The Study Of The Influence Of Different Opening Models Of Exterior Covers To The Effect Of Fruits And Vegetables Precooling

Researches indicated that after the harvest of the fruits and vegetables,precooling can eliminate the field heat as soon as possible and control its respiratory rate,which is one of essential steps to make the fruits and vegetables to maintain freshly.In order to know the effect of different exterior opening models on the precooling of fruits and vegetables,a series experiments and numerical simulations were carried out,whose results would be a reliable guidance to the side ventilation precooling of fruits and vegetables.Based upon the practical background of fruits and vegetables preservation,the experimental scheme of pressure precooling was designed and the experiments were carried out to cabbage using two different materials of exterior covers including tarpaulin and PE plastic sheeting separately.Through analysis the better one as the exterior covers material was chosen to do the successor experiments.Five different exterior opening models were designed.Experiments were carried out to potatoes using the five different models of opening separately.Through contrasting and analyzing the center temperature and the skin temperature,the influence to the precooling effect of different opening models was studied.The precooling experiments were carried out respectively to west orchid with three exterior opening models.The influence of precooling effect to the same measuring position in different transport boxes and the different measuring position in the same transport boxes with the three opening models were contrasted and analyzed.The experimental study indicated that when the opening ration is bigger,the larger is the cooling rate.The temperature decreased more quickly on the side of a little further from the blower than the nearer side of it with a small opening ration.The exterior covers should be better avoiding setting uniformly.The opening ration should be larger on the near side of the blower than the further side appropriately.By using the standard equation k-εin the CFD software of FLUENT,the potato was considered as the simulated sample to simulate the field distribution of the air velocity,the air temperature and the pressure in the transport boxes which were covered outlayers with different exterior opening models.The results showed the average air velocity of the outlets increased with the opening ration increasing on the two sides of the transport boxes.The velocity reduced gradually from outlet edges to the center and the nearer from the outlets,the bigger the flow around intensity.The internal air pressure difference all assumed step change in X axis direction. The smaller of the exterior cover opening ration,the lower temperature distributed on the cross section which is a little further from the blower.The simulated results can be used to explain the experimental results perfectly.The agreement between the experimental and the theoretical results is found to be good which showed the correctness and the reliability of the established mathematical model and the computational methods,which can provide theoretical basis for designing the pressure precooling system.