Performance Study And Economic Analysis Of The Phase Change Emulsion Composite Solar Water Heating System

The phase change material compound solar water heating（SWH-PCM）is a system which combines the traditional solar water heating system with the phase change material.The technology not only improves the thermal efficiency of the traditional solar water heating（SWH）system,but also store the latent heat in time and space.Most of the researches about SWH-PCM system focus on the modified performance of heat collector or water tank using phase change materials.A little part about the application of functional fluid in SWH is on the characteristic of functional fluid.However,under the actual radiation conditions,the thermal and flow properties of fluids in the SWH need to be compared with the traditional SWH system to analysis the characteristics of the new system.In this study,the compound paraffin emulsion used in SWH-PCM system was prepared as a functional flow medium,and compared with the traditional SWH system,the operation characteristics of the new system were obtained.And a single household water heating（WH）system was taken as the research object,the economic and environmental benefits of different WH systems are analyzed.The paraffin emulsion was prepared by the phase transformation method,while it had a supercooling degree of 14.23°C,and the thermal conductivity was only 0.4485W·m^-1·K^-1.The supercooling of the composite emulsion was reduced to 0.27°C by adding graphene as a nucleating agent,and the thermal conductivity was increased by20.22%.The particle size,phase change enthalpy and viscosity of the composite emulsion were measured after 300 heating/cooling cycles,which proved that the stability of the composite emulsion was excellent.Based on the principle of SWH system,the experimental rig was built.And the reliability of the rig was calculated by the error analysis.The homemade composite paraffin emulsion and water are used as the flow medium to build the SWH-PCM system and the SWH system.First,the influence of different fluids on the heat collection characteristics is studied.Through the analysis,the SWH-PCM system has a higher average heat storage capacity when the phase change material has not been melted.By changing the radation and flow rate,the total heat storage capacity of the two systems increased while the radation increased.But the thermal efficiency showed the opposite trend.For the increase of the flow rate,the heat storage and thermal efficiency of the SWH-PCM system decreased,while the heat storage and thermal efficiency of the SWH system have little change.It shows that compared with SWH system,SWH-PCM system has advantages not only in heat storage and thermal efficiency,but also in low flow rate,which leads to a certain reduction in the cost of the system.Finally,taking the electric heating water system,the gas heating water system and the SWH system as the contrast,the economy of the SWH-PCM system is analyzed by comparing the economic indexes such as unit hot water cost,accumulated discount value,dynamic investment recovery period and internal rate of return.What’s more the system can reduce the use of fossil energy,reduce the emissions of carbon dioxide and other pollutants by computing.Thus the SWH-PCM system has extraordinary economic benefits as well as the good environmental benefits.