Temperature Field Characteristics In Transport Container Cooled By PCM Of Al₂O₃-H₂O Nanofluids

New type of cooled transport containers can be researched and developed for improving the current status of food cold chain.Due to the excellent thermal physical properties of Al2O3-H2 O nanofluids materials, such as high thermal conductivity, small sub-cooling degree and so on, the nanofluids materials can be used as the new type cold storage materials.In this paper, the homogeneous dispersion Al2O3-H2 O nanofluids are prepared through supersonic oscillating and addition of the dispersant. Then, the low density porous sponges are used to adsorb nanoparticles to reduce settlement, polyvinyl chloride bags are used as packaging bags, and sealing machines are used to seal the cold storage materials. The polystyrene box is used as the incubator and the cold storage bags are put in the incubator. By this method, the transport container cooled by PCM of Al2O3-H2 O nanofluids is prepared.Experiments mainly divided into the following kinds:The control experiments are classified into two kinds, the winter jujubes are used to study the difference between the nanofluids cold storage materials and water cold storage materials. Secondly, the cauliflowers are used to study the difference between the nanofluids cold storage materials and the conditions pre-cooling treatment.In the orthogonal experiments, the carrots are used as the experimental object. Based on the analysis of the thickness of porous sponge, the mass fraction of nanofluids, the quality of cold storage materials, and pre-cooling temperature of vegetables, the effects of the factors and their levels on the temperature variation in the incubator are studied.In the stacking experiments, the carrots are used as the experimental object. The temperature field distributions of the five stacking method are analyzed in the conditions of pre-cooling treatment(-1℃ and 4℃) and the condition of non-pre-cooling treatment(13℃).In this paper, the COMSOL simulation software is used to study the temperature variation. The two-dimension model is established to analyze the difference between the nanofluids cold storage materials and pre-cooling conditions. And the three-dimension model is established to research the temperature field distribution in the five kinds of stacking method.The studies indicate that:1. The performance of nanofluids cold storage container is better than that of the water cold storage container, whose cooling time is twice more than that of water.. And the heat insulation is significant. So the subject container can prolong the preservation time, and improve the transportation distance.2. The preservation performance of nanofluids cold storage container is better than that of the pre-cooling conditions only. In Al2O3-H2 O nanofluids cold storage transport container, the experimental temperature can be kept at about 1 centigrade degree for 40 hours and reach the ambient temperature 15 centigrade degree after 92 hours later; the simulation temperature keep about 0 to 1 centigrade degree for about 40 hours and reach 8 centigrade degree aftre 92 hours. Under pre-cooling conditions, the experimental temperature reach ambient temperature 15 centigrade degree in 30 hours; the simulation temperature reach 9 centigrade degree in 30 hours and 13 centigrade degree in 92 hours.3, The orthogonal experiments show that the importance of factors affecting the temperature is pre-cooling temperature of vegetables, mass fraction of nanofluids, the quality of cold storage materials, the thickness of porous sponge. The experimental results show that the level of the optimal combination is: pre-cooling temperature of 4 centigrade degree, the mass fraction of 0.2%, the material quality of 400 g, the thickness of porous sponge of 20 mm.4. The stacking experiments of three conditions indicate: the preservation time(from long to short) is :group 1, group 2, group 3, group 4, group 5. 1 and 2 are close, 3, 4, 5 rise in turn. The performance of pre-cooling to-1 centigrade degree and 4 centigrade degree are better than 13 centigrade degree. The pre-cooling two are slightly different, when considering energy conservation and economic factors,-1 centigrade degree can be replaced by 4 centigrade degree.5. Three-dimension simulation including flow field can be calculated for 10000 s.When compared to the results without flow field, the temperature curves show that temperature reach to the balanced and uniform temperature rapidly, and have smaller temperature difference. The results are more close to the experimental results.6. The three-dimension simulation results are different from experimental results but they have the same trendency. Compared with experiments, simulation value spend more time to downgrade to the low temperature, the low temperature point maintain higher, hold shorter time temperature rise slower, keep lower temperature in the end.