How do you convert grams/second into cubicfeet/minute or hg (vacuum).?

Question

I need to convert 4 grams/second of flow or pressure into cfm or hg?

here's the deal. My friend is a mechanic and he is working on an oil drill or whatever. anyway - he needs the "vacuum" (opposite of pressure?). Of whatever liquid (is mercury used here) that is moving at 4 grams/second. I converted this into cubic feet/minute (6.554) and then converted that to lbs/min (409.16622).

Not really sure if this is going to work for him. Just looking to see if anyone can clarify this.

Answer 1

Did you mean cubic feet OF mercury? If so, the density of mercury will let you convert cubic feet to grams. If your density is given in g/ml (or relative-to-water density), then use

mass rate / density = volume rate

g/s / (density in g/ml) = ml/s

then convert cubic feet as follows:

a cubic foot is (12 in) cubed, which is (12*2.54 cm) cubed. A ml is a cubic centimeter, so a cubic foot is (12*2.54) cubed ml.

OKAY--I read your update:

Unfortunately, you can't get directly from mass flow rate to pressure without knowing some more stuff about the pipes and the fluid flowing in there. It's been a long time since I took the engineering class that covered that--I forgot what it's called even. I think it has something to do with a flow coefficient (which probably isn't given, so you have to calculate it). Sorry.

Answer 2

You need more information. Bernoulli's principal says that a fluid moving at higher speed has lower pressure. So a fluid flowing through a tube which has a "pinched" section that restricts the flow will have higher velocity and lower pressure in the pinched section. The amount of pressure drop is related to the amount of pinch, the flow speed and the characteristics of the fluid. You did not specify the fluid, the amount of pinching in the pipe, or even really say there was a pipe at all.

Or he could be reading a mass flow meter. In either case, the mercury is the measuring device, it is some other fluid, like oil or air or water that is flowing in the pipe. The height of a column of mercury is just one way to measure pressure. Even when it is measured with a mechanical gauge, it is often specified in units of "mm of mercury", even though no mercury is present at all.

Answer 3

You need more information. Grams per second is [mass] per [time]. CFM is cubic feet per minute, which is [volume] per [time]. See the difference? What you need is a relationship between mass and volume. That's usually density, which is [mass] per [volume].

[mass]/[time] * [volume]/[mass] = [volume]/[time]

Be sure to convert everything into SI units (meters, kilograms, seconds) to make sure everything works out.

If you want to get pressure, you need to know some details about the size and shape of the setup.