Onset of nucleate boiling

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Next: Saturated boiling heat transfer Up: Flow boiling heat transfer Previous: Single-phase heat transfer Contents Index

Onset of nucleate boiling

Since we have to detect when the boiling process start we need a requirement for the onset of nucleate boiling. The expression originally derived by Davis and Anderson has received a wide acceptance. Their requirement^11.2 can be stated as

$\begin{displaymath} T_w - T_{\mbox{\protect\scriptsize sat}} > \left[ \frac{8 \... ...ect\scriptsize sat}} q_w'' v_{fg} }{h_{fg} k_f} \right]^{0.5} \end{displaymath}$

(11.38)

where the specific volume v_fg [ ${\mbox{m}}^3$ /kg] is defined by

$\begin{displaymath} v_{fg} \;\hbox{$=$\kern-0.68em\raise1.1ex \hbox{$\scriptscriptstyle\triangle$}}\;\frac{1}{\rho_g} - \frac{1}{\rho_f} \end{displaymath}$

(11.39)

and the properties are all evaluated at the saturation temperature.

If the wall temperature, T_w, calculated by utilizing (11.37) satisfies (11.38) we know that we have passed the point of onset of nucleate boiling and (11.37) is as a consequence insufficient for the evaluation of the convection heat transfer coefficient.

For explanatory reasons let us at this point disregard the subcooled boiling region (this subject is treated in section 11.2.4) and move directly to a description of saturated boiling heat transfer.

Next: Saturated boiling heat transfer Up: Flow boiling heat transfer Previous: Single-phase heat transfer Contents Index

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