Thermodynamic Derivatives

After the determination of equilibrium composition, to proceed further in rocket performance calculations we require the values of three key derivatives: change of volume with respect to temperature at constant pressure, change of volume with respect to pressure at constant temperature, and specific heat at constant pressure, which is the change of enthalpy with respect to temperature at constant pressure. The determination of these is dealt in this chapter. These key derivatives assume different values for the reacting composition and the frozen composition and hence lead to different values of rocket performance parameters. Linked to this, against the conventional ratio of specific heats γ, the concept of the isentropic exponent γs for reacting composition is considered along with worked examples. Also a brief treatment on the use of Bridgman table is presented.