Kim Nanoscale Research Letters 2011, 6:415 http://www.nanoscalereslett.com/content/6/1/415 Page 7 of 18 lower pressures. This discovery is consistent with the system pressure vs. CHF trend of the experimental results obtained by You and his coworkers [5,22,28,29] with an identical heater geometry and experimental setup. Figure 6 shows the pressure dependency of CHF enhancement in nanofluids. It is of interest that the CHF enhancement apparently decreases with increasing the pressure. This pressure effect cannot be simply explained by traditional boiling CHF theory, but how- ever, some insight can be given based on a comparison of behaviors of dry patches, whose irreversible growth can cause CHF [26,30], under different pressure condi- tions. Van Ouwerkerk [31] found that when the CHF is approached, the mechanism of formation of dry areas is different for atmosphere and low-pressure conditions: the large dry patch is created by coalescence of small vapor bubbles that forms at atmospheric pressure but underneath are individual bubbles growing to immense size at low pressure. This different mechanism of forma- tion of dry patches under atmospheric and low-pressure conditions suggests that the pressure in nanofluid boil- ing can have strong impact on the CHF enhancement. In addition, if the use of nanofluids alters local proper- ties of individual bubbles growing on the heating sur- face, such as wetting ability, its impact on the CHF value can be more significant in low-pressure condition where a dry patch underneath a single bubble plays a key role in triggering CHF. Influence of additive Ionic additives and surfactants can significantly distort the nucleate boiling heat transfer and CHF phenomena in nanofluids by influencing the stability of the particles and their mutual interactions near the heated surface. Kumar and his coworkers [32-35] primarily investigated the effects of ionic additives. Their experimental results demonstrated that when the surface tension of a Figure 6 Effect of pressure on the maximum CHF enhancement in nanofluids. The used heater geometries are 40 × 40 mm2 [20,27] and 10 × 10 mm [5,22,28,29].