Boiling Limit

All the limitations discussed earlier depend upon the axial heat transfer. The boiling limit, however, depends upon the evaporator heat flux (radial). Boiling limit occurs when the radial heat flux into the heat pipe causes the liquid in the wick to boil and evaporate causing dryout. It also occurs when the nucleate boiling in the evaporator creates vapor bubbles that partially block the return of fluid. The presence of vapor bubbles requires both (1) the formation of bubbles and also (2) the subsequent growth of these bubbles. Let us imagine a spherical vapor bubble that is very close to the heat pipe surface. At equilibrium, we have 

The liquid pressure is equal to the difference between the liquid-vapor interface pressure, and the capillary pressure, P, that is. 

Clausius-Clapeyron equation relating T and P along the saturation line is 

We can approximate the left-hand side of the above equation as 

Tp - is the temperature drop of the liquid at the evaporator due to conduction. Total heat transfer at the evaporator section can be written based on 1-D conduction in a pipe as 

---

The waxlike condensation product so obtained is mixed with 60 parts by volume of petroleum ether (boiling limits 30°C to 40°C) and agitated with hydrogen in the presence of a little active palladium lead catalyst (Pd-CaC03... 

The plane passing through these points and lines is the boiling-limit of all the unsaturated solutions, and completes the figure on the right. 

ESTIMATION OF THE EXPLOSIVE BOILING LIMIT OF METASTABLE LIQUIDS... 

Boiling Limitation. At very high radial heat fluxes, nucleate boiling may occur in the wick-ing structure and bubbles may become trapped in the wick, blocking the liquid return and resulting in evaporator dryout. This phenomenon, referred to as the boiling limit, differs from the other limitations previously discussed in that it depends on the evaporator heat flux as opposed to the axial heat flux [7],... 

These preliminary results indicate that with passive RVACS cooling and a coolant boiling temperature of 1430°C, there will be a considerable safety margin for an LOFC accident. An additional calculation performed by UCB for a 4000 MW(t) core yielded a peak core temperature of 1325°C, still more than 100°C below the salt boiling limit. These transient response calculations confirm early scaling analyses that predicted passive safety characteristics because of the very large thermal inertia of the AHTR. ... 

A Viscous limit B Sonic limit C Capillary limit D Entrainment limit E Boiling limit (low T fluids)... 

There are reports on the gas-phase oxidation of C5—Cg saturated hydrocarbons. For example, the gas-phase oxidation of hexane gives a-oxides and derivatives of oxacyclobutane and tetrahydrofuran. There is evidence of the possibility using the gas-phase oxidation of hydrocarbons to increase the octane number of gasoline without changing their boiling limits... 

For the purposes of the maximum design output evaluation, we define the maximum core outlet temperature as the saturation temperature at the primary pressure. Thus the ultimate limit is taken as bulk boiling at the core exit and not conventional DNB. We consider the two-phase (boiling) limit later and use results available from the literature (Dufifey and Sursock, 1987) (Duffey and Rohatgi, 1996). 

---