Component 615: Steam Nozzle by HVACSIM+ General Description The steam nozzle calculates a mass flow rate and exit steam temperature, given the downstream pressure and the upstream steam stagnation temperature and pressure. The model assumes an adiabatic, isentropic process, takes condensation into account, and uses real gas correlations to determine the steam properties. Nomenclature A - nozzle exit cross sectional area H - enthalpy P - pressure S - entropy T - temperature V - specific volume w - mass flow rate x - quality Subscripts e - exit f - saturated liquid g - saturated vapor o - stagnation (upstream) r - reference sat - saturation temperature Mathematical Description The input pressure Po and Pe are first converted from gage pressure to absolute pressures by adding the second parameter, Pr, which represents the absolute pressure corresponding to zero gage pressure. The entropy, inlet enthalpy, saturation temperature, saturation entropy, and outlet temperature are then determined by calling the steam property function subprograms described in chapter 3. S = So = Se = SS(Po,To) Ho = HS(Po,To) Tsat = TSATS(Pe) Sg = SSATS(Tsat) Te = TPSS(Pe,S) Condensation occurs if Sg is greater than So. If condensation does occur, then the concept of quality is used to determine the exit properties. Sf = SSATW(Tsat) Vf = VSATW(Tsat) Vg = VSATS(Pe,Tsat) Hf = HSATW(Tsat) Hg = HSATS(Tsat) x = (S - Sf) / (Sg - Sf) Ve = Vf + x*(Vg - Vf) He = Hf + x*(Hg - Hf) If condensation does not occur, then the outlet properties are determined as follows: Ve = VS(Pe,Te) He = HS(Pe,Te) The steam mass flow rate can now be calculated. The factor of 1000 in the following equation converts the enthalpy from kJ/kg to J/kg. w = (A/Ve)*[2*(Ho - He)*1000]^0.5 Component 615 Configuration Inputs Description 1 To - upstream stagnation temperature (C) 2 Po - upstream stagnation pressure (kPa, gage) 3 Pe - exit pressure (kPa, gage) Outputs Description 1 Te - exit temperature (C) 2 w - steam mass flow rate (kg/s) Parameters Description 1 A - nozzle exit cross sectional area (m^2) 2 Pr - absolute pressure corresponding to zero gage pressure Reference: 1. HVACSIM+ Building Systems and Equipment Simulation Program Reference Manual (NBSIR 84-2996) Daniel R. Clark United States Department of Commerce National Institute of Standards and Technology Gaithersburg, Maryland 20899-0001