Flow through Nozzle

Question

Flow through Nozzle

(OP)

20 Apr 21 15:48

When considering air flow through a nozzle, compressible flow theory tells us that the temperature must drop between the inlet and outlet. This scenario assumes isentropic flow through the nozzle. For all practical purposes, a temperature drop does not occur with any noticible difference at low velocities. The question is: has anybody ever built a test apparatus and measured a definitive temperature drop? Keep in mind that I am asking about constant volume flow through a nozzle at subsonic speeds, not supersonic, and with no shocks.

Latexman (Chemical) · Answer 1 · 2021-04-20 16:36:16

Not I, and by Googling "temperature measurement of incompressible nozzle air flow" I got nothing on the 1st 10 hits. Maybe try an academic search engine.

The theoretical temperature drops at very low Mach numbers are insignificant in most engineering applications. Maybe, that's why.

Good Luck,
Latexman

LittleInch (Petroleum) · Answer 2 · 2021-04-20 17:17:13

Apply the theory and figure out how much it is supposed to drop. My guess as noted above is a very small amount.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

1503-44 (Petroleum) · Answer 3 · 2021-04-20 17:43:42

Too small to worry about it.
At low pressures, no velocity to speak of, you have little more to worry about than the ideal gas equation of state
PV = nRT

https://www.grc.nasa.gov/WWW/k-12/rocket/eqstat.ht...
https://www.rrs.org/tag/compressible-flow/

Latexman (Chemical) · Answer 4 · 2021-04-20 19:50:16

No need to calculate anything, look at the lowest Mach numbers in an Isentropic Flow Table.

At most you are looking at tenths of a ^oC.

Good Luck,
Latexman

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