| The rapid pre cooling of fruits and vegetables is almost a common understanding of the domestic and international fresh keeping world,is also an important link in the circulation of cold chain.The pre cooling time of the pressure difference pre cooling device is short, the cost is low, the operation is flexible and the application scope is wide, especially for the development of the cold chain logistics in China.However, the mobility of the equipment is poor, and it can only precool a kind of fruits and vegetables, which seriously affect the quality of some fruits and vegetables,In order to meet the demand of the actual production andsolve the problem that the pre cooling equipment haspoor mobility and that different kinds of fruits and vegetables can be pre cooled at the same time.In this paper, we designed a kind of double temperature zone of the movable fruit and vegetable pressure difference pre cooling device.In this paper, the design and type selection of the device for the cooling device of the fruits and vegetables in the movable double temperature zone has be done, including the material and the size of the box, the main equipment and auxiliary equipment of the refrigeration system, The refrigeration working fluid select non-R404A mixed refrigerant.At the same time, the box installed broccoli pressure difference precooling process of establishing the mathematical model, using ANSYS software simulation of different shape hole packing box.Through analyzing the velocity field and temperature field of the air flow in the packing box, the best opening shape is obtained, which can improve the efficiency of the pre cooling.Finally, through the experimental instrumentation of box installed broccoli at different open hole shape cooling effect test and compare with the result of simulation and experimental results.Through the analysis of the simulated cloud pictures and the experimental results, the following conclusions are obtained:(1) Based on three kinds of open hole in the form of temperature field distribution difference is not large, oval shaped opening hole cooling effect best, cooling the fastest and the keyway form open hole pre cooling effect is the worst, cooling the slowest.further observation also found:distance into the outlet nearest broccoli cool the fastest, broccoli surface temperature dropped, the outlet near the broccoli cool the slowest and placed in the middle layer of broccoli cool the fastest.(2) The comparison of cloud broccoli time under different pre cooling, precooling process of coming to an end when the majority of broccoli temperature has apparently dropped to 273K～274K. Broccoli is the most suitable for the refrigeration temperature is 273K to 276K and it can be seen in the set time, orchid has been successfully is reduced to a target temperature.(3) Experimental results show the pre cooling effect of the packing box with elliptical holes is the best, and the second is round. And with the pre cooling process, the center temperature of the broccoli decline rate tends to slow. This is due to the temperature difference of heat transfer decreases caused by; Also because of the influence of gravity and porosity changes, making the bottom of the error is the largest, the top of the minimum error.(4) Based on the experimental data and the simulation results are compared to prove the simulation result and the experimental result is roughly consistent, the maximum error is 0.3K, within the permitted range, The validity of the theoretical simulation is verified, and the reliability of the finite element analysis method is verified in the process of establishing the model. |
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