On Wed, Jun 22, 2011 at 12:42 PM, Mark Iverson <[email protected]>wrote:
> > The instrument DOES provide a (calculated) value for the mass of water > which is in the form of > vapor... No. It certainly doesn't do that. And that means your simple algebra is all wet. The device gives the mass of water vapor per unit volume of air. That's the context it is calibrated for, as Driscoll says. They have determined that for a given humidity (mass of water vapor per unit volume of air), the polymer dielectric will have a certain permittivity, resulting in a certain measured capacitance. This, however, gives no indication what the dielectric constant of the polymer will be in the presence of a mixture of pure water vapor and mist. In any case, we know the mass of the water vapor per unit volume of steam without measuring it. It is simply the density of the steam. So even if the device correctly indicated this quantity, without knowing the volume of steam, it is not possible to get the total mass of the vapor. And your equation breaks down. A RH probe is just the wrong tool for the job. They could measure the flow rate of the steam. It's easier to measure, and easier to interpret.
