Heat Transfer Fluid Flowrate Req'd to Maintain Pipe Temp? 1

[TrippL]

I have a jacketed piping system using Dowtherm-A / Therminol VP-1 heat transfer vapor @ 290 Deg C to maintain a jacketed pipeline at 290 deg C. I have calculated that the heat loss thru the pipe insulation for a 10 ft long section will be approximately 2500 BTU/hr. The heat transfer fluid will be in the outer jacket and will enter as a vapor at 290 deg C, and exit as two forms, a condensed liquid and uncondensables vent. For anyone familiar with these heat transfer mediums, how do I go about calculating the vapor flow rate required to maintain the pipe temp at 290 deg C. I do have the heat transfer fluid properties.

 

[EmmanuelTop]

Heat In = Heat Out (2,500 BTU/hr).

It will be an iterative process. Assume flow, then calculate film temperature on the inside wall of the insulation (calculate "h" for annular flow). Then look at latent heat of vaporization of Dowtherm-A at the calculated inside film temperature (heating comes predominantly from condensation of thermal fluid). Divide given Q by latent heat to get the flow. Reiterate the process till you match both "h" values. A simulator could do this quickly for you.


Dejan IVANOVIC
Process Engineer, MSChE

 

[EmmanuelTop]

And, of course, the flows from both calculations need to match each other as well.

Dejan IVANOVIC
Process Engineer, MSChE

 

[dvd]

The heat transfer fluid is going to condense and will prove difficult to carry only with the vapor motion. It seems that the pressure drop of a pipeline of any substantial length will cause a different saturation pressure/temperature along the pipe run. What length of pipeline are you referring to?

 

[TrippL]

EmmanuelTop,

Thank you for your assistance, however I do have a question.

How do I calculate the film temperature on the inside wall of the insulation?

 

[racookpe1978]

You have to iterate that as well. All you can start with is the room air (outside air temperature, outside of the insulation.)

 

[EmmanuelTop]

See if attached spreadsheet can help you (available at ChE Forums) to speed up calculations.

If latent heat of vaporization of thermal fluid does not vary much with temperature, then it definitely does not matter how temperature distribution looks like, from ambient air to process fluid.

Dejan IVANOVIC
Process Engineer, MSChE

 

[TrippL]

Thanks, I'll check it out.

 

[IRstuff]

Bear in mind that your problem constraints actually demand an infinite flow rate to maintain the jacket at the same temperature as the input, given any loss.

TTFN
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