Experimental investigation of airflow and heat transfer by natural convection in an insulated box with a Phase Change Material using a Particle Image Velocimetry technique

Abstract

Airflow and heat transfer via natural convection in an insulated box with Phase Change Material (PCM) were experimentally investigated using Particle Image Velocimetry (PIV) and temperature measurements. The effects of PCM positions (side wall and lid) on flow pattern and temperature distribution were studied under empty and loaded conditions. Two loads were considered to study the obstacle effect and the influence of heat exchange with air. When PCM was either at the side wall or at the lid of the box, laminar flow was observed and the corresponding Rayleigh number was about 10 7 . Upward flow was always observed near the side walls of the box. When PCM was on the side, downward flow occurred along the PCM; in the empty case, flow was almost 2D but became 3D when the load was added. When PCM was on the lid, the air cooled in contact with PCM, detached from it and flowed downwards. In the empty case, downward flow was unstable, and with the load, it followed preferential pathways. The type of load exerted little effect on flow patterns at thermal steady state. Thus, a simpler load (extruded polystyrene) can be used in the first approach. The maximum velocity was about 0.1 m s −1 , so free convection cannot be neglected compared with conduction. Regarding temperature performance, PCM on the side and on the lid showed no substantial difference if gaps were left between the load and the walls or PCM. • Airflow and heat transfer due to natural convection in an insulated box with PCM were studied. • Effect of PCM positions on flow and temperature fields was investigated. • The highest observed air velocities in the box were around 0.1 m s −1 . • PCM position exerted no significant effect on maximum product temperature. • Gaps should be left between the product and the box walls or PCM.