Assessment of the thermal performance of a dry-shipper used in deep frozen cold chain.

A dry shipper is a vacuum insulated transport container with a liquid nitrogen filled porous lining inside to transport frozen biomedical samples. The current understanding of the thermal characteristics of vacuum insulated vessels is based on standard cryostats, where the liquid collects in a pool at the bottom accompanied by a stratified vapor above it, wherein the temperature increases with height. However, the behavior of a dry-shipper diverges significantly from these standard cryostats, since the liquid is contained within a
porous lining rather than at the vessel’s base, stratification is absent. The current thermal models for standard cryostats cannot be applied to a dry-shipper due to the difference in temperature profile, therefore the thermal characteristics of a dry-shipper are investigated. We present experimental data of an instrumented dry-shipper subjected to various simulated conditions, namely the ambient temperature is varied from 295 K to 333 K and the positioning is varied from upright to an angle of 45◦ and 90◦. We observed that the mass of the dry-shipper reduced linearly with time, which corresponds to a constant evaporation rate of the liquid nitrogen in the container. A simplified model is developed to predict the liquid nitrogen evaporation rate in the dry-shipper as a function of ambient conditions, giving indirect measurement of the liquid nitrogen in the container. This will aid shipping firms to plan the transport as well as develop smart versions of the dry-shipper.