Selection of Optimum Heat Flux Distribution in Pipe Flow Under Laminar Forced Convection
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RESEARCH ARTICLE–MECHANICAL ENGINEERING
Selection of Optimum Heat Flux Distribution in Pipe Flow Under Laminar Forced Convection Muhammad Ahmad Jamil1 · S. Z. Shuja2 · Syed M. Zubair2 Received: 23 July 2020 / Accepted: 20 October 2020 © King Fahd University of Petroleum & Minerals 2020
Abstract The concept of non-uniform heat flux distributions has emerged because of its potential to make the design of thermal systems more flexible. Therefore, the current study highlights the impact of non-uniform heat flux distributions on the thermal characteristics of a high Prandtl number fluid for forced convective laminar flow regime in a horizontal pipe. The steady-state 2D simulations have been employed using ANSYS Fluent. The variations in heat flux distributions as a wall boundary condition are systematically analyzed while keeping the total heat transfer constant. The results obtained for various distributions are compared in terms of a dimensionless maximum wall temperature (hot spot), local and average Nusselt numbers, and entropy generation rate. The analysis showed that the heat flux distributions significantly affected the heat transfer pattern. It was found that the hot spot temperature was lower for the descending heat flux boundary conditions compared to the ascending type of distributions. However, a higher entropy generation rate was observed for descending distributions as compared to ascending ones. It was also found that the ascending heat flux distributions provided higher average Nusselt number values than the descending cases of heat flux. Keywords Optimum heat flux · Pipe flow · Entropy generation · Hot spot · Heat flux distribution
List of Symbols Br HF CHF CP D EGM EGR k L n Nu Nu P
B
Brinkman number Heat flux Constant heat flux Specific heat (J/kg K) Pipe diameter (m) Entropy generation minimization Entropy generation rate Thermal conductivity (W/m K) Pipe length (m) Heat flux distribution parameter Nusselt number Mean Nusselt number Pressure (kPa)
Syed M. Zubair [email protected]
1
Department of Mechanical Engineering, Khwaja Fareed University of Engineering and Information Technology, Rahim Yar Khan, Pakistan
2
Department of Mechanical Engineering, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia
Pr q r Re S˙ T UDF u v x
Prandtl number Heat flux at the wall (W/m2 ) Radial direction (m) Reynolds number Entropy generation rate (W/K) Temperature (K) User defined function Axial velocity (m/s) Radial velocity (m/s) Axial direction (m)
Greek Letters Φ Viscous dissipation μ Viscosity (N/ms) ψ Heat flux distribution function (Eqs. 15a, 15b) ρ Density (kg/m3 )
Subscripts D Diameter
123
Arabian Journal for Science and Engineering
f Fluid g Generation i Inlet L x L location m Mean value w Wall
Superscripts * Dimensionless form
1 Introduction Hot fluids are extensively used in industries for chemical treatment, drying of bulk material, heating of process liquids, and batch processing [1]. The required temperature at the utility point is ensured by either h
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