| 摘要 |
<p>A refrigeration system (10) which controls the temperature of a conditioned space (12) to a predetermined temperature range adjacent to a selected set point temperature (SP) via a cooling cycle which includes evaporation a cryogen, such as CO₂ or N₂, in a heat exchanger (44). In an apparatus embodiment, a controller (66) determines a desired evaporation vapor pressure value (EPX) of the cryogen as a function of the selected set point temperature (SP), and then controls (EPV) the evaporation pressure (EP) in the heat exchanger means as a function of the determined desired evaporating vapor pressure value. The controller further determines a desired superheat value (SHX) of the cryogen exiting the heat exchanger means as a function of the selected set point temperature (SP), and controls (FCV) the mass flow rate of liquid cryogen evaporating in the heat exchanger as a function of the determined desired superheat value. A method embodiment includes the steps of providing (178,179) a desired evaporation vapor pressure value (EPX) of the cryogen as a function of the selected set point temperature (SP), controlling (180-196) the evaporation pressure in the heat exchanger means as a function of the desired evaporation vapor pressure value, providing (208,179) a desired superheat value (SHX) of the cryogen exiting the heat exchanger means as a function of the selected set point temperature (SP), and controlling (202-216) the mass flow rate of liquid cryogen from the cryogenic cooling means to the heat exchanger means as a function of the desired superheat value.</p> |
