An Experimental Investigation of Packing Density of Perlite Powder Insulation on Apparent Thermal Conductivity Using Liquid Nitrogen Boil-off Calorimeter

Abstract

At very low temperatures, it becomes economical to conserve the cold using insulating material rather than to produce it because of the requirement of very large amount of energy to produce very low temperature. Therefore the cryogenic storage vessels, transport vessels and transfer lines are insulated. Perlite powder at atmospheric pressure and under vacuum is a common insulating, material used for these purposes.For the estimation of heat transfer,thermal conductivity must be known. A double guarded cylindrical boil off calorimeter is an absolute method of determining thermal conductivity. The apparatus consist of a main vessel in the middle and two guard vessels located at top and bottom. This vessel is housed in a cylindrical vessel. The present study relates to understand the effect of a change in the packing density of perlite powder type insulation (43.33 kg/m3 to 49.69 kg/m3) on the apparent thermal conductivity by the use of a liquid nitrogen boil-off calorimeter. For finding the thermal conductivity of perlite powder under vacuum, the powder is filled in the annular space of vessel and pressure is reduced to 1 × 10−6 mbar. The results of the present experiment are compared with the trends available from the previous work by Fulk et al[2].