But because motion of water has a turbulent character under experimental conditions [3], departure of bubbles is determined primarily by parameters of turbulent motion, rather than simply by the rate of the smooth floating up of bubbles.
Therefore, for any given amount of generated vapor, the hydrophobic heating surface will have greater surface tension along the triple line (slowing the departure of bubbles from the surface) since it has a larger contact area with the bubble base than the hydrophilic surface.
The experimental results indicate that the departure of bubble from photoelectrode is retarded by light irradiation, but the traditional bubble departure criterions fail to predict the bubble departure diameters especially in high light intensity.
The migration of CNTs from liquid phase to vapor phase in the refrigerant-based nanofluid pool boiling can be divided to the following four physical processes: (1) the departure of bubble from the heating surface, (2) the movement of bubble and CNTs in the liquid phase, (3) the capture of CNTs by bubble, and (4) the escape of CNTs from the liquid-vapor interface.
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In this model, CHF occurs due to macrolayer dryout if the heat flux is sufficient to evaporate the macrolayer before the departure of the mushroom bubble.
The possible reasons are as follows: (1) The increase of heat flux causes the increase of the velocity of departure bubble [21], thus the velocity of rising bubble increases.
For this experiment, the distribution of the bubble departure diameter, departure frequency, and ratio of bubble growth time to the cycle time are shown in Figure 15.
Shown are the distribution of (a) bubble departure diameter, (b) departure frequency, (c) ratio of bubble growth time to cycle time, and (d) the relationship between frequency and diameter for a given nucleation site.
Agreement may be improved with advances in the treatment of large bubbles and bubble break-up and coalescence, as well as in improved modelling of the boiling region close to the wall, and more specifically the bubble departure diameter, the wall treatment and the contribution of bubbles to turbulence.
Moreover, the increase of gas flow rate from 0.8 to 1.45 mL/min contributed to the increase of inrush number of the trailing bubble and the decrease of departure time of the leading bubble, but equivalent departure diameter and departure volume of the leading bubble were not much different under various gas flow rates.
