| The energy storage system of solar-assisted air source heat pump(SAHP)comprises the function of cooling / heating energy storage and supply.It not only contributs to the balance of the difference between peak load and vale load,but also increases the energy flux density of solar heat utilization,which is more stable and more lasting.In the thesis,the prototype of SAHP energy storage system,of which the energy storage capacity is 2572.5 k J,has been built based on the previous research.Furthermore,the various kinds of operating modes of the prototype have been tested by the experiments,and the stability as well as the reliability of the prototype under the extreme operation condition has been investigated.Focusing on the deficiency of the heating capacity,advance the e xergetic analyzing,combining experiment research to develop the heating performance of the system.The methods to improve the operation energy efficiency of SAHP energy storage system have been discovered by analyzing the heat transfer rate and the heat transfer efficiency.A new SAHP energy storage system has been proposed based on flow energy storage and heat exchange equipment,and the exper iment and the theory research have been made for the crucial problems of the new system.The research results show that there is considerable development of flow energy storage system in operation energy efficiency,exergetic efficiency,heat transfer rate and heat transfer efficiency.The SAHP energy storage system performs well under refrigeration conditions,for that different index can meet the design requirement in different operating modes.Especially when the nighttime outdoor dry bulb temperature is no more than 25.0 °C,it is presented that the energy storage heat exchanger has the high energy use efficiency within the cold storage-refrigeration cycle.The system has a poor performance under heating condition,for that the heating power never meets the design requirement in particular.The heating performance of SAHP can be positively improved by increasing the solar-heated hot water temperature / flow,and the effect of solar-heated hot water temperature is much more significant.The stability,security and reliability of the system are not negatively influenced by switching modes in the operational process.The exergetic-analysis model of SAHP has been set up.The analytical results illustrate the key factor to influence the performance of the triplex-tube energy storage heat exchanger unit.By optimal matching the energy storage heat exchanger unit,the heating capacity and energy efficiency of SAHP under heating condition have been improved,which can meet the design requirement.The principle is that within refrigeration / heat-pump cycle,the energy efficiency of heat pump increases with the greater heat flux of system evaporator.Therefore,in accordance with actual demand,especially with the various operating modes,numbers of the energy storage heat exchange unit should correspondingly be increasingly / decreasingly adjusted in order to match the capacity of other components of SAHP.The essentiality of adjusting the numbers of energy storage heat exchange unit is to rebalance the energy storage capacity with the energy storage / release rate.In accordance with the concept of Heat Transport Potential Capacity(HTPC),the heat transfer rate and heat transfer efficiency of the energy storage heat exchange unit are quantitatively analyzed within the energy storage-release circle.The analyses show that the triplex-tube energy storage heat exchanger is a special kind of dividing wall type heat exchanger,and it has the ability to transfer heat and accumulate energy,which shows character of dualism.The enhanced heat transfer rate not necessarily promotes the system's whole performance,and the basic method to increasingly promote the system energy efficiency is to improve the heat transfer rate between the phase change material and the cold or hot fluid.The ultimate factor of which to restrict the enhancement of heat transfer rate / efficiency in this kind of heat transfer process is heat transfer resistance of the energy storage medium.Based on the heat transfer analyses,the new SAHP energy storage system on account of the flow type energy storage and heat exchange equipment is proposed.Through experimental and theoretical study,the binary series viscosity model,which has been built to describe the viscous characteristic of energy storage medium within the energy storage-energy releasing temperature range,illuminates the phase-change,flow and heat transfer characteristics of the energy storage medium.It is found that when energy storage medium flows within the energy storage-energy releasing temperature range,there is no congealing which paralyzes the circulation of energy storage medium.Within that temperature range,the flow resistance of energy storage medium is about 1.2 to 6.0 times of liquid water.The transport cost is not largely increased within the range of low flow rate which is also the actual application condition.When energy storage medium flows in the heat transfer tube,the exothermic process is enhanced owing to its own phase transition(enthalpy release)and rheology.If the velocity of energy storage medium in the heat transfer tube is appropriate,the heat transfer flux can reach the maximum,of which the value approximately accounts for 60 percent of total energy storage.Based on the experimental and theoretical research of energy storage medium,the new flowing-type energy storage SAHP system has been designed.In the flow energy storage system,the influence brought by asymmetric heat transfer structure in heat exchanger can be decreased by means of sett ing the energy storage heat exchanger and energy storage container independently,and the heat transfer rate of energy storage heat exchanger is improved substantially.Because of the convective heat transfer between the energy storage medium and the cold fluid,the evaporating temperature of refrigeration / heat-pump cycle has been raised by 6~8 °C,and it effectively develops the heat transfer efficiency within the energy storage-release circulation,furthermore reducing the heat dissipation in the proces s of heat transfer.The results of exergetic analysis show that refrigerating / heating capacity and EER of flow energy storage system are promoted by more than 10%,and the exerg etic efficiency is promoted approximately from the original 28% to 32%.This project is part of the ?innovation and characteristic research in solar energy and air source heat pump integrated system with triple-sleeve energy storage(No.51178133)?,which is spent by the National Natural Science Foundation.The thesis is of great significance to deeply investigate the SAHP energy storage system,and it can provide theoretical direction to design energy storage system / device with higher efficiency.The proposed flowing-type energy storage and heat transfer device can promote the energy efficiency of the SAHP energy storage system effectively,which provide useful reference for the cold-adaptation research of air-source heat pump. |
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