DefinePK

Abstract

Heat leakage is a common problem involving cryogenics applications. Sometimes it is undesirable and should be maintained at the minimum level. At low temperature, it becomes more difficult to remove a given amount of heat and discharge it at ambient temperature. These unwanted heat leakage accounts into an economic burden and acts as a barrier in cryogenic applications. Therefore the cryogenic vessels and transfer lines are insulated with different types of Multi-Layer Insulations (MLI) which are very effective. MLI consists of alternate layers of high reflective shields or foils and separated by low thermal conductivity spacers. One of the most effective cryogenics insulations (MLI) involves a high vacuum. It is known that in high vacuum radiation plays a major role because gas conduction and convection are negligible. In order to improve mechanical strength and ease of application, Plastic materials like Mylar and Fiberglass are coated with Aluminum foil. The spacers for MLI are made of high resistive material. For the estimation of heat transfer, Apparent Thermal Conductivity must be known. Due to unpredictable changes in parameters such as uniform contact pressure and interstitial pressure, accurate theoretical performance of MLI is very difficult. Thus an experimental investigation has been carried out on a few indigenous MLI materials like Fiberglass cloth, R P Tissue, Nylon net etc. For that, a cylindrical boil off calorimeter has been developed and standardized for testing of the thermal performance of insulation. Its measurement principle for determining heat flux (Q) and Apparent Thermal Conductivity (KA) of a test specimen at fixed conditions. The present work is to develop optimum combination of shield and spacer from available materials (Aluminum foil- Fiberglass cloth, Aluminum foil-R P Tissue, Aluminum foil- Nylon net) by experimental investigation of apparent thermal conductivity.