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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: 1026-5511

Journal of Enhanced Heat Transfer

DOI: 10.1615/JEnhHeatTransf.v7.i2.20
pages 81-95

Corona Discharge Effects on Heat Transfer and Pressure Drop in Tube Flows

D. A. Nelson
Michigan Technological University Houghton, MI 49931
S. Zia
Michigan Technological University Houghton, MI 49931
R. L. Whipple
Michigan Technological University Houghton, MI 49931
Michael M. Ohadi
Small and Smart Thermal Systems Laboratory, Center for Energy Environmental Engineering, Department of Mechanical Engineering, University of Maryland, College Park, Maryland 20742, USA

ABSTRACT

This work presents and discusses the results of a series of experiments investigating effects from corona discharge in air on the heat transfer rate and on the pressure drop in tube flows. Two electrode geometries were studied: a single wire electrode, concentric with the grounded tube wall and dual equipotential wire electrodes which were offset 0.4 cm from center in the horizontal plane. Both positive and negative discharge were examined for the single-wire geometry, at Reynolds numbers in the range 1,000 ≤ ReD ≤ 20,000. The dual-wire geometry was studied using positive polarity discharge only, over the range ReD = 1,000 to ReD = 10,000. Heat transfer rates were determined at electrode potentials from 6.00 kV (DC) to 7.75 kV (DC), depending on polarity and electrode configuration. Baseline data were also obtained with the electrode(s) at ground potential.
Results demonstrate increases in the Nusselt number of more than two hundred per cent over the values obtained in the absence of discharge. Relative increases in the friction coefficients were generally comparable to the corresponding Nusselt number enhancement. The extent of the increase in either quantity was highly dependent on discharge current and on the Reynolds number. The relative enhancements of both Nusselt number and friction loss coefficient were generally reduced at higher Reynolds numbers (ReD ≥ 5000). However, the fall-off of enhancement with Reynolds number was less pronounced in the offset, dual-electrode geometry.
Results suggest the enhancement mechanism may significantly depend on the electrode geometry, independent of the geometry effects on discharge current. The observed trends are discussed in the context of current theory.


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