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Copyright of Atomic Energy Science & Technology is the property of Editorial Board of Atomic Energy Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Atomic Energy Science & Technology is the property of Editorial Board of Atomic Energy Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Irrigation & Drainage is the property of Journal of Irrigation & Drainage Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A ship is affected by the transient ocean motion during navigation, and the two-phase flow is often in a transient motion state. The two-phase flow pattern may be different from the land-based conditions, which may affect the flow and heat transfer characteristics. Therefore, it is significant to accurately distinguish the two-phase flow pattern under transient motion conditions for the calculation of two-phase resistance and heat transfer. In this paper, by using a separated flow model, the momentum equations for the liquid film and gas core of annular flow were listed separately. Meanwhile, based on introducing the transient external force field generated by the motion under two typical ocean motion conditions of rolling and heaving and considering the effects of buoyancy and additional inertial forces, a transition criterion which was suitable for churn flow to annular flow under transient motion conditions was also proposed. This criterion can also be applied to vertical upward and inclined flows. The calculation results of the transition criterion model were verified through experimental data under static and transient motion conditions, and there is good agreement with the experimental results. The results show that when the superficial liquid velocity is less than 0.35 m/s, the transition curve approximates a vertical curve, while the superficial liquid velocity is larger than 0.35 m/s, the thickness of the liquid film increases, and the axial motion of the liquid phase plays a major role in the flow pattern transformation. Similarly, by comparing the calculation results of the transition from churn flow to annular flow under different motion conditions with experimental data, it can be found that within the existing parameter range, the additional force introduced by rolling motion has little effect on the continuous gas phase at the center of the channel. Therefore, although the thickness distribution of the liquid film on the wall is uneven due to the influence of rolling motion, the annular flow structure will not be damaged, and the transition curve between churn flow and annular flow is basically consistent with the vertical upward direction. Moreover, with the increase of the heaving amplitude and the decrease of the heaving period, the transition boundary curve of the churn flow towards the annular flow shifts to the right. This is because the additional acceleration introduced by the heaving increases, and the liquid film is subjected to instantaneous volume force in the vertical direction and oscillates periodically, making it easier to fall. Therefore, a larger gas phase apparent velocity is required to maintain a stable annular flow, so the transition boundary shifts to the right. By analyzing the transition criteria, a churn flow to annular flow transition curve is given, and the influence of motion parameters on the transition boundary is obtained.

Helically coiled tube (HCT) is widely used in nuclear engineering and other fields due to its effective compactness, excellent structure robustness, heat transfer efficiency and flow stability. As one of the most important gasliquid twophase flow patterns in HCT, the characteristic of annular flow has a great influence on the heat transfer performance of helical oncethrough steam generator. Especially, the circumferential distribution of liquid film thickness in annular flow directly determines the dryout onset location. Although the liquid film flow in straight tubes has been extensively studied, due to the limitation of measurement technology, the precise measurement data of liquid film thickness in HCT are still very rare. In this paper, based on the selfdeveloped noninvasive contact ringisland array sensor (RIAS), airwater twophase flow experiments were carried out to study the threedimensional spatialtemporal distribution of liquid film thickness in vertical HCT with different structures. According to the results, four typical liquid film flow regimes were defined based on the circumferential position of the thicker liquid film appearing in the tube wall. That is, the bottom distribution (BD) dominated by gravity force, the outside distribution (OD) dominated by liquid centrifugal force, the inside distribution (ID) dominated by gas centrifugal force and the insideoutside distribution (IOD) dominated by secondary flow. The effects of coil diameter and coil pitch of HCT as well as gas and liquid velocities on the distribution of liquid film flow regimes were detailed analyzed. It is implied that the coil diameter determines the intensity of centrifugal force and secondary flow. Generally, the smaller the coil diameter, the easier the circumferential distribution forms of OD, ID and IOD are to appear. Also, increasing the coil pitch weakens the effect of centrifugal force on the liquid film. Then a small coil pitch normally results in the circumferential distribution form of OD while it is ID for large coil pitch. It is also found that the IOD occurs only when both gas and liquid velocities are large enough. By taking the influence of HCT geometry and fluid parameters into account, a general submap of liquid film flow in HCT was proposed using the modified Dean number De* and the modified LockhartMartinelli parameter X*. The transition criteria between different liquid film flow regimes were also established and verified with experimental data in present work and previous references. From this work, the mechanism of curvatureinduced centrifugal force and secondary flow on the spatiotemporal evolution of liquid film in HCT is revealed.

The void fraction and interfacial area concentration are important phase interfacial parameters in two-phase flow. Accurate acquisition of void fraction and interfacial area concentration under churn flow and annular flow in a narrow rectangular channel is the key to construct and improve the two-fluid model. In this paper, a visualization experiment was conducted to study the flow characteristics of gas-liquid two-phase flow in a narrow rectangular channel with a cross-section of 65 mm×2 mm. The range of gas-phase superficial velocity is 1.9 m/s and liquid-phase superficial velocity is 0.1-1.5 m/s. Flow pattern includes churn flow and annular flow. Based on the idea of gas-phase splitting calculation, an analytical calculation method to obtain the void fraction and interfacial area concentration under the churn flow and annular flow was proposed using high-speed camera. And the calculation method for the local parameters in the direction of the wide edge of the narrow rectangular channel was also proposed. For the two-phase flow video under each experimental condition, picture extraction and data processing were performed at 0.1 s time interval, and the duration of data processing is 60 s for each condition. The relative deviation between the calculated void fraction of the empirical formular and experiment value in the narrow channel is within 10%. The correlation coefficient K between interfacial area concentration and void fraction was proposed. As the void fraction increases, the value of K gradually converges to 1 from greater than 1. This result is consistent with the theoretical analysis and verifies the rationality of interfacial area concentration calculation method. To verify the accuracy of the local parameter calculation method, the experimental images were divided into 10 equal parts along the broad side of the narrow rectangular channel. The relative deviation between the average values of the local void fraction and interfacial area concentration and the results calculated without partitioning is within 5%. The calculation method can be helpful for the study of phase interfacial parameters in narrow rectangular channels under complex flow patterns.