Interaction effects between laminar natural convection and surface radiation in tilted square and shallow enclosures

Abstract

Interaction effects between surface radiation and natural convection in air filled tilted enclosures have been investigated numerically for a wide range of the tilt angle (θ). Two opposite walls of the enclosure are differentially heated while the other two walls are adiabatic. The interaction takes place through participation of adiabatic walls in heat transfer. Presence of radiation leads to two prominent effects, viz. (i) increase in overall convective circulation rate and (ii) pre-cooling/pre-heating influence of adiabatic walls on the recirculating flow. In positive tilt angles (hot wall moving down) the latter effect dominates leading to a reduction in the convective heat transport. However, in negative tilt angles (hot wall moving up) the former dominates leading to significant augmentation in convective heat transfer. Convective Nusselt number is maximum at θ = +15°, independent of presence/absence of radiation for all aspect ratios while the radiative Nusselt number is maximum at θ = −15°. The interaction effects are much stronger in shallow enclosures than in square enclosures. Convection can be suppressed by 50% in positive tilts, while it can be augmented by over 100% in negative tilts for an aspect ratio of 5.