Boiling Models Reference

Boiling models simulate the effect of the latent heat of vaporization for liquids that are in contact with a wall, when that wall is heated up to temperatures that exceed the boiling temperature of the liquid.

Boiling at that liquid-solid interface occurs in three characteristic stages:

Nucleate boiling involves creation and growth of vapor bubbles on a heated surface, which rise from discrete points on a surface. The temperature of the surface is only slightly above the saturation temperature of the liquid. In general, the number of nucleation sites increases with increasing surface temperature. An increased surface roughness can create more nucleation sites, while an exceptionally smooth surface can result in superheating.
Film boiling occurs when the critical heat flux is exceeded and a continuous vapor film covers the heated surface. The vapor layer has a lowerer thermal conductivity than the liquid so the vapor layer typically insulates the surface.
Transition boiling occurs at surface temperatures between the maximum attainable temperature in nucleate boiling and the minimum attainable temperature in film boiling. It is an intermediate, unstable form of boiling with elements of both types.

There are two distinct choices for modeling wall boiling in Simcenter STAR-CCM+, namely the Rohsenow Boiling model and the Transition Boiling model. The former uses the empirical correlation for nucleate boiling according to Rohsenow [417] and is applicable for boiling at relatively low solid temperatures. The Transition Boiling model has expressions for nucleate and transition boiling.

Table 1. Boiling Models Reference
Model Names and Abbreviations	Rohsenow Boiling		RB
	Transition Boiling		TB
Theory	See Boiling.
Provided By	[physics continuum] > Models > Boiling Models
Example Node Path	Continua > Physics 1 > Models > Rohsenow Boiling
Requires	Material: Liquid Flow: Segregated Flow or Coupled Flow Optional Models: Segregated Fluid Enthalpy, Segregated Fluid Isothermal, Segregated Fluid Temperature, or Coupled Energy Optional Models: Boiling
Properties	See Properties Lookup.
Activates	Materials	Boiling Temperature See Materials.
	Field Functions	See Field Functions.

Properties Lookup


	RB	TB
C_qw The empirical coefficient $C_{q w}$ in the Rohsenow expression for the wall heat flux, Eqn. (1829). This value varies with the liquid-surface combination.	✓
delT1 The positive empirical constant $Δ T_{1}$ in the Transition Boiling model, Eqn. (1831) to Eqn. (1833).		✓
delT2 The positive empirical constant $Δ T_{2}$ in the Transition Boiling model, Eqn. (1831) to Eqn. (1833).		✓
k1 The positive empirical constant $K_{1}$ in the Transition Boiling model, Eqn. (1831) to Eqn. (1833).		✓
k2 The positive empirical constant $K_{2}$ in the Transition Boiling model, Eqn. (1831) to Eqn. (1833).		✓
Latent heat The latent heat of evaporation.	✓
n_p The Prandtl number exponent $n_{p}$ (1.73 by default) in Eqn. (1829).	✓
phi The constant $ϕ$ in the Transition Boiling model, Eqn. (1831) to Eqn. (1833).		✓
q_max The positive empirical constant $q_{max}$ in the Transition Boiling model, Eqn. (1831) to Eqn. (1833).		✓
Surface tension The surface tension coefficient between the liquid and its vapor.	✓
Vapor density The density of vapor.	✓

Materials

Boiling Temperature: The saturation temperature of the liquid. This value is $T_{s a t}$ in Eqn. (1829).

Field Functions

Wall Boiling Heat Flux: The magnitude of a heat flux vector normal to the wall, expressing an estimate of how much the conductive heat transfer increases due to boiling at the wall boundary.