山梨酸钾/氯化钾复合相变材料制备及热物性分析

Preparation and thermal performance analysis of C_5H_7COOK/KCl composite phase change material

为开发出高效、性能稳定的微冻保鲜用相变蓄冷剂,保证运输中肉制品等农产品的品质,以山梨酸钾水溶液为主基液,探究添加氯化钾后相变蓄冷材料的热物性及热循环稳定性。对比30 g/L山梨酸钾溶液,当再添加氯化钾浓度为5 g/L时,相变温度为-2.8℃,潜热为254.6 J/g,热导率为1.012 W/(m·K),热扩散率为1.01 mm2/s。添加氯化钾对相变温度和潜热几乎没有影响;溶液的热导率提高了23.32%;热扩散率提高了151.37%。经200次冻融循环后,未添加氯化钾的相变溶液出现了-5.3℃的过冷度,含氯化钾的相变溶液没有过冷度,氯化钾在山梨酸钾相变过程中体现出了其良好的成核作用,使得该复合相变蓄冷剂具有优异的热稳定性。试验表明,山梨酸钾/氯化钾复合相变蓄冷剂适合于农产品的微冻保鲜用。

In the process of handover,strict logistics quality standards and inspection methods are lacking in food logistics enterprises.It makes the“broken chain”and“being not cold”of fresh and perishable low-temperature products become common phenomena during fresh and perishable low-temperature products’transportation.At present,distribution of fresh food is not effective with the application of modern technology and the implementation of the“first mile”sorting and pre-cooling scheme,and the“last mile”is still dominated by the traditional ways of circulation model represented by“ice pack&plastic foam box”.Meanwhile,the cold storage,of which the main function is cargo-storing,often does not have the ability to sort,flow and process,so it restricts the effective improvement of the cold chain logistics’service level seriously.It is particularly critical to develop more efficient storage technologies with respect to the“first mile”and the“last mile”of agricultural products.Water temperature refrigerated preservation(range from-2 to-3℃)belongs to the temperature interval of micro-frozen and fresh-keeping,and it is also a concept proposed for meat products,fruits and vegetables,etc.It can not only inhibit the growth of microorganisms effectively,but also keep food nutrients from being lost compared to traditional refrigeration technology.In order to develop a stable and efficient phase change coolants for micro-frozen and fresh-keeping to ensure the quality of agricultural products,such as meat products in transportation,the ternary complex composed of C5H7COOK,KCl and H2O was prepared in this article.Considering that the cold storage condition has a great influence on the supercooling degree and cooling rate,-20℃was selected firstly as the cooling medium temperature in this article via testing the step cooling characteristics of the PCM under different cold storage conditions;the optimal concentration of main base solution was determined by DSC(Differential Scanning Calorimeter)experiment.Then mixing KCl with it,thermodynamic properties and thermal cycle stability of the composite material were studied by Hot Disk thermal constant analyzer,DSC,Agilent temperature time recorder,low-temperature thermostat bath and other equipment.When KCl was added,under concentration of 5 g/L,into the 3 g/L C5H7COOK solution,DSC results indicated that the onset temperature and latent heat were measured as-2.8℃and 254.6 J/g,which were reduced by-0.3°C and 1.6 J/g respectively.It was indicated that there was no chemical reaction between C5H7COOK and KCl,since there shows a linear relationship between the change of properties and concentration ratio.The thermal conductivity of C5H7COOK/KCl solution was measured as 1.012 W/m·K with an increase of 23.32%;the specific heat capacity was 1.002 MJ/m3K with a decrease of 50.95%,and thermal diffusivity was 1.01 mm2/s with an increase of 151.37%.From the point of view of temperature,the higher the thermal diffusivity,the faster the propagation of internal temperature variation.Thermal cycling test results revealed that the changes of the phase change temperature and latent heat of the C5H7COOK/KCl composite solution were not obvious after 200 freeze-thaw cycles.Under condition of-20℃in cold storage,the composite PCM added with KCl showed great nucleation,which made the composite PCM has excellent thermal stability.In conclusion,the prepared C5H7COOK solution containing 5 g/L KCl composite PCM can be acted as a potential material for the refrigeration of agricultural products due to the appropriate and acceptable thermal properties,reliable thermal stability,and high thermal conductivity.