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BOILING NUMBER

DOI: 10.1615/AtoZ.b.boiling_number

The boiling number is dimensionless group involving the heat flux , defined by Bg = . It can be thought of as a ratio mass flow rates per unit area, (/hLG)/, i.e.,

This dimensionless group was used by Davidson et al. in 1943. They argued that it represented the stirring effect of the bubbles upon the flow. Later, the group was named the boiling number.

The boiling number is used in convective boiling. Shah (1982) uses an empirical boiling number correction to the single-phase liquid heat transfer coefficient in order to predict the two-phase heat transfer. This approach avoids the introduction of a nucleate pool boiling term into the correlation.

Another application is in modeling the critical heat flux. Measurements of critical heat flux can be expressed in dimensionless form, which, to a first approximation is valid for all fluids, if they are put in the form of a boiling number, i.e., Bgcrit = . Tables can then be constructed of Bgcrit in terms of other dimensionless groups (e.g., ESDU, 1986).

REFERENCES

Davidson, W. F. et al. (1943) Studies of heat transmission through boiler tubing at pressures from 500 to 3300 pounds, ASME Trans. 65:553–579.

ESDU Data Item 86032. (1986) Boiling Inside Tubes: Critical Heat Flux for Upward Flow in Uniformly-Heated Vertical Tubes.

Shah, M. M. (1982) Chart correlation for saturated boiling heat transfer: equations and further study, ASHRAE Trans. 88:185–196.

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