| 摘要 |
<p>A controlled rate freezer (10) for the controlled freezing of biological material, the freezer comprises a first chamber (14) for holding biological material to be frozen, a second chamber (20) for holding a cryogenic substance, forced convection means (22, 24) for lowering the temperature of the first chamber (14) by forcibly moving air present in the first chamber (14) towards the second chamber (20) whereby heat transfer occurs at the second chamber (20), and control means (26) for monitoring the temperature of the first chamber (14) and controlling the forced convection means (22, 24) based on the monitored temperature, so that in use the lowering of the temperature of the first chamber (14), and thus the freezing of the biological material, follows a material-dependent predetermined optimum or substantially optimum freezing profile. The forced convection means includes two recirculating flow paths (32, 40) along which air in the first chamber (14) is movable at a rate controlled by the control means (26). The first flow path (32) is solely located in the first chamber (14) and spaced from the second chamber (20) so that air travelling on the first flow path (32) is not subjected to direct cooling at the second chamber (20), and the second flow path (40) meets the first flow path (32) and extends to the second chamber (20), so that air travelling on the second flow path (40) is subjected to cooling at the second chamber (20) and feeds the air thus cooled onto the first flow path (32).
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