Boiling behaviors and critical heat flux on a horizontal plate in saturated pool boiling of water at high pressures

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

“…Particularly near the CHF (7.2 MW/m 2 ), the coalesced bubbles detach from the heating surface as large deformed spheroidal bubbles with a main axis of 10 to 15 mm even at the high 5 MPa pressure; this size is sufficient for the formation of a liquid macrolayer at the bottom of the coalesced bubbles. Based on these results and the comparisons of the measured CHF with the values predicted using the macrolayer dryout model, Sakashita and Ono 11) suggested that, at least for saturated pool boiling on flat surfaces, the macrolayer dryout model is likely to be an appropriate model of the DNB-type CHF at high pressures. Sakashita and Ono 11) did not examine this matter further because there is little information to enable a fuller discussion of the macrolayer formation mechanism at high pressures.…”

“…(The primary bubbles are not shown in the figure. The primary bubbles, with detached diameters at 5 MPa of about 0.03 to 0.1 mm, 11) commence to coalesce at heat fluxes much lower than 0.48 MW/m 2 .) With increasing heat flux, the diameter of the detached coalesced bubbles markedly increases.…”

“…For example, the well-known Kutateladze-Zuber correlation based on the hydrodynamic instability hypothesis agrees fairly well with the measured CHF for saturated pool boiling of ethanol, helium, and nitrogen in a wide range of pressures, although the correlation considerably underestimates the CHF of water on flat surfaces at high pressures. 11) As noted above, there have been several theoretical investigations of the trigger mechanism of the DNB-type CHF at high pressures; however, experimental investigations are indispensable to examine the validity of the existing models and elucidate the mechanism. However, such experimental data are very limited due to the difficulty of carrying out experiments under high-pressure and high-temperature conditions.…”

Critical Heat Flux on a Vertical Surface in Saturated Pool Boiling at High Pressures

“…135, 0.15, and 0.29 mm (1949, 1950) and with a 5 mm wide horizontal ribbon with both sides heated (1953), in the wide range of pressures up to near the critical pressure. Sakashita and Ono (2009) measured the CHF of water on an upward facing surface with 4 mm wide and 20 μm thick nichrome foil at pressures from 0.1 to 7 MPa. Figure 1 shows the data by Kazakova (1949Kazakova ( , 1950Kazakova ( , 1953 and Sakashita and Ono (2009), together with the results predicted with Eq.…”

“…(1) can be applied at higher pressures. Kazakova (1949Kazakova ( , 1950Kazakova ( , 1953, and Sakashita and Ono (2009) Further, to better understand the CHF mechanism at higher pressures, it is vital to observe the boiling behaviors at high heat fluxes close to the CHF. The study reported here measured the CHF of saturated pool boiling of ethanol, R141b, and water on a vertically oriented 7 mm diameter copper surface with large heat capacity (large S value) at high pressures, and observed the boiling behaviors from low heat fluxes till CHF.…”