Study on Heat Transfer Performance of Phase Change Thermal Storage Heat Pump Water Heater with Carbon Nanotubes

Abstract

To explore the feasibility of applying carbon nanotubes (CNTs)/paraffin composites to heat pump water heater system, heat transfer characteristics of phase change thermal storage heat pump water heater were analyzed and discussed. It was shown that the melting and solidification rates of nanocomposite were significantly improved upon the addition of CNTs nanoparticles, and the heat pump heat water with thermal storage has good stability in heat storage and release process. There are some differences in the distribution of temperature field in phase change thermal storage system, especially in exothermic stage. Thermal “stagnation” occurs near the corner of the outlet of water medium, so it is necessary to increase the amount of materials appropriately. Compared with traditional regenerative heat pump water heater with water tank, volume of regenerator of heat pump water heater is reduced by about 1/2 with the addition of nano-composites, and the thermal efficiency can reach 86%. The running experimental results of heat pump water heater suggests the reliability of designment of the thermal energy storage and the feasibility of CNTs/paraffin using in the heat pump water heater. The temperature of CNTs-paraffin composites rises faster and the heat transfer time is shorter at higher ambient temperature. Obviously, ambient temperature has a significant impact on the property of heat pump system.