Abstract
An experimental study on a plate gravity heat pipe (PGHP) with inner cavity size of length 100 mm (X), width 2.5 mm (Y), and height 210 mm (Z) with acetone as the working fluid was carried out. The effects of heating power inputs (80–180 W) and fluid filling ratios (25%, 48%, and 55%) on the start-up temperature, start-up time, temperature difference, and relative thermal resistance on the Z-axis of the PGHP in a vacuum of 1 × 10−3 Pa were studied at unsteady state. Furthermore, the gas-liquid two-phase behavior of the interior working fluid of PGHP, and the coupling heat transfer behavior of the boiling liquid and the condensate were observed through a visualizable window under different experimental conditions. The results show that, with the increase of heating power input, the start-up temperature of the PGHP increases and the start-up time is shortened. The start-up temperature of the PGHP was around 33 °C and the start-up time was about 320 s at the heating power input of 120 W and working fluid filling ratio of 55%. The relative thermal resistance and the temperature difference on the Z-axis of the PGHP increase firstly and then decrease with the increase of heating power input at unsteady state. The complex gas-liquid two-phase behavior of the PGHP mainly includes: the formation and growth of bubbles, the merging and break up of bubbles, and the coupling heat transfer between boiling liquid and condensate, which demonstrate that the novel SVPGHP can be used to effectively study the heat transfer process of PGHP.
Highlights
Due to the advantages of small volume, high heat transfer efficiency, compact structure, low pressure drop and no auxiliary power of the heat pipe [1,2,3,4,5,6], the plate heat pipe (PHP) is widely used as a highly efficient heat transfer element in various industries
The results showed that compared with the traditional plate heat pipe, the integrated heat pipe had better temperature uniformity and heat transfer characteristics
The considered operating conditions include heating power input, vacuum degree and filling ratio, where vacuum degree refers to the internal pressure value of heat pipe without working fluid before liquid injection, and the internal pressure varies with the working fluid temperature due to heat transfer after injection
Summary
Due to the advantages of small volume, high heat transfer efficiency, compact structure, low pressure drop and no auxiliary power of the heat pipe [1,2,3,4,5,6], the plate heat pipe (PHP) is widely used as a highly efficient heat transfer element in various industries. The effects of different heat fluxes and inclination angles on heat transfer resistance of PHP were analyzed through experimental study [10] and numerical simulation [11]. The results showed that the NTS structures integrated with perforated copper foil substantially increased the heat transfer coefficient and the bubble departure frequency. De Rosis et al presented a coupled lattice Boltzmann-finite element approach for two-dimensional fluid–structure interaction [28], which had been used to study the hydroelastic analysis of hull slamming [29] These methods lay the foundation for the numerical simulation of multiphase flow in heat pipe. Considering the practicality of the SVPGHP, the working fluid in the heat pipe evaporates to produce saturated steam, which requires the design of PGHP to have a certain pressure capacity. The semi-visualizable experimental method has some reference value for the study of cavitation
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