Collision Equation

Storyboard

>Model

ID:(1136, 0)



Collision Equation

Storyboard

Variables

Symbol
Text
Variable
Value
Units
Calculate
MKS Value
MKS Units
$f_{in}$
f_in
Contribución a la función distribución que ingresan (gana)
-
$f_{out}$
f_out
Contribución a la función distribución que salen (pierde)
-
$f$
f
Función distribución de la teoría de transporte
-
$\sigma$
sigma
Sección eficaz de la colisión $(\vec{v}_1,\vec{v}_2\rightarrow\vec{v}'_1,\vec{v}'_2)$
m^2
$t$
t
Tiempo
s
$\tau$
tau
Tiempo de relajamiento
s
$v$
v
Velocidad de la partícula que afecta la distribución
m/s
$v_1$
v_1
Velocidad partícula 1 que colisiona
m/s
$v_21$
v_21
Velocidad partícula 1 que resulta de la colisión
m/s
$v_2$
v_2
Velocidad partícula 2 que colisiona
m/s
$v_22$
v_22
Velocidad partícula 2 que resulta de la colisión
m/s

Calculations


First, select the equation:   to ,  then, select the variable:   to 

Symbol
Equation
Solved
Translated

Calculations

Symbol
Equation
Solved
Translated

 Variable   Given   Calculate   Target :   Equation   To be used



Equations


Examples

In the case of collisions, two particles with velocity \vec{v}_1 and \vec{v}_2 collide to have velocities \vec{v}_1' and \vec{v}_2' respectively. The probability that the velocities after the collision are \vec{v}_1' and \vec{v}_2' can be estimated with the effective section \sigma that is\\n\\n

$\sigma(\vec{v}_1,\vec{v}_2\rightarrow\vec{v}_1',\vec{v}_2')d\vec{v}_1'd\vec{v}_2')$

\\n\\nAs the probability that the particles entering the collision are \vec {v}_1 and \vec{v}_2 are calculated with the distribution function\\n\\n

$f(\vec{x},\vec{v}_1,t)f(\vec{x},\vec{v}_2,t)$



and the displacement occurs as a function of the relative velocity |\vec{v}_2-\vec{v}_1|, it is finally found that the variation of the number of particles are

equation

In the case that they leave the cell it is considered

equation=9078

Integrating on one of the speeds that initiate the collision and both resulting since the other is the contribution to the local distribution function

equation

In the case of contributions to the cell, consider

equation=9078

Integrating on the speeds that initiate the collision and one of the resulting ones since the other is the contribution to the local distribution function

equation

The equilibrium distribution can be approximated by a distribution of Maxwell Boltzmann

equation

Where m is the mass of the particle, T the system temperature and k the Boltzmann constant.

In the relaxation approximation, it is assumed that the distribution f_i(\vec{x},t) tends to relax at a time \tau to an equilibrium distribution f_i^{eq}(\vec{x},t) according to equation\\n\\n

$\displaystyle\frac{df_i}{dt}=-\displaystyle\frac{f_i-f_i^{eq}}{\tau}$



which has in the discrete approximation the equation

equation

where the term of the differences in the distribution functions represents the collisions.

With the term collisions that contribute

equation=9078

and those that reduce particles

equation=9079

you get the total exchange factor

equation

In case the particles collide, the distribution function f(\vec{x},\vec{v},t) variert und\\n\\n

$\displaystyle\frac{df}{dt}\neq 0$



Collisions cause particles of neighboring cells to undergo a collision that takes them to the cell under consideration and particles within the cell being expelled. The first leads to an increase of f_{in} particles and the second to a f_{out} time loss \tau. Thus the Boltzmann transport equation with collisions can be written as

equation


>Model

ID:(1136, 0)