Optimization of temperature regulating performance in fresh-keeping transportation by liquid nitrogen injection

An experimental platform with atmosphere controlled system by liquid nitrogen injection was established to study and solve the cold damage problem caused by liquid nitrogen during the transportation. The bore diameter of the outlet valve on the liquid nitrogen tank, the length of the vaporization coiled pile, the aperture direction on the horizontal pile, the ratio of opening area on the perforated partition, the airflow velocity and the length of the air return channel were chosen as variables to analyze their effects on the temperature regulating characteristics of liquid nitrogen and the parameters were optimized. The best regulation performance was obtained under the condition with the bore diameter of the outlet at 1.5 mm, the length of the vaporization coiled pile at 4 m, the aperture direction on the horizontal pile towards the draught fan, the ratio of the opening area on the partition at 4.03%, the airflow velocity at 8 m/s, and the length of the air return channel at 1.5 m. Under this condition, the O2 concentration was reduced from 20.95% to 5%, the maximum temperature difference among the outlets of the perforated partition was only 1.3℃，and the maximum temperature difference between the outlet of perforated partition and the air return channel was only 2.72℃. The liquefied-nitrogen atmosphere controlled system could rapidly reduce the oxygen concentration in the container from 20.95% to 5% in 43 min, while cooling the internal environment of the container. The results can provide valuable references for the design of fresh-keeping vehicle with controlled atmosphere system.