Experimental study of natural convection heat transfer between an outer horizontal cylindrical envelope and an inner concentric heated square cylinder with two slots

This paper presents the results of an experimental study of natural convection heat transfer between a horizontal cylindrical envelope and an internal concentric heated square cylinder with two slots. The internal cylinder was a hollow one with horizontal slots on its top and bottom surfaces. The ratio of slot width S to the side height H was 0.0612 and 0.3878. The ratio of the envelope inner diameter D_o to the side height H was 2.653. Air was used as the working fluid. The range of Ray-leigh number was 1.77×10²∼8.72×10⁶ for S/H=0.0612 and 1.32×10²∼6.25×10⁶ for S/H=0.3878. The results show that there are three different heat transfer regimes in different Ray-leigh number regions, i.e. pure conduction regime, transition regime and convection regime. The average heat transfer results were correlated into two empirical equations. Comparison was made with the non-slotted case. It is found that slots of the internal cylinder can significantly enhance the heat transfer.