When Should I Consider ID Enhanced Tubing?
Craig Thomas
Technical Sales Director - Finned Tubing at NEOTISS High Performance Tube, Inc.
The above photo shows dual-enhanced tubes that are commonly used in Chiller applications, for both evaporation and condensation of refrigerants shell-side with the spiral grooved internal surface enhancement on the waterside.?This type of spiral-grooved ID surface has been used in heat transfer applications for over 30 years.?
What is the Performance Benefit?
It depends on the properties of the fluid or gas and the tube diameter, however, as a general rule of thumb these types of enhancements will increase the heat transfer rate tube-side by a factor of 1.5 to 2.5 times relative to a smooth bore tube.?
What applications should be considered? ?
Any shell and tube heat exchanger where the tube side becomes controlling or limiting. ?Prior installations include the water side of all types of packaged chillers, the MR gas cooling-condensing side of C3/MR chillers in LNG plants, gas/gas heat exchangers, tube-side vaporizers in CPI market, oil coolers, and many other services.?In most of these cases, both the OD and ID of tubes are enhanced, however, the spiral-grooved ID is also available with a smooth OD surface.
How is the Spiral Groove Fin Geometry Defined?
The three main parameters that define the surface enhancement and their commercially available range are as follows: ?
No. Ribs (starts): 10 - 50
Rib Height (inches): .010 – .016
Helix angle (to tube axis): 20 – 45 degrees
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An Example of Performance Enhancement Tube-side with Cooling Water in a 19mm dia. Tube at 1.5M/sec flow rate
Pressure Drop?????????????????????????Surface Area??????????????????????????????????????Heat Transfer
Notice that the heat transfer rate increases by 100% with only a surface area increase of 25% and a pressure drop increase of 75%. This is due primariliy to the boundary layer effect at the tube wall. Actual results may vary significantly depending on the ID fin geometry used (most often this is proprietary information)
?What about Fouling and Cleaning?
This is a very interesting topic that will be taken up in my next post.?Stay Tuned.