An analysis of entropy generation through a circular duct with different shaped longitudinal fins for laminar flow

2005 ◽  
Vol 48 (1) ◽  
pp. 171-181 ◽  
Author(s):  
İhsan Dağtekin ◽  
Hakan F. Öztop ◽  
Ahmet Z. Şahin
Keyword(s):  
Laminar Flow ◽  
Entropy Generation ◽  
Circular Duct

scholarly journals Second Law Analysis of Laminar Flow in a Circular Pipe Immersed in an Isothermal Fluid

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
Vishal Anand ◽  
Krishna Nelanti
Keyword(s):  
Laminar Flow ◽  
Entropy Generation ◽  
Circular Tube ◽  
Dimensionless Temperature ◽  
Bejan Number ◽  
Uniform Wall Temperature ◽  
Thermal Boundary Conditions ◽  
Fluid Properties ◽  
Isothermal Fluid ◽  
Uniform Wall

Entropy generation and pumping power to heat transfer ratio (PPR) of a laminar flow, for a circular tube immersed in an isothermal fluid, are studied analytically in this paper. Two different fluids, namely, water and ethylene glycol, are chosen to study the influence of fluid properties on entropy generation and PPR. The expressions for dimensionless entropy generation, Bejan number and PPR are derived in a detailed way and their variations with Reynolds number, external Biot number, and the dimensionless temperature difference are illustrated. The results of the analysis are compared with those for a laminar flow in a circular tube with uniform wall temperature boundary condition. Finally, a criterion is established to determine which type of thermal boundary conditions is more suitable for a particular fluid, with respect to its influence on entropy generation.

Effects of Buoyancy on Laminar Flow in Curved Elliptic Ducts

1992 ◽  
Vol 114 (4) ◽  
pp. 936-943 ◽  
Author(s):  
Z. F. Dong ◽  
M. A. Ebadian
Keyword(s):  
Laminar Flow ◽  
Stokes Equations ◽  
Control Volume ◽  
Boussinesq Approximation ◽  
Navier Stokes ◽  
Uniform Heat Flux ◽  
Published Data ◽  
Circular Duct ◽  
Uniform Wall Temperature ◽  
Wide Range

This paper numerically investigates the effects of buoyancy on fully developed laminar flow in a curved duct with an elliptic cross section. The flow of Newtonian fluids is assumed steady in terms of Boussinesq approximation. The curved elliptic duct is subjected to thermal boundary conditions of axially uniform heat flux and peripherally uniform wall temperature. The numerically generated boundary-fitted coordinate system is applied to discretize the solution domain of the elliptic duct, and the Navier-Stokes equations and the energy equation, including the curvature ratio, are solved by use of the control volume-based finite difference method. The solution covers a wide range of curvature ratios, and Dean and Grashof numbers. The results presented are displayed graphically and in tabular form to illustrate the buoyancy effect. It is further shown that buoyancy acts to increase both the Nusselt number and the friction factor and changes the distribution of the velocity and the temperature. The results for the curved circular duct with and without buoyancy are compared with the data available in the open literature for all cases. Also compared with the published data are the results of laminar flow in a curved elliptic duct, and very good agreement is obtained.

Laminar Flow Model in Ducts of Circular Section With Arbitrary Axial Variation

2010 ◽  
Author(s):  
Mario F. Letelier ◽  
Dennis A. Siginer ◽  
Juan S. Stockle ◽  
Andy Huilcan
Keyword(s):  
Laminar Flow ◽  
Flow Model ◽  
Pressure Field ◽  
Axial Direction ◽  
Working Fluid ◽  
Circular Section ◽  
Circular Duct ◽  
Variable Section ◽  
Axial Variation ◽  
Laminar Flow Model

Laminar flow inside a circular duct of variable section in the axial direction is modeled, assuming that the working fluid is Newtonian, incompressible, with laminar flow, a permanent state, and constant properties. The results describe the behavior of the stream function, the velocity field, and the pressure field, and graphic results are presented for each of those functions. The method used to solve the problem makes use of regular perturbations around the shape factor ε parameter. This research can be used for the design of new technological devices important to industry, optimizing processes in which fluids are transported, energy is transferred, etc.

