Development Of The Cold Storage Divice With High Temperature Phase-change Material

This paper in view of the present situation of air-conditioning load dynamicchange, low load and low efficiency of chiller system in operation, with refrigeratorefficient operation and energy-saving for the target, using phase change material（PCM）whose phase change temperature within the scope of7to15℃as phase change coldstorage medium, developed a high temperature phase change cold storage device, theapplication of this device can keep refrigerator running in the design condition withhigh efficiency and energy saving, reduce operation time, electricity saving, energysaving, consumption reduction effect, which has considerable application prospect inenergy-saving renovation and remarkable economic and environmental benefits.Phase change cold storage device including phase change materials and the coldstorage package structure. Research showed that the phase change properties oforganic phase change materials dodecanol/capric acid system met the requirements ofhigh temperature phase change storage, according to the very low coefficient ofthermal conductivity, in this paper through add high thermal conductivity coefficientnanoparticles to modification, prepared of nano composite PCM as a cold storagemedium for high temperature cold storage, experimental study on nano compositeorganic phase change materials preparation, nano fluid technology and heat transferenhancement mechanism, the thermal physical parameters, high temperature coldstorage device design and storage/release cold properties of high temperature phasechange storage device, the operation stability had been taken, the conclusions are asfollowing:（1） through adding a certain amount of nano graphite, carbon nanotubes or nanoTiO₂particles to dodecanol/capric acid compound system, with the dispersants andultrasonic oscillations developed nano composite organic phase change cold storagematerials. Analysis had been taken on the mechanism of scatter stability ofnanoparticles in nano composite organic PCM, through experimental study on the scatter stability of the nanoparticles concentration, dispersant type, ultrasonic time,dispersants’ concentration under optimum ultrasound time, utmost preparationmethods to get stable scattered nano composite organic phase change cold storagematerials was achieved.（2） Used differential scanning calorimetry （DSC） to measure the latent heat andphase change temperature of dodecanol/capric acid system and nano composite phasechange materials. The results showed that: by composite with nano graphite, carbonnanotubes and nano TiO₂, the phase change temperature and latent heat of compositephase change material are slightly lower than the liquid only, but not much.Used transient plate heat source method （Hot Disk） to measure the coefficient ofthermal conductivity of phase change materials, the results showed that: because ofthe nanoparticles change liquid fundamental structure as well as micro motion effect,the coefficient of thermal conductivity increased significantly by adding nanoparticlesin liquid.（3） The cold storage performance of dodecanol/capric acid system and nanocomposite materials were measured respectively under7℃waterbath temperature,their temperature-time curves was analyzed, combined with scattered stability, thethermal physical parameters, and the effect of heat transfer enhancement, nanographite composite phase change material was considered as best phase changemedium of high temperature cold storage,and its preparation conditions are: nanographite mass concentration of0.2g/L, dispersant span-80（0.1g/L）, ultrasonicoscillations time for70min; its latent heat of163.6kJ/kg, phase change temperatureof10.1℃under7℃water-bath temperature; its coefficient of thermal conductivityof0.2320W/（m·k）, increased by16.1%.Storage performance of high temperature phase change medium was measuredin cold storage ball and other different sizes, types storage cells, determined the beststorage cell is cylinder of100mm long and20mm in diameter, with high densitypolyethylene materials for packaging, to form a high temperature phase change cold storage tube,the storage/release cold performance of the tube under differenttemperature condition were tested, the results showed that the phase change thermalparameters of the tube of phase change temperature,time,latent heat were meet storageair conditioning system with high temperature of cold storage device requirements.（4） Used small cold storage air conditioning test system, experimental study ofthe operation stability of high temperature phase change cold storage tube was taken,50times repeat experiment was taken under cold storage （7℃） and cold release（15℃） conditions respectively, analysised the temperature-time curve,found thatphase change temperature, latent heat,phase change time are fit for the applicationconditions of high temperature phase change cold storage, after50times alternatingcycles, latent heat declined, but not much. DSC test was taken on the medium, theconclusion is consistent, the latent heat and phase change temperature kept constant,that meant the thermal stability of cold storage materials is very good, hightemperature phase change cold storage tube has a high application value.