Thermal and Flow Characteristics in a Concentric Annular Heat Pipe Heat Sink

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.

Thermal and Flow Simulation of Concentric Annular Heat Pipe with Symmetric or Asymmetric Condenser

“…We used the FLUENT V17.2 software to carry out numerical analyses under a variety of conditions. The analysis focused on the following conditions and assumptions, in order to compare the simulated and experimentally derived temperatures [24,25]…”

“…The basic model of the CAHP to be simulated is shown in Figure 2. The current numerical models are divided into 2D geometrical simulation assuming symmetry and a 3D model simulated using the same models used in previous experimental work [24]. The 2D numerical model has a faster analysis time than the 3D model, making it easy to determine the tendency of various conditions.…”

“…The presented 2D simulation model had an outer diameter of 98 mm, inner diameter of 78 mm in the shape of D + = 1.3, and the wall thickness of 1 mm. The container material was set as steel, which is the same as the experimental system [24]. The thermal resistance of the wall condition is given as = * (20) where R is the thermal resistance of the solid material, t is the wall thickness, k is the thermal conductivity of the solid material, and A is the area.…”

“…As shown in Figure 4, the conventional simple heat pipe (Figure 4a) and the CAHP shape (Figure 4b) were set The presented 2D simulation model had an outer diameter of 98 mm, inner diameter of 78 mm in the shape of D + = 1.3, and the wall thickness of 1 mm. The container material was set as steel, which is the same as the experimental system [24]. The thermal resistance of the wall condition is given as…”

“…Song et al [24] experimentally studied concentric annular heat pipe heat sink (CAH-PHS). They proposed and manufactured the CAHPHS in order to study its thermal performance.…”