Research On Thermal Performance Of The Electric Heater With Composite Phase Change Materials For Thermal Storage

The renewable energy generation brought by the green energy revolution has been greatly supported by the national government.The renewable energy generation has broad prospects for development for its prominent energy saving and emission reduction effect,no pollution and renewable.Beijing vigorously implement the replace coal to electricity project,scatter coal users policy compensation and other measures to achieve clean energy replace coal,effectively improve the increasingly serious environmental problems.The electric heater has the advantages of high conversion efficiency of electric energy,simple and easy heating mode,low energy consumption in the area of peak and valley electricity price and can be widely used in areas where the district heating pipe network cannot be reached.The electric heater with phase change material(PCM)for latent heat thermal storage takes PCM as heat storage medium and stores heat in the low electric price period during nighttime,so as to meet the heating demand during daytime.Because of the heat storage density of the latent heat storage medium is far greater than that of the sensible heat storage medium as well as the phase change temperature can be kept unchanged during the phase change transition period and high heating thermal comfort,this paper researches on the thermal performance and optimization analysis of the electric heater with composite PCM for thermal storage.This paper selected phase change temperature and latent heat as screening basis and the 60# paraffin was selected as the PCM for the decentralized energy storage electric heater.This paper select stainless steel ribbon,aluminium wire,copper wire and expanded graphite(EG)as the heat transfer enhancement materials,compare the composite PCM with different heat transfer materials.Through the heat storage and heat release test,the EG can be selected with the best heat transfer enhancement effect after comparing the density of heat flow rate during the heat storage and heat release period,meanwhile,the EG is beneficial for the flow and heat transfer of PCM and can be used as the adsorption material at the same time.The best mass content of EG in the composite PCM is 10% through the test of phase change temperature,latent heat and heat flow rate during the heat storage and heat release period of the composite PCM with different mass content of EG.Then take the carbon fiber as heat transfer enhancement materials,the best mass content of carbon fiber in the composite PCM is 15% through the test of phase change temperature,latent heat and heat flow rate during the heat storage and heat release period of the composite PCM with different mass content of carbon fiber.Taking paraffin/expanded graphite/carbon fiber composite PCM as thermal storage material,this paper design and calculate the electric heater with composite PCM for thermal storage through the thermal performance design,the structure design,operation design and operating protection design four aspects and prepared model machine of the electric heater with composite PCM for thermal storage by a factory.Through the research on thermal performance of the electric heater with composite PCM for thermal storage and test heating room,the test results show that the best operation condition of the electric heater with composite PCM for thermal storage is closing the ventilator during the heating storage period and open the ventilator during the heating release period.This paper analysis and evaluate the design calculation and testing process of the electric heater with composite PCM for thermal storage,finds that changing the preparation materials can effectively reduce the initial investment,better security and suitable for peak valley electricity price valuation area.The energy storage ratio of the electric heater with composite PCM for thermal storage is 0.44,the thermal storage effect is poor,so deepening research and improvement of the electric heater with composite PCM for thermal storage is obtained.The numerical results show that when the thickness of the thermal storage tank is not greater than 60 mm,the melting time of the composite PCM is 9750 s and the liquid fraction of the composite PCM close to 1,the composite PCM in the thermal storage tank all can be melted and the average temperature of the composite PCM near the left side is not more than 358.15 K.When the spacing of the thermal storage tank is 15 mm,the outlet temperature can reach 337.87 K.High outlet temperature can increase risk,so the spacing of the thermal storage tank is not less than 15 mm.