Studies on Thermal Characteristics of Nanofluids in Heat Pipe

Abstract

High heat fluxes due to densification of electronic components in integrated circuits pose a challenge in their heat dissipation rates. Use of forced convective or micro conductive fin attached to the integrated circuits limit their performance at high heat flux loads. Phase change heat transfer devices play an excellent role in dissipating the heat from the highly concentrated heat sources, thus providing superior cooling capabilities. Over the past decade, comprehensive research work has been carried out on the operating characteristics of heat pipe using conventional working fluids. The heat pipes using nano-suspensions of metallic and oxide particles in the base fluid termed as nanofluids have attracted the attention of researchers worldwide because of enhanced thermophysical properties of the nanofluids. In the present work, the potential of using Al2O3 / Deionised (DI) water based nanofluids as working fluids in heat pipe has been investigated at various orientations. The nanofluids prepared by two step method without the use of any surfactant are stabilized by ultrasonication. Structural modifications in the manufacturing of heat pipe have been made to delineate any vapor velocity fluctuation effects. A heating chamber has been constructed around the evaporator section of the heat pipe for uniform heat flux and the condenser section has been cooled by natural convection. The thermal conductivity enhancement of Al2O3 / DI water nanofluids measured by transient hot wire (THW) method demonstrates a nonlinear relationship with increase in volume fraction of dispersed nanoparticles and attains a maximum enhancement of 15 % for 1 vol. % of Al2O3 loading in distilled water at 70°C. The thermal performance of heat pipe has been investigated at increasing concentrations of Al2O3 / DI water nanofluids (0.005 %, 0.05 %, 0.5 % and 1 %) and Watt loads of heat inputs (12 W, 32 W and 72 W) to cover the operating temperature range of the electronic equipments ( lt 70oC).