Mixing of Carbon Dioxide and Ethanol (VOF) CFD Simulation

Description

Project Description

The present problem simulates the mixing of two substances including carbon dioxide and ethanol in a rectangular tank. The VOF multiphase model has been used to simulate the present model. The constituents of this process include carbon dioxide with a molecular weight of 44.00995 kg.kmol-1 and ethanol with a molecular weight of 28.966 kg.kmol-1. The input flow enters the tank from the lower part with a temperature of 300 K. The inlet flow pressure is variable and time dependent. For this purpose, the pressure inlet boundary condition at the input boundary is used, which has a UDF in the form 8000000 + 66666.666 * t. This simulation process was performed in 180 s with a time step of 0.5 s.

Geometry & Mesh

The present model is drawn in two dimensions using Design Modeler software. The present model consists of a vertical rectangular tank for mixing materials with dimensions of 0.06 m * 0.3 m, which has an inlet section at the bottom with a width of 0.002 m. The following figure shows a view of the geometry.

The meshing of the model is done using ANSYS Meshing software and the mesh type is structured. The element number is 73788. The following figure shows a view of the mesh in zoomed mode.

CFD Simulation

To simulate the present model, several assumptions are considered:

• We perform a pressure-based solver.
• The simulation is unsteady. Because the model examines the changes in the volume fraction of existing phases over time.
• The gravity effect on the fluid is equal to -9.81 m.s-2 along the Y-axis.

A summary of the defining steps of the problem and its solution is given in the following table:

	Models
Viscous Model			k-epsilon
	k-epsilon model		standard
	near-wall treatment		standard wall function
Multi phase Model			Volume of Fluid
	number of Eulerian phases		2 (CO2 & ethanol)
	formulation		Implicit
	type of interface modeling		sharp
Energy			on
Boundary conditions
Inlet			Pressure Inlet
	gauge total pressure		UDF
	total temperature		300 K
Walls			Wall
	wall motion		stationary wall
	heat flux		0 W.m-2
	Solution Methods
Pressure-velocity coupling			SIMPLE
Spatial discretization	pressure		PRESTO
	density		second order upwind
	momentum		second order upwind
	volume fraction		compressive
	turbulent kinetic energy		first order upwind
	turbulent dissipation rate		first order upwind
	energy		second order upwind
	Initialization
Initialization method			Standard
	gauge pressure		0 pascal
	x-velocity , y-velocity		0 m.s-1
	temperature		300 K

Mixing Results

At the end of the solution process, two-dimensional contours of temperature, pressure, velocity, and volume fraction for each of the ethanol and carbon dioxide phases are obtained. These contours are obtained at the last second of the simulation process interval.

All files, including Geometry, Mesh, Case & Data, are available in Simulation File. By the way, Training File presents how to solve the problem and extract all desired results.