ANALYSIS OF HEAT TRANSFER MECHANISMS IN THE SOLIDIFICATION OF PCM WITH DIFFERENT PASSIVE ENHANCEMENT TECHNIQUES FOR FREE COOLING APPLICATIONS

Abstract

The continuous increase in the level of green-house gas emissions and the depletion of fossil fuels are identified as the major driving forces behind efforts to effectively utilize different sources of renewable energy.  Free cooling concept is gaining importance in building cooling applications.  The medium which is used to store energy is Phase Change Material.  Among the phase change materials available commercial PCM is of great use.  The only drawback with the PCM is its thermal conductivity is very low.  Various heat-transfer enhancement techniques between the phase change material (PCM) and the heat transfer fluid (HTF) were tried by researchers.  Passive enhancement techniques are very simple and gives good heat transfer enhancement which decreases the solidification time and increases the solidification rate.  In the present work two types of passive enhancement techniques like increasing the roughness of the heat transfer surface and dimples over the heat transfer surface were tried and it has been observed that the dimpled surface will provide better results compared to rough surface over normal surface. Overall there is decrease in solidification time of 37 min. and increase in solidification rate of 19.37% with dimpled surface over normal surface.