| Nowadays,power load peak is obvious in our country,although the supply of electric energy is relatively stable,the demand is uncertain.Because of its energy storage characteristics,phase change materials can effectively alleviate the imbalance between energy supply and demand in time and space.The application of phase change materials to electric water heater can improve the heat storage capacity of electric water heater,and combine it with regional peak and valley electricity prices,so that users can use electric energy more economically and rationally,and then improving the overall economic benefit.In this paper,the domestic water storage electric water heater is taken as the research object,establish four different structural models?vertical heating pipe and ordinary inlet pipe,horizontal heating pipe and ordinary inlet pipe,vertical heating pipe and inlet pipe of 1.5 times diameter,horizontal heating pipe and inlet pipe of 1.5times diameter?to study the internal water flow and heat transfer characteristics,compare and analyze the internal temperature distribution and water temperature attenuation,and select the optimal structure.Based on the research on the internal structure of electric water heater,the effects of different types and different amounts of phase change materials on the energy storage of electric water heater are studied,finally,the energy consumption and economy are analyzed.The research shows as follows.?1?During the heating process,the flow velocity of hot water around the heating pipe is larger,the maximum flow velocity of hot water in scheme 1?vertical heating pipe?and scheme 2?horizontal heating pipe?are 0.061 m/s and 0.059 m/s respectively,and the difference between them is small.Compared with the vertical heating pipe,the horizontal heating pipe makes the water uniformity better in the heating process,and the improvement effect is mainly reflected in the low temperature region at the bottom;in addition,the horizontal heating pipe makes the heating efficiency increase by about 2.2%.In the case of heating for the same time,the horizontal heating pipe will increase the rate of hot water withdrawal slightly,about 5.2%.?2?In the water supply and water discharge process of electric water heater,compared with the normal inlet pipe,the thicker inlet pipe makes the water supply process of cold water gentler,and the impact on the hot water in the upper area is smaller,which is more conducive to the discharge of hot water.The change of the inlet pipe diameter has a great influence on the rate of hot water withdrawal,the 1.5times thick inlet pipe increase the rate of hot water withdrawal by 16.9%;the combination of the horizontal heating pipe and the thick inlet pipe can improve the situation of hot water withdrawal greatly,it can increase the rate of hot water withdrawal by 24%.?3?In the same situation of heating,the thermal insulation layer containing paraffin+10%graphite enters the melting process earlier than the thermal insulation layer containing paraffin,and their average change rates of liquid phase ratio are0.001/s and 0.0004/s,respectively.The slope of the water temperature varying curve of the tank with phase change materials is smaller than that of the tank without phase change materials,it takes 56 minutes for the water in the tank without phase change materials to heat to 62?,while it takes 82 minutes for the water in the tank with phase change materials to heat to 62?,it can be concluded that the addition of phase change materials delays the process of temperature rise in the tank.?4?During the solidification process,the average change rate of the liquid volume fraction of the phase change energy storage layer is 1.74×10-5/s,which is much smaller than the average change rate of the liquid volume fraction in the heating process.Because the total thickness of the insulation layer is certain,before the 12hours for thermal insulation,the temperature drop of the water in the tank with phase change materials is faster than that of the water in the tank without phase change material,12 hours later,the phase change materials begin to release heat to the surrounding area,and the temperature drop of the water in the tank with phase change materials is slower than that of the water in the tank without phase change materials.The thicker the phase change energy storage layer is,the larger the decreasing range of average temperature drop in the tank.In the 24 hours for thermal insulation,compared with the average temperature of the tank without phase change materials,the three different thickness phase change energy storage layers increased the water temperature by 1.9%,2.9%and 3.4%,respectively.?5?The inherent energy consumption in 24 hours of electric water heater using vertical heating pipes?scheme 1 and scheme 3?and horizontal heating pipes?scheme2 and scheme 4?are 0.88 kW·h and 0.86 kW·h,respectively.The energy efficiency index of the electric water heater in scheme 1 and scheme 2 are both level 2,and the energy efficiency index of the electric water heater in scheme 3 and scheme 4 are both level 1,it can be known that increasing the size of the inlet pipe can significantly improve the energy efficiency index of the electric water heater.Compared with the traditional electric water heater,the annual operating costs of the three kinds of the phase change energy storage electric water heater are reduced by 36%,24.8%and10.73%,respectively.In terms of total cost,the economic benefit of phase change energy storage electric water heater is better. |
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