|
ISSN: 1065-5131 Print
|
|
|
|
| |
You can order a single issue or an individual article, as well as view the table of contents or article abstract by clicking on the volume number, then the issue number in the right sidebar.
|
|
|
|
|
|
Institutional price: $654.00
|
|
Online subscription
|
|
Pages: 64
| Article price - $35.00 |
 |
Development and Testing of a Novel, Variable-Roughness Technique to Enhance, On Demand, Heat Transfer in a Single-Phase Heat Exchanger
Peter R. Champagne
Heat Transfer Laboratory, Department of Mechanical Engineering, Aeronautical Engineering and Mechanics, Rensselaer Polytechnic Institute, Troy, NY 12180-3590, USA
Dr. Arthur E. Bergles
Department of Mechanical, Aerospace, and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York; University of Maryland, College Park, Maryland; Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
ABSTRACT
A novel enhancement concept involves a variable-roughness heat-exchanger-tube insert that can repeatedly fluctuate between enhanced and unenhanced heat transfer states. The desired response of the heat-exchanger-tube insert is dictated by an excessive tube-wall temperature. A well-known correlation for the heat transfer coefficient due to roughness in turbulent pipe flows was applied to the tube-side of a double-pipe heat exchanger. This correlation was used to determine the material deformation required to produce "effective" enhancement, a roughness change that would produce at least a 10°C reduction in tube-wall temperature. Shape-memory alloys (SMA's) can be used to develop a variable-roughness, heat-exchanger-tube insert that can respond to an excessive tube-wall temperature. The final design consists of Nickel Titanium (NiTi) shape-memory-alloy wire coils that ride along a support-structure insert in close proximity to the tube wall. At low temperature, the shape-memory coils are close-coiled and produce little heat transfer enhancement. In response to an excessive tube-wall temperature, the coil extends and produces substantial heat transfer enhancement. Experiments were conducted at three test-fluid flow rates [0.14 kg/s (18.52 lb/min), 0.30 kg/s (39.68 lb/min), 0.58 kg/s (76.72 lb/min)] while maintaining constant test-fluid inlet temperatures [30°C (86°F), 35°C (95°F), 40°C (104°F)]. Extension oftheSMA coils does produce heat transfer enhancement and a pressure drop penalty. The increase in heat transfer coefficient between compressed-coil and extended-coil states ranges from 28 to 64 percent. The corresponding increase in friction factor is between 18 and 25 percent.
pages 341-352
|
