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Multiphase Science and Technology

A Quarterly

ISSN for PRINT: 0276-1459

Institutional price:	$694.00
Issues per year:	4

Best Paper Award Selection - Editorial Board Site

2006, Volume18

111 pages

DOI: 10.1615/MultScienTechn.v18.i4

Issue price - $150.00

HEAT TRANSFER AND FLOW CHARACTERISTICS OF A NON-UNIFORMLY HEATED TUBE UNDER LOW PRESSURE AND LOW MASS FLUX CONDITION

Hisashi Umekawa
Kansai University, Department of Mechanical Engineering, Yamate-cho 3-3-35, Suita, Osaka 564-8680, Japan

Mio Hirayama
Kansai University, Department of Mechanical Engineering, Yamate-cho 3-3-35, Suita, Osaka 564-8680, Japan

T. Kitajima
Dept. of Mechanical Engineering, Kansai University, Osaka, Japan

Mamoru Ozawa
Department of Mechanical Engineering, Kansai University, Yamate-cho 3-3-35, Suita, Osaka 564-8680, Japan

K. Mishima
Kyoto University, Research Reactor Institute, Osaka, Japan

Y. Saito
Kyoto University, Research Reactor Institute, Osaka, Japan

ABSTRACT

In an actual boiling channel, the circumferential heat flux is not uniform. Thus, the understanding of the heat transfer characteristics of non-uniformly heated tube becomes an important design factor for conventional boilers, especially for the compact water-tube boiler with tube-nested combustor. The small compact boiler is operated at low-pressure and low-mass flux condition compared with the large scale boiler, so that the non-uniformity in heat flux may strongly affect the heat transfer characteristics. In this investigation, non-uniform heat flux distribution along the circumferential direction was generated by using Joule heating of SUS304 eccentric tubes. The heated length of test-section was 900mm, inner diameter was 20mm, and outer diameter was 24mm. The eccentricity of the tube was s = 0, 0.5, 1.0 and 1.5mm. Corresponding maximum/minimum heat fluxes rations were 1.0, 1.7, 3.0 and 7.0, respectively. Experiments were conducted for upward and downward flows, with system pressures 0.3 and 0.4MPa, mass flux range 10-100kg/m²s and inlet temperatures 30 and 80deg.C. The eccentricity resulted in an increase in the CHF of the upward flow, while the effect was hardly observed in the downward flow. The effect of eccentricity on the CHF was well interpreted by the liquid film redistribution. In this paper, the local heat transfer coefficient along the circumferential direction was also presented.