Study of thermal performance and properties of 1-pyrene carboxylic-acid functionalized graphene nanofluids in a heat pipe / Alireza Esmaeilzadeh

Alireza , Esmaeilzadeh (2022) Study of thermal performance and properties of 1-pyrene carboxylic-acid functionalized graphene nanofluids in a heat pipe / Alireza Esmaeilzadeh. PhD thesis, Universiti Malaya.

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Abstract

A new trend in the heat pipes and successful thermosyphons application is related to nanotechnologies. Nano liquids, nanocoating, and nanocomposites invention open a new niche in the heat pipe and thermosyphon design and use. This research is carried out experimentally and analytically to investigate the thermal performance of heat pipe when functionalized graphene nanoplatelets (GNP) with 1-pyrene carboxylic acid (PCA) is utilized as a working fluid. In this study's first stage, three influential parameters on the viscosity and thermal conductivity, including concentration, temperature, and specific surface area of nanofluid, were investigated. In the second stage, an experimental investigation was accomplished to study a sintered wick heat pipe's thermal performance using stable aqueous dispersions of noncovalently functionalized graphene nanofluids. The experiments are conducted to characterize a low-cost nanofluid and evaluate its effect on the sintered-wick heat pipe efficiency. The various parameters being investigated include different fluids, tilt angles of the heat pipe, and input powers. The result shows the enhancement of thermal conductivity of PCA-functionalized graphene nanofluids in the range of 21% and 40%. It is found that the tilt angle of heat pipe has a substantial impact on the thermal properties, which could enhance the thermal performance by 79%. The experimental results indicated that the heat pipe thermal resistance is reduced using PCA-functionalized graphene nanofluids. The reduction in thermal resistance was the best at the high heat flux. The last stage focused on the CFD modeling of nanofluid heat transfer in the heat pipe. Numerical modeling of a heat pipe included with a phase change heat transfer was developed to assess the effects of three parameters of nanofluid, heat pipe inclination angles, and input heating power. Distilled water (DW) and 1-pyrene carboxylic-acid (PCA)-functionalized graphene nanofluid (with concentrations of 0.06 wt%) were used as working fluids in the heat pipe. A computational fluid dynamic (CFD) model was developed to evaluate the heat transfer and two-phase flow through the heat pipe's steady-state process. It was found that inclination significantly affects the heat transfer of the heat pipe. The maximum increment of thermal performance in the heat pipe peaked at 49.4% by using the amount of 0.06 wt% of PCA-functionalized graphene as working fluids. The result associated with this comparison indicates that the highest deviation is less than 6%, consequently confirming that the CFD model was successful in reproducing the heat and mass transfer processes in the DW and nanofluids charged heat pipe. The results of the CFD simulation have good agreement between predicted temperature profiles and experimental data.

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