about single region model

wuhuayong · Post by **wuhuayong** » Mon Dec 14, 2009 9:11 am

Hi all,
Transport of a partitioning gas tracer into and out of homogenous soil columns can be described by a single-region model.In this model, the entire gas phase is assumed to be mobile and the water immobile. Partitioning of tracers between the gas and immobile water phase is assumed to be linear and described by a first-order rate equation, while tracer interaction with the solid phase is assumed to be negligible.
I am using CXTFIT to simulate such single-region model. But I have a question.The question is how to defines the dimensionless parameters(P,R,Beta,omega) ?
Thank you a lot.

ntoride · Post by **ntoride** » Tue Dec 15, 2009 3:35 pm

wuhuayong:
It would be interesting to try MIM to the gas transport. Please look at the CXTFIT manual(p.16-18). Nondimensional parameters are defined in Table 3.1. Also refer to van Genuchten and Wagnet (1989, SSSAJ, 1303-1310) . If any further questions, please do not hesitate to ask me.
Nobuo

wuhuayong · Post by **wuhuayong** » Wed Dec 16, 2009 2:40 am

Dear Nobuo,
Thank you for suggestion. I already have the manual on hand. But I sitll have some doubts.
In MIM, Beta is defined as (¦?m+f*¦?*Kd)/(¦?+¦?*Kd). As we know, f=¦?m/¦?. So can I make a conclusion that Beta=f?
Thanks a lot.
wuhuayong

ntoride · Post by **ntoride** » Sun Dec 20, 2009 5:15 pm

wuhuayong:
Sorry for my late reply. For nonreactive solutes, Kd is equal to zero. In this case, beta is the fraction of the mobile phase, theta_m/theta. I think this is a possible MIM assumption for the gas transport. Nobuo

wuhuayong · Post by **wuhuayong** » Tue Dec 22, 2009 3:19 am

Dear Nobuo,
I think maybe it's a possible MIM model.I still have a doubt. For nonrective tracer, R=1. But how to character the retardation by gas tracers partitioning into water.
I am sorry to have so much doubts. Thanks a lot for your patience.

rvang · Post by **rvang** » Wed Dec 23, 2009 12:19 am

Wuhayong:

Assume one-site kinetic partioning from the gas phase into the liquid phase. Use f=0 (no sorptio in gas phase), and interpret k (or Kd) as the partionining coefficient between the gas and liquid phases.

Good luck. --Rien van G.