Second Law Analysis of Slip Flow Heat Transfer in Annulus Microchannel

2009 ◽  
Author(s):  
Arman Sadeghi ◽  
Abolhassan Asgarshamsi ◽  
Mohammad Hassan Saidi
Keyword(s):  
Aspect Ratio ◽  
Velocity Distribution ◽  
Entropy Generation ◽  
Temperature Difference ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Dimensionless Temperature ◽  
Second Law ◽  
Brinkman Number ◽  
Geometrical Aspect

In the present work, the second law of thermodynamics analysis has been carried out for steady state hydrodynamically and thermally fully developed laminar gas flow in annulus microchannels with asymmetrically heated walls. The rarefaction effects are taken into consideration using first order slip velocity and temperature jump boundary conditions. Viscous heating is also included for both the hot wall and the cold wall cases. Using the velocity distribution obtained in earlier works, the energy equation is solved to get analytically the temperature distribution and consequently to compute the entropy generation rate. The effects of rarefaction and the annulus geometrical aspect ratio on velocity distribution are discussed. The complicated interactive effects of rarefaction, viscous dissipation, the ratio of Brinkman number to dimensionless temperature difference, annulus geometrical aspect ratio and asymmetry on entropy generation rate and Bejan number are shown in graphical form and also discussed in details. The analytical results obtained are compared with those available in the literature and an excellent agreement is observed. It is realized that the effect of the wall heat fluxes ratio on entropy generation is negligible at great values of the ratio of Brinkman number to dimensionless temperature difference, while the effect of increasing values of the annulus geometrical aspect ratio is to severely increase entropy generation. The entropy generation decreases as Knudsen number increases, however the effect of increasing values of Brinkman number and the ratio of Brinkman number to dimensionless temperature difference is to increase entropy generation.

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 Analysis of Effects of Wall Suction on Entropy Generation Rate in Laminar Condensate Layer on Horizontal Tube

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Tong-Bou Chang
Keyword(s):  
Entropy Generation ◽  
Horizontal Tube ◽  
Generation Rate ◽  
Film Condensation ◽  
Entropy Generation Rate ◽  
Dimensionless Temperature ◽  
Wall Suction ◽  
Suction Parameter ◽  
Condensate Layer ◽  
Dimensionless Entropy Generation

The effects of wall suction on the entropy generation rate in a two-dimensional steady film condensation flow on a horizontal tube are investigated theoretically. In analyzing the liquid flow, the effects of both the gravitational force and the viscous force are taken into account. In addition, a film thickness reduction ratio,Sf, is introduced to evaluate the effect of wall suction on the thickness of the condensate layer. The analytical results show that, the entropy generation rate depends on the Jakob number Ja, the Rayleigh number Ra, the Brinkman number Br, the dimensionless temperature differenceψ, and the wall suction parameterSw. In addition, it is shown that in the absence of wall suction, a closed-form correlation for the Nusselt number can be derived. Finally, it is shown that the dimensionless entropy generation due to heat transfer,NT, increases with an increasing suction parameterSw, whereas the dimensionless entropy generation due to liquid film flow friction,NF, decreases.

An Entropic Minimization Technique for Turbine Blade Profiles

2002 ◽  
Author(s):  
Ed Walsh ◽  
Mark Davies ◽  
Roy Myose
Keyword(s):  
Boundary Layer ◽  
Velocity Distribution ◽  
Boundary Layers ◽  
Turbine Blade ◽  
Entropy Generation ◽  
Incompressible Flows ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Minimization Technique ◽  
Boundary Layer Edge

The optimization of the boundary layer edge velocity distribution may hold the key to the minimization of entropy generation in the boundary layers of turbomachinery blades. A preliminary optimization analysis in the laminar region of a non film cooled turbine blade is presented, which demonstrates the concept of how the entropy generation rate may be reduced by varying the boundary layer edge velocity distribution along the suction surface, whilst holding the work done by the blade constant. In the laminar region the analytical technique developed by Pohlhausen and others to predict the boundary layer momentum thickness in the presence of pressure gradients has been adopted to predict the entropy generated as described in other papers by the same authors. The result gives an expression for the entropy generation rate in terms of the boundary layer edge velocity distribution for incompressible flows. The boundary layer edge velocity distribution may then be represented as a polynomial with undefined variables. This allows a minimization technique to be used to minimize the entropy generation rate on these variables. Constraints are included to keep the work output constant and the diffusion low to avoid separation. In this analysis it is only the laminar region that is considered for minimization, thus it is necessary to ensure that the modified boundary layer edge velocity distribution does not undergo transition earlier than the baseline boundary layer edge velocity distribution. This is accomplished by considering transition and separation criteria available in the literature. The result of this analysis indicates that the entropy generation rate may be reduced in the laminar boundary layers by using this technique.

scholarly journals Numerical studies for effect of geometrical parameters on water jet pump performance via entropy generation analysis

2021 ◽  
Vol 15 (3) ◽  
pp. 8319-8331
Author(s):  
Muhammad Penta Helios ◽  
Wanchai Asvapoositkul
Keyword(s):  
Shear Stress ◽  
Aspect Ratio ◽  
Entropy Generation ◽  
Water Jet ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Geometrical Parameters ◽  
Jet Pump ◽  
Pump Performance ◽  
Stress Layer

This paper presented an implementation of entropy generation analysis in the main flow field of a water jet pump via the CFD method. This study aimed to identify the inefficient location of energy conversion and to analyse entropy generation sources in each region of the water jet pump. The 2D-axisymmetric model and realisable k-ε (RKE) turbulence model at steady-state conditions were performed to validate jet pump performance and to assess the entropy generation. Likewise, the effects of the projection ratio  and throat-aspect ratio as independent parameters were investigated. As a result, the throat is the most inefficient part due to the high total entropy generation rate, following by diffuser part. Also, the entropy generation rate was assessed dominant than viscous dissipation due to the turbulent dissipation, which was caused by a turbulent shear stress layer of mixing the streams. In conclusion, the projection ratio influenced the growth of the shear stress layer as well as the entropy generation. Further, the throat-aspect ratio affected the distribution of entropy generation in the throat section. An appropriate combination of both parameters has an impact on the jet pump performance improvements reducing the entropy generation rate in the future.

