Novel Charging Station and Computational Modeling for High Thermal Conductivity Heat Pipe Thermal Ground Planes

Thermal ground planes (TGPs) are planar, thin (thickness of 3 mm or less) heat pipes which use two-phase heat transfer. TGPs are innovative high-performance, integrated systems able to operate at a high power density with a reduced weight and temperature gradient. Moreover, being able to dissipate large amounts of heat, they have very high effective axial thermal conductivities and can operate in high adverse gravitational fields due to nano-porous wicks. A key factor in the design of the TGP is evacuation prior to filling and introduction of the proper amount of working fluid into the device. The major challenge of this work is to fill heat pipes with a total liquid volume of less than 1 ml, without being able to see into the device. The new filling station is an improvement over the current state of the art as it allows for accurate filling of micro liter sized volumes. Charging station validation demonstrated the capability of charging TGPs with accuracy of ±1.64 µA thermal resistance model is developed to predict the thermal performance of the TGP, including the effects of the presence of non-condensable gases (NCGs). This work shows that the axial effective thermal conductivity of the TGP decreases when the substrate and/or wick are thicker and/or with the presence of NCGs. Moreover, it was demonstrated that this model may be utilized to optimize the performance of the TGP by estimating the limits of wick thickness and vapor space thickness for a recognized internal volume of the TGP.A three-dimensional ANSYS model is used to predict the temperature field in the TGP, the effective axial thermal conductivity, and the evaporation and the condensation rates. A key feature of this model is that it relies on empirical interfacial heat transfer coefficient data to very accurately model the interfacial energy balance at the vapor-liquid saturated wick interface. Wick samples for a TGP are tested in an experimental setup to measure the interfacial heat transfer coefficient. Then the experimental heat transfer coefficient data are used for the interfacial energy balance. To verify the results of the ANSYS model several of the experimental work was done for different TGP samples. The results show the comparison of temperature distributions between the ANSYS model and the experimental results for the TGP with LTGP= 9, 15 cm, different input power levels (Qin= 10W, 15W and 20W) and condenser temperature Tcondenser = 60, 75, and 90 °C. The ANSYS model showed excellent agreement with the experimental results.CFD model is introduced to determine the capillary limit in TGPs. In addition, the effect of wall shear stress and the interfacial shear stress in the liquid pressure of the TGP is studied. This model shows that the vapor pressure to the liquid pressure is not significant and the FLUENT results verify this conclusion. Finally, this dissertation offers a design for heat pipe charts that avoids the effects of vapor pressure, wall shear stress and the wick-vapor interface to the liquid pressure for most well-known working fluids.

Name thesis:degree_name

PhD

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Engineering and Applied Science: Mechanical Engineering

Grantor dc:publisher

University of Cincinnati

Year dc:date

2012

Author dc:creator

• Ababneh, Mohammed

Contributors dc:contributor

• Gerner, Frank

• Mechanical Engineering
• heat pipes
• Thermal ground planes
• Charging

Statement dc:rights

• unrestricted
• This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws.

Language dc:language

English

Repository record dc:identifier

http://rave.ohiolink.edu/etdc/view?acc_num=ucin1353950640

OAI identifier oai:identifier

oai:etd.ohiolink.edu:ucin1353950640