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Calculating Pressure Drop and Heat Transfer for Hot Air in Pipe

Calculating Pressure Drop and Heat Transfer for Hot Air in Pipe

Calculating Pressure Drop and Heat Transfer for Hot Air in Pipe

(OP)
I am looking for a procedure/spreadsheet/Mathcad to calculate the exit temperature of a pipe that is used for aeration blower air.

Inlet conditions from blower are P=180 kPaA T=110C, Outlet P=100kPaA T=?.

Flow is 5965 m3/hr. Pipe is 150m DN400 2mm thick ss, ambient air temperature 40C.

The temperature is needed to determine if the outlet pipe can be metallic or thermoplastic.

I know this sounds like a homework question but it is a real situation. I only ask as I generally work with liquids and slurries.

Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng
www.waterhammer.bigblog.com.au

RE: Calculating Pressure Drop and Heat Transfer for Hot Air in Pipe

You could use 3Eplus and iterate to a solution.    http://www.pipeinsulation.org/pages_v4/download.html
If you need a full description how to do this I can provide further details.  Anyways, most of the hard work would be done in the 3Eplus program.

RE: Calculating Pressure Drop and Heat Transfer for Hot Air in Pipe

(OP)
Zapster,

I looked at 3E plus but it required one layer of insulation to be included as a minimum?

Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng
www.waterhammer.bigblog.com.au

RE: Calculating Pressure Drop and Heat Transfer for Hot Air in Pipe

I can't think of a thermoplastic I'd use at 110C.

Mike Halloran
Pembroke Pines, FL, USA

RE: Calculating Pressure Drop and Heat Transfer for Hot Air in Pipe

Mike,

Pressure reduction will cool down the gas to 610C and then you have heat losses.

RE: Calculating Pressure Drop and Heat Transfer for Hot Air in Pipe

The expanding gas won't cool the plastic except in the immediate vicinity of the holes.  

For the remainder of the plastic, the air boundary layer will be thin on the inside, and probably thicker on the outside, so the bulk temperature will be nearer the inlet gas temperature than the ambient.  

Rather than attempting to calculate that bulk temperature and then worry about how plastically the plastic will behave at that temperature and under the stress applied by supports, clamps, and fittings, I'd specify a marine grade thermoset FRP that's actually rated for service above 110C, or ss.

YMMV, of course.

Mike Halloran
Pembroke Pines, FL, USA

RE: Calculating Pressure Drop and Heat Transfer for Hot Air in Pipe

(OP)
MikeHalloran,

There will be 64m of DN400 stainless steel pipe to the first dropper. It is the dropper that I want to be in a thermoplastic. ABS is rated to 70C and PP will go higher. Problem is the thermal expansion of the plastic.

We needed to get on and palce the order so the end spool became a 316ss flange welded to a SAF 2205 dropper. Nozzle embedded in concrete floor was SAF 2507 to resist crevice corrosion.

Concern existed re FRP gel coat taking the temperature.

quark ,

It was the heat losses I was after predicting. Guess I could take the mean of the inlet and outlet temperaturtes and do a convection calculation based on that.

Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng
www.waterhammer.bigblog.com.au

RE: Calculating Pressure Drop and Heat Transfer for Hot Air in Pipe

stainer,

The last time I used 3E Plus you had to pick one layer of insulation; however, when you ran the calculations it always compared the one layer of insulation with the bare metal pipe.  Unless they changed something in the latest version, just pick any insulation material and thickness.  Run the 3E Plus calculations and in the results, you should find the heat loss for bare metal pipe.

RE: Calculating Pressure Drop and Heat Transfer for Hot Air in Pipe

Gelcoat is a thermoset; it can take heat better than ABS.
You have to pay extra for gelcoat on FRP.
You have to pay a lot extra for gelcoat with a nice finish.

In boat exhausts, the usual termination of FRP tube to SS tube is reinforced silicone hose, double clamped.  With custom- fitted 16ga SS crush sleeve inside the FRP.  The crush sleeve supports the FRP when it behaves like a thermoplastic, at temperatures that would liquefy a thermoplastic.  At 110C, you don't need a crush sleeve for FRP, but you might for ABS or PP.


Is the SS header accessible?  One fine day some kind soul is going to insulate it, either to reduce the likelihood of skin contact burns or just to save energy.  

...





Mike Halloran
Pembroke Pines, FL, USA

RE: Calculating Pressure Drop and Heat Transfer for Hot Air in Pipe

(OP)
Mike,

Thanks for the heads up on FRP. Will speak to our suppliers.

Access points to the SS will be guarded not insulated.

Geoff

Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng
www.waterhammer.bigblog.com.au

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