orifce size calculation 2

[accurate1]

any one know how to calculate an orfice size when the btu/h and manifold pressure is given? I would like to be able to determine the correct size for natural or LP. I know there are charts for this but sometimes run in to weird pressure specs on data plates that are not on charts.

Also, what do the numbers on a index drill stand for, example #56 drill - how is this related to inch's. is it a decimal?

thanks

 

[wilg]

Drills come in either fractional, letter sizes,
wire gauge sizes (like your number 56) or metric (mm).
A size number 21 drill is 0.1590 inches in diameter,
and it cooresponds to a tap size of 10-32.The 10-32
is a number 10 screw with 32 threads per inch.
If you wanted to drill a hole to recieve a
10-32 thread then you would use a wire size number 21
drill. A letter size k drill is 0.2810 inches in diameter.
Drills come in fractional sizes as well and
coorespond to the exact fractional equivalent
decimal diameter. Your number 56 wire size drill
is 0.0465 inches in diameter...the larger the
wire size the smaller the diameter. Get yourself a
drill size chart, machinerys handbook or a drill
catalog from a vendor.

 

[ProfSporlan]

The orifice equation should get you close:

m = Cf * A * (2 * gc * rho * deltaP)^0.5

where:

m = mass flow rate, lbm/sec
Cf = flow coefficient, 0.61 is appropriate for a flat plate orifice
A = orifice area, ft2
gc = gravitational conversion factor, 32.174 lbm-ft/lbf-sec2
rho = density, lbm/ft3
deltaP = pressure drop across orifice, lbf/ft2

Once you establish mass flow rate, you should be able to convert to btu/h