For all-glass vacuum tube solar water heater, which integrates heat collection and storage, night heat loss affects its continuous and stable energy supply for users. For this reason, taking a set of 30 all-glass vacuum tube solar water heaters with specifications of Φ58 mm×1800 mm as the research object, the temperature changes of 20:00-07:00 water heater storage tank and vacuum tube within 10 days were experimentally studied, and the night heat loss of each part of the water heater was analyzed. In addition, a three-dimensional unsteady numerical model of allglass vacuum tube solar water heater was established, and the flow and heat transfer characteristics of the water heater during night heat dissipation were analyzed. The results show that among all kinds of heat loss of water heater, the radiation heat loss of vacuum tube is the largest, accounting for 57.8% of the total heat loss of water heater. The convective heat loss of hot water storage tank accounts for 32.1%, that of vacuum tube accounts for 3.7%, and that of other heat loss accounts for 6.4%. With the development of heat dissipation, temperature stratification in water heater becomes more and more obvious, fluid flow becomes slower and slower, and the static stagnation area in vacuum tube expands gradually from bottom to top.
Keywords all-glass vacuum tube solar water heater, nocturnal heat loss, internal flow characteristics