Improving the thermal insulation of nitrogen cryocontainers using the loop-shaped evacuation process

Abstract

The improvement of serial cryobiological Dewar containers with the use of the lowest thermal conductivity in calorimetric samples of screen-vacuum thermal insulation (SVTI) during storage of liquid nitrogen became possible after the development of fundamental methods for determining heat fluxes for each element of cryocontainers structure and the study of the peculiarities of heat transfer in SVTI. It is established that the deterioration of thermal insulation on cryocontainers by 7–8 times occurs from its gluing when they are heated during the manufacturing process. An additional decrease in the quality of thermal insulation by ∼2 times during operation is due to the formation of cryocondensate from the pumped-out gas separation products in the cold layers of SVTI and an increase in radiant heat transfer. Eliminating the adhesion of the SVTI, as well as changing the direction of evacuating gas separation products towards the warm wall of cryocontainers through 35 perforated SVTI layers using an open loop-shaped evacuation process allowed to increase their service life by ∼2 times (up to 145–148 days). However, it remains practically unchanged over 15 years of operation.