Differential motion of smoke particles?

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Discussion Overview

The discussion revolves around the technical challenges of designing a smoke exposure chamber for mice, specifically focusing on the differential motion of smoke particles and the effects of using multiple pumps to control smoke concentration. Participants explore theoretical and experimental approaches to ensure a representative range of smoke particle sizes is delivered to the exposure chamber.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant describes the setup of a smoke exposure chamber and the issue of smoke concentration, questioning whether different pump speeds will preferentially draw smoke particles of varying sizes.
  • Another participant suggests using principles from thermodynamics and vector calculus to model the behavior of smoke particles, proposing that each particle has a constant velocity vector and that the pumps exert constant pressure.
  • This participant further elaborates on a mathematical approach involving momentum, pressure, and the relationship between particle size and flow rates, although they acknowledge the need for experimental validation.
  • A later reply indicates that if the openings of the pumps are equal and conditions are controlled, the pressure ratios could be directly proportional to the number of particles, suggesting that higher pump pressure would theoretically lead to more smoke being drawn in.
  • Another participant recommends adding a third pump to maintain air supply and prevent pressure issues in the smoke chamber.

Areas of Agreement / Disagreement

Participants express various theoretical approaches and assumptions regarding the behavior of smoke particles and pump dynamics, but there is no consensus on the effectiveness of the proposed solutions or the validity of the assumptions made.

Contextual Notes

Participants mention several assumptions, such as constant pressure from the pumps and neglecting energy losses, which may not hold true in practical scenarios. The discussion also highlights the complexity of modeling smoke particle dynamics and the need for experimental data to support theoretical claims.

chason
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Hi All,

I work in a bio research lab. We are trying to set up a smoke exposure chamber to expose mice to low levels of cigarette smoke. In the contraption we have, a cigarette is burned in a small chamber and the smoke is pumped into the mouse exposure chamber. In my tests so far, the smoke is either too concentrated in the exposure chamber or too concentrated in the cigarette chamber (cigarette burns too slowly). I want to use a second pump to draw off smoke from the cigarette chamber and release it into the fume hood the instrument is in, rather than the exposure chamber. This should reduce the concentration of smoke in both the exposure and cigarette chambers.

My question is, if I have one pump running faster than the other, will smoke particles of different sizes be more likely to be drawn by one pump or the other? Tobacco smoke particles range from 0.01 to 1.0 microns. I am trying to make sure that the mice get exposed to the typical range of smoke particles, not one that is enriched for the lower or higher sizes
 
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I really don't know how to technically help out but I was seriously interested in the problem and I'd like you to try out these solutions and see if experimentally they apply...Am using knowledge of pressure exerted due to small suspendable particles from A-level thermodynamics physics and university 2nd year primary knowledge in vector calculus and electric flux,surface density,gauss's law and a bit of the divergence theorem...My assumptions on approaching the problem are 1. A constant velocity vector V is associated with each and all smoke particles independent of time and temperature variations[to overcome this assumption plotting and formulating the equation of a vector field V(x,y,z,t=time,T=Temperature) would be a basically good approach.Initially!I can't do that because it requires physical experimentation)...2.the pumps provide constant compression and/or tension pressure at any time t...3.other assumptions would be made automatically under whatever circumstances either by or you..that is there might be other assumptions I've made do not see the importance of listing out,and am expecting you to just know,like no energy losses,perfectly elastic collisions e.t.c!...APPROACH: take an opening to pump 1 have area A1,consider an imaginary plane on top of this opening such that a smoke particle of mass m1 collides with momentum=m1v1=Ft...devide by t<which is very small,just couldn't get the delta sign,but its very small> then divide by area A1 giving pressure P1<on imaginary plane at opening 1>=(m1v1)/tA1...now am thinkin t is time time between collisions on plane so its inversely proportional to number N1 of smoke particles passing through the opening..taking a constant k for proportionality then t=k1/N1 thus pressure P1=(m1v1N1)/k1A1...but v1 in the above equation is the magnitude of the smoke's velocity vector normal to the imaginary plane...mathematically this equal to dot product of vector v_1 of smoke particles and the unit normal vector n_1 to the plane v1=v_1.n_1...thus P1=[m1(v_1.n_1)N1]/k1A1...this is almost it because almost all the quantities above can be experimentally obtained and settin m1 to the typical values of 0.1 and 1 microns..also using Gauss' law,giving analogy of the smoke particles inclosed in a spherical region of radius R as flux enclosed in that spherical region{am not sure if this is correct but it might help!}...then number of particles N=surface closed integral of D.ds where D=smoke number particle density per unit surface=£N/A and ds=small vanishing surface s...where £=summation of!To get £N=total physicall measured mass enclosed in the spherical region/typical mass...to compare wether your question of the 2 pumps would work,take ratios of P1/P2 then compare dependency of the ratio over the other parameters,keeping some constant and others variable as much as you wish...I know this is not very technical but inorder to prove it useful start by experimenting on it...I'd like some feedback if possible through

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In addition...To give a theoretical answer to the question...Using above formulation and ratio,keeping the openings to have the same opening area,the same orientation relative to some x,y,z axes somewhere and with air tight conditions then you can achieve the pressure ratios P1/P2 directly proportional to the number-of-particles ratio N1/N2...with k1=k2...with this then YES theoretically more pump pressure more smoke!
 
I would also advise a third pump to provide constant air supply to preven crushing of the smoke chamber due to airtight conditions!