| Solar energy has the disadvantages of instability and intermittent,which bring a certain difficulty to its use.While phase change thermal storage technology has a large heat storage density and approximately constant temperature in the processes of heat storage and heat release,the good properties can weaken the imbalance between solar heat supply and demand.This paper combined the solar collector technology and phase change heat storage technology,and proposed a kind of the solar collector-multiple phase change thermal storage device.The device consists of solar energy collector layer(SECL),high temperature phase change heat storage layer(HTPCHSL),automatic heat conduction layer(AHCL)and low temperature phase change heat storage layer(LTPCHSL).In the heat charging,the SECL absorbs the solar radiation and conducts the heat to the high temperature phase change material(HT-PCM)in the HTPCHSL,the temperature of HT-PCM begins raising and PCM is melting,when the HT-PCM reaches to the melting temperature,the AHCL automatically fills with water,then the heat transfer coefficient increases,the heat begins to conduct from HTPCHSL to LTPCHSL,the temperature of low temperature phase change material(LT-PCM)begins raising and PCM is melting.In the heat discharging,the cold water enters the HTPCHSL and LTPCHSL respectively,and the high temperature water and the low temperature water are respectively obtained after heat exchange.The device realizes the integrated design of solar collector technology and phase change heat storage technology,and it can adapt to the change of solar radiation,automatically adjust the heat storage temperature and heat storage of PCM,and also realize the purposes of multiple storage and multiple utilization of solar energy.Based on the above principles,this paper has done the theoretical research and experimental research,the main contents and conclusions are as follows:1.Proposing a kind of the solar collector-multiple phase change thermal storage device,and analyzing the heat transfer process.In the heat charging,the solar heat is conducted from the SECL to the HTPCHSL by the means of radiation,and the first-order heat storage is completed.The excess heat gets through the AHCL to the LTPCHSL by the means of conduction and convection,and the second-order heat storage is completed.In the heat discharging,the heat stored in the paraffin is conducted to the heat transfer fluid by the means of conduction and convection.2.The heat charging experiments show that the ratios of heat storage in HTPCHSL and LTPCHSL to the total heat storage are 63%and 33%respectively when the PCM is paraffin,and the result realize the purpose of heat multiple storage.In addition,the ratio of AHCL is only 4%,and the temperature rise is less than 5? before the water injection,thus proving that the AHCL has a good effect in adjusting the heat transfer process.In the condition of simulated solar radiation,the central temperature of HTPCHSL and LTPCHSL can be heated to 52 ? and 36 ? respectively,and its heating time is 350min.Taking the date of May 21 in the Beijing meteorological year as an example,the solar radiation maintains upon 400 W//m2 is 7 hours,the former time is longer than the latter,which indicating that the device has a certain practical application prospect.In addition,the compared experiments between paraffin and water is done,when the heating power density is 1637 W/m2,and the central temperature of LTPCHSL is 35? the total heat storage of paraffin can be 2 times than the total heat storage of water.3.The heat discharging experiments show that the total heat exchange of paraffin is 1.15 times than the total heat exchange of water,and the total heat exchange ratio of the former is among 65%and 45%,which is far less than the 86%of the latter.When the PCM is paraffin,and heating power density is below 1000W/m2;the device can keep the temperature of the heat transfer fluid over 30? about 28?45min,which the time is 45min under the simulated heating condition. |
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