Square root units question

Forum|Forum|3 years ago
December 26, 2022
2 replies
2220 views

I have to identical equations using a square root (flow calculation). If I use the "psf" units for lbm/ft^2, the radical doesn't evaluate the squared units correctly. But if I force the units to be lbm/ft^2 under the radical, then the expression evaluates correctly to lb/s; mass flow.

I don't understand why this doesn't evaluate correctly. Is there a way to make this more robust?

See attached.

1_Flow-calc.zip

Mechanical_Engineering

Best answer by Werner_E

Why do you think that psf = lbm*ft^-2 ??

There is a gravity factor missing:

So you possibly are looking for

W

Werner_E

Answer

25-Diamond I

Why do you think that psf = lbm*ft^-2 ??

There is a gravity factor missing:

So you possibly are looking for

G

gshockxcc

Author

7-Bedrock

Yes, you're correct. Oversight on my part. Thanks for catching that mistake.

F

Fred_Kohlhepp

23-Emerald I

In your second line you change psf into lbm/ft^2. This introduces a (happy in this case) unit balance error.

Mathcad recognizes pounds force (lbf), pounds mass (lb or lbm). When you edited the units you (happily) removed an extraneous gravity acceleration from your first line. Since Mathcad recognizes and converts units, There's a better way: