CFD study of heat transfer in power-law fluids over multiple corrugated circular cylinders in a heat exchanger

Abstract

The heat transfer in power-law fluids across three corrugated circular cylinders placed in a triangular pitch arrangement is studied computationally in a confined channel. Continuity, momentum, and energy balance equations were solved using ANSYS FLUENT (Version 18.0). The flow is assumed to be steady, incompressible, two-dimensional, and laminar. A square domain of side 300D_h is selected after a detailed domain study. An optimized grid with 98,187 cells is used in the study. The convergence criteria of 10⁻⁷ for the continuity, x-momentum, and y-momentum balances and 10⁻¹² for the energy equation were used. Constant density and non-Newtonian power-law viscosity modules were used. The diffusive term is discretized using a central difference scheme. Convective terms are discretized using the Second-Order Upwind scheme. Pressure–velocity coupling between continuity and momentum equations was implemented using the semi-implicit method for pressure-linked equation scheme. Streamlines show wake development behind the cylinders, which is very dominant at large Re_N and n. Isotherm contours are cramped at higher values of Re_N and Pr_N, implying higher heat transfer. Global parameters, like, C_d and Nu, are computed for the wide ranges of controlling dimensionless parameters, such as power-law index (0.3 ≤ n ≤ 1.5), Reynolds (0.1 ≤ Re_N ≤ 40), and Prandtl (0.72 ≤ Pr_N ≤ 500) numbers. The Nu_Local plot attains a pitch near the corrugation of the surface due to abrupt changes in velocity and temperature gradients. Nu increases with Re_N and/or Pr_N and decreases with n under ot herwise identical situations. Nu is correlated with pertinent parameters, namely, Re_N, Pr_N, and n.