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- Thread starter mcampbell615
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The pressure drop across your rectangular entrance is the usual form:

DP = K * rho * vel ^2 / 2

DP = pressure drop

rho = density

vel = velocity = volumetric flow / cross sectional area

For now, use an entrance loss coefficient value of K = 0.32 for your channel.

Now, your velocity will decrease as you increase the height or width (height is better) of the rectangular entrance. This will decrease your velocity and pressure drop.

Determine your new entrance dimensions to reduce the pressure drop to the number you need.

Typed in a hurry - let me know if you have any questions.

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By the way edgepflow, I really appreciate your help!

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You can make the units work by introducing the gc factor:

DP = K * rho * vel ^2 / ( 2 * gc )

where,

gc = 32.2 lbm-ft / (lbf-sec^2)

Multiply out your units or you can use MathCAD, programmable calculator, or some other digital package if you have access to it.

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I also figured a K = 0.9 is a better number.

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Dh = 2bh / (b+h) = 2h / (1 + AR)

where,

h = height of rectangular channel = 2.75 in.

b = width = 48 in

AR = aspect ration = height / width = 2.75 / 48 in = 0.057

Usually, the AR should be > 0.25, so there is some error here.

As you can see, as b and AR -> infinity, then Dh -> 2h. So it is best to increase height only to lower pressure drop. You could use Dh in your velocity calculation for better accuracy.

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