| Solar energy is inexhaustible and non-polluting,which has the possibility to replace traditional fossil energy in the future and has a good development prospect.As one of the most widely used and representative solar energy utilization methods,solar water heater has a vast market in China.However,the traditional solar water heater has problems such as poor combination with high-rise residential buildings,system breakdown frequently,and high requirements on installation location,which has affected the development of the solar water heater industry.In this thesis,a porous foam metal copper was used as the capillary core and anhydrous ethanol as the working fluid.A pump-assisted plate evaporator loop heat pipe system was designed and the experiment bench was built.A micro-assisted pump was introduced in the loop heat pipe system to overcome the shortcoming,which is low thermal efficiency and failure to start at low heat flux(such as weak solar radiation).The pump-assisted plate evaporator loop heat pipe is applied to the solar water heater system.As a solar collector,the flat plate evaporator can be directly suspended on the outdoor wall,which greatly reduces the requirement of the installation position of the solar water heater system,and Integration of high-rise residential buildings.Based on the study of heat flux,filling ratio and pump power intensity on the system operation and heat transfer performance of the pump-assisted system.The starting characteristics and stable operating characteristics of the pump-assisted system and the pumpless system were compared.The main findings were as follows:(1)When the heat flux is low,the start-up time of the pump-assisted system is long and the evaporator temperature is low during stable operation.When the heat flux is high,the system starts faster and the evaporator temperature is higher.(2)When the system filling ratio is 55%,regardless of the heat flux is low or high,the thermal resistance and thermal efficiency of the system are relatively better during stable operation,that is,the lower thermal resistance and the higher thermal efficiency.Therefore,55%is the optimal filling ratio for this pump-assisted plate evaporator loop heat pipe system.(3)When the experimental system is in stably running,the evaporator temperature will decrease with the increase of the pump power intensity.Within the system heat flux range of 0.125 W/cm~2-0.5 w/cm~2,20 W/m~2 is the optimal pump power intensity value of the system.Under the condition of 0.625 W/cm~2 and 0.75 W/cm~2 heat flux,17.5 W/m~2 is the optimal pump power intensity value of the system.When the heat flux of the system is within the range of 0.875 W/cm~2-1.25 W/cm~2 and the pump power intensity is within the range of 17.5 W/m~2-20 W/m~2,the system operates under optimal state.(4)The pumpless system starts work and heat exchange after generating gaseous working fluid in the evaporator.However,the pump-assisted system starts work and heat exchange after starting,and the pump-assisted system can work without being affected by the heat flux.The overall thermal efficiency of the pump-assisted system is higher than pumpless system.When the heat flux is low,the pump-assisted system is more advantageous.When the heat flux is 0.25 W/cm~2,the thermal efficiency of the pump-assisted system is 22.1%higher than pumpless system.However,this value is2.7%when the heat flux is 1.25 W/cm~2. |
