Prediction of the minimum point of the pressure drop in a narrow rectangular channel under a transversely non-uniform heat flux

Kim, Taewoo,Song, Yong Jae,Al-Yahia, Omar S.,Jo, Daeseong Elsevier 2018 Annals of nuclear energy Vol.122 No.-

<P><B>Abstract</B></P> <P>It is necessary to accurately predict the minimum point of pressure drop to ensure the safety of nuclear reactors. However, the non-uniform heat flux distribution along the transverse direction is encountered when the plate-type nuclear fuels are used. This study shows the effect of a transversely non-uniform heat flux on the minimum point of the pressure drop. The pressure drop-flow rate curve under the non-uniform heat flux was obtained by the experiment, and the trend of curve was different with the one of uniform heat flux case. Under the non-uniform heat flux, even when the inlet mass flow rate decreased, the value of the pressure drop was constant for a while with the development of a two-phase flow. With further reduction of inlet mass flow rate, the pressure drop started to decrease until the minimum point of the pressure drop was reached. Moreover, the inlet mass flow rate at the minimum point of pressure drop is much lower than that in the uniform heat flux case. For a detail analysis, the numerical approach is proposed along with the application of multi-channel concept. A single narrow rectangular channel is divided along the transverse direction, and the heat flux is given non-uniformly to the divided channels. Although the pressure drop is separately calculated for each divided channel, the mass is transferred between the channels. In the calculation, the mass flow rate is non-uniformly distributed in the transverse direction. If the mass flow rate is uniformly distributed, the non-uniform heat flux causes an unbalanced pressure drop because of the non-uniform distribution of void fraction. As a result, at the edges where the void fraction is high, the mass flow rate is transferred to the middle of channel to balance the pressure drop in transverse direction. When the void fraction in the middle becomes significantly large, the minimum point of the pressure drop can be obtained.</P> <P><B>Highlights</B></P> <P> <UL> <LI> One-dimensional multi-channel approach is applied to predict the minimum point of pressure drop under non-uniform heating. </LI> <LI> The pressure drop-mass flow rate curves between uniform and non-uniform heating are different. </LI> <LI> In the single-phase flow, the pressure drop curve is the same for the uniform and non-uniform heat flux cases. </LI> <LI> In the experiment, the pressure drop is abruptly increased after the minimum pressure drop is reached. </LI> <LI> The predicted pressure drop curve is not matched well with the experiment after the minimum pressure drop. </LI> <LI> For a better prediction, the flow regime effect in narrow rectangular channels should be considered. </LI> </UL> </P>

수평 배관의 메탄 폭발특성에 있어서 불균일성 혼합기의 영향

한우섭,최이락,김형욱,임진호 한국화학공학회 2024 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.62 No.1

메탄, 프로판 등을 주성분으로 하는 연료가스는 폭발위험장소에서 사용될 수 있으며, 누출로 인한 공정조건의 영향으로 불균일한 혼합기를 형성할 수 있다. 균일한 혼합기를 대상으로 측정된 문헌 데이터를 이용한 화재 폭발 위험성평가, 손상 예측은 가스 누출에 의한 실제 폭발 사고와 다른 결과를 얻을 수 있다. 본 연구에서는 가스 누출시 나타날수 있는 농도 변화에 있어서 불균일성 혼합기의 폭발압력, 화염속도 등의 폭발특성을 조사하였다. 길이 0.82 m의 스테인리스 재질의 밀폐 배관에서 수행하였으며 컬러 초고속 카메라 및 압력 센서를 사용하여 관찰하였다. 또한 배관 내의시간에 따른 농도차이 변화에 대해 회귀분석 모델을 사용하여 불균일 혼합물의 정량화 방법을 제안하였다. 본 연구의농도 불균일성 조건에 있어서 메탄 폭발 시 전파화염은 불균일성 농도가 높아짐에 따라 화염 면적의 증가가 관찰되었고 이는 난류 화염의 주름진 화염 구조와 유사하였다. 메탄의 최대압력까지 걸리는 소요시간은 불균일성이 클수록 감소하였고, 폭발압력은 불균일성이 클수록 증가하였다. 농도가 불균일한 메탄의 KG(폭연지수)의 범위는 1.30~1.58 [MPa·m/s] 으로서 메탄의 농도가 균일성에서 불균일성로 변화하면서 17.7% 증가하였다. Fuel gases such as methane and propane are used in explosion hazardous area of domestic plants and can form non-uniform mixtures with the influence of process conditions due to leakage. The fire-explosion risk assessment using literature data measured under uniform mixtures, damage prediction can be obtained the different results from actual explosion accidents by gas leaks. An explosion characteristics such as explosion pressure and flame velocity of non-uniform gas mixtures with concentration change similar to that of facility leak were examined. The experiments were conducted in a closed 0.82 m long stainless steel duct with observation recorded by color high speed camera and piezo pressure sensor. Also we proposed the quantification method of non-uniform mixtures from a regression analysis model on the change of concentration difference with time in explosion duct. For the non-uniform condition of this study, the area of flame surface enlarged with increasing the concentration non-uniform in the flame propagation of methane and was similar to the wrinkled flame structure existing in a turbulent flame. The time to peak pressure of methane decreased as the non-uniform increased and the explosion pressure increased with increasing the non-uniform. The ranges of KG (Deflagration index) of methane with the concentration non-uniform were 1.30 to 1.58 [MPa·m/s] and the increase rate of KG was 17.7% in methane with changing from uniform to non-uniform.

