*4.3. Type of Nanoparticles*

The authors Shogl et al. [6] performed the evaluation of the boiling performance of zinc oxide, alumina, and carbon nanotube nanofluids under heat fluxes up to 300,000 W/m<sup>2</sup> . The results showed that, using nanoparticles may deteriorate or improve the HTC. To better understand the mechanism of the nanofluid pool boiling, it should be clarified that the decrement or enhancement in the HTC is an intrinsic characteristic of the nanofluids, or is the direct consequence of the heating surface modification, or a combination of both. The deterioration or enhancement depends on the type, size, and surface roughness of the nanoparticles. Inthis experimental work, the zinc oxide and alumina nanofluids formed smoother surfaces and the carbon nanotube CNT formed a rougher surface than the bare one. The overall effect of the zinc oxide/water and alumina/water nanofluids was the worsening of boiling heat transfer, whereas the effect of carbon nanotubes/water nanofluids was the improvement of boiling heat transfer. The type of the nanomaterials can also influence the thermal performance of the boiling systems, given that the different nanoparticle materials result in different thickness and surface relief of the deposits on the heating surface. It was also shown that with decreasing the available heat transfer area of the heating surface along with the boiling-induced nanoparticle deposition, the CHF using nanofluids increased significantly.
