Abstract
The heat transfer from the condenser of a heat pipe installed vertically in the heat storage tank which stores a natural cold heat in winter is studied experimentally. It is proved that the heat pipe doesn't transport a heat to the water of the tank and is able to transport only from the water of the tank to the condenser. The heat transportation from the condenser to the ambient mainly depends on the radiation heat transfer, so the estimation of the temperature of the sky is necessary to design the optimum heat storage tanks