A Improved Scene based Non-uniformity Correction Algorithm for Infrared Camera

Ho-Jin Hyun(현호진),Byung-In Choi(최병인) 한국컴퓨터정보학회 2018 韓國컴퓨터情報學會論文誌 Vol.23 No.1

In this paper, we propose an efficient scene based non-uniformity correction algorithm which performs the offset correction using the uniform obtained from input scenes for Infrared camera. In general, pixel outputs of a infrared detector can not be uniform. Therefore, the non-uniformity correction procedure need to be performed to make the image outputs uniform. A typical non-uniformity correction method uses a black body at the laboratory to obtain the output of the infrared detector’s pixels for two temperatures, HOT and COLD, and calculates the non-uniformity correction parameters. However, output characteristics of the Infrared detector changes while the Infrared camera is operated, the fixed pattern noise of the Infrared detector and dead pixels are generated. To remove the noise, the offset correction is generally performed. The offset correction procedure usually need the additional device such as a thermo-electric cooler, shutter, or non-uniformity correction lens. Therefore, we introduce a general scene based non-uniformity correction technique without additional equipment, and then we propose an improved non-uniformity correction algorithm based on image to solve the problem of the existing technique.

Experimental study on the Onset of Nucleate Boiling in a narrow rectangular channel under transversely non-uniform and uniform heating

Kim, Taewoo,Al-Yahia, Omar S.,Jo, Daeseong Elsevier 2018 Experimental thermal and fluid science Vol.99 No.-

<P><B>Abstract</B></P> <P>Onset of Nucleate Boiling (ONB) in a narrow rectangular channel was experimentally studied under transversely non-uniform and uniform heating conditions. The experiment was performed under various mass fluxes and inlet subcooling conditions. The behavior of the bubbles was recorded using a high-speed camera, and was analyzed using an image processing technique. In the case of uniform heat flux, the wall temperature was uniformly distributed in the transverse direction. In the case of non-uniform heat flux, the wall temperature had the lowest value in the middle of the heated surface, and increased along the transverse direction toward the edges. At the same mass flux and inlet subcooling temperature, the thermal power at the ONB under non-uniform heat flux was lower than that under uniform heat flux. However, the local heat flux and wall temperature at the ONB were similar at both heating conditions. In the subcooled boiling region, it was found that the boiling heat transfer under non-uniform heat flux was lower than that under uniform heat flux. Additionally, the slope of the wall temperature-thermal power curve after the ONB was higher in the non-uniform heat flux case. Using the results elicited from image processing, the evaporation and quenching heat transfers were evaluated to analyze the differences in boiling heat transfers. The boiling heat transfer was less affected by evaporation and quenching in the case of non-uniform heat flux.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Experimental study on ONB in a narrow rectangular channel under transverse non-uniform heating. </LI> <LI> For uniform heating, wall temperature is uniformly distributed in transverse direction. </LI> <LI> For non-uniform heating, wall temperature increases along transverse direction toward the edges. </LI> <LI> For both heating conditions, local heat flux and wall temperature at ONB are similar. </LI> <LI> Evaporation and quenching heat transfers in non-uniform heating are approximately twice lower than in under uniform heating. </LI> </UL> </P>

