polytropic efficienvy

Question

polytropic efficienvy

hassann (Civil/Environmental)

(OP)

25 Jan 24 11:29

polytropic efficiency formula used in compressors is equal to"

((?-1)/?)/((n-1)/n)) that ?=gamma

foe example when n=1.3 and ?=1.4
polytropic efficiency is:
(.4/1.4)/(.3/1.3)= .29 / .23= 1,24

polytropic efficiency for this compressors is equal 1.24.(greater than 1.00)

We know that the maximum polytropic efficiency for ideal process is equal to 1.00. Could someone please correct me on my interpretation of compression polytropic efficiency, greater than 1.00.

georgeverghese (Chemical) · Answer 1 · 2024-01-25 22:59:41

That is polytropic exponent ( not eff.) used only for the purposes of computing compressor power and polytropic head.

hassann (Civil/Environmental) · Answer 2 · 2024-01-26 00:52:41

as mentioned above the following
((?-1)/?)/((n-1)/n)) is polytropic eff
n is polytropic exponent.
? is isentropic exponent (gamma)

georgeverghese (Chemical) · Answer 3 · 2024-01-26 01:47:42

Ok
Its the other way around.
n/(n-1) = k/(k-1).Ep, where Ep = poly eff, as a ratio <1
See GPSA in the section on polytropic path compressor calculation

hassann (Civil/Environmental) · Answer 4 · 2024-01-26 11:28:18

dear

Quote:
georgeverghese (Chemical)

your formula (gpsa) is exately same as my formula.

(k-1)/k / (n-1)/n = n/(n-1) / k/(k-1)

therefor based on each formula polytropic eff is 1.24 > 1 !?

georgeverghese (Chemical) · Answer 5 · 2024-01-26 22:45:26

Pls note that n, the polytropic exponent, is always > k, the isentropic exponent.
For example, when k=1.18, Ep=0.751, and n = 1.255
See also fig 10-65 in Perry 7th edn.

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polytropic efficienvy