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Okay... this is a bit desperate...

I am reverse engineering an excel program that is used for calculating outputs for a pressure vessel used for industrial process fluid heating.

There is a part in the excel sheet where a pressure drop is being calculated. But there are too many unit conversions and other magic constants in intermediate steps i cannot regonise. I have some physics background but not enough in fluid mechanics to decipher.

For starters, I have intermediate step formulas like:

(fluid flow rate[lbs/h]]) * (1545) * ((inlet plus outlet temp[deg c] / 2)*9/5+460) / 
    ((molecular weight[??])*((pressure[psig])+14.5)*144)

The formula looks like this:

$\frac{\dot{m} \times 1545 \underbrace{\left[\frac{(T_\text{in} + T_\text{out})}{2}\times(\frac{9}{5}) + 460 \right]}_\text{Degrees C to Deg F to Rankine}}{M_w \times (P_g + 14.5) \times 144}$

I am hoping someone who deals with fluid mechanics will be familiar with many formulae to tell what it might be.

The inputs to the entire calculation steps consists of flow rate, inlet and outlet temperatures, molecular weight, viscosity and thermal conductivity; and also dimensions of the vessel.

Greatly appreciate everyones help! Thanks.

EDIT: The actual problem is here and the birthplace of the image is here

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closed as too localized by dmckee Dec 11 '12 at 21:19

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Can you double-check that formula? The parentheses and brackets aren't balanced, which makes me wonder if something is missing. (Plus, the formula isn't even correct - for one thing it converts a temperature difference from Celsius to Fahrenheit incorrectly) – David Z Oct 31 '11 at 19:46
@DavidZaslavsky I have corrected the formula. Really sorry for that. Also, actually you might be correct that the formula is wrong. That is why I need to remake a new program from this in the first place. But before that, I need to at least know what this part is trying to calculate. In my edit, the red box on the image shows where this step is from, the green box shows the start of the pressure calculation. – Jake Nov 1 '11 at 7:24
Is this gas flow? Then you should look at the thermodynamics and the equation of state of this gas. – Bernhard Jan 22 '12 at 9:32
It seems to be volumetric flow. I do not see viscosity in the formula. – Boris Apr 10 '12 at 14:12
@Jake The formula is still incorrect or missing something. The numerator has mass flow rate multiplied with temperature in Rankine while the denominator has molecular weight multiplied with pressure in pounds per square feet. As for the 1545 it is a british thermal units thingy that I can't put my finger on. – drN Nov 6 '12 at 20:25

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