Transient cooling characteristics of Al₂O₃-water nanofluid flow in a microchannel subject to a sudden-pulsed heat flux

Transient cooling characteristics of Al₂O₃-water nanofluid flow in a microchannel subject to sudden-pulsed heat flux are numerically examined in details. The attention is focused on the effects of microencapsulated phase change material (MEPCM) inside top wall of a microchannel on the transient cooling heat transfer behaviour of the microchannel. Two small portion of the bottom channel wall are exposed to a pulse heat flux. The Al₂O₃- water nanofluid as the working fluid with a fully developed velocity profile flows into the microchannel to cool the channel walls. Transient conjugate heat transfer is studied using a three-dimensional model in the three parts of the microchannel which are the nanofluid flow, the solid walls of the channel, and the MEPCM layer. The partial differential equations governing the energy conservation are presented and transformed into a dimensionless form. The finite volume method is employed to numerically integrate the equations for the temperature distribution in the microchannel. The numerical results are compared with the available works in the literature and found in good agreement. Besides, the predictions show that the presence of the MEPCM layer cannot effectively control the rise of the temperature of the microchannel in the presence of a pulse heat flux. For a typical pulse heat flux, the bulk temperature of the channel can be raised up to 2 °C while the presence of the MEPCM layer would only suppress the temperature rise by 0.2 °C. It is also found that the temperature of the top wall is under the significant influence of the MEPCM layer. The increase of the amplitude of the heat flux pulse results in better cooling effect of the MEPCM layer.