New BEV/E+E Elektronik Low-Frost-Point/High-Pressure Generator

Abstract

Currently, the humidity standard at BEV/E+E is limited in the lower frost-point range to $-60\,^{\circ }\hbox {C}$ at pressures up to 1 MPa and to $-75\,^{\circ }\hbox {C}$ at ambient pressure. The system is also mainly designed for use with pure nitrogen as the carrier gas. In recent years, there has been a demand for humidity measurements in non-air gases (NAG) in contrast to “air gases” such as nitrogen, synthetic air, and $\hbox {CO}_{2}$-free standard air, even at pressures up to 10 MPa and in the frost-point range down to $-60\,^{\circ }\hbox {C}$. NAGs can be gases such as $\hbox {SF}_{6}$, $\hbox {CH}_{4}$, and gas mixtures such as natural gas. To fulfill the requirements for humidity standards—especially in the high-pressure range—and to give the opportunity to determine thermodynamic properties such as enhancement factors in different carrier gases, a new “low-frost-point/high-pressure humidity generator” has been designed and verified at BEV/E+E Elektronik. The new humidity generator is designed as a single-pass generator with a maximum standard flow of $5\,\hbox {L}{\cdot }\min ^{-1}$ and can be operated in the two-pressure mode as well as in the single-pressure mode at pressures up to 10 MPa. The design of the saturator focussed on reliability at high pressures and on achieving sufficient saturation efficiency at temperatures down to at least $-60\,^{\circ }\hbox {C}$. First results of verification are presented in the range of saturator temperatures from $+20\,^{\circ }\hbox {C}$ to $-40\,^{\circ }\hbox {C}$ and at pressures up to 10 MPa. High-pressure data are presented for nitrogen and methane as carrier gases.