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The term thermal diode is sometimes used for a (possibly non-electrical) device which causes heat to flow preferentially in one direction. Or, the term may be used to describe an electrical (semiconductor) diode in reference to a thermal effect or function. Or the term may be used to describe both situations, where an electrical diode is used as a heat-pump or thermoelectric cooler. ==One-way heat-flow== A thermal diode can be: * a heat engine which converts a heat difference directly into electric power. * a heat engine working backwards as a refrigerator, such as a Stirling engine. * a type of heat pipe which will only allow heat to flow from the evaporator to the condenser. When the condenser is hotter than the evaporator, the coolant in the heat pipe condenses in a reservoir at the evaporator end. This reservoir does not have a capillary connection with the condenser, preventing the liquid from returning to the condenser. During normal heat pipe operation, when the evaporator and reservoir become hotter than the condenser, the reservoir is emptied by evaporation, and heat is transferred to the condenser. Due to the second law of thermodynamics a passive system cannot move heat from a cold source to a hot destination. But the law allows to avoid or minimize the flow in this direction. If the source is hotter than the destination heat flows with a low thermal resistance towards the destination. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「thermal diode」の詳細全文を読む スポンサード リンク
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