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Questions for all of you HVAC massters, please help

by vlajky
Tags: hvac, massters
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Feb19-12, 04:16 PM
P: 3
I would like to know couple of things ?:)

1. With U shaped manometer attached to the surface of the pipe we are measuring static pressure drop? Pressure exerted by the water on the surface of that pipe? Am i right ?
2. Is that pressure field uniform for some observed cross sectional area of the pipe ? I know that pressure is the function of length. But for some cross section is it distributed equally ( radial ( circular) , in all directions ) among the pipe wall ?
3. in central heating closed circuit installation, what gives the pressure of 6bar in pipes if it is not the centrifugal pump? If it is, how is kinetic energy of the flow transferred in the pressure energy.
Somewhere i read that "common misconception about pumps is the thought that
they create pressure. Pumps alone do not create pressure;
they only displace fluid, causing a flow. Adding resistance
to flow causes pressure " ?
4. I' confused about that, how adding resistance to flow causes pressure, it would be more natural that is cousins pressure to drop ( head loss ).. but than, what generates pressure ?

and for the final and most important for my understanding

5. I know that we have head loss in pipes due to a friction and local resistances like bends, valves, change of pipes diameter ..etc. We all know how to calculate them using Darcy - Weisbach formula. I also know from Brenuli equation that with larger diameter i have less friction losses, lower velocity and gather static pressure and vice verse.

But how is than possible that for same diameter of the pipe , same average velocity, same volume flow ....i still have static pressure drop . I understand the reasons ( listed above) I understand the math.....but i don't understand physics of that phenomena ?
Can somebody enplane me in plane English what is relay going on in there. .. Just some simple Cause and affect story line.

Thank you!:)
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