| The contradiction between the limitation of fossil energy and the rapid growth of global energy consumption is becoming increasingly sharp,therefore,the energy problem has become one of the main problems that human beings must to solve in the new century.Solar energy has attracted much attention as a safe,clean and sustainable resource.Solar energy resources are abundant in our country,and solar photothermal utilization has been widely used in life and engineering.Using solar water heater to make domestic hot water can effectively reduce the energy consumption,but there is a problem of low thermal efficiency when the solar radiation intensity is low.Based on this background,this paper puts forward a design idea of adding reflector to solar vacuum tube heater that can improve heat-collecting efficiency,that is,the solar light in the surrounding space and the sunbeam passing through the vacuum tube gap are gathered to vacuum heat-collecting tube by the reflection of parabolic concentrators,in order to increase the received solar radiation intensity.The design modeling and optical performance simulation of the reflector model are carried out to determine the structural parameters of the reflector,as well as analyzing the performance of the vacuum heat-collecting tube after installing the reflector.This paper introduces the structure and working process of the vacuum heat-collecting tube,establishes the heat transfer mathematical model,analyzes thermal resistance of each part of the structure and the heat loss during the heat transfer process.Using the experimental data collected by predecessors to carry out theoretical calculation,verify the validity of the mathematical model and analyze the factors affecting the thermal efficiency of the collector tube,such as the inlet temperature of the thermal conductive fluid,the solar radiation intensity,the flow rate of the thermal conductive fluid,the temperature of the surrounding environment of the vacuum collector tube,etc.The Pro E software is used to establish a multi-group reflector model,and the radiation intensity of the light source is controlled to 800 W/m~2.The optical performance of the reflector is simulated and analyzed by Trace Pro software,which can help to calculate the design parameters of the reflector.The original model of vacuum heat-collecting tube with reflector is established,and the vacuum heat-collecting tube without reflector is taken as the control model at the beginning.Next,the solar radiation intensity data of Shijiazhuang area obtained from theoretical calculation are imported into Trace Pro software,then original model and control model are simulated and analyzed.It is concluded that the solar radiation energy received by the vacuum tube can be enhanced and the heat collection efficiency can be increased about 11%by installing the reflector.When the solar radiation intensity is low in winter,the heat collection efficiency can be increased which is the same as that without reflector in other seasons.In this paper,the factors affecting the heat collection efficiency are analyzed by establishing the heat transfer mathematical model of vacuum heat-collecting tube,and.when the solar radiation intensity received by vacuum heat-collecting tube is enhanced,the thermal efficiency can be effectively improved.A total of 33 groups of models were designed by using Trace Pro software to simulate and analyze the optical properties,then the design parameters of the final reflector were calculated.The simulation was carried out again according to the solar radiation intensity data at each time so that we can analyze the effect and feasibility of adding reflector on thermal efficiency.There is no denying that the designed reflector is simple in structure and easy to make,and it is expected that it can be applied to bring convenience in daily life. |
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