Development of a Cold Gas Propulsion System for the ... - SSL - MIT

The other new variables in equation (4-21) are the partial derivatives of specific enthalpy with respect to
pressure and temperature. The Golkar model was written for a pressurant tank using helium gas, for
which these derivatives were constant over the range of pressures and temperatures experienced [42].
However, these partial derivatives were not constant for nitrogen over the range of conditions expected
in the TALARIS CGSE tanks. This difference is illustrated in Figure 4-1.
Figure 4-1. Enthalpy relations for helium and nitrogen.
(a) Helium specific enthalpy vs. pressure [42]. (b) Nitrogen specific enthalpy vs. pressure.
(c) Helium specific enthalpy vs. temperature [42]. (d) Nitrogen specific enthalpy vs. temperature.
In Figure 4-1(a), the plots of specific enthalpy vs. pressure for helium are all linear with the same slope
regardless of temperature, which shows that