气调保鲜液氮充注沉浸式汽化器工作特性研究

针对液氮充注气调方式液氮温度较低,直接充注将对果蔬产生冻害问题,为提高液氮汽化器出口温度的控制精度,提高冷量利用率,设计了一种蓄冷液氮充注沉浸式汽化器并搭建试验平台,研究盘管长度、蓄冷剂类型和液氮流量等因素对汽化器工作特性的影响。基于传热理论建立了汽化器出口温度计算模型。计算得到的汽化器出口温度与试验值基本一致,相对误差为2.01%和8.06%。试验结果表明:盘管长度、蓄冷剂类型和液氮流量都对汽化器工作特性有显著影响,盘管长度和液氮流量与充注时间呈线性关系,随着盘管长度增加或液氮流量减小,相关系数升高;当盘管长度为3 m、液氮流量为0.0075 kg/s和蓄冷剂类型为水时,汽化器的换热性能较佳,而当盘管长度为3 m、液氮流量为0.01 kg/s和蓄冷剂类型为水时,汽化器的蓄冷效率较佳。

Operation Characteristics of Liquid Nitrogen Injection Heat Exchanger in Fresh-keeping Transportation Container with Controlled Atmosphere

The fresh-keeping transportation container with controlled atmosphere by liquid nitrogen injection is an advanced and efficient equipment for transporting fruits and vegetables.The temperature of liquid nitrogen is-196℃.When liquid nitrogen was injected directly into the container,fruits and vegetables would be damaged.A heat exchanger with low control precision of the outlet temperature was used in the container.In order to improve the control precision of the outlet temperature of heat exchanger and utilization rate of cold quantity,a liquid nitrogen injection heat exchanger capable of storing energy was designed.A test platform was set up to study the effects of copper tube length,the type of phase change materials and liquid nitrogen flow rate on the operation characteristics of the heat exchanger.Based on heat transfer theory,a calculation model for heat exchanger outlet temperature was established.Calculated value was basically consistent with the experimental value,and the relative error values were 2.01%and 8.06%.The test results showed that the copper tube length,the type of phase change materials and liquid nitrogen flow rate had a significant effect on the operation characteristics of the heat exchanger,the copper tube length and liquid nitrogen flow rate had linear relationship with the injection time.When the copper tube length increased or the liquid nitrogen flow rate decreased,the linear relationship correlation coefficient was higher.When the coil length was 3 m,the liquid nitrogen flow rate was 0.0075 kg/s and the phase change materials was water,the heat exchange efficiency of heat exchanger was better.When the coil length was 3 m,the liquid nitrogen flow rate was 0.01 kg/s and phase change materials was water,the thermal storage efficiency of heat exchanger was better.The results provided references for control outlet temperature of heat exchanger accurately and recycle of cooling capacity.