Design and test of a heat pipe for geothermal applications
P.J. Hogendoorn (TU Delft - Mechanical Engineering)
R. Delfos – Mentor (TU Delft - Support Process and Energy)
Bendiks J. Jan Boersma – Graduation committee member (TU Delft - Process and Energy)
M. J. Tummers – Coach (TU Delft - Fluid Mechanics)
A. Twerda – Coach (TU Delft - Energy Technology)
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Abstract
Heat pipes are typically used in the semiconductor industry. This means that the scale of these heat pipes is typically in the order of centimeters. Zijm suggests that heat pipes could be used for geothermal applications, but literature is lacking. To further investigate the geothermal application of heat pipes, a large scale heat pipe is built. This thesis gives an insight in the typical design challenges that one faces when constructing a heat pipe of this scale. The heat pipe that is constructed can support a heat flow of 10 kW. The heat pipe is constructed from mainly 54 millimeter copper and glass pipes. The evaporator section is 1.5 meters long and facilitates controlled electric heating. Then follows a 4 meter long adiabatic section. The condenser section is 2.5 meters long. The total length of the heat pipe is 9 meters. The individual sections are held together by EPDM connectors. The dimensions of the heat pipe are compared to the operational limits posed by the Engineering Sciences Data Unit. Then the thermal resistances of the heat pipe sections are calculated and afterwards validated. The interfacial thermal resistance between the electric heaters and evaporator wall was reduced by applying thermal conduction paste to the band heaters. It was found that at coolant flows of 1000 l/h and higher, the vapour temperature in the heat pipe drops significantly. The drop in temperature facilitates a higher heat flow through the heat pipe. Also, the resistance across the evaporator and the condenser section gets smaller for higher coolant flows. The results found are supported by theory and formulae from the Engineering Sciences Data Unit.