Okay, all right. allego excel files with practical case but I doubt that the diameter received is too small. Did I do something wrong?density (and therefore the flow rate in volume) of a gas varies according to pressure and temperature, as you said: so it is not that it is "right" to consider a pair of values rather than another, but that you are consistent with hiring.
in practice, if you need to size a tube, I always recommend to proceed in this way (maybe a little pedant but that eliminates every uncertainty):
1. you calculate the mass flow starting from the flow in normal volume (note), multiplying the latter by the normal density of the gas (also known). the mass flow is obviously independent of the reference conditions and constant throughout the plant;
2. knowing that the mass flow is equal to rho x c x a, being rho the density (this time to the reference conditions) and c the average speed, you calculate to (tube area) once limited c (es 20 m/s) to the reference conditions you have in that section, considering the always constant mass flow (as mentioned in 1). the calculation of rho to the reference conditions must be done with the law of rho gas = p/zrt, with p absolute pressure, r specific constant of the gas (=8314/mw), t absolute temperature, neglecting the compressibility (z=1) if you are low pressure (otherwise z is to be evaluated in other ways).
I should basically consider the "normal" conditions to determine the mass flow and then the "effective" ones to dimensional the piping, correct?density (and therefore the flow rate in volume) of a gas varies according to pressure and temperature, as you said: so it is not that it is "right" to consider a pair of values rather than another, but that you are consistent with hiring.
in practice, if you need to size a tube, I always recommend to proceed in this way (maybe a little pedant but that eliminates every uncertainty):
1. you calculate the mass flow starting from the flow in normal volume (note), multiplying the latter by the normal density of the gas (also known). the mass flow is obviously independent of the reference conditions and constant throughout the plant;
2. knowing that the mass flow is equal to rho x c x a, being rho the density (this time to the reference conditions) and c the average speed, you calculate to (tube area) once limited c (es 20 m/s) to the reference conditions you have in that section, considering the always constant mass flow (as mentioned in 1). the calculation of rho to the reference conditions must be done with the law of rho gas = p/zrt, with p absolute pressure, r specific constant of the gas (=8314/mw), t absolute temperature, neglecting the compressibility (z=1) if you are low pressure (otherwise z is to be evaluated in other ways).
no, because you have no normal conditions throughout the plant (in fact, maybe anywhere!), and therefore the density varies according to p and t: you have to know pressure and temperature of the section in question, and then determine the density at that point.I should basically consider the "normal" conditions to determine the mass flow and then the "effective" ones to dimensional the piping, correct?
sizing the piping with the only "normal" sizes is wrong, correct?
to accurately calculate the density of a gas (real) at a given pressure and temperature you can also refer to nist, extremely referenced but that in the free version only manages pure fluids (as you need anyway) and not mixtures.Okay, all right. allego excel files with practical case but I doubt that the diameter received is too small. Did I do something wrong?
Okay, all clear and thank you. we talk about hydrogen 300 bar and 0°c and I am given density about 26,4 kg/m3 both on website that I found and be using the perfect gas laws. instead nist says 22,2. the important gap that you get from comparison is due to the real gas difference vs perfect gas?to accurately calculate the density of a gas (real) at a given pressure and temperature you can also refer to nist, extremely referenced but that in the free version only manages pure fluids (as you need anyway) and not mixtures.
the density at 300 bar and 0 °c is therefore, from nist, of 22,2 kg/m3 (just different from what you have calculated). the diameter internal of the tube is 12 mm, and it seems absolutely realistic. you must then determine the thickness, using a suitable calculation code and choosing between the commercial tubes. I guess the pipe is in 316...
a question: would you give me a value to consider for distributed load losses (bar/km) admissible for a piping containing high pressure gas?density (and therefore the flow rate in volume) of a gas varies according to pressure and temperature, as you said: so it is not that it is "right" to consider a pair of values rather than another, but that you are consistent with hiring.
in practice, if you need to size a tube, I always recommend to proceed in this way (maybe a little pedant but that eliminates every uncertainty):
1. you calculate the mass flow starting from the flow in normal volume (note), multiplying the latter by the normal density of the gas (also known). the mass flow is obviously independent of the reference conditions and constant throughout the plant;
2. knowing that the mass flow is equal to rho x c x a, being rho the density (this time to the reference conditions) and c the average speed, you calculate to (tube area) once limited c (es 20 m/s) to the reference conditions you have in that section, considering the always constant mass flow (as mentioned in 1). the calculation of rho to the reference conditions must be done with the law of rho gas = p/zrt, with p absolute pressure, r specific constant of the gas (=8314/mw), t absolute temperature, neglecting the compressibility (z=1) if you are low pressure (otherwise z is to be evaluated in other ways).