Computational study of twisted-tape-induced swirl flow heat transfer and pressure drop in a vertical circular tube under velocities controlled

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• 作者：K. Hata ; Y. Shirai ; S. Masuzaki ; A. Hamura
• 刊名：Nuclear Engineering and Design
• 出版年：2013
• 出版时间：October, 2013
• 年：2013
• 卷：263
• 期：Complete
• 页码：443-455
• 全文大小：3187 K

文摘

The twisted-tape-induced swirl flow heat transfer due to exponentially increasing heat inputs with various exponential periods and twisted-tape-induced pressure drop were systematically measured with mass velocity G = 4120 to 13 570 kg/m²/s, inlet liquid temperature T_in = 300.13 to 305.78 K and inlet pressure P_in = 866.52 to 945.86 kPa by an experimental water loop flow. Measurements were made on a 59.2 mm effective length and its three sections (upper, mid and lower positions), which were spot-welded four potential taps on the outer surface of a 6 mm inner diameter, a 69.6 mm heated length and a 0.4 mm thickness of Platinum circular test tube with the twisted-tape insert. The SUS304 twisted-tape of width w = 5.6 mm, thickness ¦Ä_T = 0.6 mm, total length l = 372 mm, pitch of 180¡ã rotation H = 20.34 mm and twist ratio y = H/d = 3.39 was employed in this work. On the other hand, theoretical equations for k-? turbulence model in a circular tube of a 6 mm in diameter and a 636 mm long with the twisted-tape insert were numerically solved for heating of water with heated section of a 6 mm in diameter and a 70 mm long by using PHOENICS code under the same conditions as the experimental ones considering the temperature dependence of thermo-physical properties concerned. The twisted-tape of w = 5.6 mm, ¦Ä_T = 0.6 mm, l = 370 mm, H = 20 mm and y = 3.33 was installed under the same experimental position. The surface heat flux q and the average surface temperature T_s,av on the circular tube with the twisted-tape of y = 3.33 obtained theoretically were compared with the corresponding experimental values on q versus the temperature difference between average heater inner surface temperature and liquid bulk mean temperature ¦¤T_L [=T_s,av ? T_L, T_L = (T_in + T_out)/2] graph. The numerical solutions of q and ¦¤T_L are almost in good agreement with the corresponding experimental values of q and ¦¤T_L with the deviations less than 0 % to +20 % for the range of ¦¤T_L tested here. The numerical solutions of the local surface temperature (T_s)_z, local average liquid temperature (T_f,av)_z and local liquid pressure drop ¦¤P_z were also compared with the corresponding experimental data of (T_s)_z, (T_f,av)_z and ¦¤P_z versus heated length L or distance from inlet of the test section Z graph, respectively. The numerical solutions of (T_s)_z, (T_f,av)_z and ¦¤P_z are within ¡À5 % difference of the corresponding experimental data on (T_s)_z, (T_f,av)_z and ¦¤P_z. The thickness of the conductive sub-layer ¦Ä_CSL [=(¦¤r)_out/2] and the non-dimensional thickness of the conductive sub-layer y⁺_CSL [=(f_F/2)^0.5¦Ñ_lu¦Ä_CSL/¦Ì_l] for the turbulent heat transfer on the circular tube with the twisted-tape insert are clarified based on the numerical solutions at the swirl velocity u_sw ranging from 5.39 to 18.03 m/s. The correlations of ¦Ä_CSL and y⁺_CSL for twisted-tape-induced swirl flow heat transfer in a vertical circular tube are derived.