Lecture 1: Introduction

Multiphase flows are defined as
Two or more chemically inert phases
Mixture of two or more gasses such as oxygen and nitrogen
Gases dissolved in liquid such as carbon dioxide in water
Mixture of two or more liquids such as water and ethanol
All of the above

Which one of the following is NOT a multiphase flow
Boiling water
Mixture of oxygen and nitrogen

Which of the following problems does NOT involve multiphase flow
Boiling heat transfer
Atomization of liquids
Mixing of carbon dioxide in the atmosphere

The interface between immiscible fluids
Gradually disappears due to diffusion
Remains sharp at all times
Has zero surface tension
Allows a finite jump in tangential velocity
Allows a finite jump in temperature

For two-fluid systems it is true that:
They can only be simulated using molecular dynamics simulations
They are generally impossible to model mathematically
In many cases the governing equations are reasonably well known
In most cases the governing equations are not known
None of the above

The term direct numerical simulations (DNS) as used here refers to
Fully resolved simulation of a bubble or drop
Accurate simulations of simple model equations
Accurate solution of equations describing complex unsteady evolution of a large system
Large-scale industrial simulation of a full-scale industrial system
Any numerical simulation of multiphase flows

For atomization we are interested in
The size of the drops
The velocity of the drops
The time it takes for drops to form
The spatial distribution of drops
All of the above

For bubbly flows we are interested in
The velocity of the bubbles
The bubble size distribution
The bubble spatial distribution
If bubbles coalesce and/or break apart
All of the above

An indicator function is used to:
Identify the different fluids
Compute the void fraction
Compute "phasic" averages
All of the above
Only to identify the different fluids and find the void fraction

Efforts to do numerical simulations of multiphase flows
Started in the early fifties
Started in the early sixties
Started in the early seventies
Did not start until very recently
None of the above