A study on the flow induced vibration in two phase flow under heating and non-heating conditions

Critical heat flux (CHF) enhancement devices, like a spacer grid with mixing vane, cause flow-induced vibration (FIV) due to turbulence made by structural resistance. CHF enhancement and FIV reduction are usually studied separately. The main purpose of this article is to investigate the relationship between CHF and FIV. Information of flow-induced vibration due to wire coil design, is experimentally presented in this study by detecting flow-induced vibration under the two-phase flow condition with wire coil inserts. CHF experiments were performed in an upward vertical annulus tube under controlled vibration conditions to determine the effect of vibration on CHF. FIV was measured in an upward vertical tube with various wire coil inserts using air-water as flow material. CHF experiments were performed at one atmosphere with mechanically controlled vibration. A quartz tube (inner diameter of 17 mm, thickness of 2mm and length of 0.72 m) was used for outer tube and a SUS-304 tube (outer diameter of 6.35 mm, thickness of 0.89 mm and length of 0.7 m) was used for the inner heater. Vibration of the heater tube with an amplitude range of 0.1 mm to 0.5 mm and a frequency range of 10 Hz to 50 Hz was carried out at a mass flux of 115 kg/m²s and 215 kg/m²s. CHF was enhanced by vibration with a maximum ratio of 16.4 %. CHF was increased with increased amplitude and quality. The CHF correlation was developed with R (coefficient of correlation) of 0.903. FIV measuring experiments were performed at one atmosphere by changing the inserted wire coil type. An acrylic tube was used for the test section with inner diameter of 25 mm, thickness of 10 mm and length of 0.5 m. Four types of wire coil, which have a thickness of between 2 mm and 3 mm and pitch length of between 25 mm and 50 mm, were used. FIV and dynamic pressure were detected in water mass flux range of 100 ∼ 3060 kg/m²s and air mass flux range of 5.02 ∼ 60.3 kg/m²s. Vibration increased along with mass flux and quality. Insertion of the wire coil increased the vibration. Increased vibration was also seen by increasing water mass flux. Decreasing pitch length produced more flow-induced vibration. The FIV correlation was developed with R of 0.956. FIV was accurately predicted under two-phase flow condition with wire coil inserts. CHF enhancement ratios were compared by wire coil insertion and by vibration. The wire coil produced FIV that increased CHF. Contribution of vibration on CHF enhancement was less than 1 % of CHF enhancement by turbulence and swirl produced by the wire coil. Vibration for CHF enhancement caused amplitude increasing that induces fuel damage by friction. It is concluded that CHF enhancement by wire coil must consider the level of increased vibration and pressure drop. Designs need to reduce them. CHF enhancement ratio was compared with flow-induced vibration and pressure drop by calculation. The wire coil with pitch length of 70 mm, showed the best performance at the mass flux condition of 3000 kg/m²s. This paper investigated the effect of vibration on CHF enhancement, suggested predicting correlation of FIV under two-phase flow condition with wire coil inserts for wire coil design for CHF enhancement