David W. Spitzer, P.E.

For a fixed differential pressure measurement (say 100 inches of water column) in a differential-pressure steam flow measurement system, increasing density causes the compensated steam mass flow measurement to:

A. Decrease proportional to the square root of steam density
B. Decrease proportional to the steam density
C. Increase proportional to the square root of steam density
D. Increase proportional to the steam density

Commentary
Differential pressure flow measurement devices are commonly applied to measure steam flow. In addition, pressure and temperature measurements are typically implemented using individual or multivariable transmitters. The compensated steam mass flowrate can be calculated using flow computer functionality that can be implemented in a flow computer or other computational device.
For differential-pressure flowmeters, the volumetric flow (Q) is proportional to the square root of the ratio of the differential pressure (ΔP) divided by the fluid density (ρ).

Q α (ΔP / ρ) ½

However, the mass flow (W) is the product of the volumetric flow and density:

W α ρ ● Q = ρ ● (ΔP / ρ) ½ = (ρ ● ΔP) ½

Therefore, for a given raw differential-pressure measurement, the compensated mass flow of steam is proportional to the square root of the steam density. Answer C is correct.