scholarly journals Entropy Generation during Turbulent Flow of Zirconia-water and Other Nanofluids in a Square Cross Section Tube with a Constant Heat Flux

Entropy ◽  
2014 ◽  
Vol 16 (11) ◽  
pp. 6116-6132 ◽  
Author(s):  
Hooman Yarmand ◽  
Goodarz Ahmadi ◽  
Samira Gharehkhani ◽  
Salim Kazi ◽  
Mohammad Safaei ◽  
...  
Keyword(s):  
Heat Flux ◽  
Turbulent Flow ◽  
Cross Section ◽  
Entropy Generation ◽  
Constant Heat Flux ◽  
Constant Heat

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 CuO-water nanofluid turbulent convective heat transfer in square cross-section duct under constant heat flux

2016 ◽  
Vol 33 (6) ◽  
pp. 1714-1728 ◽  
Author(s):  
Hsien-Hung Ting ◽  
Shuhn-Shyurng Hou
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Cross Section ◽  
Convective Heat ◽  
Constant Heat Flux ◽  
Constant Heat ◽  
Content Type

Purpose – The purpose of this paper is to numerically investigate the convective heat transfer of water-based CuO nanofluids flowing through a square cross-section duct under constant heat flux in the turbulent flow regime. Design/methodology/approach – The numerical simulation is carried out at various Peclet numbers and particle concentrations (0.1, 0.2, 0.5, and 0.8 vol%). The finite volume formulation is used with the semi-implicit method for pressure-linked equations algorithm to solve the discretized equations derived from the partial nonlinear differential equations of the mathematical model. Findings – The heat transfer coefficients and Nusselt numbers of CuO-water nanofluids increase with increases in the Peclet number as well as particle volume concentration. Also, enhancement of the heat transfer coefficient is much greater than that of the effective thermal conductivity at the same nanoparticle concentration. Research limitations/implications – Simulation of nanofluids turbulent forced convection at very high Reynolds number is worth for further study. Practical implications – The heat transfer rates through non-circular ducts are smaller than the circular tubes. Nevertheless, the pressure drop of the non-circular duct is less than that of the circular tube. This study clearly presents that the nanoparticles suspended in water enhance the convective heat transfer coefficient, despite low volume fraction between 0.1 and 0.8 percent. Adding nanoparticles to conventional fluids may enhance heat transfer performance through the non-circular ducts, leading to extensive practical applications in industries for the non-circular ducts. Originality/value – Few papers have numerically studied convective heat transfer properties of nanofluids through non-circular ducts. The present numerical results show a good agreement with the published experimental data.

scholarly journals Heat transfer coefficient in elliptical tube at the constant heat flux

2019 ◽  
Vol 23 (Suppl. 4) ◽  
pp. 1323-1332
Author(s):  
Stanislaw Lopata ◽  
Pawel Oclon ◽  
Tomasz Stelmach ◽  
Pawel Markowski
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Cross Section ◽  
Measurement Data ◽  
Constant Heat Flux ◽  
Working Fluid ◽  
Constant Heat ◽  
The Heat Transfer Coefficient

Cross-flow heat exchangers with elliptical tubes are often used in industrial application. In comparison with round tubes, the elliptical tubes have a better aero-dynamic shape, which results in a lower pressure drop of working fluid flowing through the inter-tubular space of heat exchanger. Also, a higher heat flux is transferred from gas to the wall of such a tube due to the more intense heat exchange process. To prove this thesis, the values of the heat transfer coefficient from the wall of the elliptical pipe to the water flowing inside were determined, using the data from the conducted measurements. This study presents also research stand with a vertically positioned tube. In order to obtain a constant heat flux through the wall of elliptical tube, a resistance wire is used, evenly wound on the external surface of tube measuring section. The use of thermal insulation minimized heat loss to the environment to a negligible value. Installed K-type thermocouples allowed one to obtain, for various measurement conditions, the temperature distribution within the elliptical tube wall (for a given cross-section) and the water flowing inside it (in a given cross-section, at different depths, for both axes of the ellipse). The design of the stand allows such measurements in several locations along the length of the measurement section. The measurement results were used to verify numerical calculations. The relative error of the heat transfer coefficient value determined on the basis of CFD calculations using the SST-TR turbulence model in relation to the one determined on the basis of the measurement data is about 11%.

Generalized Lévêque Solution for Ducts of Arbitrary Cross-Section

2021 ◽  
Author(s):  
Ted Bennett
Keyword(s):  
Heat Flux ◽  
Shear Stress ◽  
Cross Section ◽  
Constant Heat Flux ◽  
Arbitrary Cross Section ◽  
Regular Polygons ◽  
Constant Heat ◽  
Original Analysis ◽  
Wall Condition ◽  
Generalized Correlation

Abstract The asymptotic limit for perimeter averaged convection is generalized for short ducts of arbitrary cross-section. A correction factor to Lévêque's original analysis is derived in terms of the state of wall shear stress under conditions of fully developed flows for walls of constant temperature (T) and constant heat flux (H1 and H2). This analysis is performed for four duct geometries: elliptic, rhombic, rectangular, and regular polygons. The importance of this correction is greatest for the H2 wall condition and for ducts having walls with acute corners. The results of this analysis can be incorporated into a generalized correlation for the full Graetz problem in ducts of arbitrary cross-section.

Laminar Entropy Generation Over a Flat Plate With Isothermal and Constant Heat Flux Boundary Conditions Using the Von Ka´rma´n Integral Method

Volume 1 ◽  
2004 ◽  
Author(s):  
Eric B. Ratts ◽  
J. Steven Brown
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boundary Conditions ◽  
Flat Plate ◽  
Entropy Generation ◽  
Single Phase ◽  
Constant Heat Flux ◽  
Constant Heat ◽  
Fundamental Study ◽  
Flux Boundary Conditions

This paper is a fundamental study on the irreversibility of single-phase laminar convective heat transfer over a flat plate with isothermal and constant heat flux boundary conditions. It quantifies the losses due to viscous momentum transfer losses and heat transfer losses and presents the irreversibility of the convective flow based on the entropy generation (EG) method. This paper determines the entropy generation for incompressible, single phase, laminar flow for large and small Prandtl numbers over a flat plate with isothermal and constant heat flux boundary conditions using von Ka´rma´n’s integral theory.

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