Entropy Generation Minimization of Confined Nanofluids Laminar Flow Around a Block

2010 ◽  
Author(s):  
Mehdi Boghrati ◽  
Ehsan Ebrahimnia Bajestan ◽  
Vahid Etminan
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Laminar Flow ◽  
Entropy Generation ◽  
Control Volume ◽  
Spherical Shape ◽  
Temperature Fields ◽  
Heating Process ◽  
Water Mixture ◽  
Entropy Generation Minimization

According to the importance of cooling and heating process of a solid object, entropy generation in confined flow around a block is studied. In the current study, numerical simulation of laminar flow and heat transfer of nanofluids with nanoparticles of different shapes is considered. The nanofluids are water mixture with either Al2O3 nanoshperes or carbon nanotubes (CNTs). The incompressible Navier-Stokes and energy equations are solved numerically in a body fitted coordinates system using a control volume technique. The flow patterns and temperature fields for different values of the particles concentrations are examined in detail. Furthermore, the effects of nanoparticles shape and concentration on the heat transfer are studied. Furthermore the influences of nanofluids on pressure drop and pump power is examined. On the other hand, the entropy generation minimization is considered as the optimization criterion. The results indicate that in most cases the nanofluids enhance the heat transfer as well as pressure drop. It is interesting to note that the shape of nanoparticles is critical in determining the key mechanism of heat transport in nanofluids. Nanofluids with cylindrical nanoparticles exhibit a greater increase in heat transfer compared with nanofluids having spherical shape nanoparticles.

Entropy Generation Minimization of Fully Developed Internal Convective Flows With Constant Heat Flux

2003 ◽  
Author(s):  
Eric B. Ratts ◽  
Atul G. Raut
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Number ◽  
Laminar Flow ◽  
Turbulent Flow ◽  
Entropy Generation ◽  
Cross Sections ◽  
Constant Heat Flux ◽  
Constant Heat ◽  
Entropy Generation Minimization

This paper addresses the thermodynamic optimum of single-phase convective heat transfer in fully developed flow for uniform and constant heat flux. The optimal Reynolds number is obtained using the entropy generation minimization (EGM) method. Entropy generation due to viscous dissipation and heat transfer dissipation in the flow passage are summed, and then minimized with respect to Reynolds number based on hydraulic diameter. For fixed mass flow rate and fixed total heat transfer rate, and the assumption of uniform heat flux, an optimal Reynolds number for laminar as well as turbulent flow is obtained. In addition, the method quantifies the flow irreversibilities. It was shown that the ratio of heat transfer dissipation to viscous dissipation at minimum entropy generation was 5:1 for laminar flow and 29:9 for turbulent flow. For laminar flow, the study compared non-circular cross-sections to the circular cross-section. The optimal Reynolds number was determined for the following cross-sections: square, equilateral triangle, and rectangle with aspect ratios of two and eight. It was shown that the rectangle with the higher aspect ratio had the smallest optimal Reynolds number, the smallest entropy generation number, and the smallest flow length.

Numerical Investigation of Local Entropy Generation for Laminar Flow in Rotating-Disk Systems

2010 ◽  
Vol 132 (9) ◽  
Author(s):  
Mohammad Shanbghazani ◽  
Vahid Heidarpoor ◽  
Marc A. Rosen ◽  
Iraj Mirzaee
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Laminar Flow ◽  
Entropy Generation ◽  
Generation Rate ◽  
Entropy Generation Rate ◽  
Bejan Number ◽  
Local Entropy ◽  
Fluid Friction ◽  
Local Entropy Generation

The entropy generation is investigated numerically in axisymmetric, steady-state, and incompressible laminar flow in a rotating single free disk. The finite-volume method is used for solving the momentum and energy equations needed for the determination of the entropy generation due to heat transfer and fluid friction. The numerical model is validated by comparing it to previously reported analytical and experimental data for momentum and energy. Results are presented in terms of velocity distribution, temperature, local entropy generation rate, Bejan number, and irreversibility ratio distribution for various rotational Reynolds number and physical cases, using dimensionless parameters. It is demonstrated that increasing rotational Reynolds number increases the local entropy generation rate and irreversibility rate, and that the irreversibility is mainly due to heat transfer while the irreversibility associated with fluid friction is minor.

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