Investigation on effect of surface properties on droplet impact cooling of cladding surfaces

Wang, Zefeng,Qu, Wenhai,Xiong, Jinbiao,Zhong, Mingjun,Yang, Yanhua Korean Nuclear Society 2020 Nuclear Engineering and Technology Vol.52 No.3

During transients or accidents, the reactor core is uncovered, and droplets entrained above the quench front collides with the uncovered fuel rod surface. Droplet impact cooling can reduce the peak cladding temperature. Besides zirconium-based cladding, versatile accidental tolerant fuel (ATF) claddings, including FeCrAl, have been proposed to increase the accident coping time. In order to investigate the effect of surface properties on droplet impact cooling of cladding surfaces, the droplet impact phenomena are photographed on the FeCrAl and zircaloy-4 (Zr-4) surfaces under different conditions. On the oxidized FeCrAl surface, the Leidenfrost phenomenon is not observed even when the surface temperature is as high as 550 ℃ with We > 30. Comparison of the impact behaviors observed on different materials shows that nucleate and transition boiling is more intensive on surfaces with larger thermal conductivity. The Leidenfrost point temperature (LPT) decreases with the solid thermal effusivity (${\sqrt{k{\rho}C_p}}$). However, the CHF temperature is relatively insensitive to the surface oxidation and Weber number. Droplet spreading diameter is analyzed quantitatively in the film boiling stage. Based on the energy balance a correlation is proposed for droplet maximum spreading factor. A mechanistic model is also developed for the LPT based on homogeneous nucleation theory.

Positive Observer Design for Positive Markovian Jump Systems with Mode–dependent Time–varying Delays and Incomplete Transition Rates

Jiyang Wang,Wenhai Qi,Xianwen Gao,Yonggui Kao 제어·로봇·시스템학회 2017 International Journal of Control, Automation, and Vol.15 No.2

The paper is concerned with positive observer design for positive Markovian jump systems with incompletetransition rates and time delays that are mode-dependent and time-varying. Firstly, by applying an appropriateco-positive type Lyapunov-Krasovskii function and free-connection weighting vectors, sufficient conditions areproposed to ensure stochastic stability of the error positive system and existence of the positive observer. All theproposed conditions are derived in linear programming. Finally, an example is given to demonstrate the validity ofthe main results.

Experimental investigation on flow field around a flapping plate with single degree of freedom

Hanyu Wang,Chuan Lu,Wenhai Qu,Jinbiao Xiong Korean Nuclear Society 2023 Nuclear Engineering and Technology Vol.55 No.6

Undesirable flapping motion of discs can cause the failure of swing check valves in nuclear passive safety systems. Time-resolved particle image velocimetry (PIV) was employed to investigate the flow characteristics around a free-to-rotate plate and the motion response, with the Reynolds numbers, based on the hydraulic diameter of the channel, from 1.32 × 10⁴ to 3.95 × 10⁴. Appreciable flapping motion (±3.52°) appeared at the Reynolds number of 2.6 × 10⁴ with the frequency of 5.08 Hz. In the low-Reynolds-number case, the plate showed negligible flapping. In the high-Reynolds-number case, the deflection angle increased with reduced flapping amplitude. The torque from the fluid determined the flapping amplitude. In the low-Reynolds-number case, Karman vortices were absent. With increasing Reynolds numbers, Karman vortices developed behind the plate with larger deflection angles. Strong interaction between the wake flow from the leading and trailing edge of the plate was observed. Based on power spectrum density (PSD) analysis, the vortex shedding frequency coincided with the flapping frequency, and the amplitude was positively correlated to the strength of the vortices. Proper orthogonal decomposition (POD) modes evince that, in the case of appreciable motion, coherent structures exhibited a larger spatial scale, enhancing the magnitude of the external torque on the plate.

