Optimum Design Methods of Pressure Cooling System for Fruits and Vegetables

为了建立果蔬压力冷却系统的优化设计方法，首先通过实验测量了部分果蔬的冷却时间、表面速度和能耗，其次采用有限元法计算了果蔬填充床冷却的传热系数。得到的结果如下：(1)定义了在负荷下每千克冷却一摄氏度所需的能量为单位冷却能耗（U.C.E.C）。(2)浅层速度对农产品的冷却有一个最小的综合能耗，即制冷机能量与总综合能耗之比最大，轴流风机能量与总能耗之比最小。(3)此时，任何农产品填料床的表面速度为0.2 ~ 0.4m/s，农产品的U.C.E.C.为1.6 ~ 3.3 × 10 kw. hr/kg c，均小于强制风冷。(4)云树柑填料床的最佳换热系数为20，芋头填料床的最佳换热系数为25 kcal/m^2 hr C。

In order to establish the optimum design methods of pressure cooling system for fruits and vegetables, first, cooling time, superficial velocity and energy consumption for some fruits and vegetables were measured by experiment, secondly, heat transfer coefficients for cooling packed beds of fruits and vegetables were calculated by finite element method. Results obtained were as follows:(1) The author defined that the energy required to cool one centigrade per kilogram with opparatus load was a unit cooling energy consumption(U.C.E.C).(2)The cooling of agricultural products by superficial velocity correspond to a minimum U.C.E.C. meant that the ratio of refrigerator energy to total U.C.E.C. had a maximum and it of axial flow fan had a minimum.(3) The superficial velocities at that time were 0.2-0.4m/s for any packed beds of agricultural products, and U.C.E.C. of agricultural products were 1.6-3.3x10 kw. hr/kg C. these values were smaller than that of forced air cooling.(4) The optimum heat transfer coefficient were 20 for packed bed of Unshu Mandarin and 25 kcal/m^2 hr C for taro, respectively.