SIMULATION OF FLOW BOILING HEAT TRANSFER IN A

SINGLE HORIZONTAL MICROCHANNEL

• In this study both the single phase and multiphase models are used for solving the

Problems.

At first the single phase model is used to obtain fully developed velocity profile at outlet of the pipe and then this velocity profile is used as the inlet profile of multiphase pipe flow simulation

WHY???

• THIS IS AN TECHNIQUE TO REDUCE COMPUTATIONAL BURDEN.

FOR SINGLE PHASE FLOW1)Continuity eqn2)Momentum eqn3)Energy eqn

To calculate velocity

To calculate turbulent energy and energy dissipation rate

TWO PHASE MODELING EQUATIONS there are two approaches for the numerical calculation of multiphase flows: 1)Euler-Lagrange approach. 2)Euler-Euler approach.

Euler-Lagrange approachThe fluid phase is treated as a continuum by solving the Navier Stokes equation.

Dispersed phase is solved by tracking a large number of particles, bubbles, or droplets through the calculated flowfield.

Euler-Euler approach In the Euler-Euler approach, the different phases are treated mathematically as interpenetrating continua.

Three different Euler-Euler multiphase models are available: • Volume of fluid (VOF) model • Mixture model • Eulerian model.

VOF

It is used for two or more immiscible fluids where the position of the interface between the fluids is of interest.

MIXTURE MODELThe mixture model is designed for two or more phases (fluid or particulate).The mixture model solves for the mixture momentum equation .

This is applicable for liquid-solid flows.

EULERIAN MODEL

The phases can be liquids, gases, or solids in nearly any combination.

Eulerian multiphase model, the number of secondary phases is limited only by memory requirements and convergence behavior.

A single pressure is shared by all phases.

Momentum and continuity equations are solved for each phase.

In ANSYS Workbench a rectangular cross-sectional micro channel of equivalent hydraulic diameter is drawn and is represented as a 2-D computational domain. The geometry consists of inlet, outlet, wall (upper wall) & heated wall (uniform heat flux is given to this wall)

WHY 2-D

In 3-D we need more mesh ,that means more calculation, so for a particular caser if we can represent our 3-D model into 2-D it will save a lot of time.

MESHING OF THE COMPUTATIONAL DOMAIN In meshing the geometry is divided into small small computational domain.