Comparative Study On Heat Collection Performance Of Horizontal And Vertical Vacuum Tube Water Heater

All-glass vacuum tube water heater has great application potential in the field of low-temperature heating.The horizontal and vertical drain tube water heaters are two important types of all-glass vacuum tube water heaters.Because of the different installation structures of vacuum tubes,there are some differences in their heat collection performance.At present,there are many studies on all-glass vacuum tube water heaters at home and abroad,but the comparison of all-day heat collecting performance of all-glass vacuum tube water heaters with horizontal and vertical drains under forced circulation is not comprehensive enough,and the reasons for the differences are not given a comprehensive and in-depth analysis.In this thesis,four typical days(spring equinox,summer solstice,autumn equinox and winter solstice)of two kinds of water heaters are theoretically calculated,including the effective collector area,the instantaneous solar radiation received by the collector and the total solar radiation received by the collector throughout the day.The difference of energy collection between the two kinds of water heaters during the whole day heat collection process and the change of the annual collector performance are analyzed.Rule of chemistry.In order to verify the reliability and accuracy of theoretical analysis,an experimental platform for measuring the collector performance of horizontal and vertical water heaters was built.The experiments were carried out for five consecutive days on four typical days.The experimental data and theoretical results were compared and analyzed,which not only verified the reliability and accuracy of theoretical analysis,but also further discovered the internal flow of horizontal and vertical water heaters.There are some differences in heat transfer.In order to reveal the difference of flow and heat transfer between the two water heaters in the process of collecting heat,the whole-day collecting heat process of the two water heaters under forced circulation was simulated by using FLUENT simulation software,and the variation law of temperature field and flow field in the process of collecting heat was obtained.Through the comparative analysis of temperature field and flow field,the reasons for the difference of flow and heat transfer between horizontal and vertical water heaters are revealed.The main research contents and conclusions are as follows:(1)In terms of the total solar radiation received by water heaters throughout the day,only in the summer solstice,the total solar radiation received by horizontal pipe water heaters is higher than that of vertical pipe water heaters.In the spring equinox,autumn equinox and winter solstice,the total solar radiation received by vertical pipe water heaters throughout the day is significantly higher than that of horizontal pipe water heaters.(2)In terms of effective heat collection and average effective heat collection efficiency,at the summer solstice,horizontal pipe water heaters have Effective heat collection and average effective heat collection efficiency are always higher than vertical drain water heater.In the spring equinox,autumn equinox and winter solstice,the effective heat collection efficiency and average effective heat collection efficiency of vertical pipe water heater are higher than that of horizontal pipe water heater.The results are consistent with the theoretical analysis of the total solar radiation received by the water heater throughout the day.(3)In terms of instantaneous effective heat collection,when the difference of solar radiation received on the surface of the water heater is large,the instantaneous effective heat collection of the water heater with more instantaneous solar radiation received is higher.When the instantaneous solar radiation received on the surface of the water heater is similar,the instantaneous effective heat collection of the water heater depends on the fluid flow and heat transfer inside the collector.(4)When the solar radiation is 448.1 W/m~2,there is no good stratification phenomenon in the inner part of the transverse tube water heater vacuum tube;a good stratification phenomenon has been formed in the inner part of the vertical tube water heater,and the convective heat transfer intensity of the vertical tube vacuum tube is better than that of the transverse tube water heater;when the solar radiation is 987.2W/m~2,the inner part of the transverse tube except the tail end area.Good stratification has been formed in other areas.Vortex phenomena have appeared in the front and middle and upper parts of the vertical drain pipe water heater.Vortex phenomena have led to a significant decrease in the heat exchange rate between the vertical drain pipe and the external fluid,and the heat exchange intensity of the horizontal drain pipe vacuum pipe is obviously better than that of the vertical drain pipe.(5)In the aspect of convective heat transfer between vacuum tube and water tank,due to the existence of forced convection in the water tank of vertical tube water heater,the flow of fluid in the middle is slow and the local pressure increases,which has a certain restraint on the heat transfer between the central part of the vacuum tube and the water tank,resulting in the evident high temperature of the middle part of the vacuum tube,while the velocity of fluid at the outlet of the vacuum tube of the horizontal tube water heater is faster,forming a whirlpool.Phenomenon,the flow velocity in the header is faster and the pressure is smaller,which promotes the heat transfer speed between the vacuum tube and the header to a certain extent.