For saturated boiling, the heat transfer coefficient α_tp is defined by the relationship

\[\label{eq1} \dot{q}=\alpha_{tp}(T_w-T_{\rm sat}) \tag{1}\]

where T_w is the wall temperature, T_sat the saturation temperature and q̇ the wall heat flux.

A. Saturated nucleate boiling region

The mechanism of heat transfer in the saturated nucleate boiling region is essentially identical to that in the subcooled region. A thin layer of liquid near the heated surface is superheated to a degree sufficient to allow nucleation. The heat transfer coefficient and heater surface temperature variation is smooth and continuous through the thermodynamic boundary (x = 0) marking the onset of saturated boiling. The methods and equations used to correlate experimental data in the subcooled region remain valid for this region with the proviso that T_ℓ (z) = T_sat. Just as the heat transfer mechanism in the subcooled region is independent of the subcooling and, to a large degree, the mass velocity, so it may be inferred that the heat transfer process in this region is independent of the “mass quality” x(z) and the mass velocity (ṁ). This, indeed, is found to be the case for experimental studies of fully developed nucleate boiling. Because the bulk temperature is constant in this region, the heat transfer coefficient is also constant, since ΔT_sat is fixed for a given heat flux and system pressure.