How are the variable names selected?

The naming convention largely follows SAE ARP 5571 (see references). Variables defining the thermodynamic state are pressures p, temperatures T, specific enthalpies h, entropies s, or mass fractions X. They either refer to total conditions or static ones. If they refer to total quantities there is usually a subscript t. If they refer to static quantities there is not any subscript. Mass flow rate is abbreviated W. Subscript In refers to the inlet, Out to the outlet. p and c refer to corrected flow rates. q means quotient or ratio. Des refers to a variable under design conditions.

For a complete outline of the rules followed while naming components, variables and parameters in Jet Propulsion Library, check here.

What kind of thermo-fluid connector is used in this library?

This library uses the concept of stream connectors on its thermo-fluid connectors. More details about this can be found in Franke et al. "Stream connectors—an extension of Modelica for device-oriented modeling of convective transport phenomena" (see literature). There are two main differences to the connector proposed there however. First, instead of the static pressure and static specific enthalpy the connector contains the total pressure and the total specific enthalpy. Unfortunately the connector is still not directly compatible with libraries using the standard fluid connector (e.g., Modelon.ThermoFluid or Modelica.Fluid) due to the use of a different package structure for the computation of the thermodynamic properties.