H. Tatsumoto

K. Hama

K. Hata

M. Shiotsu

Y. Shirai

National Institute for Fusion Science (NIFS-Repository)

§3. Critical Heat Fluxes on a Flat Plate Attached to One End of a Rectangu lar Duct Containing Pressurized He II Tatsumoto, H., Shirai, Y, Shiotsu, M . (Dept. of Energy Science & Technology, Kyoto University), Hata, K., Hama, K. (Institute of Advanced Energy, Kyoto Univer-sity) The purpose of this study is twofold. The first is to obtain the experimental data of steady-state heat transfer and critical heat flux (CHF) on rectangular ducts with a sudden change in cross-sectional area in pressurized He II for wide ranges of experimental conditions. The second is to present a GIF correlation which can describe the experimental data. Six FRP ducts of the same lengths L, 100 mm with different cross-sectional area were used. One side of the flat plate heater made of Manganin was attached to the end plate of each FRP duct and the other end of the duct was opened to a pool of pressurized He II. All flat plate heaters were 10 mm in width, 40 mrn in length and 0.1 mrn in thickness. The widths of the cross-sectional duct area, w', were 10, 16.1, 19.6, 22.1, 26.3 and 35.0 mm, respectively. Therefore, the ratio of the cross-sectional area Ad to the heater area All' A/All, of six duct heaters was varied from 1.0 to 3.5. The CHFs of steady-state heat transfer were measured on six ducts with the various size of Ad/All in subcooled He II at atmospheric pressure for the bulk liquid temperatures ranging from 1.8 to 2.1 K Figure 1 shows the relationship between critical heat flux, qcn and bulk liquid temperature, TB, at atmospheric pressure with Ad/All as a parameter. The CHF increases with the decrease in bulk liquid temperature, TB• As Ad /All increases, the values of CHF for a fixed TB tend to increase and approach a constant value: Q-IF on the infmitely long flat plate immersed in a pool of pressurized He II for the corresponding conditions. The CHF correlation for a duct with a sudden change in cross-sectional duct area was derived from a CHF model on a flat plate and on a Gorter-Mellink duct First, if the heat flow rapidly expands from the flat plate attached to the end of the FRP duct to the duct containing He II and is uniform in the duct, the CHF qcr can be expressed by using Gorter-Mellink equation. q<, ~[~:: ±£f(T r'dT r ~(M £f(T r'dT r (1) where M=A/I(A/L). On the other hand, it is assumed from the experimental results that the values of the CHF for the duct with large Ad /AII approaches the value for the flat plate with width, w, and infmitely long length under the corresponding conditions. Therefore the CHF for the infmitely long flat plate can be described by using a CHF correlation on a flat plate [1]. (4XO 583 T )113 ( T 113 (2) qcr = - w-' - tf(T rldT = Ntf(T rldT) whereN=O.7&1w. It can be seen from Eg. (1) and Eg. (2) that the value of the coefficients, M and N, are dependent only on the heater geometry. Therefore it is expected that the CHF for the duct with a sudden change in cross sectional area can be expressed in terms of geometry-dependent coefficient k. (3) 224 The coefficient k may be expressed as the approximate form by using the geometry coefficients, M and N. (4) where the exponent n will be determined by the experimental data. Figure 2 shows the relationship between the values of the coefficient k in Eq. (3) obtained from the experimental data and the value of A/All with bulk liquid temperature as a parameter. The data of the coefficient for each bulk liquid temperature were obtained by substituting the measured values of CHF and integrated values of J(n-I under each condition into Eq. (3). The values predicted by N in Eq.(2) and M in Eq.(1) are expressed in this figure. The experimental data become lower than the values predicted by Eq. (1) with increasing Ad/All and approach the constant value given by Eg. (2). It is assumed that the heat flow for the duct with a sudden change in cross-sectional area would not rapidly expand from the flat plate heater to the duct unlike Photenhauer's treatment [2]. The exponent n in Eq. (4) was determined to be 1.5 based on the experimental data. The values of the coefficient predicted by Eg. (4) with n=1.5 . were drawn as a broken line in the figure. It was confmned that the CHF correlation can describe the data of the coefficient within 20 % difference. I 1.8 I 1.9 a ~ • 8 I Bulk liquid tCfTllCrdture • Ad IAh=l .00 o Ad IAh=1.61 • Ad IA h=l .96 <> Ad IA h=2.21 • Ad IAh=2.63 .& AdIAh=3.50 21 -Fig.1 Relationship between critical heat flux and bulk liquid temperature .1 .8 K 01.9 K 100 • Z.O K 50 . t - • - - n = 1.5 in Eq. (4) o~--~--~--~--~----~~ I Fig.2 Relationship between coefficient and ratio of cross sectional duct area to heated surlace area References 1. H. Tatsumoto, K. Hata, K. Hama Y Shirai and M. Shiotsu, ''Proc. of 17111 International Cryogenic Engineering Conference", !PC Science and Technology Press, Guildford (1998),683 2. J.M. Pfotenhauer, Oyogenics. 32(1992)466 

Critical Heat Fluxes on a Flat Plate Attached to One End of a Rectangular Duct Containing Pressurized He II

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