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Thermomax - World Leading Solar Tubes

A heat pipe acts like a high conductance thermal conductor. Due to its thermal-physical properties, its heat transfer rate is a thousand's times greater than that of the best solid heat conductor of the same dimensions. The basic heat pipe is a closed container consisting of a capillary wick structure and a small amount of vaporizable fluid. A heat pipe employs an evaporating-condensing cycle, which accepts heat from an external source, uses this heat to evaporate the liquid and then releases heat by reverse transformation (condensation) at a heat sink region. This process is repeated continuously by a return feed mechanism of the condensed fluid back to the heat zone. In the solar collector, the condensation zone is at a higher level than the evaporation zone. The transport medium condensed (in the condensation zone) returns to the evaporation zone under the influence of the gravity.

The maximum operating temperature of a heat pipe is the critical temperature of the used heat transfer medium. Since no evaporation/condensation above the critical temperature is possible, the thermodynamic cycle interrupts when the temperature of the evaporator exceeds the critical temperature. The maximum working temperature in a heat-pipe solar collector is controlled by means of a memory metal spring which is positioned inside the heat-pipe's condenser.

The memory metal spring is programmed to change its shape at a pre-set temperature. This allows for the condenser fluid to be retained inside the condenser. When the programmed temperature has been achieved, the memory metal spring expands and pushes a plug against the neck of the heat pipe blocking the return of the condensed fluid and stopping heat transfer.   

 At temperatures below the maximum programmed limit, the spring contracts allowing the condensed fluid to return to the lower section of the heat pipe. It is than evaporated due to the heat from the absorber plate, transferring thermal energy to the condenser. 

The Temperature Limiting feature protects a solar system during short term system component failure serving as its last safety level.

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