Heat Loss Calculator for a Stainless Steel Complex Pipe System

1
Heat Loss Calculator for a Stainless Steel
Complex Pipe System

• By Thomas Morris
• Jacob Hannon

2
The Problem Background

• We work at a Research and Development company
  that designs various hot fluid systems.
• Systems are on machines that are subject to wind
  and cold weather.
• The systems have heat exchangers with known
  temperature inputs, and then long complex
  arrangements of stainless steel pipe to deliver
  the hot water.
• Each prototype is costly to build and test.
• We need a way of estimating the temperature and
  pressure loss in a system before building a
  prototype.

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Objective

• Determine the final temperature and pressure
  loss.
• Determine if the losses are significant if the
  wind is blowing and for different outside
  temperatures.

4
Setup of Heat Transfer Problem
5
Partial Continuation 1
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Partial Continuation 2
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Initial Conditions
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Excel Spread Sheet Solution

• All calculations including property
  interpolations are self contained
• Perform iterations without switching between a
  property tables calculator
• Could easily be adaptable for other fluids than
  water or other pipe materials.

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Excel Spread Sheet

• Link

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Summary of results pertaining to initial
conditions

• Only required one iteration to decrease error
• Change in temperature lower than expected
• Pressure loss seems appropriate
• Internal flow was turbulent
• Changing wind speed had little effect
• Radiation had a small to negligible effect

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Conclusions

• Small temperature change due to these factors
• Large internal heat transfer coefficient
  (116449.3 W/m2K) is 1047.4 times bigger than
  the small external heat transfer coefficient
  (111.179 W/m2K)
• Small diameter pipe (13.7 mm)small surface area
  thus the heat rate between the pipe and the air
  was very small
• The pipe actually stored most of the energy.
  During an experiment the pipe changed color
  validating this result.
• Changing Wind Speed only changed output
  temperature a few degrees because the external
  heat transfer coefficient did not change enough
  to have significant effect.
• The Pressure Drop seemed appropriate for the
  length, diameter, and relative roughness.
• Experiment was performed using very cold outside
  temperatures and a high temperature loss was
  expected. The results do not support this
  hypothesis and in fact show that on a hot day the
  losses could be even smaller/negligable.
• We anticipated the need to insulate the pipe but
  according to the results this is not necessary.
• Under 140 mph hurricane winds there was only a
  11.8 degree change (Due again to previously
  stated conlusions)
• Significantly increasing the length adds surface
  area and can make a huge difference in the
  temperature loss. For example with a 105.4 m pipe
  the delta T was 76.6 degrees.
• A lot of factors not investigated here can also
  affect the result (ie mass flow rate, pipe
  diameter, thickness, etc.) and using this
  spreadsheet will help determine the optimal
  configuration for any future fluid system.

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Appendix

• Property tables were entered into the
  spreadsheet from Fundamentals of Heat and Mass
  Transfer 6th edition by Incropera, Dewitt,
  Bergmann, and Lavine Copywright 2007 John Wiley
  and Sons
• Equations used also from the same source