Revisiting melting heat transfer of nano-enhanced phase change materials (NePCM) in differentially-heated rectangular cavities using thermochromic liquid crystal (TLC) thermography

Abstract

The melting of nano-enhanced phase change materials (NePCM) in differentially-heated rectangular cavities was revisited by employing a novel indirect visualization method, i.e., the thermochromic liquid crystal (TLC) technique, to track the invisible phase interfaces. Detailed natural convective flow and heat transfer during melting were also predicted by numerical simulations based on the enthalpy-porosity method, which were validated by comparing with the TLC observations. Two height-to-width aspect ratios of the cavity, i.e., 0.8 and 1.25, were studied. Based on the observed evolutions of the phase interface, it was shown that natural convection originating from the upper corner nearby the phase interface causes the difference in melting patterns between the upper and lower parts of the cavity. The decelerated melting in the presence of NePCM samples with higher loadings (and hence much greater viscosity) was confirmed intuitively by the more vertical and flatten phase interfaces captured by TLC, indicating that heat conduction becomes the dominant mode of heat transfer during melting as a result of the significantly deteriorated natural convection effect. Moreover, when the cavity becoming more slender, the advantage of increased thermal conductivity could be more sufficiently taken because the shorter characteristic length inherently lowers the contribution of natural convection.