New Non-uniformity Correction Approach for Infrared Focal Plane Arrays Imaging

Qu Hui-Ming,Gong Jing-tan,Huang Yuan,Chen Qian 한국광학회 2013 Current Optics and Photonics Vol.17 No.2

Although infrared focal plane array (IRFPA) detectors have been commonly used, non-uniformity correction (NUC) remains an important problem in the infrared imaging realm. Non-uniformity severely degrades image quality and affects radiometric accuracy in infrared imaging applications. Residual non-uniformity (RNU) significantly affects the detection range of infrared surveillance and reconnaissance systems. More effort should be exerted to improve IRFPA uniformity. A novel NUC method that considers the surrounding temperature variation compensation is proposed based on the binary nonlinear non-uniformity theory model. The implementing procedure is described in detail. This approach simultaneously corrects response nonlinearity and compensates for the influence of surrounding temperature shift. Both qualitative evaluation and quantitative test comparison are performed among several correction technologies. The experimental result shows that the residual non-uniformity, which is corrected by the proposed method,is steady at approximately 0.02 percentage points within the target temperature range of 283 K to 373K. Real-time imaging shows that the proposed method improves image quality better than traditional techniques.

Experimental analysis about the magnitude of the shaft frequency growth near stall in the axial compressor

임형수,Young-Cheon Lim,강신형,송성진,양수석 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.5

The experimental study investigates the cause of prestall, which the magnitude increases of the shaft frequency near stall. This prestall phenomenon is related to the geometric non-uniformity of the axial compressor, which can be classified into blade non-uniformity and casing non-uniformity. The instant static pressure was decomposed into several signal components to investigate this phenomenon. To verify the blade non-uniformity, the dimensionless revolution aperiodic component (Ψ) distribution, which was measured at one arbitrary circumferential location, was analyzed, and to verify the casing non-uniformity, the amplitude of Ψ was analyzed at 8 equally spaced circumferential locations of the first stage. The measurements showed that the blade non-uniformity directly caused the increase of the magnitude of the shaft frequency near stall but that the casing non-uniformity induced the increase of the magnitude of the shaft frequency in the Seoul National University compressor.

Modeling of flow uniformity by installing inlet distributor within the inflow part of a pressurized module using computational fluid dynamics

Changkyoo Choi,Chulmin Lee,In S. Kim 대한환경공학회 2020 Environmental Engineering Research Vol.25 No.6

Uniform flow distribution is a significant parameter for designing pressurized membrane modules because non-uniform flow distribution can cause serious local flux and fouling problems within a module. Thus, this study investigated the fluid behavior with regards to the evenness of water distribution using newly designed inlet distributors in the inflow part of a pressurized membrane module. From the results of velocity and pressure at the cross-sectional and outlet planes, we confirmed that a conventional membrane module with no distributor (non-distributor) had fluid that was concentrated at the central part. Case 1, which had a cross-shaped distributor, reduced the central concentration tendency, and Case 2, which had a round-shaped distributor, displayed a relatively uniform flow based on the velocity, pressure, flux, and standard deviation data. Here, the non-uniformity coefficient (N) and energy utilization (η) for Cases 1 and 2 showed a lower non-uniformity coefficient (0.030 and 0.017, respectively) than for the Non-distributor (0.039). The energy utilization of Cases 1 and 2 were higher (1.35e-0.5 and 1.46e-05) than the Non-distributor (1.64e-05). Overall, we confirmed that the inlet distributors led to increased evenness of flow distribution within an inflow part.

