pressure drop

[amitavaghosh]

hi all,
the following data was obtained with the glc
(a)column temp.,60°c,inlet pressure1270ton,outlet pressure 770ton,flowrate of carrier gas at 25°c,18ml/min and retention time for air , 0.30 min,the pressure drop correction factor will be?
(b) corrected retention volume for air (ml)?

regards
Amitava Ghosh

[JI2002]

For question (a), if you are asking about Pressure Correction Factor j'

then, j'=0.75*(P^2 - 1)(P+1)/(P^3 - 1)

in which P = Pi/P0
Pi: inlet pressure
P0: outlet pressure

j'=0.75 when Po is zero.

I'm not sure about the pressure unit "ton", pressure units such as psi, atm, pa, torr and bar are usually used. Can you explain how to convert from ton to atm?

For question (b), if you are asking about retention volume of air under average pressure, then you need to calculate average flow rate Fc first. There are two ways to calculate Fc:

1)use Poiseuille's Law to calculate average flow rate, Fc

Fc=3.14*r^4*(Pi-Po)*j'/8nL

r: column radius
n: carrier gas viscosity (carrier gas viscosity increases with temperature)
L: column length

2)use P1*V1/T1 = P2*V2/T2 to calculate Fc

P1 = 1 atm
V1 = 18 ml/min (flow rate is used for volume here)
T1 = 298 T

P2 (average pressure) = 2/3 * (P^3 - 1)*P0/(P^2 - 1)
V2 (average flow rate Fc) is unknown
T2 = 273 + 60 =333 T

Once you have Fc, retention volume of air can be calculated by Fc * 0.30 (retention time of air)