Component 614:  Ideal Gas Nozzle by HVACSIM+

General Description
	Component 614 models a convergent nozzle for any ideal gas and assumes 
the nozzle to be isentropic, adiabatic, and without condensation.  The model 
calculates a mass flow rate and exit temperature given the upstream stagnation 
pressure and temperature and the downstream pressure.  The model uses absolute 
pressures internally, but allows the input and output pressure to be gage 
pressures.  The second parameter is the absolute pressure corresponding to zero
gage pressure.  The third and fourth parameters specify properties of the ideal
gas.

Nomenclature
	A - nozzle exit cross sectional area
	P - pressure
	T - temperature
	w - mass flow rate
	y - specific heat ratio, Cp/Cv

Subscripts
	c - critical
	e - exit
	o - stagnation

Mathematical Description
	The two input pressures are first converted from gage to absolute 
pressures by addition of the second parameter, which represents the absolute 
pressure corresponding to zero gage pressure.  The critical pressure ratio is 
then defined as:
	Pc = C1^(-C2)
where
	C1 = 2/(1 + y)	
	C2 = y/(1 - y)
The method used to determine the flow rate depends on the critical pressure 
ratio and on another pressure ratio, Ra:
	Ra = Pe/Po
The maximum flow rate is obtained when the pressure ratio, Ra, is less than or 
equal to the critical pressure ratio:
	w = 1000*A*Po*[(y*C1^(C2*C3)) / (R*To)]^0.5
where
	C3 = (1 + y)/y
Otherwise, the flow rate is defined by
	w = 1000*A*Po*[(2*C2*{Ra^(C1*C3) - Ra^C3}) / (R*To)]^0.5
Lastly, the exit temperature is defined by the following equation:
	Te = To*Ra^(-1/C2)

Component 614 Configuration
	Inputs		Description
	1	Po	- upstream stagnation pressure (kPa, gage)
	2	Pe	- downstream pressure (kPa, gage)
	3	To	- stagnation temperature (C)
	Outputs		Description
	1	w	- mass flow rate (kg/s)
	2	Te	- exit temperature (C)
	Parameters	Description
	1	A	- nozzle exit cross sectional area (m^2)
	2	Pr	- absolute pressure corresponding to zero 
			  gage pressure (kPa)
	3	y	- ratio of specific heats ( - )
	4	R	- gas constant per unit mass (J/kg-K)

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