热泵冷冻干燥系统的循环性能优化

为降低冷冻干燥过程的能耗,提高冷冻干燥装置的经济性,构建了以 NH3为工质的二级压缩和复叠式热泵冷冻干燥系统。通过对热泵系统的循环特性计算,研究了冷冻干燥操作条件变化对循环特性的影响,并对中间温度进行了优化。计算结果表明:复叠式热泵循环和二级压缩热泵循环均可用于冷冻干燥系统;在常规的冷冻干燥条件下,选用复叠热泵循环较优;在满足冷冻干燥操作条件的前提下,可适当降低加热温度、提高冷阱温度来提高系统的循环性能;系统中间温度的变化对系统的供热系数影响较小,由等压比法确定的中间温度更为合理。

Optimization on performances of heat pump for freeze-dryer

To reduce energy consumption and improve economics of freeze-dryer, a two-stage compression cycle and cascade heat pump cycle for freeze-dryer, in which NH3 is used as working medium, had been constructed. The influences of operational conditions during freeze-drying on the characteristics of the two systems were investigated through calculation of performances on the heat pump cycles. The intermediate temperatures of the two systems are optimized. The results shows that both of the cycles can be used in freeze-dryer, the cascade heat pump cycle is better than two-stage compression cycle under the conventional operational conditions. Higher performances can be obtained by lowering the temperature ofheating platen and increasing the temperature of vapor condenser. The reasonable intermediate temperatures arepresent by the equal pressure ratio method due to the little variation of COP with the intermediate temperature of the systems.