Address consistency for terms in moisture PDE #224
Description
Bug Description
The equation for moisture transport in concrete is expressed as:
In BlackBear, the solution variable is H (relative humidity). It's not immediately obvious how the terms are consistent. The term on the left (time derivative) and the term on the far right (dehydration) appear to be in terms of W (moisture content) rather than H. However, multiple authors (e.g. Wang and Xi, 2017) write the equation this way. If the correct units are used in the moisture diffusivity coefficients (D_h and D_{ht}), this can be an acceptable way to express this, but we need to make sure that we are actually using the correct units in the models we currently have, and document them accordingly.
Steps to Reproduce
This inherently affects any model using moisture transport.
Impact
At a minimum, the current documentation needs to be improved to clarify the units used in the moisture transport model and coefficients. This needs further investigation, and if there is an inconsistency in the models, we may need to adjust one or more of the terms in the differential equation accordingly.