An In Vitro Biomechanical Analysis of Contralateral Sacroiliac Joint Motion Following Unilateral Sacroiliac Stabilization with and without Lumbosacral Fixation

Cho Woojin,Wang Wenhai,Lim Hyun Jin,Bucklen Brandon S. 대한척추외과학회 2023 Asian Spine Journal Vol.17 No.1

Study Design: Cadaveric biomechanics study.Purpose: This study investigated the effects of unilateral sacroiliac joint (SIJ) fixation for fusion with/without L5–S1 fixation on contralateral SIJ range of motion (ROM).Overview of Literature: SIJ fusion raises concerns that unilateral SIJ stabilization for fusion may increase contralateral SIJ mobility, leading to accelerated SIJ degeneration. Also, prior lumbosacral fixation may lead to accelerated SIJ degeneration, due to adjacent level effects. SIJ fixation biomechanics have been evaluated, showing a reduced-ROM, but SIJ fixation effects on contralateral nonfixated SIJ remain unknown.Methods: Seven human lumbopelvic spines were used, each affixed to six-degrees-of-freedom testing apparatus; 8.5-Nm pure unconstrained bending moments applied in flexion-extension, lateral bending, and axial rotation. The ROM of left and right SIJ was measured using a motion analysis system. Each specimen tested as (1) intact, (2) injury (left), (3) L5–S1 fixation, (4) unilateral stabilization (left), (5) unilateral stabilization+L5–S1 fixation, (6) bilateral stabilization, and (7) bilateral stabilization+L5–S1 fixation. Both left-sided iliosacral and posterior ligaments were cut for injury condition to model SIJ instability before surgery.Results: There were no statistical differences between fixated and contralateral nonfixated SIJ ROM following unilateral stabilization with/without L5–S1 fixation for all loading directions (<i>p</i>>0.930). Injured condition and L5–S1 fixation provided the largest motion increases across both joints; no significant differences were recorded between SIJs in any loading direction (<i>p</i>>0.850). Unilateral and bilateral stabilization with/without L5–S1 fixation reduced ROM compared with the injured condition for both SIJs, with bilateral stabilization providing maximum stability.Conclusions: In the cadaveric model, unilateral SIJ stabilization with/without lumbosacral fixation did not lead to significant contralateral SIJ hypermobility; long-term changes and <i>in vivo</i> response may differ.

Effect of Cu2O Content in Electrodeposited CuOx Film on Perovskite Solar Cells

Xu Miao,Shuo Wang,Wenhai Sun,Yu Zhu,Chen Du,Ruixin Ma,Chengyan Wang 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2019 NANO Vol.14 No.10

It is well known that the different proportions of CuO and Cu2O in CuOx hole transfer materials have a great influence on the hole transport property as well as the device performances of perovskite solar cells (PSCs). In this paper, we changed the content of Cu2O in the film by controlling the deposition voltage during electrodeposition, and the effects of different contents of Cu2O in the films on the device were investigated for the first time. It was found that the content of Cu2O in the film reached the highest point with the deposition voltage 0.5 V, such films have the highest transmittance and carrier mobility. After assembling the device, the power conversion efficiency (PCE) of the champion device reached 13.48% under a one-sun AM 1.5G (100 mW/cm2) illumination. Furthermore, the unpackaged device based on CuOx still retained over 75% PCE after being placed in the ambient condition (30–40% humidity, 20–30 ℃) for 500 h.

Evaluation and decision of products conceptual design schemes based on customer requirements

Hong-Zhong Huang,Yanfeng Li,Wenhai Liu,Yu Liu,Zhonglai Wang 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.9

Within the competitive market environment, understanding customer requirements is crucial for all corporations to obtain market share and survive competition. Only the products exactly meeting customer requirements can win in the market place. Therefore, customer requirements play a very important role in the evaluation and decision process of conceptual design schemes of products. In this paper, an evaluation and decision method based on customer requirements is presented. It utilizes the importance of customer requirements, the satisfaction degree of each evaluation metric to the specification, and an evaluation metric which models customer requirements to evaluate the satisfaction degree of each design scheme to specific customer requirements via the proposed BP neural networks. In the evaluation and decision process, fuzzy sets are used to describe the importance of customer requirements, the relationship between customer requirements and evaluation metrics, the satisfaction degree of each scheme to customer requirements, and the crisp set is used to describe the satisfaction degree of each metric to specifications. The effectiveness of the proposed method is demonstrated by an example of front suspension fork design of mountain bikes.