Study On Enhancement And Its Time Response Of PCM Thermal Storage

As a kind of effective waste heat recovery technology, phase change heat storagetechnology is gradually applied in the field of energy engineering. For automotiveapplications, especially electric vehicles whose on-board energy is extremely sensitive,development and application of energy recycle technology of phase change energystorage is becoming more and more attention. In this paper, the phase change heatstorage device for application on the electric vehicle will be discussed. Hope to beable to design a kind of phase change heat storage device, It not only has higherstorage capacity and can enhance time response of heat storage and heat release, butalso is associated with thermal control system of battery pack and electric control unitand can store heat which generate from the battery pack and electric control unit. Thisis not only conducive to energy reuse, but also improve the thermal stability andtemperature comfort of the electric power system, at the same time also moreconducive to cohesion of heat storage using the outside heat source. Thus to solve theproblem of the battery pack preheating, excess heat can also be used for heating of themotor, reduce automobile electrical energy consumption. This requires the phasechange heat storage device has good thermal efficiency and short heat storage time fordifferent heat storage temperature and flow rate during heat storage process, and canrealize fast heat release and export fluid has good heat performance during heatrelease process. According to the above points, In this paper we study the structuredesign of phase change heat storage device and the heat storage and release propertiesduring phase change process through the numerical simulation, these provide areference for design optimization of phase change heat storage device for applicationon electric car.First, we put forward a flat tube bundle heat storage structure that is with flat tube as the heat storage unitand conduct the research in computational analysismethod, through the heat transfer analysis, model establishment and the definitecondition setting, and experimental verification of model algorithm, the reliability ofthe model was validated. Under basic conditions, the changes of liquid rate, outlettemperature, enthalpy difference of import and export, heat power, the temperaturedistribution and velocity distribution with time during phase change process isobtained through the numerical simulation. Simulation results show that heat storagetime and heat release time all greatly shortened, and the main factors influencing heatstorage time of the whole structure is phase transformation time of a single flat tubeunit and the row number of the flat tube. During phase change process, the middle flattubes start phase change slightly earlier than flat tubes on both sides in the same row,and the front flat tubes start phase change earlier than the back flat tubes. The effectsof working conditions, flow path, geometric parameters material properties on theheat storage and release properties are studied. Results show that the inlet fluidtemperature and flow rate and melting point have a great influence on heat storagetime and heat release time, and the initial temperature, flat tube spacing and latentheat have a large effect on the temperature of outlet fluid during heat release process.These provide the basis for further optimization of structure. This paper also discussesthe effect of the multiple melting point cascade heat storage on the heat storage andrelease properties. Results show that the multiple melting point cascade heat storagecan integrate the advantages of high melting point and low melting point, to get whatwe want heat storage and release properties. Considering heat storage and heat releasecharacteristics, when need higher outlet temperature, from the front row to the backmelting point arrange from low to high, when need longer heat release time, from thefront row to the back melting point arrange from high to low. By changing the ratio ofthe number of different melting point, which can further improve its performance.In order to further analysis of dispersion type sphere accumulation regeneratorperformance, exploring energy storage performance and features of energy storagebody, we put forward another sphere unordered accumulation heat storage structure that is with Small diameter ball as the heat storage unit. In this paper, we introducedthe modeling process of the three-dimensional sphere unordered accumulation, andthe mathematical model is validated by experimental data. Through the numericalsimulation, we obtain the changes of liquid rate, the changes of outlet temperature, theheating performance of export fluid and the changes of sphere internal temperatureunder basic conditions during phase change process, and analyses the characteristicsof the heat storage and release. Results show that the main reason of restricting theheat transfer time of the overall structure is not the number of sphere, but a single ballphase transition time. We analyzed the influence of different diameter sphere on theheat storage and release properties through the numerical simulation. Results showthat the smaller the sphere diameter, the shorter the heat storage and release time, andthe flow resistance is also increased. This paper also discusses the effect of differentmelting point regenerative ball and their mixture according to the different way on theheat storage and release properties, and results show that by properly adjusting thenumber of different melting point, this heat storage structure can integrate theadvantages that high melting point can quick release heat and the advantages that lowmelting point can quick release heat, and heat distribute in different temperature.