I am hitting a road block here and

[UtilityLouie]

I am hitting a road block here and am hoping that this is the correct forum for this question. If anyone thinks there is a better forum for this question, please let me know.

I am having a problem with a vacuum system on the press section of a paper machine. To make sure my piping is not the problem, I have been trying to calculate a pressure drop on my vacuum piping. I have looked at freecalc and efunda. They both have scripts to calculate friction loss of duct, but neither addresses any change in the viscosity of air in the vacuum system.

I would guess that hot (180 degrees) saturated air has a different viscosity than standard air and all calculators use the viscosity of standard air. I think I can make the final calculation myself, but I don't like using numbers that I don't think are correct. Now if the difference in viscosities between saturated hot air and standard air results in less than 5% in the final answer, this should be stated.

I am breaking out the thermo book, fluids book and Crane 410 tonight, but all of the formulas result from there and do not address these concerns.

Am I worrying too much?

Looking for some confidence in the numbers.

 

[TBP]

I've got an older version (2.1) of the ABZ program (based on Crane 410), and if I punch in atmospheric pressure air (0 PSIG) at 70*F, it says the absolute viscosity is 0.018 centipoise, and the kin vis is 14.953. At 180*F, these change to 0.02 and 20.882 repectively.

Being an older version, it doesn't have any fancy graphics, but I don't care. I LOVE that program. One of the best $150 I ever spent.

 

[dcasto]

Here the output from a simulator that saturates the air. Notice that the air is 53% water at the temperature and pressure (14 psig and 180 F).

K-VALUES: ASOA ENTHALPY: ASOA DENSITY: STD FLOW RATES /HR
VAP VISC: NS81 VAP THC: NS81

TOTAL LIQUID VAPOR TOTAL TOTAL
COMPONENT NAME LBMOL LBMOL LBMOL LB MOL PCT KVALUE
--------- ---- -------- -------- -------- -------- -------- --------
AIR 26.3555 0. 26.3555 763.361 46.120
WATER 30.7898 0. 30.7898 554.689 53.880
-------- -------- -------- -------- --------
TOTAL 57.1453 0. 57.1453 1318.05 100.000
TOTAL LB 1318.05 0. 1318.05

STREAM NUMBER 1
TEMPERATURE DEG F 180.00
PRESSURE PSIA 14.000
ENTHALPY BTU/HR 62859.
VAPOR FRACTION 1.0000

PROPERTIES TOTAL VAPOR
---------------- ---------- ----------
FLOWRATE LBMOL/HR 57.1453 57.1453
MOLECULAR WT. 23.0649 23.0649
ENTHALPY BTU/LBMOLE 1099.9913 1099.9912
ENTROPY BTU/LBMO/R 3.4325 3.4325
CP BTU/LBMOL/R 7.5872
CV BTU/LBMOL/R 5.5764
CP/CV 1.3606
DENSITY LB/FT3 0.047185
Z-FACTOR 0.997059
FLOWRATE FT3/SEC T-P 7.7594
MMSCFD STP 0.520380
VISCOSITY CP 0.012973
TH.COND BTU/FT/HR/F 0.019687

 

[ArtR]

Don't forget that the delta-p should be less than 10% of the absolute pressure or the pipes will choke. Do you have welded or screwed joints? Threads leak (by definition)