Subcooling effect

A phenomenological correlation of CHF can be developed by combining the subcooling effect and the flow friction effect on the CHF. This is done by substituting Eq. (5-19) into Eq. (5-18), yielding... 

For an inlet temperature less than 70°C, the weak subcooling effect can be correlated as... 

Therefore, to include subcooling effects, hfg is simply replaced by a modified latent heat, hy, which is>given by ... 

Now the heat transfer rate depends on hxj. If it is assumed, therefore, that subcooling effects are negligible if the term (1 + 0.687a)1/4 is 1.01 or less, it will be seen that subcooling effects are negligible if Ja is approximately less than 0.06, i.e., if ... 

The basic Nusselt analysis ignores inertial effects in the condensed film and subcooling effects. Approximate methods of accounting for subcooling were discussed above. A method of accounting for both effects is discussed in this section. To illustrate the method, condensation on an isothermal vertical plate is again considered [52] to [54]. Interfacial shear stress effects will be neglected. 

Now, the result of the Nusselt analysis which ignores subcooling effects can be written as ... 

Consider the situation described in Problem 11.15 in which stagnant saturated steam at 80°C condenses on a 0.4-m high vertical plate with a surface temperature of 75°C. Calculate the heat transfer rate per meter width of plate with and without taking subcooling effects into account. Do subcooling effects have a significant influence on the condensation rate in this situation ... 

Warm pressurant gas bubble point tests from Chapter 8 were conducted in normally saturated liquid, essentially nulling out the subcooling effect. Examination of the heated gas data indicates that warm pressurant gas acts as a degradation factor on bubble point, and that the loss in performance is proportional to the difference between the liquid and... 

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