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throttle example

# throttle example - 2 at the inlet as H in = 199 J/mol To...

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Example: Chapter 6 Throttling Process Calculation using SRK Equation of State Nitrogen at 100 bar and 35 o C is expanded (throttled) through a partially opened valve to a pressure of 2 bar. What is the temperature of the N 2 downstream from the valve? Solution The flow through the valve is assumed to take place quickly so that there is not much time for heat transfer. Thus, the system is assumed to be adiabatic. This is a steady-state, adiabatic system, in which no work is done so that the first law simplifies to Δ H = 0 H in = H out If N 2 were an ideal gas at these conditions, then H would only depend on temperature and the outlet temperature would be 35 o C. For a real gas, the temperature will be different from 35 o C because H depends on both temperature and pressure for a non-ideal gas. The equations-of-state spreadsheet (Cubic EOS. xls) was used to determine how much N 2 differs from an ideal gas. Inlet conditions : 100 bar, 35 o C 100 bar = 10 MPa 35 o C = 308 K The Cubic EOS program for the Soave-Redlich-Kwong EOS calculates an enthalpy for N
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Unformatted text preview: 2 at the inlet as H in = 199 J/mol To determine the outlet temperature, the temperature in the EOS program was adjusted , for a pressure of 0.2 MPa (2 bar) until the enthalpy was 199 J/mol H out = 199 J/mol It took about 6 tries to get a temperature to 4 significant figures, which is more accurate then justified by the data. The exit temperature from the Cubic EOS program is 280.7 K, which is rounded to 281 K, which is equal to 8 o C. Thus expansion through a throttle valve decreased the temperature by 27 o C. Check- this makes sense, the temperature usually decreases for throttling processes. According to the SRK equation, the initial compressibility factor was 0.92, which means the gas was non-ideal initially so it would be expected to behave as a non-ideal gas. Moreover, the initial pressure was quite high (100 bar is about 1470 psia) so non-ideal behavior is expected....
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