Re: [PFLOTRAN] Question about units of mineral nucleation rate

[Hammond, Glenn E]

Koichi,

You’re absolutely right. The documented units for the nucleation rate do not align with the code. I started investigating this issue back in March:

https://bitbucket.org/pflotran/pflotran-documentation/branch/glenn/correct-nucleation-rate-const-units 

However, as I recall, the inconsistency remained unresolved, so I never merged that branch. This is still something I need to address.

I am cc’ing the user list to keep everyone informed.

Glenn

From: 平田光一 <koichi...@tepsco.co.jp>
Date: Tuesday, September 1, 2026 at 4:49 PM
To: Hammond, Glenn E <glenn....@pnnl.gov>
Cc: 大塚悠一 <yuichi...@tepsco.co.jp>; 茂木寛之 <mot...@tepsco.co.jp>; 窪川嵩之 <takayuki...@tepsco.co.jp>
Subject: [PFLOTRAN] Question about units of mineral nucleation rate

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Dear Glenn,

I have a question about the units of the mineral nucleation rate in reaction_mineral.F90.
For the ordinary mineral kinetics, the rate constant has units of mol/m^2/s, and the code multiplies it by the mineral surface area per bulk volume:
++++++++++

! rate: mol/m^2 mnrl/sec

! area: m^2 mnrl/m^3 bulk

Im_const = -rt_auxvar%mnrl_area(imnrl)

! units: mol/sec/m^3 bulk

Im = Im_const*sign_*dabs(affinity_factor)*rate_constant
++++++++++
Thus, rt_auxvar%mnrl_rate has units of mol/m^3-bulk/s.

For nucleation, however, the rate is calculated as
++++++++++
rate = nucleation%rate_constant * exp(exp_term)
++++++++++
and then added directly to rt_auxvar%mnrl_rate:
++++++++++
rt_auxvar%mnrl_rate(imnrl) = rt_auxvar%mnrl_rate(imnrl) + & 

nucleation_rate
++++++++++
This seems to imply that nucleation_rate should also have units of mol/m^3-bulk/s.

However, the documentation appears to describe the nucleation rate constant in mol/sec.

Could you clarify the intended units of NUCLEATION_KINETICS RATE_CONSTANT and the intended normalization of nucleation_rate?

I may be overlooking an area or volume conversion elsewhere in the code.

Best regards,
Koichi Hirata

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平田　光一　／　Koichi Hirata

東電設計株式会社

新領域研究開発推進室　高度解析ソリューショングループ

Tel : 090-3439-0143

Email: koichi-hirata@tepsco.co.jp

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