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How to Calculate for a Tube-in-Tube Heat Exchanger

A tube-in-tube, or tubular, heat exchanger is constructed using a smaller tube inside a larger one, to transfer heat from one fluid to another. Two fluids with different temperatures flow either parallel or countercurrently through each tube. A tubular heat exchanger's flexible design, temperatures and pressures can handle high-particulate flows, is resistant to fouling and is easy to maintain. The design calculations deliver a total Btu/hr heat transfer rate, and the designer must know the heat transfer coefficient of the pipe, the surface area of the pipe and the temperature change required.

Things You'll Need

Pen
Paper
Calculator

Instructions

- 1
  Determine the length and size of the tubular heat exchanger you're designing. For instance, assume there is a 100-foot long carbon steel tubular heat exchanger with a 2-inch diameter pipe inside a 4-inch diameter pipe.
- 2
  Determine the heat transfer coefficient of the carbon steel pipe and the total heat transfer surface area (A) of the smaller pipe. The heat transfer coefficient (U) can be found using "Perry̵7;s Chemical Engineering Handbook." For carbon steel pipe, a typical heat transfer coefficient value is 28.9 Btu/hr-ft-F. The total heat transfer surface area is 2 inches / 12 (inches per foot) x 3.14 x 100 feet long or 52.3 square feet.
- 3
  Determine the required temperature change from one fluid to another. For instance, assume the cold, inner fluid is 45 degrees F and the warmer outer fluid is 75 degrees F. And you want to change the inner fluid̵7;s final temperature to 60 degrees F. Therefore, the change in temperature (dT) is 15 degrees (60 - 45).
- 4
  Determine the total heat transfer (q) of the tubular exchanger using the formula q = U x A x (dT) or 28.9 x 52.3 x 15 -- for a value of 22,672 Btu/hr.

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