Determination of the efficiency of insulation systems for cryogenic equipment by thermal imaging

Abstract

Possibilities are considered for using the thermal imaging method for analyzing the operation of insulation systems of cryogenic equipment. Requirements are given for thermal images and features of their use in diagnosing cryogenic equipment. It is shown that thermal imaging makes it possible to record the location of a local increase in heat influx for articles with such high quality thermal protection as cryogenic vessels with layered vacuum insulation under high vacuum conditions in the thermal insulation cavity. Thermograms are presented for the faceplate of cryogenic vessels with participation of increased heat influx. The possibility is analyzed of calculating excess heat influx on the basis of thermograms.Thermal imaging analysis of the operation of objects and equipment is used quite extensively, and in particular: in power engineering in order to determine disruption of electrical insulation quality, wear of current-carrying parts; in medicine in order to localize areas of inflammatory processes, observation of the healing of wounds, and in many other fields. Thermal imaging methods are based on photographing objects in infra-red beams and preparation of an image (thermal portrait) within which the density of shading is proportional to the object surface temperature. Recording is accomplished by special photographic equipment, i.e., thermal imagers. Thermal portraits are processed in computers using special programs.Features of using thermal imaging for analyzing the efficiency of thermal insulation for cryogenic equipment. The task of this method is to evaluate the temperature distribution for the surface of cryogenic equipment that, as studies have shown, is on average 0.01-6 K lower than the temperature of the surroundings. Consequently, the thermal imager should operate in the radiation range as close as possible to the thermal radiation range of the surrounding objects or slightly more than cooled bodies, i.e., the operating radiation range of the thermal imager is 9-13 µm, that corresponds to the average temperature drop.Preparation of cold is a power-consuming process that gives rise to a requirement for highly effective insulation for cryogenic equipment. For normal operation of cryogenic equipment, the temperature of its surface is only a little lower than the surrounding temperature (average temperature drop 0.01-6 K). In order to record changes in temperature fields with these drops, a high resolving capacity is necessary for the thermal imager with respect to temperature (not less than 0.1 K) and this is provided by a special programmed device.The list of materials that may be used for the external surface of cryogenic equipment is quite limited:• unpainted carbon steel (external container of cryogenic vessels in the period of delivery trials and other equipment); • painted carbon steel (external container of cryogenic vessels during operation, housing of air-separation units (ASU) and other equipment);