When the vacuum tube water heater absorbs heat, the solar radiation passes through the outer tube of the vacuum tube and is absorbed by the heat coating and transmitted along the inner pipe wall to the water in the tube. When the water in the tube absorbs heat, the temperature rises and the specific gravity decreases, forming an upward power to form a thermal siphon system.
As hot water continues to move up and stored in the upper part of the tank, while the lower temperature of the water along the other side of the tube continues to replenish so cycle, and eventually the whole box of water rises to a certain temperature. Flat type water heater, generally split water heater, the medium is in the heat collector due to the heat siphon natural circulation, the solar radiation in the heat collector in time to transfer to the water tank, the water tank through the heat exchange (jacket or coil) to transfer heat to cold water. The medium can also be passed through the pump cycle to achieve heat transfer.