The Role of Fin Geometry in Heat Sink Performance

2003 ◽  
Author(s):  
Waqar A. Khan ◽  
J. R. Culham ◽  
M. M. Yovanovich
Keyword(s):  
Aspect Ratio ◽  
Entropy Generation ◽  
Heat Sink ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Rectangular Plates ◽  
Minimum Entropy ◽  
Axis Ratio ◽  
Pin Fins ◽  
Minimum Entropy Generation

The following study will examine the effect on overall thermal/fluid performance associated with different fin geometries, including, rectangular plates as well as square, circular and elliptical pin fins. The use of EGM allows the combined effect of thermal resistance and pressure drop to be assessed through the simultaneous interaction with the heat sink. A general expression for the entropy generation rate is obtained by using the conservations equations for mass, energy, and entropy. 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 minimum entropy generation rate corresponding to different parameters including axis ratio, aspect ratio, and approach velocity. The results clearly indicate that the preferred fin profile is very dependent on these parameters.

Second Law Analysis for Extended Graetz Problem Including Viscous Dissipation in Microtubes

2010 ◽  
Author(s):  
Arman Sadeghi ◽  
Mostafa Baghani ◽  
Mohammad Hassan Saidi
Keyword(s):  
Entropy Generation ◽  
Integral Transform ◽  
Entropy Generation Rate ◽  
Dimensionless Temperature ◽  
Brinkman Number ◽  
Axial Coordinate ◽  
Entropy Generation Number ◽  
Nusselt Numbers ◽  
Heating Effects ◽  
Second Law Analysis

The entropy generation rate has become a useful tool for evaluating the intrinsic irreversibilities associated with a given process or device. This work presents an analytical solution for entropy generation in hydrodynamically fully developed thermally developing laminar flow in a microtube. The rarefaction effects as well as viscous heating effects are taken into consideration, but axial conduction is neglected. Using fully developed velocity profile, the energy equation is solved by means of integral transform. The solution is validated by comparing the local Nusselt numbers against existing literature data. From the results it is realized that the entropy generation decreases as Knudsen number increases, while the effect of increasing values of Brinkman number and the ratio of Brinkman number to dimensionless temperature difference is to increase entropy generation. The average entropy generation number over the cross section of channel increases with increasing values of axial coordinate, until it reaches a constant value at fully developed conditions.

Second Law Analysis for Free Convection in Non-Newtonian Fluids Over a Horizontal Plate Embedded in a Porous Medium: Prescribed Surface Temperature

2011 ◽  
Vol 133 (5) ◽  
Author(s):  
W. A. Khan ◽  
Rama Subba Reddy Gorla
Keyword(s):  
Porous Medium ◽  
Free Convection ◽  
Surface Temperature ◽  
Entropy Generation ◽  
Newtonian Fluids ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Second Law ◽  
Bejan Number ◽  
Horizontal Plate

Second law characteristics of heat transfer and fluid flow due to free convection of non-Newtonian fluids over a horizontal plate with prescribed surface temperature in a porous medium are analyzed. Velocity and temperature fields are obtained numerically using an implicit finite difference method under the similarity assumption and these results are used to compute the entropy generation rate Ns, irreversibility ratio Φ, and the Bejan number Be for both Newtonian and non-Newtonian fluids. The effects of viscous frictional parameter G, Rayleigh number Ra, temperature variation λ, axial distance (x) on the dimensionless entropy generation rate Ns, and the Bejan number Be are investigated for Newtonian and non-Newtonian fluids and presented graphically.

Second Law Analysis of Different Channel Geometries for Micro-Mixing

2015 ◽  
Author(s):  
Zhaotong Meng ◽  
Evan C. Lemley ◽  
Mohammad R. Hossan
Keyword(s):  
Entropy Generation ◽  
Flow Direction ◽  
Second Law Of Thermodynamics ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Second Law ◽  
Viscous Effects ◽  
Ansys Fluent ◽  
Experimental Profile ◽  
Computational Fluid Dynamics Cfd

Micro-mixing in different channel geometries may increase entropy generation and lead to improved efficiency of fluid mixing. The entropy generation rate corresponds to irreversibility due to the heat transfer and viscous effects in fluid flow through a channel. The objectives of this study are to validate the entropy generation rate of three expansion/contraction geometries [1] by using an analysis based on the Second Law of Thermodynamics (SLT) numerically and to study how entropy generation rate changes by placing flow obstacles in the channel. The geometries presented are not unique. In this paper the focus is on using CFD combined with the SLT as a tool to explore the effectiveness of micro-mixers. The entropy generation field in the expansion/contraction region between a 100 micrometer wide and a 200 micrometer wide rectangular micro-channel was analyzed using computational fluid dynamics (CFD) ANSYS-Fluent, and compared with the experimental results from Saffaripour et al. [1]. The numerical velocity profiles in the fully developed region of the channel in the flow direction and normal to flow direction were compared with experimental profile [1], and determined to be in agreement with the experimental profile. Using CFD, the entropy generation rates were determined for combinations of channel expansion/contraction geometry and the presence/lack of flow obstacles. The results presented here show that flow obstacles, which generally lead to better mixing, also lead to higher entropy generation rates.

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