Enhanced heat transfer and flow analysis in a backward-facing step using a porous baffle
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Enhanced heat transfer and flow analysis in a backward‑facing step using a porous baffle Chuanchang Li1 · Guohua Cui1 · Jianguang Zhai1 · Saixuan Chen1 · Zhi Hu1 Received: 16 January 2020 / Accepted: 11 February 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract The backward-facing step or the sudden expansion in internal flows is an important problem in different areas. In this study, a porous baffle is mounted on the opposite wall of a sudden expansion to enhance heat transfer near the step. Unlike the solid baffle, which is extensively studied in the literature, the porous baffle has a lower pressure drop, and its properties can be tuned to reach the optimal prospected performance. Effects of different porous baffle geometrical parameters including its normalized height (Hb = 0.5, 1.0, 1.5, 1.75), width (Wb = 0.5, 1, 1.5, 2.0, 2.5), porous baffle-step relative distance (D = 1, 2, 3, 4), Darcy number (10−2, 10−3, 10−4, 10−6), and Reynolds number (100, 200, 300, 400, 500) on the heat transfer and pressure drop are investigated. The simulation indicates that higher Reynolds numbers enhance more the heat transfer (35% improvement at Re = 500 with respect to 10% at Re = 100). Also, longer baffles can lead to higher heat transfer rates (5% improvement in Hb = 0.5 with respect to 32% at Hb = 1.5). Keywords Porous · Baffle · Backward-facing step · Numerical modeling · Enhanced heat transfer List of symbols Cp Specific heat of the fluid (kJ kg−1 K−1) D Normalized distance of the baffle F Inertial factor H Duct height downstream of the step (m) h Duct height upstream of the step (m) hb Baffle height (m) Hb Normalized baffle height k Thermal conductivity (W m−1 K−1)) K Porous media permeability (m2) kf Thermal conductivity of fluid (W m−1 K−1) Nu Nusselt number Nu* Nu/Nub Nub Nusselt number when a porous baffle is not used p Pressure (pa) p* Normalized pressure drop Rem Reynolds number S Step height (m) * Guohua Cui [email protected] Chuanchang Li [email protected] 1
T Temperature (K) T0 Inlet temperature (K) Tw Wall temperature (K) u Velocity component in the x-direction (m s−1) um Mean velocity (m s−1) v Velocity component in the y-direction (m s−1) wb Width of the baffle (m) Wb Normalized width of the baffle x Streamwise coordinate direction (m) X Normalized streamwise coordinate y Transverse coordinate direction (m) Y Normalized transverse coordinate Greek symbols ε Porosity μ Dynamic viscosity (N m−1 s−1) μe Effective dynamic viscosity (N m−1s−1) ρ Density (kg m-3) Subscripts b Base state m Mean w Wall e Effective
School of Mechanical and Automotive Engineering, Shanghai University of Engineering Science, Shanghai, China
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Introduction Enhanced heat transfer is an important topic in thermal analysis problems, and various active and passive techniques have been extensively implemented to improve its performance in engineering applications. In many engineering applications, the heat transfer enhancement techniques have been applied and am
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