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

•The melting of NePCM in differentially-heated rectangular cavities was revisited.•Effects of loading and aspect ratio were studied experimentally and numerically.•The invisible phase interface evolutions of NePCM were captured indirectly by TLC.•The negative effect of viscosity growth on melting was verified by the TLC images.•The slender cavity helps take advantage of increased thermal conductivity of NePCM.