as cooling, heating and drying processes. Originality/value – In this paper the entropy generation of pulsed impinging jet was studied for the first time and a comprehensive discussion on numerical results is provided.

Second Law Analysis Through a Porous Poiseuille–Benard Channel Flow

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
Amel Tayari ◽  
Nejib Hidouri ◽  
Mourad Magherbi ◽  
Ammar Ben Brahim
Keyword(s):  
Heat Transfer ◽  
Finite Element Method ◽  
Channel Flow ◽  
Entropy Generation ◽  
Control Volume ◽  
Second Law ◽  
Brinkman Model ◽  
Second Law Analysis ◽  
Medium Porosity ◽  
Control Volume Finite Element

This paper proposes a numerical analysis of entropy generation during mixed convection inside a porous Poiseuille–Benard channel flow, where the Darcy–Brinkman model is used. Irreversibilities due to heat transfer and viscous dissipation have been derived, and then calculated by numerically solving mass, momentum, and energy conservation equations, by using a control volume finite element method (CVFEM). For a fixed value of the thermal Rayleigh (Ra = 104) and the modified Brinkman (Br* = 10−3) numbers, transient entropy generation exhibits a periodic behavior for the medium porosity ε ≥ 0.2, which is described by the onset of thermoconvective cells inside the porous channel. Highest irreversibility is obtained at ε = 0.5. More details about the effects of the Darcy, the Rayleigh, and the modified Brinkman numbers on entropy generation and heat transfer are discussed and graphically presented.

scholarly journals Using Graphene Nanoplatelets Nanofluid in a Closed-Loop Evacuated Tube Solar Collector—Energy and Exergy Analysis

2021 ◽  
Vol 5 (10) ◽  
pp. 277
Author(s):  
Soudeh Iranmanesh ◽  
Mahyar Silakhori ◽  
Mohammad S. Naghavi ◽  
Bee C. Ang ◽  
Hwai C. Ong ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Entropy Generation ◽  
Flow Rate ◽  
Closed Loop ◽  
Heat Transfer Fluid ◽  
Second Law ◽  
Bejan Number ◽  
Pumping Power ◽  
Energy And Exergy ◽  
Second Law Analysis

Recently, nanofluid application as a heat transfer fluid for a closed-loop solar heat collector is receiving great attention among the scientific community due to better performance. The performance of solar systems can be assessed effectively with the exergy method. The present study deals with the thermodynamic performance of the second law analysis using graphene nanoplatelets nanofluids. Second law analysis is the main tool for explaining the exergy output of thermodynamic and energy systems. The performance of the closed-loop system in terms of energy and exergy was determined by analyzing the outcome of field tests in tropical weather conditions. Moreover, three parameters of entropy generation, pumping power and Bejan number were also determined. The flowrates of 0.5, 1 and 1.5 L/min and GNP mass percentage of 0.025, 0.5, 0.075 and 0.1 wt% were used for these tests. The results showed that in a flow rate of 1.5 L/min and a concentration of 0.1 wt%, exergy and thermal efficiencies were increased to about 85.5 and 90.7%, respectively. It also found that entropy generation reduced when increasing the nanofluid concentration. The Bejan number surges up when increasing the concentration, while this number decreases with the enhancement of the volumetric flow rate. The pumping power of the nanofluid-operated system for a 0.1 wt% particle concentration at 0.5 L/min indicated 5.8% more than when pure water was used as the heat transfer fluid. Finally, this investigation reveals the perfect conditions that operate closest to the reversible limit and helps the system make the best improvement.

Second Law Analysis of Solid Desiccant Rotary Dehumidifiers

1988 ◽  
Vol 110 (1) ◽  
pp. 2-9 ◽  
Author(s):  
E. Van den Bulck ◽  
S. A. Klein ◽  
J. W. Mitchell
Keyword(s):  
Local Maximum ◽  
Operating Conditions ◽  
Second Law ◽  
Transfer Coefficients ◽  
Adiabatic Flow ◽  
Transfer Processes ◽  
Air Stream ◽  
Second Law Analysis ◽  
Pass Through ◽  
Air Streams

This paper presents a second law analysis of solid desiccant rotary dehumidifiers. The equations for entropy generation for adiabatic flow of humid air over a solid desiccant are developed. The generation of entropy during operation of a rotary dehumidifier with infinite transfer coefficients is investigated and the various sources of irreversibility are identified and quantified. As they pass through the dehumidifier, both the process and regeneration air streams acquire nonuniform outlet states, and mixing both of these air streams to deliver homogeneous outlet streams is irreversible. Transfer of mass and energy between the regeneration air stream and the desiccant matrix occurs across finite differences in vapor pressure and temperature and these transfer processes generate entropy. The second law efficiency of the dehumidifier is given as a function of operating conditions and the effect of finite transfer coefficients for an actual dehumidifier is discussed. It is shown that operating the rotary dehumidifier at conditions that minimize regeneration energy also yields a local maximum for the second law efficiency.

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