| The direct plug-in natural circulation all glass vacuum tube solar water heater is widely used,but the horizontal split type forced circulation water heater is usually used for the vacuum tube solar water heater installed on the vertical wall of the building.One of the reasons is that the hot siphon circulation caused by the mixing of cold water and hot water in the tube is not smooth,the heat energy can not be transmitted to the water tank in time,and the system efficiency is low.One of the effective technical methods to solve the problem of poor circulation caused by cold and hot mixing in the pipe is to set up a deflector in the pipe to form a hot siphon circulation circuit for cold and hot water separation,so as to improve the thermal efficiency of the system.In this paper,the influence of the built-in deflector on the flow and thermal performance of the system is studied by the way of experiment and simulation,and the feasibility of solar energy application of the natural circulation all glass vacuum tube is explored.In order to compare and study the influence of the built-in deflector on the flow and thermal performance of the system under different installation angles,two sets of water heaters with the same structure were manufactured.Each set of water heater consists of 10 47 / 58 tubes and 81.67 liter water tank.One set of water heater tube is equipped with deflector.The flow and thermal performance of two systems with different inclination angles(i.e.conventional 45 ° angle and large inclination angles of 75 °,80 ° and 85 °)were compared.It is found that the daily efficiency of system 1(with deflector)is always higher than that of system 2(without deflector).However,the average daily efficiency of system 1 is 0.7% lower than that of system 2 at a small angle of 45 °.Because the value is too small,it can be considered that the significance of adding a deflector at a 45 ° angle is not great,and system 1 and system 2 are almost the same.The maximum efficiency difference between system 1 and system 2 is 4.2% at an angle of 80 °.The results show that the maximum average daily efficiency of system 1 is 66.4% at an inclination of 75 ° and that of system 2 is 64.2% at an inclination of 85 °.It can be seen that the water circulation effect of the water heater with deflector at large angle(75 °-85 °)is better than that of the water heater with deflector at small angle(45 °),and it is of little significance to add deflector at small angle(45 °).In the simulation,ICEM is used to model and mesh,and then it is imported into fluent for numerical analysis and simulation.Finally,the relevant cloud map is obtained and analyzed through the post-processing of Tecplot.In the simulation,it is found that the maximum temperature of the whole system with guide plate added is higher than that without guide plate.The temperature in the water tank with deflector is more dense than that in the water tank without deflector.The overall flow velocity of the water heater with guide plate is higher than that without guide plate,so the water heater with guide plate circulates faster,so the temperature is higher.At 45 ° angle,the velocity of water flow in the water heater with guide plate is lower than that without guide plate,which means that the speed of circulation becomes slower after the guide plate is added,and the maximum temperature of hot water is slightly lower.At a large angle of inclination(75 °-85 °),the water flow in the water heater with a guide plate is faster and circulates faster,and the upper temperature in the water tank is higher.At this time,the simulation results are consistent with the experiment,which verifies the accuracy of the experiment. |
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