On a Lumped Heat Transfer Model of Freezing Process of Cryopreservation Media

Abstract

In cryopreservation, biological cells are usually suspended in and cooled together with a cryopreservation medium. A lumped heat transfer model and an apparent specific heat form of energy equation were developed to formulate the cooling process of the cryopreservation media. Using glycerol as a model cryopreotective agent, the freezing process of ternary cryopreservation media (glycerol-NaCl-water) in cylindrical plastic straws were studied numerically by computer simulation. Effects of four important factors on the temperature history in the media during the cooling process were investigated. These factors include: glycerol concentration, supercooling temperature of the media, ambient constant cooling rates, and radius of the straw. Results from computer simulation showed that these factors significantly influenced the thermal history in the ternary media, especially during the water phase transition period. It was also revealed that actual cooling rate in the media varied as a function of time and the maximum rate was much higher than the ambient constant cooling rate.