2.3.9. Vaporization Core Sites Density

2.3.9. Vaporization Core Sites Density The deterioration of the boiling HTC is caused mainly by the deposition of nanoparticles on the heating surface that enhances the heat transfer resistance. However, the wettability of the surface and the CHF were enhanced. For instance, welding metal foams onto a plain heating surface is a common technique to enhance the heat transfer area. Moreover, this procedure impacts the growth and detachment of vapor bubbles in the The deterioration of the boiling HTC is caused mainly by the deposition of nanoparticles on the heating surface that enhances the heat transfer resistance. However, the wettability of the surface and the CHF were enhanced. For instance, welding metal foams onto a plain heating surface is a common technique to enhance the heat transfer area. Moreover, this procedure impacts the growth and detachment of vapor bubbles in the course of boiling. Moreover, to enhance the heat transfer capability of the metal foam structure, the researchers Xu et al. [69] studied the influences concerning the size and concentration of AlO and SiC nanoparticles deposited onto a copper foam of 7 mm thickness. The testing pore density was 5 PPI, 60 PPI, 100 PPI, and the corresponding porosity was of 0.9, 0.95, and 0.98. Some preliminary works reported that the boiling induced nanoparticle deposition onto the foamed copper might increase its capillary wicking and number of active vaporization core sites. Moreover, the thermal performance of nanofluids on the gradient hole surface was investigated by Xu and Zhao [70], since adding nanoparticles clogged the voids of the higher 100 PPI density copper foam, and, consequently, the vapor bubbles escape resistance became enhanced and the heat transfer capability degraded. One of the main effects of the heating surface modification is to increase the available heat transfer surface and, hence, enhance the number of available vaporization core sites. Moreover, the density of the nucleated bubbles will become higher in addition to the increasing density of gasification core sites. Therefore, during the pool-boiling process, the nanoparticles deposited onto a bigger heat transfer area, allowing high concentrations of the nanofluid to

be employed, rapidly increased the thermal conductivity of the base fluid, and thus the nanoparticles did not deteriorate because of the porous deposition layer. Moreover, the vapor bubbles nucleated on a rough heating surface alter the capillary motion of the vapor bubbles, which are only impacted by the upward action of the buoyancy force.
