Heatline analysis on thermal management with conjugate natural convection in a square cavity

Abstract

Conjugate natural convection finds various thermal applications in chemical industries, where the heat transfer is controlled by the presence of solid walls such as heat exchanger, nuclear reactors, fin type cooling and solar storage systems. Heat flow distribution within square cavity enclosed by vertical conducting walls of definite thickness (t1 and t2) is analyzed for various fluids (Pr) in this study based on the location of the wall thickness [left wall (case 1)/ right wall (case 2)/ both side walls (case 3)] and conductivity ratios between solid and fluid regions (K). At Ra=105, circular heatlines are observed near core of the cavity at K=0.1 whereas they are distorted and pushed towards the hot wall at K=10 with low Pr (Pr=0.015). On the other hand, heatlines are horizontally stretched at core of the cavity for higher Pr (Pr=0.7 and 1000) at K=10. End to end heatlines are highly compressed near top portion of the cavity at K=10 irrespective of Pr. Closed loop heatlines are absent for case 2 at Ra=103 whereas closed loop heatlines with lesser magnitude than cases 1 and 3 are observed for case 2 at Ra=105 due to less heat transfer from the hot solid wall irrespective of Pr at K=0.1 and 1. The heat transfer rate can be maintained constant at low thermal conductivity ratio (K) even for the high convective regime (Ra=105) irrespective of wall thickness (t1 and t2). Average Nusselt number shows overall larger heat transfer rate for higher K (K=10), which is almost identical with classical natural convection (zero wall thickness) compared to lower K (K=0.1 and 1) irrespective of location of wall thickness (cases 1–3). In order to achieve almost invariant or lower fluid temperature at Ra=105 for t1+t2=0.2 and 0.8, solid wall at hot side (case 2) may be useful. This heating strategy may be viewed for high temperature shielding or minimization of thermal runaway for temperature sensitive applications, such as environmental control system, chemical storage reservoirs, etc., where heat flow is controlled by solid wall resistance.