Thermal performance of inclined screen mesh heat pipes using silver nanofluids☆
Introduction
Heat pipe as a two phase heat transfer device, with high effective thermal conductivity in comparison with common thermal conductors such as metal rods and fins, plays a vital role in many industrial applications including cooling of electronics, power generation, aerospace and chemical processes. Large quantities of heat with minimum temperature gradient are transported by vaporization and condensation of a working fluid and also capillary force action for pumping the liquid back to the evaporation section. However, traditional heat transfer fluids like water and alcohols have been extensively used in heat pipes, their poor thermal properties become a primary obstacle limiting the thermal performance of heat pipe-heat exchangers. Nanofluids, as a new class of heat transfer fluids, are proposed and developed over the past decade for heat transfer applications. It has been revealed that nanofluids have greater heat transfer characteristics than traditional heat transfer fluids [1], [2], [3], [4], [5], [6], [7], [8]. A novel idea which has been suggested is to utilize nanofluid as a working fluid in heat pipes to enhance heat pipes thermal efficiency. During recent years, researchers have concentrated mainly on investigation of nanofluids on heat pipe performance at different working conditions [9], [10], [11], [12], [13], [14], [15], [16]. Different types of nanofluids such as water based copper, aluminum oxide and silver nanofluids have been used in the common types of heat pipes primarily include cylindrical heat pipes [17], [18], oscillating heat pipes [19], [20] thermosyphons [21] and pulsating heat pipes [22] and it has been shown that nanofluids can effectively improve the heat transfer performance of heat pipes. Kang et al. [23] studied the effect of silver nanofluids on thermal performance of a sintered heat pipe experimentally. They investigated the effects of nanoparticles size and concentration on thermal performance of the heat pipe. They found that the wall temperature difference of the heat pipe using nanofluid decreased 0.56–0.65 °C at an input power of 30–50 W. Wang et al. [24] performed experiments to investigate the effect of CuO nanofluids on a cylindrical miniature grooved heat pipe. They found that heat transfer coefficient and maximum heat flux were increased significantly for the heat pipe with nanofluid. Asirvatham et al. [25] carried out an experiment to study the heat transfer performance of a screen mesh heat pipe using silver nanofluids with average nanoparticle diameter of 58 nm. They found that using nanofluid enhanced the heat pipe thermal efficiency. The thermal resistance decreased by 76% for silver nanofluid with volume concentration of 0.009%. Do et al. [26] studied the thermal performance of screen mesh heat pipe using water based Al2O3 nanofluids. Based on their experiments, the thermal resistance at the evaporator-adiabatic section decreased by 40% at volume concentration of 3% compared with water. Furthermore, the maximum heat flux with nanofluid was found to be higher than that with water. Effect of inclination angle on the thermal performance of heat pipe with nanofluid has been investigated in some experimental studies as summarized in Table 1.
It can be seen that the inclination angle affects the thermal performance of the heat pipes remarkably. In this study, effect of inclination angle on thermal performance of the heat pipes with silver/water nanofluids at three different mass concentrations of 0.25%, 0.5% and 0.75% is studied experimentally and the results are compared with those of the heat pipe with water. The aim of this study is to evaluate the feasibility of using water based silver nanofluids in inclined heat pipes and assesses its thermal performance.
Section snippets
Working fluid
Commercial stable Ag nanofluid (NF) with 0.75 wt.% was purchased and nanofluids with 0.5 wt.%, and 0.25 wt.% were prepared by diluting the original suspension. All nanofluids were stable for six months without any visual precipitation. Transmission electron microscopy (TEM) analysis of the Ag nanoparticles (NPs) size and morphology was performed using JEOL 2100 at 200 kV acceleration. Average hydrodynamic particle size distribution of Ag nanoparticles was assessed by Beckmann–Coulter Delsa Nano C
Data reduction
The water based Ag nanofluid with mass concentrations of 0.25%, 0.5% and 0.75% was used to investigate the evaporator heat transfer coefficient and thermal resistance of the heat pipe. The temperature drop between evaporator and condenser and consequently the thermal resistance of a heat pipe is of particular interest to evaluate its thermal performance. The overall thermal resistance of the heat pipe is calculated from:where Q, Te and Tc are heat input, evaporator and condenser wall
Result and discussion
To investigate the thermal performance of inclined heat pipes using nanofluids, four different screen mesh heat pipes containing distilled water as a reference and three water based silver nanofluids at mass concentrations of 0.25%, 0.5% and 0.75% were tested. The heat input was increased consecutively and the heat pipe wall surface temperatures were measured and recorded at steady conditions, approximately after 20 min. Fig. 4 shows the thermal resistance of the heat pipes using water and Ag
Conclusion
An experimental study was performed to find the effect of nanofluids on the performance of inclined screen mesh heat pipe. For this purpose, water based Ag nanofluids at three different mass concentrations of 0.25%, 0.5% and 0.75% were chosen as working fluids for heat pipes and the results were compared with heat pipe using water as the reference. Experimental results revealed that Ag nanofluids have an influence on heat pipe thermal performance and the thermal resistance of the heat pipes
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2022, Progress in Nuclear EnergyCitation Excerpt :Many researchers are working on different aspects of heat pipes in order to enhance their thermal performance. Different techniques have been developed to enhance the thermal performance of heat pipes which includes; use of nanofluids (Nemati et al., 2020; Reza et al., 2019; Run-ping et al., 2020; Li et al., 2016; Huminic and Huminic, 2013; Mehrali et al., 2016), use of self-rewetting fluids (Ghanbarpour et al., 2015; Vijayakumar et al., 2017; Do et al., 2010; Poplaski et al., 2017; Hu et al., 2014), by developing wettability gradient (Naresh et al., 2018), and by using optimum inclination angle (Savino et al., 2010; Singh et al., 2018) etc. But still there exist a gap which dictates to do further research in this interesting area to develop more compact and effective heat pipes.
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Communicated by W.J. Minkowycz.