Vibration Effects on Heat Transfer During Solidification of Paraffin

Abstract

Previous work looked at the solidification process of PCM (phase change material) paraffin wax. Experimental results were compared with numerical work done in CFD package FLUENT. In the current study, the effects of vibration on heat transfer during the solidification process of PCM in a sphere shell are investigated. Enhancement of heat transfer results in quicker solidification times and desirable mechanical properties of the solid. The amount of PCM used was kept constant during each experiment by using a digital scale to check the weight, and thermocouple to check consistent temperature. A small amount of air was present in the sphere so that the sphere was not filled completely. Commercially available paraffin wax, RT35, was used in the experiments. Experimentations were done on a sphere of 40 mm diameter, wall temperature 20°C below mean solidification temperature, and consistent initial temperature. A vibration frequency was varied from 10-300 Hz was applied to the set-up and results compared with that of no vibration. Samples were taken at different times during the solidification process and compared with respect to solid material present. INTRODUCTIONDirectional solidification is a topic of wide interest due to its importance to the iron and steel industry. Solute convection in the solidification process results in channel formation, which has a freckle like appearance in the cross-section and has a critical effect on the mechanical strength of casting. Rotational effects [1,2,3] as well as gravitational effects [4,5] on solidification are well documented and show a stabilizing effect on convection for the synchronous solutions, but slowly destabilizes convection for the region of sub-harmonic solutions [6]. Additional numerical results for convection in a porous layer subjected to vibration and heated from below, show that increasing the frequency of vibration causes the amplitude of convection to approach zero [7]. Experimental results using a hand tapping technique have shown an improvement in density, hardness, ultimate tensile strength, and % elongation [8]. This has proven to be an