Minimum film boiling temperature

FIGURE 15.70 Minimum film boiling temperature for boiling of water from horizontal cylinders as a function of system pressure (from Sakurai and Shiotsu [180], with permission from ASME). 

Mechanisms of Post-CHF Heat Transfer in Pool Boiling. It is convenient to divide the discussion of mechanisms into three areas, namely transition boiling, film boiling, and minimum film boiling temperature. 

A. Sakurai and M. Shiotsu, Pool Him Boiling Heat Transfer and Minimum Film Boiling Temperature, in Pool and External Flow Boiling, V. K. Dhir and A. E. Bergles eds., pp. 277-301, ASME, New York, 1992. 

Minimum boiling azeotropes, 3 802-807 Minimum film-forming temperature (MFFT), 16 291 20 378-379 Minimum film thickness equation, 15 211 Minimum fluidization velocity, 11 793, 797-798... 

Each emulsion polymer or co-polymer is characterised by its minimum film forming temperature (MFFT), which, if found to be too high for a given application, can be lowered by the addition of plasticiser or high boiling point coalescing solvent... 

The film boiling data shows that at the minimum temperature difference of about 40°R the heat flux is 20,000 Btu/hr-ft. The data could have been extended beyond 300°R temperature difference, but the temperature of the heating coil was not monitored and so power input was limited to make certain that burnout of the coil did not occur. 

Similarly to Nusselt s film condensation theory, in the condensation of vapour mixtures, the heat flux transferred increases with the driving temperature difference — 1 0. According to Nusselt s film condensation theory, the heat transfer coefficient decreases with the driving temperature difference according to a ( oo- o) 1/4 (4-12). The heat flux increases in accordance with q co — q)3/4. Fig. 4.21a shows clearly that a minimum for the transferred heat flux exists at a certain temperature oa. This is because the temperature difference dj — r)(j between the condensate surface and the wall, which is decisive for heat transfer, also assumes a minimum this can be explained by the boiling diagram, Fig. 4.21. 

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