Study On The Critical Heat Flux Of Nanofluids In Rectangle Microchannels

The boiling heat transfer is constrained by a crucially important factor—the critical heat flux (CHF) condition—which sets the upper limit on the boiling heat transfer. With the rapid development of the nano-technology, some scholars attempted to enforce the heat transfer process with nanofluids, which brings a new method to the heat transfer enhancement. But the study is just in its outset, and far from understood. The investigation on the CHF condition of nanofluids in microchannels is outset in blank.For this, extensive experimentation was performed in microchannels to obtain the flow boiling critical heat flux with two volume percents of Al 2 O3 nanofluids. These data have been obtained in microchannels ranging from diameters as low as 0.6mm to about 2mm over a wide range of mass fluxes and inlet subcoolings . The effect of different operating parameters—mass flux, inlet subcoolings, exit quality and diameter—were assessed in detail and compared with other microchannels data from literature. There was a characteristic sharp rise in wall temperature at the point of CHF. CHF generally refers to the outcome of events that cause a sudden, appreciable decrease in the heat transfer coefficient for a surface on which boiling is occurring. The results show that CHF increases monotonically with increasing G, inlet temperature has virtually no effect on CHF, decreases with an increase in exit quality and increase with an decreases diameters.A new model to predict saturated critical heat flux (CHF) conditions in microchannels was introduced. The simplicity, consistent performance, and broad applicability of this model demonstrate it as a viable tool for predicting the CHF in minichannels and microchannels of various shapes under a broad range of working conditions. The experimental data in literature and this study obtained from microchannels were used to test the model. The mean absolute error (MAE) for the comparisons is within 20%.