Ch7
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Introduction to Chemical Engineering
Thermodynamics
Chapter 7
1 KFUPM Housam Binous CHE 303
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2 KFUPM Housam Binous CHE 303
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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3 KFUPM Housam Binous CHE 303
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4 KFUPM Housam Binous CHE 303
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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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6 KFUPM Housam Binous CHE 303
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7 KFUPM Housam Binous CHE 303
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 KFUPM Housam Binous CHE 303
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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10 KFUPM Housam Binous CHE 303
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11 KFUPM Housam Binous CHE 303
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12 KFUPM Housam Binous CHE 303
Pumps
Need to determine enthalpy of compressed subcooled liquids
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13 KFUPM Housam Binous CHE 303
Other useful relations:
Both equations are usually integrated assuming that:
CP, β and V are constant