Phenomenon of Boiling Curve

  Boiiling heat transfer is defined as a mode of heat
  transfer that occurs with a change in phase from liquid
  to vapour. The various flow patterns exert different
  effects on the hydrodynamics conditions near the
  heating wall. Thus, they produce different modes of
  heat transfer. The most dangerous heat transfer mode
  is the boiling crisis occurrence. Following this Critical
  Heat Flux (CHF) condition, the produced vapour forms
  an insulating layer over the heating surface and raises
  the surface temperature. As the cooling water re-enters
  the part where the steam surrounds the heating surface
  the increase in heat removal takes place, followed by
  complex hydrodynamics and heat transfer processes
  related to rewetting (quenching), which corresponds to
  Minimum Film Boiling (MFB) temperature. A functional
  form presenting heat flux transferred from the heating
  surface to the coolant versus superheating of the two
  phase flow mixture wetting the surface is known as a
  boiling curve.

2-Phase Flow 6 Fluids Schematization

  Upward two-phase flow in vertical heated channels or
  around rods or tubes bundle can take a variety of flow
  patterns which are determined by the phases mass
  fluxes,  inlet conditions, intensity and profile of the
  heat flux, and presence of the obstacles. Prediction of
  these flow regimes are important for the proper
  calculation of heat transfer from the heated walls to the
  fluid streams, as well as for the indication of Critical
  Heat Flux (CHF) occurrence. A methodology for the

  schematization of the multi-fluid flow is introduced,
  together with the multi-fluid models application,
  solution of the mass, momentum and energy governing
  equations and various criteria for fluids flow existence
  and transformation. The possible multi-fluid patterns
  are described with up to six fluid streams. Multi-fluid
  field equations are given as conservation of mass,
  momentum and energy for each fluid. Mechanistic low-
  and high-quality CHF models coupled  with selection
  criteria for a number and components of fluids are
  implemented into multi-fluid concept. This methodology
  is applied to the prediction of the CHF conditions in the
  complex geometry. The results of one-dimensional
  transient calculations are the input boundary conditions
  for further numerical investigations with the multi-
  dimensional Computer Fluid Dynamics (CFD).

2-Phase Flow Porous Media 3D Approach

  A three-dimensional two-fluid model for two-phase flow
  across tube or rod bundles is developed and presented.
  The porous media concept is applied in model
  statement. The positions and dimensions of the rods/
  tubes determine the porosity and flow resistance within
  the bundle. The model implies non-equilibrium thermal
  and flow conditions. The mass, momentum and energy
  equations are written and solved for both vapour and
  liquid phase.Closure laws for interfacial mass,
  momentum and energy transfer, bundle flow resistance
  and heat transfer are presented. New correlations for
  the interfacial drag force are proposed. Developed
  model is suitable for the simulation and analyses of

  complex multi-dimensional thermal-hydraulics of rod
  and/or tube bundles or shell-and-tube heat exchangers
  with vapour generation within a tube bundle on the shell
  side. Mechanistic model of liquid film dry-out is applied
  for occurrence of Critical Heat Flux (CHF).

2-Phase Flow around Obstacles in 3D

  Spacers are built into rod/tube bundles to support
  structure. They also have positive effects on
  enhancement of the heat transfer and increase of the
  Critical Heat Flux (CHF). Besides design
  characteristics, the axial position and distance
  between spacers play a significant role in thermal
  performance of bundles. The evaluation of these
  effects can be efficiently supported with the numerical
  simulation of the turbulent multi-dimensional coolant
  flow around the spacers. A numerical procedure is
  developed for this purpose, and presented.It is based on
  the numerical solution of the Reynolds Averaged Navies-
  Stokes Equations in two or three dimensions, with the
  application of the modified k-
e turbulence model.
  Coolant two-phase flow is simulated with the application
  of the multi-dimensional two-fluid model,
  where turbulence viscosity is predicted for the
  continuous phase. Boundary turbulent flow parameters
  are predicted with the "wall functions" at the flow
  channel walls and spacers. The SIMPLE numerical
  method is applied and the transient form of mass,
  momentum, k and
balance equations are solved in
  Cartesian co-ordinates. Numerical solution algorithm is
  based on the control volume approach.