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International Heat Transfer Conference 13

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

PREDICTION FOR NONLINEAR TREND OF SUBCOOLED WATER FLOW BOILING CHFS WITH DIFFERENT MECHANISMS FOR OUTLET SUBCOOLINGS IN HEATED TUBES AT OUTLET PRESSURES FOR FLOW VELOCITIES

A. Sakurai
Kyoto University, Professor Emeritus, Kyoto, Japan

Katsuya Fukuda
Kobe University, Graduate School of Science and Technology, Kobe, Japan

DOI: 10.1615/IHTC13.p28.440
12 pages

Résumé

The mechanisms and corresponding correlations for the nonlinear trend of subcooled water flow boiling CHFs for outlet subcoolings in a vertical or horizontal tube having an inside diameter, D, and a length-to-diameter, L/D, ratio for a flow velocity at outlet pressures as a parameter were previously investigated: the existing flow boiling CHF data measured using the tubes having the diameters ranging from 0.4 to 12 mm, and the L/D ratios ranging from 2.4 to 96.6 for the flow velocities ranging from 5 to 130 m/s, at the pressures ranging from 0.34 to 17.2 MPa were analysed. Namely the CHF, qcr,sub, versus outlet subcooling, ΔTsub,out, for a flow velocity with outlet pressures were divided into four regions for outlet subcoolings: first the CHF decreased down to minimum one (1st region), secondly it increased up to maximum one (2nd region), thirdly it decreased down to minimum one in a small range (3rd region), and finally it again increased monotonously with an increase in outlet subcooling (4th region). The CHFs in 2nd and 4th regions are important to understand accurately for high heat flux component cooling system design. The former clearly depending on the pressure and tube diameter, and the latter being almost independent of the pressure, and tube inside diameter, D, and length-to-diameter, L/D, ratio were well expressed by the CHF correlations representing the CHFs resulting from the hydrodynamic instability, HI, and resulting from the heterogeneous spontaneous nucleation, HSN, on the inside surface near the exit of heated tube respectively. Quite recently, the prediction of maximum qcr,sub of the qcr,sub data belonging to 2nd region became possible. In the present paper, as an extension of previous work, (1) the nonlinear trends of qcr,sub versus ΔTsub,out measured using test sections such as a rectangular cross section channel with a heated strip, and heated tubes with various Ds and L/D ratios for a flow velocity with outlet pressures under various initial inlet water temperatures and (2) the nonlinear trends of qcr,sub versus flow velocity measured using a certain tube with a D and a L/D ratio at an outlet pressure under a fixed initial inlet water temperature for various flow velocities are clarified respectively based on the nonlinear subcooled flow boiling CHF model developed.

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Bibliothèque numérique IHTC

Measurement of fluid temperature with an arrangement of three thermocouples