Drag Force Available to move a Particle

Given the mass and velocity of an impact, one can calculate the momentum of an impact and the momentum per unit time is force of the impact.

Using the average velocity of water vapour as derived from the rate of sublimation and the mass of that water vapour for some arbitrary volume we know the momentum for water molecules striking an unattached particle of product at the lyophile interface. The shape of the "arbitrary volume element" and the particle must be such that water vapour impacts the particle and transfers all of its momentum to the particle.

Dt depends on the distance traveled and the velocity

Further recall that the Mass_{H20} came from the PV/(RT*18gm/mol) and make that substitution

Finally, notice that the "Arbitrary Volume" is the particle face Area x distance.

Of course we know

So we can substitute and simplify.

This force can be compared to the force of gravity on the particle to assess whether it might be lifted.

Example:

<= 7.5 mTorr

The saturation temperature can either be looked up, or calculated from the Classius Clapeyron equation. I will calculate it.

<= Degrees C

Description of Particle:

AS the pressure goes up, while maintaining the RateSub the same, the velocity must clearly go down, and thus the Drag Force decreases.