1. Introduction to
Chemical Engineering
Thermodynamics
Chapter 7
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2. Throttling Process
Fluid flows through a restriction results in a pressure drop
No change in kinetic or potential energy
No shaft work produced and no heat transfer
∆H=0
For an ideal gas: no change in T occurs
For real gases: T reduction results from a throttling process
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5. Turbines (Expanders)
Expansion of a gas in a nozzle to produce a high-velocity stream
This kinetic energy is converted into shaft work when the stream
impinges on blades attached to a rotating shaft
Overall result is conversion of internal energy of a high-pressure
stream into shaft work
Steam : device is called a turbine
High-pressure gas (e.g., ethylene) device called expander
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7. Neglect potential energy, heat transfer is negligible, inlet and
outlet are sized so that fluid velocities are roughly equal
T1, P1 and P2 are known but ignore T2, Ws and H2
Reversible isentropic turbine (constant entropy)
S2=S1.
Thus, one can determine H2 and then Ws.
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9. Compressors
Rotating blades (not too high discharge pressure) or
cylinders with reciprocating pistons (for high pressures)
Kinetic and potential energy changes negligible.
Adiabatic compression
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12. Pumps
Need to determine enthalpy of compressed subcooled liquids
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13. Other useful relations:
Both equations are usually integrated assuming that:
CP, β and V are constant
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