First point: sccm= standard cubic meters per minute. The term "standard" refers to a reference temperature and pressure. The reference conditions depend on the industry but for example NIST ( the National Institute of Standards and Technology) in the US the standard conditions are specified at 273.15K and an absolute pressure at 101.325 kPa. Check which industry is relevant in your case to get the correct standard conditions.

Second point: To equate sccm equal to a "pressure" value is nonsensical, the units do not match up.

Third point: The term "partial pressure" is the hypothetical pressure of a gas species in a gas mixture, if that species occupied the volume of the gas mixture.

Fourth Point. If the gas mixture can be assumed to be an ideal mixture so that the ideal gas law holds, then at a given T and P one can associate a volume with that spices. And if the gas mixture is flowing, then one can associated a volumetric flow rate for that species in the mixture.

Fifth Point: If you specify the sccm for the species you can use the ideal gas law to determine the flow rate at the given T and P ( which typically are not at standard conditions).

Flow rate is flow of gas (even mixture of gas) in litres per minutes

partial pressure is the pressure of specific gas in the mixture of gas.

First point: sccm= standard cubic meters per minute. The term "standard" refers to a reference temperature and pressure. The reference conditions depend on the industry but for example NIST ( the National Institute of Standards and Technology) in the US the standard conditions are specified at 273.15K and an absolute pressure at 101.325 kPa. Check which industry is relevant in your case to get the correct standard conditions.

Second point: To equate sccm equal to a "pressure" value is nonsensical, the units do not match up.

Third point: The term "partial pressure" is the hypothetical pressure of a gas species in a gas mixture, if that species occupied the volume of the gas mixture.

Fourth Point. If the gas mixture can be assumed to be an ideal mixture so that the ideal gas law holds, then at a given T and P one can associate a volume with that spices. And if the gas mixture is flowing, then one can associated a volumetric flow rate for that species in the mixture.

Fifth Point: If you specify the sccm for the species you can use the ideal gas law to determine the flow rate at the given T and P ( which typically are not at standard conditions).

I would say nothing more to say.

The relation between the flow rate and gas partial pressure can be explained using the general gas equation, PV=NkT or PV=nRT. Please refer to the following web:

http://www.ecse.rpi.edu/~schubert/Course-Teaching-modules/A020-MOCVD-1.pdf

For the case where a gas flowing through the pipe the relation is given by:

http://www.anesthesia2000.com/physics/Chemistry_Physics/physics19.htm

1sccm=1.69x10-2 Pa ? (this should be in Pa/time). Pls refer to the following web:

http://descanso.jpl.nasa.gov/SciTechBook/series1/Goebel_AppB_GasFlow.pdf

Prof Samsudi Sakrani

Flow rate shows, how much of gas is let into a chamber. Pressure in a chamber depends on chamber volume, pumping speed (if there is any) and flow rate. If there is no pumping, pressure can be derived using ideal gas model. If there is pumping, no obvious relation exists (especially because pumping speed itself depends not only on pumping system, but also on piping and pressure in the pumped volume) exists. It can be computed using special software, but for lab systems much better idea id just to measure both and to have a table with measured parameters in hand.

In the ideal gas approximation one can use a simple relation such as PV=nRT, where P is partial pressure, V-volume, T - temperature and nR is molecules (atoms) number.

For real system it is profitable to use the real gas equation of state, for example [Kaplun A.B., Meshalkin A.B. High Temp. High Press, 1999, V.31. P 253-258]

Brian Higgins, you are wrong - sccm= standard cubic centimeters per minute (not meters). Muhammed Ali, at a gas flow of 1 sccm, you can observe any pressure in your camera (even atmospheric). Everything depends on the pumping rate of the gas. The pumping speed is higher - the pressure is lower.

Let me elaborate on my first answer. First, thank you SA Linnik for pointing out the typo in my first answer. Let m_f be mass flow rate and V_f volumetric flow rate of a a gas containing a single species. Then m_f=rho*V_f, where rho is the density of the gas. Now at standard conditions (273.15K and 1atm) the density of the gas is rho=M/V, where M is the mass of the gas and V is its volume at standard conditions. If the gas contains n moles and its molecular weight is MW, then rho=(n*MW)/V. Now at standard conditions the gas can be described as an ideal gas (noting Michael Anisimov's caution about using an appropriate EOS at non standard conditions- see later), then the density can be expressed as rho=MW P/RT. Hence the mass flow rate at standard conditions is:

m_f=(MW*P/(R*T))*V_f

Thus if you specify V_f at standard conditions you can compute the mass flow rate.

This calculation can also be extended to non standard conditions, at T_x and P_x. Of course the mass flow rate at non-standard conditions (m_fx) is the same at standard conditions, so that m_fx=m_f. Using the ideal gas law we can write

V_fx=V_f*( P/P_x)*(T/T_x). Thus one can compute the non standard volumetric flow rate at T_x and P_x from a measured value of V_f. These calculations can be extended to gas mixtures where now partial pressures must be used.

A final comment. If the gas is flowing through a narrow tube, where the flow rate is now determined by the pressure drop due to viscous drag at the pipe walls, then in that case (taking the gas to be incompressible -which is a good approximation as low to moderate Reynolds numbers) the measured pressure drop is NOT related to the thermodynamic pressure, that one uses in the gas law. In a large chamber viscous effects are likely negligible and the previous calculation is appropriate for an ideal gas.

Dear all

Simply (as already mentionned in thother words), the following relation between flow F and pressure P in a Maxwell-Boltzmann gas holds: F = 1/4 n = P/(2*PI*m*kT)^1/2 where n = is the gas density and ( = (8 kT/ PI*m)^1/2 ) the quadratic mean velocity, m the mass of gas specie, T the gas temperature, k the Boltzmann constant, PI = 3.141592...

Problem has no relevant formulation. Please, send the Set-Up scheme, then answer can be given.

Please send a Set-Up cheme, then you have chance to get a reasonable answer.

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