Abstract
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.
Highlights
Heat transfer is a fundamental source of thermodynamic irreversibility in all real engineering devices
Dimensionless entropy generation, Be, and pumping power to heat transfer ratio (PPR) of laminar flow in a circular tube immersed in an isothermal fluid are studied in this paper
(4) The entropy generated due to heat transfer is more for water than for ethylene glycol, while the entropy generated due to pressure is more for ethylene glycol than for water, for the same mass flow rate
Summary
Heat transfer is a fundamental source of thermodynamic irreversibility in all real engineering devices. Apart from heat transfer, fluid friction is the other source of loss of available work. Both heat transfer and fluid friction generate entropy This entropy generation must be minimized to reduce the loss of available work. Sahin [3] studied the entropy generated in a circular duct with uniform wall temperature for two fluids, namely, water and glycerol. Sahin [4, 5] considered the effect of duct geometries on the entropy generation, both for uniform wall temperature and for uniform heat flux boundary conditions. The present study is concerned with entropy generation in a circular duct immersed in an isothermal external fluid, which is a more general thermal boundary condition. A comparison has been made with uniform wall temperature boundary condition
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