Static pressure small tube

[jim hatfield]

Sorry for my lack of knowledge but I have searched and searched to no avail. I am in a unique situation. I have to figure out how to cool a 4000kva transformer in a existing coal mine power center. I am going to have a tube above the coils on this transformer with holes cut out above each coil. It will have a fan at each end of the tube pulling air out. I need to cauculate the static pressure in the tube so I can pick the correct fans. The tube has inner dims of 3"x2.5" and about ten feet long. there will be three rectangular holes in the bottom 3"x14" centered in the tube 3" apart. If someone can give me the formula or point me in the right direction, any help would be better than what I am finding using google

 

[IRstuff]

https://www.engineeringtoolbox.com/heat-gain-equipment-d_1668.html

suggests that your transformer will have 60kW of heat dissipation. I'm having trouble picturing this as anything but a water-cooled scenario.

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[jim hatfield]

Irstuff, actually i have to deal with 90Kw losses but that is not what i need i just need to calculate the static pressure the fans will be dealing with. Thanks man.

 

[Compositepro]

You are proposing to move 90 kW with air flow through 3 inch by 2.5 inch holes? Perhaps you mean feet (') rather than inches (")?

 

[IRstuff]

heat capacity of air ~ 1 kJ/kg-K, and assuming 50K temperature rise --> 1.5 m^2/s --> 996 ft/s

That's almost the speed of sound (1125 ft/s) and about 60 times higher than recommended air speeds for HVAC

https://www.engineeringtoolbox.com/duct-velocity-d_928.html

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[MintJulep]

50K rise for ventilation cooling is pretty high.

More like 5K.

You will not keep this thing cool by trying to suck air through a straw.

 

[jim hatfield]

THERE ARE OTHER COOLING AFFECTS TAKING PLACE NATURAL CONVECTION AND ENCLOSURE ITSELF. THESE LASTED ABOUT 7 YEARS, ONE OF THE POWER CENTERS TRANS FORMER FINALLY FAILED DUE TO HEAT. THEY WANT US TO COME UP WITH A SOLUTION. WE ARE PULLING AIR THROUGH THE DUCTS IN THE COILS WITH THIS SETUP I AM MAKING, WHICH I AM SURE WILL DO THE JOB. I JUST NEED TO FIGURE HOW MUCH STATIC PRESSURE THESE TUBES WILL CREATE SO I CAN PICK THE RIGHT FANS. THEN WE ARE GOING TO DO A HEAT RUN ON THE FUNCTIONAL POWER CENTER WE HAVE HERE WITHOUT THE NEW ADDITION AND WITH. SO CAN SOMEONE QUIT TRYING TO PICK APART THIS EXISTING UNIT AND HELP ME WITH THE FORMULA FOR STATIC PRESSURE?

 

[IRstuff]

50K rise for ventilation cooling is pretty high.

Agree; it just means that someone would need 10x the mass flow. Conversely, it means that it only provide 10% additional capacity.

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[MintJulep]

Ok, since you are sure that it will work.

What you need is the Colebrook equation.

https://www.engineeringtoolbox.com/colebrook-equation-d_1031.html

With convenient calculator even.

 

[LittleInch]

Jim,

first off please don't SHOUT in a post. All it does is put people off from answering.

This system would benefit hugely from a sketch as it's taken me about four times of reading it to try and figure out what you're trying to do. I'm sure it's clear in your mind, but it's not in mine.

It sounds like you are trying to have a 3" pipe with three large sections (14" long) taken out of it and then stick a fan on the end? I suspect the only flow you will get is into the first of these holes, or 90% at best.

Also what do you meant by "static pressure?" Static pressure to me is the pressure of something (air) which isn't moving. Do you mean the pressure / density of air at the bottom of your mine?

Believe it or not but most people here are trying to help you with your problem given your admitted "lack of knowledge". It seems to me and a few other I think that your system has some serious flaws in it and we are suggesting some others which would work better. But a sketch or drawing would really really help.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[jim hatfield]

I WASNT SHOUTING I USE ALL CAPS MOST OF THE TIME DUE TO A DISABILITY ITS REAL HARD TO USE SHIFT AND TYPE WITH MY MESSED UP HANDS...COMBAT INJURY. ACTUALLY MY BUDDY TYPED THE FIRST FEW POSTS BECAUSE I AM SICK AND TIRED OF PEOPLE THINKING IM YELLIN. IVE GOT IT FIGURED OUT I AM GOING ORDER A CHEAP MANOMETER THAT ALSO HAS STATIC PRESSURE FUNCTIONALITY. THEN HAVE A SMALL ADJUSTABLE GATE RIGHT BEFORE THE FANS AND ADJUST FOR MID RANGE OF THE FANS SPEC FOR STATIC PRESSURE. I AM GOING TO TRY A FEW SCENARIOS. A FAN ON EACH END OF THE TUBE BOTH PULLING THEN BOTH PULLING WITH A DIVIDER AT THE CENTER. THANKS FOR THE HELP GUYS.

 

[LittleInch]

On the first point, I'm sorry about that but clearly didn't know.

I'm sure you know, but if it helps if you first type your post in WORD all in capitals and then highlight the whole thing with a mouse and click the

button there is an option for "Sentence case" which you can then cut and paste into the post. just an idea.

I hope it works, but we can offer better help if you can attach some drawings or a sketch.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ProcessHVAC]

May I suggest that you type all in lower case instead? A sketch will definitely help, having a hard time figuring out your scenario, all I can say that trying to cool a transformer your size with 3" hole (if that is correct), does not sound right.

 

[IRstuff]

It's almost preferable to leave out all the capitalizations, so long as punctuation is maintained. Lower case letters have more shape variegation than upper case.

TTFN (ta ta for now)
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https://www.youtube.com/watch?v=BKorP55Aqvg

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[Charm City Engineer]

Mineral oil closed loop for the transformer and a heat exchanger would be my suggestion