利用相变释能的农产品冷藏设备主动防除冰方法

为减小农副产品冷藏设备表面的结冰危害,提高部件表面的抗结冰能力和设备运转效率,该文提出利用相变释能的主动防除冰方法。试验以带有不同凹坑尺寸的聚甲基丙烯酸甲酯(polymethyl methacrylate,PMMA)和6061铝合金作为基体材料,凹坑内填充气体或不同冰点的介质,表面覆盖双向拉伸聚丙烯薄膜(biaxially oriented polypropylene,BOPP)。试验采用水杯制冰法,测量表面结冰附着强度,结合剥离界面的形态,分析相变时差对界面附着强度的影响机理。结果表明:相对于光滑PMMA试样的表面附着强度169.81 kPa,试样(凹坑内分别填充纯净水和体积分数为6%乙醇溶液)表面的附着强度分别降低了100%和82%;对比无凹坑铝合金试样表面的附着强度,凹坑内填充体积分数为15%乙醇溶液低冰点溶液的试样表面附着强度可减小76.52%。因此利用不同水溶液的相变时间差和膨胀释能可减小试样表面的附着强度,并且试验表明试样材料、凹坑尺寸对附着强度的降低作用影响较小。利用相变时差和相变膨胀释能破坏冰在弹性冻结界面的接触稳定性,达到降低结冰表面附着强度的目的,并且水溶液中水的体积分数越大,试样结冰表面的附着强度的越小。研究结果为农产品冷藏领域中的防、除冰方法研究和开发提供参考。

Active anti-icing method for agricultural product refrigerated equipment based on phase change energy release

The application of refrigeration in agricultural and sideline products preservation is getting more and more extensive. However, the surface of refrigeration equipment, such as evaporator, condenser and chiller, is prone to freeze, and ice and frost are easy to occur, which seriously affect the operation efficiency of refrigeration equipment and increase the cost. The formation of ice must be accompanied by the phase expansion. So, why not use the phase transition expansion as the deicing power, and make the refrigeration equipment surface own active control ability of ice? During the test, the polymethyl methacrylate (PMMA) with pit and the aluminum alloy were used as the matrix materials, which were bonded with the biaxially oriented polypropylene (BOPP) elastic film as the freezing interface. The pit of the PMMA was filled with gas or aqueous solution with different freezing point. The test adopted the cup method to make the ice under -25℃ temperature. With the same cup, the test directly adopted the measured peeling force as the icing adhesion strength. The experimental results showed that the influence of the freezing medium with different freezing point on the icing adhesion strength was different. Compared with icing adhesion strength on the smooth specimen surface 169.81 kPa, the icing adhesion strength of the sample filled with the pure water in the pit was 0 kPa, decreased by 100%. And the icing adhesion strength of the sample filled with 6% ethanol solution was declined by 82% compared with the smooth specimen. Compared with the aluminum alloy sample surface, the icing adhesion strength of the sample filled with the solution of low freezing point was reduced by 76.52%. The icing adhesion strength of the sample filled with 6% ethanol solution was the smallest among the samples with the pits filled with alcohol solution. After the test, it was found that the expansion bump with different height occurred on the surface of the BOPP film on the surface of the pits, and the maximum height (3.34 mm) was on the surface of the specimen filled with pure water, followed by the sample filled with 6%, 8% and 10% ethanol solution, whose swell bump heights were 1.25, 1.13 and 1.04 mm, respectively. The results showed that the icing adhesion strength would be reduced by the phase expansion energy owing to the time difference of phase change. What was more, the influence of sample material, size of pit and filled solution on the icing adhesion strength decrease was very small. During the test, BOPP elastic film was used as the icing interface, and the rigid freezing interface under normal conditions was transformed into a flexible freezing interface. Due to the different thermal conductivity, the moisture on the film was first frozen, and the water solution in the pit formed the boundary constraints. After the aqueous solution was frozen into ice, the swell was generated and the energy was released. The energy played a role on the BOPP elastic film, and it destroyed the contact stability of the interface and reduced the icing adhesion strength. Therefore, it is feasible to destroy the contact stability of the elastic freezing interface and reduce the surface icing strength by the phase transition expansion caused by the coupled effect of ice itself and time difference of the phase transition using different aqueous solutions. The experimental results could provide a reference for studying and developing of anti-icing during agricultural product refrigeration field.