Application Of Computational Fluid Dynamics To Air Flow Optimization For The Cold Store

The cold store is a place to store agricultural products, medicine, military productsat low temperature and prevent them from putridity. Since1990s, with the developmentand improvement of living standard to citizens, both the needs of quality and quantity offood have been improved. Therefore, the scale and quantity of cold store in our countryis increasing. However, the problem of unreasonable air flow distribution in the storehas not been solved efficaciously. This is due to that the non uniform zone of air flowcan not be obtained by traditional experiments, what’s more, visualization research costshigh and the results are probably not ideal. The unreasonable air flow will increase theoperation cost of a cold store and decline the quanlity of preserved foods, which shouldbe solved during the operation of the store. As the branch of hydromechanics,computational fluid dynamics is used to research the properties of heat transfer andmass transfer to different flows. Recently application field of CFD is being widenedcontinuously. The purpose of this study is to seek for precise methods to simulate the airflow distribution of different scales of cold store. After the methods are proved to beaccurate by practical experiment, they will be applied to analyze influence to unitary airflow in a cold store that caused by different air outlet styles, positions of fan, productarrangements. The purpose of this article is also aimed to be useful to design a coldstore. The main work and conclusions of our study are listed as followed:(1) The2D and3D technology were used to build the model, respectively. Bothtwo models were combined with wall function and Boussineq assumption to simulatethe air flow distribution in a small cold store (4.5m(length)×3.3m(width)×2.5m(height)). The results showed that simulation by3D method was closer to theexperimental results than those of2D method. Moreover, the unstructured mesh had ahigher accuracy than that of the structured mesh due to it was suitable to complicatedmodel like a cold store. The SIMPLE algorithm was better than PISQ algorithm todecouple the relation of pressure and velocity to the air flow in a cold store in unsteadycomputation, which had the less error by SIMPLE algorithm than that of PISQ one compared with experimental data. The most suitable size of mesh to the cold storemodel was10. The air flow distribution in the cold store was showed a good symmetryin the horizontal plane, while it had high velocity in top and bottom zone of the smallcold store, and low velocity in center zone of the store relatively. The whole style of theflow was a large circulation in the cold store.(2) To obtain the change of air flow distribution caused by different air returnstyles, this work applied the previous3D methods which was validated in the smallstore and combined with k equation. The conclusion was that the lateral return airstyle saved more energy than the style of rearward air return style. The highesttemperature was located at the corner of wall and under the fan. The simulation was alsodone to get the flow field in a cold store of210m3(10m(length)×7m(width)×3m(height)) with different air outlet styles of the fan. The result showed that the air flowin the cold store with two fans of three-outlets was more uniform than that with threefans of two-outlets of air.(3) Since the air flow was hard to obtain at the huge cold store by traditionalexperiments. The refrigeration capacity of a huge cold store (48m(length)×46m(width)×6m(height)) was calucated and the cooling fans were also allocated. Then CFDsimulation was applied to get the different air flow fields caused by different positionsof fans. The results showed that the air flow was more uniform at the situation that thelocation of fans were at the center of the cold store with the air direction to the two sidesof the cold store. Since the interference to air flow of this condition was week. Whatwas similar to previous study, the highest temperature was located at the corner of walland air return zone. The temperature fields was influenced by the air flow distributionduring the operation of cold store and showed a good symmetry at the horizontal plane.(4) Based on the air flow distribution in the huge cold store by previous study, andsome design standards of cold store as references, the simulation work was involved inthe air flow distribution of the products zone and the whole cold store at the situation ofdifferent intervals between products in vertical direction to the huge store, the intervalswas chosen as10cm and15cm, respectively. The conclusion was that since the productsarrangement took the interval of10cm occupied less room and had a lower air velocityat the zone where products were stored, this arrangement was better than the plan withthe interval of15cm. The result of simulation showed that the average air velocity of theplane which was much closer to the fan increased obviously. The outlet velocity of fan was3m/s was propitious to imbursement of products. It suggested that the products atthe top of the cargo area should be packaged because of the high air velocitywhen thevelocity of fan was5m/s. However, the velocity of the products area would be beyondthe standard when the fan outlet velocity was7m/s.