Spray cooling by solid jet nozzles using alumina/water nanofluids

An experimental and theoretical investigation of spray cooling with a solid jet nozzle was performed to assess the associated heat transfer coefficients (HTC) using water/alumina nanofluids. Based on a thermal probe embedded in a heated testing plate, the cooling curves, which represent the transient temperature variations of the plate, have been measured at various spraying conditions. An inverse heat transfer technique was then applied to convert these measured cooling curves into the HTC. The results indicated that, after its first peak, the HTC became very stable with the associated standard deviation less than 3% of its mean and the single mean value could reliably represent the performance of spraying cooling for all cases considered. The results also showed that the HTC increased with the flow rate intensities, following a power-law type of correlation. By comparing the nanofluid results with that of pure water, it was found that an approximately 45% decrease of HTC of spray cooling with the volume fraction of the nanoparticle suspension increasing from 0 to 0.1645. The reduction of HTC caused by the change of the spraying impact duration due to the presence of nanoparticles was specifically analyzed and an analytical formula to correlate this effect was developed to further explain the combined effects of nanoparticles on HTC.

► Heat transfer behavior of spray cooling using water/alumina nanofluids was studied.
► The nanoparticles were found to have adversary effects on the heat transfer coefficient (HTC).
► The HTC reduction by changing the impact duration of nanofluid spraying was analyzed.
► Correlations of HTC with flow flux, particle fraction, and Prandtl No. were developed.