Phase change actuated valve for use in heat pipe applications

A heat exchanger for use in a two-phase system, the heat exchanger comprising:

• a plurality of heat pipes, each of the heat pipes having a thermally actuate control valve;
• each thermally actuate passive control valve comprising:
• a housing having a first end and a second end, a first opening extending through the first end for receiving a condenser portion of a respective heat pipe of plurality of heat pipes, a second opening extending through the second end for receiving an evaporator portion of the respective heat pipe of the plurality of heat pipes therein, a passage extending through the housing from the first opening to the second opening, the passage configured to receive working fluid from the respective heat pipe therein;
• a phase change material actuator positioned in the housing, the phase change material actuator having a sealed chamber with phase change material positioned therein;
• a passage closing member positioned in the housing proximate to or in the passage and proximate to the phase change material actuator, the passage closing member having a surface which cooperates with a wall of the passage;
• a return spring cooperates with passage closing member to move the passage closing member to an open position after a temperature of the working fluid drops below the melting point of the phase change material of the phase change material actuator, allowing the working fluid to flow through the passage and the valve, the return spring having sufficient spring force to recompress the solidified phase change material within the phase change material actuator;
• a relief spring proximate to the phase change material actuator, the relief spring cooperates with the phase change material actuator to allow additional expansion of the phase change material actuator after the passage closing member is fully closed, the relief spring having a greater spring force than a return spring;
• wherein the phase change material of first respective thermally actuate passive control valves positioned in first heat pipes of the plurality of heat pipes has a different melting point than the phase change material of second respective thermally actuate passive control valves positioned in second heat pipes of the plurality of heat pipes.