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The University of Memphis
Using MERLOT Learning Objects in Mechanical Engineering
Dr. Edward H. PerryDepartment of Mechanical Engineering
The University of Memphis
The University of Memphis
Using MERLOT Learning Objects in Mechanical Engineering
Engineering Thermodynamics
Gas Dynamics
The University of Memphis
Steam Turbine Typical
Problem:
Determine the enthalpy for steam leaving an ideal steam turbine at 1 psia if the steam enters at a pressure of 1500 psia and a temperature of 1000 oF.
The University of Memphis
Steam Table Approach - Step 1
Using conventional superheated steam tables, we find that at 1500 psia and 1000 oF, the entropy s of the steam at the turbine inlet is:
s1 = 1.6001 Btu/lbm-R
The University of Memphis
Steam Tables - Step 2Ideal Steam Turbine => Entropy remains constant (i.e., s2 = s1)
Using the Saturation Tables, we find the quality of the steam at the turbine exit (p2 = 1 psia , s2 = s1 = 1.6001 Btu/lbm-R) is:
x2 = (s2 - sf)/sfg = (1.6001 - 0.13266)/1.8453 = 0.795
Thus, the enthalpy at the exit is:
h2 = hf + xhfg = 69.74 + (0.795)(1036.0) = 893.4 Btu/lbm
The University of Memphis
Online Calculator Approach www.mathpad.com
Inlet Conditionsp1 = 1500 psiaT1 = 1000 oFThus, s1 = 1.60037… Btu/lbm-R
Exit Conditionsp2 = 1 psias2 =s1 = 1.60037...Thus, h2 = 893.7 Btu/lbm
“Ideal” Turbine => Entropy remains constant (s2=s1)
The University of Memphis
Determining Exit Conditions in a Rocket Nozzle
Typical Problem:
Determine the Mach number and speed of the combustion products leaving a converging-diverging nozzle with an area ratio of 50:1. Assume a specific heats ratio g of 1.20 for the gases.
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Traditional Approach - Calculations
This non-linear equation is not only messy. It cannot be solved directly. A trial-and-error root-finding approach must be used.
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Traditional Approach The results of one such iterative method are shown below and indicate that the correct answer is approximately M = 4.3958
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Online Calculator Approach
http://www.aoe.vt.edu/~devenpor/aoe3114/calc.html
Using the calculator, we immediately find the Mach number to be 4.3958
The University of Memphis
Nozzle Simulatorhttp://www.grc.nasa.gov/WWW/K-12/airplane/ienzl.html
The University of Memphis
Thanks Merlot!
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