nonequilibrium transport model in rate module

[bannings]

hi,
I am using the phreeqc module of HYDRUS-1D.  I want to write two formulas of nonequilibrium transport model (two-site model) in rate module.  I've written a piece of code that works, but I'm not sure it does, exactly as the formulas say.  So I am hoping you could help me correct it!  Here are two formula and code.

Code: [Select]

#formula 1: Se(Sea,Seb)=-rho*f*kd*(d(conc^beta)/dt)
#formula 2: Sk=-rho*omega*((1-f)*kd*(conc^beta)-Sk)
Rates
Sea
-start
20 beta = parm(1)
30 rate  = TOT("Cd")^ beta
40 moles = rate * time
50 PUT(rate, 10)
200 SAVE moles
-end

Seb
############################
-start
20 rho = parm(1)
25 f = parm(2)
26 kd = parm(3)
30 rate1 = GET(10)
40 rate2  = f * rho * kd * rate1
50 moles = - rate2 * time
51 if (moles >  m) then moles = m
200 SAVE moles
-end

Sk
############################
-start
20 rho = parm(1)
25 f = parm(2)
26 kd = parm(3)
27 beta = parm(4)
28 w = parm(5)
30 rate = rho * w * (1 - f) * kd * TOT("Cd") ^ beta - rho * w * kin("Sk")
50 moles = - rate * time
51 if (moles >  m) then moles = m
200 SAVE moles
-end


[dlparkhurst]

I can't say whether your RATES definitions are correct. It depends in part on your KINETICS definition. The rates are evaluated in the order in which they are defined in the KINETICS data block. I also cannot tell if you need 3 RATES definitions, or whether they could be consolidated.

I think you will have to convince yourself that your definitions are correct. If you simplify to a PHREEQC calculation, you can use PRINT statements in your RATES definitions to print the various terms and factors of each RATES definition that result in the SAVEd values, and, of course, you can plot the values of KIN and KIN_DELTA with USER_GRAPH. The result will be a series of output at different times (TOTAL_TIME), which are not monotonic. The last evaluation of RATES may not be at the end of the time interval. The total integral may be the result of integrations over a series of sub intervals. A linear combination of the sequence of evaluations is used as the integral over a time sub interval.