The selective absorber coating on the inner cover of vacuum tubes absorb solar energy, then convert solar energy into thermal energy and transfer thermal energy to heat pipe by aluminum fin.
As the gas moves to the top of the pipe, it cools and releases the heat of vaporization as it condenses back to a liquid. The liquid runs down the tube, completing the cycle. The outer tube contains a hard vacuum, so it eliminates conduction or convection loss from the gas. Figure 2 Solar Heat Pipe Construction
Which type of heat pipe should be used for solar collectors?
On the other hand, to transfer the converted thermal energy timely and avoid overheating on the surface of solar collectors, a heat pipe which depends on liquid–vapor phase change heat transfer is an efficient choice, , , .
Heat pipe solar collectors (HPSC) Heat pipes in solar collectors can be operated in any orientation. They are mechanically bonded or integral part of an absorber, receives and transfer absorbed heat to working fluid i.e. air, water or heat transfer fluid which is circulated through the manifold connected to solar collector .
The radiation crosses the vacuum space between the outer and inner pipe without energy loss. Finally, solar radiation heats the working fluid inside the inner pipe and vaporizes it. The heated vapor goes to the condenser, transferring its heat energy to the solar working fluid through the manifold.
Heat pipes in solar collector absorbs and covert solar energy to heat and transmit it to heat transfer fluid in indirect system or directly to water flowing through well-insulated manifold in direct system .
Does solar-driven heat pipe have a low thermal resistance?
The experimental results showed that the solar-driven heat pipe with a filling ratio 20% had a lowest thermal resistance of 0.25 K/W when it was placed vertically at a solar power density of 17.5 W/cm 2. 4. We demonstrated that the fabricated solar-driven heat pipe could directly harvest solar irradiation for efficient hot water production.