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In reviewing the chart for Pressure-Drop for Capillary Liquid, If I reference the 5LB PER HOUR line, and hit the .031 ID department, the indicated pressure drop per foot = 3.0
What chart might this be? If this chart estimates pressure drop for liquid flow only, it would underestimate pressure drop for a capillary tube used as the expansion device, as it will see two-phase flow somewhere along its length.
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If I assume a condensing pressure of about 170 R-409a, and a suction of 10"Hg vaccum (-5 psig?), at 175 psi pressure drop, I would require 58 feet?
In the Prof's humble opinion, 58 ft won't be necessary here... :)
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and using this information, referencing a chart 39 (the book was saying reference chart 42... but that was an error) I come up with about 375" of .031.
...or 31.25' of .031" I.D. cap tube...
Not too far from the Prof's guesstimate... :)
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hmmmmm. 24'..... or ...... 31'
It will always be easier to shorten the capillary... :D
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Perhaps Prof could explain it to us. :D
The ASHRAE Refrigeration Handbook has a rather complicated eight term correlation to predict capillary tube flow rate... It includes the refrigerant's vapor and liquid specific volume, vapor and liquid viscosity, surface tension, specific heat, among other variables. This model apparently have been found to work well with R-22, R-134a, and R-410A. Other than the surface tension variable, the Prof has an Excel spreadsheet capable of generating the necessary thermodynamic data for this correlation. Mmmmm.... But it would hardly be appropriate for the Prof to be developing a cap tube selection program.. :D :D