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CHE 3010 - Thermodynamics Tennessee Tech University
Venkat Padmanabhan, PhD Department of Chemical Engineering
Tennessee Tech University
CHE 3010 - Thermodynamics of Chemical Processes
Lecture 35 - Turbines, Compressors and Pumps 11/29/2017
1
Tennessee Tech UniversityCHE 3010 - Thermodynamics 2
Turbines (or expanders)
Inlet
Outlet
Ws
Combination of a nozzle and blades connected to a rotating shaft
Expansion of gas to produce high-velocity stream converts internal energy to kinetic energy
Kinetic energy converted to shaft work when steam impinges on blades
When steam is the gas, its called a turbine
When any other gas such as ammonia or ethylene is used, its called an expander
Tennessee Tech UniversityCHE 3010 - Thermodynamics 3
Turbine Efficiency
The maximum possible work achievable from a turbine operating at given conditions is possible when the process is isentropic (ΔS = 0)
This is possible when the gas in the turbine expands reversibly and adiabatically
Therefore, efficiency is defined as, η =·Ws
·Ws (isen tro pic)In a good turbine design, heat transfer is negligible, inlet and exit pipes are sized to make fluid velocities roughly equal, and is horizontal
So, from energy balance, ·Ws = ΔH
and efficiency is η = ΔH(ΔH)S
Tennessee Tech UniversityCHE 3010 - Thermodynamics 4
Compressors and Pumps
Inlet
Outlet
Ws
Compressors cause the pressure in the flowing fluid to increase
Compression of gases accomplished by rotating blades (for high-volume flow) or reciprocating pistons (for high pressures)
Energy equations are independent of type of equipment
Design principles are the same — potential and kinetic energy changes are negligible, and adiabatic compression is followed
Turbine operated in reverse
Turbines or expanders cause the pressure in the flowing to fluid to decrease
Tennessee Tech UniversityCHE 3010 - Thermodynamics 5
Compressor Efficiency
The minimum amount of work required for compression of a gas is possible when the process is isentropic (ΔS = 0)
Therefore, efficiency is defined as, η =·Ws (isen tro pic)
·Ws= (ΔH)S
ΔH
Tennessee Tech UniversityCHE 3010 - Thermodynamics 6
Example
P35.1 — A steam turbine with rated capacity of 56,400 kW operated with steam an inlet conditions of 8000 kPa and 500 oC, and discharges into a condenser at a pressure of 10 kPa. Assuming a turbine efficiency of 0.75, determine the state of the steam at discharge and the mass flow rate of the steam.
Tennessee Tech UniversityCHE 3010 - Thermodynamics 7
Example
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Example
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Example
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Example
Tennessee Tech UniversityCHE 3010 - Thermodynamics 11
Example
P35.2 — Saturated-vapor steam at 100 kPa is compressed adiabatically to 300 kPa. If the compressor efficiency is 0.75, what is the work required and what are the properties of the discharge stream?
Tennessee Tech UniversityCHE 3010 - Thermodynamics 12
Example
Tennessee Tech UniversityCHE 3010 - Thermodynamics 13
Example
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