2 replies to this topic

[deltaChe]

Dear Sir

The fan blower vender to me the acceleration head V^2/2g * density is gauge pressure, so I have to add 1 atm to get the vapor density through PM/RT equation.

But, from Bernoulli equation, P1/(density*g) + H1 + V1^2/(2g) = P2/(density*g) + H2 + V2^2/(2g), the term P1 should be gauge pressure so it hence that the V1^2/(2g) must be gauge pressure. Am I right?

Besides that, P=density*g*h is absolute pressure or gauge pressure?

From the given data for the blower

flow rate = 2300kg/hr
MW=29
viscosity=0.02
temperature=35C
the length =200m
inintal density=1.2kg/m3
inintal velocty for the blower v =40m/s

so I got the blower accerlation head v^2/2g*density = 961pa =0.0961barg(gauge pressure)

And, I split this 200m lenght pipe line for 4 section, and calcuatie each sec for thier presure drop and gas density.

initial P= 0.0961 barg, density=1.256kg/m3

Sec1. P=0.0561 barg, density=1.211kg/m3, delta P = 0.04 bar

Sec2. P=0.0161 barg, density=1.166kg/m3, delta P =0.04 bar

Sec3. P=-0.0239barg, density=1.12kg/m3, delta P = 0.04bar

Sec4. P=-0.0739barg, density=1.064kg/m3, deltaP=0.05 bar

Total delta P=0.17 bar

So is the suction pressure for this blower = discharge pressure - 0.17 ?

Please give me any comment and thank you verym much.

[GS81Process]

Bernouilli's equation should be solved using absolute pressures.

The static head, P=density*g*h, will be in gauge pressure, unless of course you add atmospheric pressure to it.

[S.AHMAD]

1. All engineering calculation requires pressure to be in absolute term unless the calculation is related to differential pressure that you can use either one
2. In blower/fan calculation, what we are interested in is to determine the power required which is calculated from the pressure differential: discharge pressure - suction pressure
3. Discharge pressure = destination pressure + head losses due to friction of discharge piping system + KE change
4. Suction pressure = atmospheric pressure - head loss at suction piping system - KE Change
5. Take note that the temperature at fan outlet is higher than inlet
6. If the destination pressure is also atmospheric then the the total head required = Head loss at discharge piping + head loss at suction piping + KE Change

Edited by S.AHMAD, 01 November 2011 - 08:08 PM.