Calculate or Estimate the Heat Transfer Coefficient of Condensing Butane 2

[ChEMatt]

Where can I find, or calculate, this value? Looking for Btu/(hr ft2 °F).

Is there any other information I need to provide to help locate this value?

Thanks!!

-m

 

[Latexman]

How accurate do you need? Is this for a study or design? Perry's list some typical overall heat transfer coefficients you can use for a study. If for design, you need to crunch a lot of numbers. Again, Perry's has the detailed design equations too.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[ChEMatt]

This is a study. I'm trying to estimate the heat losses on an insulated pipe coming off a compressor. The normal outlet temperature is pretty close to the dew point. I wanted to quantify, in general, how much heat they're losing and therefore how much butane is condensing.

I'll check Perry's here on my desk but I'll be honest, I'm not good with this book. I never seem to be able to find the right section for what I'm looking for, heh.


edit: Table 3-222 gives values for saturated normal butane, kf has units of W/(m K). That's thermal conductivity, not U.

 

[Latexman]

From a design manual. Line up the numbers. 30 C = 0.5 for insulated.

Approximate Coefficients for Pipe Line Losses*
(Based on Outside Pipe Area)
Temperature Difference °C
30 55 85 110 140 165 195 220 250 280 305 335
Calm Air 2.5 2.7 3 3.3 3.7 4 4.5 5 5.6 6.1 6.7 7.3
Windy Day 5 5.4 6 6.6 7.4 8 9 10 11 12 13 14
Rainy Day 12 13 15 16 18 20 23 25 28 30 32 35
Insulated 0.5 0.54 0.6 0.66 0.74 0.8 0.9 1 1.1 1.2 1.3 1.4

U-*Overall Heat Transfer Coefficients Btu/hr-sq ft-ºF



Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[don1980]

The overall heat transfer coefficient accounts for the individual film coefficients (inside and outside the pipe) plus the resistance caused by the insulation. The calculation is easily found by a Google search. U = 1/[(1/hi) + (1/ho) + insulation]. The film coefficient (ho) for heat transfer from the outer insulation to the outside air is very low, ~5 Btu/hr-ft2-F. Inside the pipe, the condensing coefficient is relatively high (~200-300), but that's effectively negated by the very poor rate of heat transfer through the insulation and to the air.

For quick estimation purposes, I'd use an overall U of say 5, and I think that's probably on the generous side. For a more accurate estimate, do the U calculation, including the specific resistance for your insulation.

 

[ChEMatt]

Thanks for the feedback guys. Don1980, I do know that calculation but I haven't used it since, oh, I'm not gonna say... but it's been a while! <grin> But yes, I think I have hi from Perry's. I think I'm good here.

Latexman, as always you are very helpful, thank you for taking the time out of your schedule to help me with my questions.

It appears there's an opportunity within this organization to build something that will help other engineers in the future, and at least automate things bit for repeated calculations. Once I build this, is this forum an appropriate place to post and ask for validation and/or review? Or would that be inappropriate?