Anisotropic, non-uniform misfit strain in a thin film bonded on a plate substrate

Huang, Y.,Ngo, D.,Feng, X.,Rosakis, A.J. Techno-Press 2008 Interaction and multiscale mechanics Vol.1 No.1

Current methodologies used for the inference of thin film stresses through curvature measurements are strictly restricted to stress and curvature states which are assumed to remain uniform over the entire film/substrate system. These methodologies have recently been extended to non-uniform stress and curvature states for the thin film subject to non-uniform, isotropic misfit strains. In this paper we study the same thin film/substrate system but subject to non-uniform, anisotropic misfit strains. The film stresses and system curvatures are both obtained in terms of the non-uniform, anisotropic misfit strains. For arbitrarily non-uniform, anisotropic misfit strains, it is shown that a direct relation between film stresses and system curvatures cannot be established. However, such a relation exists for uniform or linear anisotropic misfit strains, or for the average film stresses and average system curvatures when the anisotropic misfit strains are arbitrarily non-uniform.

A Non-uniform Correction Algorithm Based on Scene Nonlinear Filtering Residual Estimation

Hongfei Song,Kehang Zhang,Wen Tan,Fei Guo,Xinren Zhang,Wenxiao Cao 한국광학회 2023 Current Optics and Photonics Vol.7 No.4

Due to the technological limitations of infrared thermography, infrared focal plane array (IFPA) imaging exhibits stripe non-uniformity, which is typically fixed pattern noise that changes over time and temperature on top of existing non-uniformities. This paper proposes a stripe non-uniformity correction algorithm based on scene-adaptive nonlinear filtering. The algorithm first uses a nonlinear filter to remove single-column non-uniformities and calculates the actual residual with respect to the original image. Then, the current residual is obtained by using the predicted residual from the previous frame and the actual residual. Finally, we adaptively calculate the gain and bias coefficients according to global motion parameters to reduce artifacts. Experimental results show that the proposed algorithm protects image edges to a certain extent, converges fast, has high quality, and effectively removes column stripes and non-uniform random noise compared to other adaptive correction algorithms.

Flow Instability (FI) for subcooled flow boiling through a narrow rectangular channel under transversely uniform and non-uniform heat flux

Al-Yahia, Omar S.,Kim, Taewoo,Jo, Daeseong Elsevier 2018 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.125 No.-

<P><B>Abstract</B></P> <P>Transversely non-uniform heating enforces high local heat fluxes at a few areas on the heated surface and low local heat fluxes at others. Differences in the heat flux distribution may generate differences in the boiling behavior when compared with that under uniform heating. Thus, the present experiments investigate the influence of transverse heat flux distribution on the flow instability through a narrow rectangular channel (2.35 mm × 54.0 mm × 566 mm). A wide range of experimental operation conditions, such as inlet temperatures (35–65 °C), thermal power (500–6250 W), and mass flow rates (0.03–0.13 kg/s), are applied to the upward flow channel. The working fluid corresponds to demineralized water under atmospheric pressure. The channel is heated from a side, and the other side is a transparent polycarbonate window from which the bubble behavior is visualized by using a high-speed camera. The heating surface is composed of aluminum with a width of 50 mm and a length of 300 mm. The experiments are performed by using two different procedures to achieve the flow instability, namely (1) constant mass flow rate with power increases and (2) constant power with mass flow rate decreases. The results show that the flow instability occurs at similar thermal power and similar mass flow rates for both uniform and non-uniform heating conditions. However, the pressure drop and wall temperature curves exhibit differences in the trends between the two heating conditions, especially after the fluctuation in the inlet pressure. In the uniform case, bubbles are generated uniformly on the whole transverse direction of the heated surface. In the non-uniform case, more bubbles are generated at the higher local heat flux, which disturbs the velocity profile in the transverse direction. The differences in bubble generation in the transverse direction leads to differences in the flow instability in a narrow rectangular channel.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Heat flux distribution has no effect under single-phase flow. </LI> <LI> Heat flux distribution has a high influence on the first bubble generation. </LI> <LI> Pressure drop trend is different between uniformly and non-uniformly heating conditions. </LI> <LI> Inlet pressure fluctuates after significant bubble generation. </LI> <LI> Void fraction oscillation is affected by the heat flux distribution. </LI> </UL> </P>