TEMPERATURE-GRADIENTS IN FREEZING CHAMBERS OF RATE-CONTROLLED COOLING MACHINES

Self designed temperature probes with identical transmission patterns were placed at different positions within the cooling chamber of a modern cooling machine under defined conditions. Dependent on the rate of cooling, considerable differences between two-point temperature measurements were noted at various locations. On-line temperature records at a cooling rate of 10°C/min showed maximum temperature differences (ΔTmax) of 12.6°C vertically and 10.8°C horizontally at a given time during the freezing cycle. Maximum differences were recorded at absolute temperatures between 0 and -20°C, the crucial phase of cryopreservation of biological systems. We conclude that in order to define cryobiological cooling methods better, one should be aware of these differences and test each set-up individually. © 1993 by Academic Press, Inc.