Bubble Growth Rates and Nucleation Site Densities in Saturated Pool Boiling of Water at High Pressures

Abstract

Experiments were carried out to observe boiling behaviors of water on horizontal and vertical surfaces at pressures from 0.35 to 5 MPa. The growth curves of the primary bubbles are well described by the t 1=2 variation over the whole range of pressures. The growth rates of primary bubbles are proportional to the square root of the Jakob number, and agree with the correlation by Labuntsov with the arbitrary constant ¼ 3. The conventional correlations of bubble growth rates, which are directly proportional to the Jakob number, predict slower growth rates at higher pressures. The coalescence behaviors of the primary bubbles were also measured on the vertical surface at 3.66 MPa. The coalesced bubbles, which were formed by the coalescence of two primary bubbles, grow at rates similar to the rates of the primary bubbles. The nucleation site densities measured on the vertical surface at pressures up to 5 MPa increase in proportion to about the 1.5th power of the pressure under equivalent heat flux conditions. The dependence of the nucleation site densities on the heat flux is very similar to the results obtained near atmospheric pressure where the nucleation site density is proportional to the 1.5th power of the heat flux. The nucleation site densities measured in the range of pressures of 0.35 to 5 MPa and at heat fluxes of 0.05 to 0.35 MW/m 2 agree fairly well with the available correlations.

The hydrodynamics of microlayer formation beneath vapour bubbles

“…As noted above, there are very few experimental studies under high-pressure conditions and the data available is limited to relatively low superheats of only a few Kelvin, and consequently slow bubble growth rates. The very tiny bubbles of ~100µm observed under these conditions remain spherical, and do not to trap microlayers at their underside (Sakashita, 2011).…”

“…Overview of the main experimental data (Duan et al, 2013, Gerardi, 2009, Jung and Kim, 2014, Moore and Mesler, 1961, Sakashita, 2011, Utaka et al, 2014, Yabuki et al, 2013 available for nucleate boiling of saturated water.…”

High-Pressure Pool-Boiling Heat Transfer Enhancement Mechanism on Sintered-Particle Wick Surface

“…The results showed that the pressure affects the size of the nucleating bubbles, whereas the bubble departure frequency of the coalesced bubbles does not change (Sakashita, 2011). In the following year, a direct correlation between pressure and the nucleation site densities was found (Sakashita, 2011). A significant enhancement in the performance of pool-boiling has also been reported at low pressure for the microporous surfaces (Rainey et al, 2003a) and the square pin-finned surfaces (Rainey et al, 2003b).…”

“…The pool-boiling behavior has been studied at high-pressures (up to 7 MPa) on a horizontal surface (normal direction of the surface is aligned with the direction of the gravitational acceleration). The results showed that the pressure affects the size of the nucleating bubbles, whereas the bubble departure frequency of the coalesced bubbles does not change (Sakashita, 2011). In the following year, a direct correlation between pressure and the nucleation site densities was found (Sakashita, 2011).…”

Interface Tracking Simulation for Subcooled Flow Boiling Using VOSET Method

“…It is our understanding that the interface tracking algorithms, such as VOF, Level set and VOSET, suffer from poor stability at large density difference between the liquid and the vapor phases. Hence if our method can get converged solution at 1 MPa, then it is easier to handle boiling simulations at higher pressure, except for the need of finer mesh for smaller departure diameter (Sakashita, 2011). That is why we select 1 MPa as the simulation condition.…”