Flow is 2,000 SCFH Normal (3,000 SCFH max)
Supply Pressure is 4 psig (min) to 17 psig (max..which can be regulated down further) at Temperature of 68 F and feed dew point in range of -40f to -94f.
Require that the h2 gas be delivered at constant flow with +68f dew point (assuming +/- 10% water content range) slightly above atmospheric pressure (i.e. 0 to 1/2" w.c.) for furnace application.
The quantity of your basic data has increased; the quality is still confusing. You state you are flowing a range of H2 flows, not one. If you need to vary the water addition, state that so we can better understand. You further fail to state the temperature and pressure of your "standard" conditions.
The confusion starts when you state you want the flow gas (which you state is at 68 oF) to have a product dew point of 68 oF. Are you trying to say that you want to vary the product dew point of a varying H2 flowrate from 46 oF to 100% water saturation? I think so.
If that's the case, then I would employ a positive displacement pump (a Milton Roy piston type) with a variable speed control or a variable stroke control. I would use the pump to feed the pre-determined quantity of liquid water into the flowing H2 at an adiabatic mixer apparatus, which would be in-line upstream of the site where you will measure and utilize the humid H2.
You can't get any more accurate than that. The type of dew point meter and controls depends on your pocket book and your need for accuracy. You haven't stated how you plan to vary the flow rate, when, and for how long. So little can be added on the specific type of instrumentation.
