... circulation pump makes heat-conducting liquid circulate automatically. Then the heat-conducting liquid transfers heat to water by heat exchanger in the ... , inner: Rock wool with red copper pipe. 8.The standards of vacuum tubes with heat pipe: 14, 16, 18, 20, 24 ... time of heat insulation: 72h11.High heat effectiveness: Higher than all glass evacuated solar collector tube by 15 Heat pipe split pressure ...