Design and experiment of fresh-keeping transportation vehicle with controlled atmosphere for fruits and vegetables

A new fresh-keeping transportation technology with controlled atmosphere (CA) system featuring liquid nitrogen injection was designed to resolve the current problems of low efficiency and high cost present in fruits and vegetables transportation. The transportation vehicle consists of chassis, container based on differential pressure principle, CA equipments utilizing liquid nitrogen injection, ultrasonic humidification devices, refrigeration appliances, variable air volume ventilation assembly, air change valves and control unit. The vehicle performance test result indicated that under the condition of ambient temperature of (33.5±1)℃，relative humidity of (59±3)%, "blanks in the middle" stack mode and internal rear temperature of (22.3±0.3)℃, the container took 52 minutes and 90 minutes to reach the target environment when the cargo initial temperature was 4.82 and 6.38℃ respectively. Under the same condition and the cargo initial temperature of 4.65-4.82℃, it accordingly took 52 minutes, 30 minutes and 77 minutes to reach the target environment when the stack mode was separately using "blanks in the middle", "blanks on both sides and middle", and "no blanks left". And the container took 26 minutes, 9 minutes and 33 minutes to increase the relative humidity from 85% to 90%, respectively, according to the three stack modes mentioned above. Therefore, the "blanks on both sides and middle" stack mode was superior to "blanks in the middle" and "no blanks left" stack modes in terms of target environment regulation time. Decreasing the O2 concentration from 20.9% to 5% cost 28 minutes and 18.99 kg of liquid nitrogen on average under the "full loaded" stack mode, demonstrating that the vehicle had high CA efficiency and low cost. It is concluded this new design could serve as reference for further development on CA fresh-keeping transportation technology.