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Journal of Enhanced Heat Transfer
IF: 0.562 5-Year IF: 0.605 SJR: 0.211 SNIP: 0.361 CiteScore™: 0.33

ISSN Print: 1065-5131
ISSN Online: 1563-5074

Journal of Enhanced Heat Transfer

DOI: 10.1615/JEnhHeatTransf.v8.i5.50
pages 341-352

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
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.