Preparation Of Paraffin Based Carbon Nanotube Composite Phase Change Material And Its Application In Refrigerated Display Cabinet

As the terminal device of food cold chain,vertical open refrigerated display cabinet(VORDC)plays an important role in the food quality and safety,however,which exists wildly the fellowing disadvantages: such as the overflow of cooling capacity of the air curtain,unreasonable temperature distribution in cabinet,and the food temperature fluctuation during the defrosting period.In this paper,theoretical and expermental investigation are applied on optimizing the structure of air curtain outlet,enhancing heat transfer of food in cabinet,improving uniformity of temperature,and reducing temperature rise during defrost period,and main research contents and results are as follows:Firstly,wind shield and increasing the length of the base deck are applied to overcome the overflow of cooling capacity of the air curtain.The results show that wind shield and increasing the length of the base deck can reduce of cooling capacity of the air curtain,the bottom of food packages decreases by 0.16~0.65 K by increasing the wind shield;When the length of the base deck increases by 0~200mm,which can effectively reduce the temperature of food packages on the base deck and cool the temperature of increasing food packages.furthermore,which can ensure the food packages to meet the requirements of refrigeration temperature.2Secondly,the experiment conditions have very important affected for measuring thermal properties of phase change materials used different scanning calorimeter,by changing heating rate,sample mass,and atmosphere flow of experimental conditions on the experimental study.The results show that the sample mass and heating rate have great influence on the phase transition temperature and latent heat of the sample,and the air flow rate has little effect,in order to ensure the accuracy of the experimental results,the sample mass should be about 10.0mg,and the lower heating rate(less than 5K/min)Thirdly,in order to improve the thermal conductivity of paraffin which is regarded as cool storage of phase change material,six kinds of paraffin-carbon nanotubes composite phase change materials are prepared by adding different mass fractions of carbon nanotube into paraffin,and their thermo-physical properties and stability are tested.The results show that,with the increasing of carbon nanotubes,the phase transition temperature of composite phase change materials remain the same,phase change latent heat dwindles and thermal conductivity gradually increases.Compared with the pure paraffin,when the mass fraction of carbon nanotube is 5%,the melting and solidifying of latent heat of composite phase change materials reduce by 15.5% and 13.8%,respectively;the thermal conductivity of the solid and liquid increase 39.5% and 40.3%,respectively;Furthermore,it has good cycling stability.Finally,RT4-3%MWCNT composite shelf applied on refrigerated display cabinet is constructed,the temperature distribution of the food packages is studied.The results show that the shelf filled the composite PCM have good cold storage performance and can decrease the food temperature of food packages and temperature fluctuation during the defrosting period.Compared with the ordinary shelf,the lengthways and depthwise temperature different of composite shelf filled into only RT4 reduce by 80.0% and 7.6%,respectively;the lengthways and depthwise temperature different of composite shelf filled into RT4-3%MWCNT composite PCM reduce by 92.0% and 12.2%,respectively.It indicates that the composite PCM further increases the heat transfer of composite shelf and improve the performance of VORDC.