(22c) Effect of Free Convection on Melting in Cylindrical Containers

ABSTRACT Melting of single materials of PCMs (Phase change Materials) is a thermal transport process in latent thermal energy storage systems. Container surfaces above the melting point cause natural convection in the molten liquid which increases the melting rates.Melting front movement with time was determined from the temperature distribution by El-dessouky etal.(J Solar Energy Engineering,Trans.ASME, 121, Pg 98-109,1999) . They also developed expressions in dimensionless group ofBiot number, Stefan number and Fourier number. Paraffin Wax(M.P 48.51C) was used as PCM.

While the work of El-dessouky etal is for melting outside the cylindrical tube, our experimental work pertains to melting a PCM in cylindrical copper containers.n-Octadecane with a melting point 26.9C was used as PCM.The experimental container filled with the PCM was heated by immersing in an isothermal water bath of known temperature(+/-1K).The cylindrical container was insulated at the bottom and the top was covered with acrylic sheet having a provision to insert temperature sensors. Temperature distribution measurement with PT-100 sensors was possible only in the container of diameter 7.8cm . In another set of experiments experimental data of mass of liquid melt varying with time was generated. For this purpose the container is withdrawn after a known time and the liquid melt is separated and weighed. L/D 1.1 to 3 Water Temperature 35-80c Volume of material 130-400 cc Initial PCM Temperature 8.1C to 18.7C. Temperature drop across the melt 16 to 33C

The discussion of results includes the effect of initial PCM temperature on melting,effect of temperature drop across the melt on the total melting time and temperature disribution.