Magnetic nanofluids as heat transfer media in heat pipes

Anggito P Tetuko, Lukman F Nurdiyansah, Muhammad Addin, Eko A Setiadi, Masno Ginting and Perdamean Sebayang

Abstract

The analytical models of the magnetic nanofluid (ferrofluid) have been developed to investigate the effect of the temperature on its physical and thermal properties. The purpose of the model is to analyse the properties of the ferrofluid used as the heat transfer media (working liquid) in the heat pipe. The models developed also includes the heat dissipation capability (capillary limitation) of the heat pipe filled with the ferrofluid as a function of temperature, effective length, diameter and the direction angle of the heat pipe. These modelling investigations were also accompanied by material characterisations (XRD and TEM analyses) of the magnetite (Fe₃O₄) sample that has been synthesised. The stability of the magnetite particles dispersed in the water to be used as the ferrofluid was also analysed using a zeta potential analyser. Heat pipe performance tests using ferrofluid as the working liquid were also conducted to validate the analytical model. The models revealed that the increase of the temperature reduces the density and the viscosity of the ferrofluid that reach the values of 0.97 g cm⁻³ and 0.32 g m⁻¹.s at 90 °C. On the other hand, the increase of the temperature has no significant effect on the specific heat (4.21 kJ kg⁻¹. °C at 90 °C). However, the temperature increases the thermal conductivity to 0.66 W m⁻¹. °C at 90 °C. The models also confirmed that the increase of the temperature, the diameter, and the direction angle enhance the capability of the heat pipe for removing the heat at a maximum capacity of 15 W at 90 °C (effective length of 150 mm and diameter of 12.5 mm). However, the increase of the effective length reduces the heat pipe performance where the value at an effective length of 500 mm and diameter of 12.5 mm at the temperature of 90 °C is 12 W. The XRD and TEM analyses confirmed that a single phase of magnetite (Fe₃O₄) is obtained with an average particle size of 80–100 nm. The ferrofluid that used magnetite as additives shows good dispersion stability (31 mV). The heat pipe performance investigation using ferrofluid as the working liquid has a good agreement with the analytical model.