BY : Dr S V Zhubrin, CHAM Ltd

DATE : October, 2000

FOR : Demonstration case for V3.3.3.

An IMMERSOL application is presented aimed at the demonstration of the method for the real-life 3D simulation when the convection, chemical reactions, thermal radiation and conjugate heat transfer have to be considered simultaneously.

A direct-fired furnace for heat treating solid materials is a rectangular 3D box in shape. The side walls and roof are naturally cooled by ambient air with an estimated heat transfer coefficient. The have an emmitance of 0.9. The furnace floor is refractory and covered by three beams of load made from brick material with an emmitance of 0.9.

The preheated methane gas premixed with air enters the furnace with an angle to the floor through closely spaced ports at the side wall. It ignites and steady kinetically- controled combustion takes place producing hot non-scattering furnace gases with an absorption coefficient equal to 0.8. The exhaust opening is at the opposite side wall.

The task is to calculate the operating temperatures of the load and furnace gases along with all related field distributions.

The independent variables of the problem are the three components of cartesian coordinate system, namely X, Y and Z.

The main dependent (solved for) variables are:

- Pressure, P1
- Three components of velocity, U1, V1, W1
- Turbulence energy and its dissipation rate, KE, EP
- Gas total enthalpy, H1
- Gas mixture fraction, MIXF
- Mass fraction of fuel, FUEL and
- Gas radiosity/solid temperature T3.

The K-epsilon model, KEMODL, closed by wall functions is used to calculate the distribution of turbulence energy and its dissipation rate from which the turbulence viscosity is deduced.

Combustion is treated as a single-step irreversible chemical reaction with a finite reaction rate between fuel and oxygen. The rate of combustion is modelled according to the "eddy-break-up" concept.

The IMMERSOL model is used to simulate the distribution of T3 within the space filled with combustion gases and solid blocks. From the temperature fields the radiant heat fluxes, QRX, QRY and QRZ, W/m^2, are calculated and used as the heat sources for H1 in iterative manner.

The gas density is computed from the local pressures, gas temperatures and local mixture molecular masses.

The specific enthalpies are related to gas temperatures, fuel mass fraction and the heat of combustion.

The plots show the distribution of temperatures, velocities and other related fields within the furnace and loads.

Pictures are as follows :

- Furnace geometry
- Streamlines showing flow distribution
- Velocity vectors
- Temperatures within gas and solid
- Gas radiosity temperatures
- Radiant fluxes in X-direction
- Radiant fluxes in Y-direction
- Mass fractions of fuel
- Mass fractions of combustion products
- Mass fractions of air
- Density of gas
- Gas turbulent viscosity
- Energy of turbulence
- Reciprocal turbulence time scale
- Distance to the nearest wall
- Pressure distribution

All model settings have been made in VR-Editor of PHOENICS 3.3.3.

The relevant Q1 file can be inspected by clicking here.

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