ME 309 Fall 2008
Section 2
Homework # 35
Due Monday 1 December 2008
Problem 351
Air is throttled from an initial pressure at onehundred atmospheres to 50
atmospheres by an adiabatic process.
The kinetic energy change across the throttle
can be neglected.
For the initial temperature conditions given below, estimate the
temperature on the downstream side of the throttle and the temperature change across
the throttle assuming that the change in temperature can be estimated by replacing the
Joule Thompson coefficient,
h
J
p
T
∂
∂
=
μ
on the upstream side of the valve by the
linear relation:
J
downstream
upstream
downstream
upstream
p
p
T
T
μ
≈


on a line of constant enthalpy.
Note that this is a rough approximation, but gives an
indication of the type of temperature change that can be expected in a throttling
process.
Note that for a perfect gas, the JouleThompson coefficient is zero and for reference, the
compressibility coefficient is given.
A perfect gas has a compressibility coefficient of
unity and a JouleThompson coefficient of zero.
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 Spring '08
 MERKLE
 Fluid Dynamics, Thermodynamics, Stagnation pressure

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