Abstract
A concentric annular heat pipe heat sink (AHPHS) was proposed and fabricated to investigate its thermal behavior. The present AHPHS consists of two concentric pipes of different diameters, which create vacuumed annular vapor space. The main advantage of the AHPHS as a heat sink is that it can largely increase the heat transfer area for cooling compared to conventional heat pipes. In the current AHPHS, condensation takes place along the whole annular space from the certain heating area as the evaporator section. Therefore, the whole inner space of the AHPHS except the heating area can be considered the condenser. In the present study, AHPHSs of different diameters were fabricated and studied experimentally. Basic studies were carried out with a 50 mm-long stainless steel AHPHS with diameter ratios of 1.1 and 1.3 and the same inner tube diameter of 76 mm. Several experimental parameters such as volume fractions of 10–70%, different air flow velocity, flow configurations, and 10–50 W heat inputs were investigated to find their effects on the thermal performance of an AHPHS. Experimental results show that a 10% filling ratio was found to be the optimum charged amount in terms of temperature profile with a low heater surface temperature and water as the working fluid. For the methanol, a 40% filling ratio shows better temperature behavior. Internal working behavior shows not only circular motion but also 3-D flow characteristics moving in axial and circular directions simultaneously.
Highlights
A heat pipe with a very high thermal conductance is an efficient passive heat transfer device
To investigate thermal behavior related to heat transfer performance of the annular heat pipe heat sink (AHPHS), various parameters such as filling ratios, air flow velocity, diameter ratios, and supplied heat flux were tested using the AHPHS, which was specially designed and fabricated as described above
The working fluid charged volume compared to the total internal volume as the filling ratio (D+ ) is an important experimental parameter in the optimization of a heat pipe
Summary
A heat pipe with a very high thermal conductance is an efficient passive heat transfer device. One side end of the tube, the evaporator, is heated, and the liquid vaporizes, which induces the movement of the vapor to the other end of the tube, the condenser. A large amount of heat from this phase change process can be transferred for certain purposes such as cooling, heating, or energy usage with a small temperature difference between the evaporator and condenser. Various heat pipes have been adopted and tested as efficient heat transferring devices in many demanding applications such as energy transfer, electronics cooling, and space application [1,2,3,4]. The current annular heat pipe heat sink (AHPHS) concept for electronics cooling has an unconventional structure, where the cross-section of the vapor space becomes annular and has a three-dimensional flow to accommodate uneven liquid motion, unlike previous annular heat pipes for dryers or furnaces [5,6,7]
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