Prediction of dryout and post-dryout wall temperatures using film thickness model

In this paper, a model for calculating dryout and post-dryout wall temperature for two phase flow in a vertical tube using film thickness model is presented. The model is based on the mass and energy balance equations for vapor core, liquid film and corresponding closure laws for interface transfer processes. It is assumed that the dryout is reached when the local film thickness in the annular flow approaches zero. Thermal-hydraulic processes along the whole length of the boiling channel are simulated, from sub-cooled liquid flow at channel inlet, up to the liquid film dryout, gas entrained droplets, mist flow and post dryout region at tube exit. In the post dryout region, thermal non-equilibrium was assumed between vapor and entrained droplets and wall temperature was obtained iteratively by using a wall heat flux partitioning model. Also, the model is verified against several available experimental data and proved viable for prediction of the wall temperature and the dryout location.

► An annular flow model of dryout heat transfer for flow boiling is presented.
► The model predictions have been tested against literature data from experiments.
► Range of parameters investigated: pressure 30–100 bar; mass flux 500–2000 kg/m2 s.
► The model provides good results for dryout location and wall temperature.
► Important closure laws for interface transport process are identified.