Heat Pipe Performance: Latent Heat Transfer Demo

Heat Pipe Performance: Latent Heat Transfer Demo

Demonstrating the effectiveness of latent heat transfer via evaporative cooling in an evacuated heat pipe.

Heat pipes are used in the solar industry to transfer thermal energy from one point to another by the evaporation and condensation of a working fluid or coolant. They're most commonly used in solar thermal collectors in conjunction with evacuated tube glazing to achieve a much higher thermal absorption and transfer efficiency than conventional flat panel collectors.

When one end of the heat pipe is heated, the working fluid inside the pipe at that end evaporates and increases the vapour pressure inside the cavity of the heat pipe. The latent heat of evaporation absorbed by the vaporisation of the working fluid reduces the temperature at the hot end of the pipe.
The vapour pressure over the hot liquid working fluid at the hot end of the pipe is higher than the equilibrium vapour pressure over the condensing working fluid at the cooler end of the pipe, and this pressure difference drives a rapid mass transfer that's as fast as the speed of sound to the condensing end where the excess vapour condenses, releases its latent heat, and warms the cool end of the pipe. The condensed working fluid then flows back to the hot end of the pipe. In the case of vertically oriented heat pipes the fluid may be moved by the force of gravity. In the case of heat pipes containing wicks, the fluid is returned by capillary action.
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