The burning rate’s effect on the flame length of weak fire whirls

This paper discusses why the visibly-determined flame length of a weak fire whirl increases as compared with the corresponding pool fire without spin. Here, a fire whirl is called weak when the pure aerodynamic effect of flow circulation has a negligible influence on the flame length. Split cylinders were used to apply a flow circulation to a 3-cm-diameter methane burner flame and a 3-cm-diameter ethanol pool fire. After applying the flow circulation, the flame length of the ethanol pool fire increased about three times, while little change was observed in the flame length of the methane burner flame. The difference is explained by the fact that the burning rate of the methane burner flame was fixed constant, whereas that of the ethanol pool fire increased due to the increased heat input to the fuel surface caused by a change in flame shape pushed toward the fuel surface. The experimental observations thus demonstrate that the burning-rate effect can significantly increase the flame length even under a weak circulation condition. Computational fluid dynamics (CFD) simulations were conducted to understand the detailed flow structure of a fire whirl. An analytical model was then developed based on the experimental observations and CFD calculations; the predicted relationship between the flame height and the burning rate agreed with experimental data.     

SGSN Pool技术及部署策略研究

在对SGSN Pool技术的关键概念、业务流程以及组网方式进行研究的基础上,对SGSN Pool技术的优劣势进行了分析,并归纳出核心网分组域中部署SGSN Pool技术的策略。     

基于MSC Pool内负荷的动态反馈控制

本文针对MSC Pool中出现的负荷不均衡现象,提出了一种简单的基于负荷的动态反馈控制技术。仿真结果及相关分析显示此种反馈技术在理论和实际应用中均可行。     

MSC Pool组网对性能统计的新要求

由于MSC Pool组网与传统组网特性功能不同,需要很多的新统计指标来反映和衡量。本文从全局性能统计与实时负荷性能统计两方面来介绍新的性能统计指标及其必要性。     

SGSN Pool相关技术探讨及组网规划

简要介绍了SGSN Pool的技术原理,对目前SGSN Pool实现的前提条件、关键技术、重点难点分别进行了分析和阐述。讨论了SGSN Pool组网的要点和原则,并给出了SGSN Pool组网规划的相关建议。     

Bubble nucleation characteristics in pool boiling of a wetting liquid on smooth and rough surfaces

Quantitative measurements are obtained from high-speed visualizations of pool boiling at atmospheric pressure from smooth and roughened surfaces, using a perfluorinated hydrocarbon (FC-77) as the working fluid. The boiling surfaces are fabricated from aluminum and prepared by mechanical polishing in the case of the smooth surface, and by electrical discharge machining (EDM) in the case of the roughened surface. The roughness values (R_a) are 0.03 and 5.89 μm for the polished and roughened surfaces, respectively. The bubble diameter at departure, bubble departure frequency, active nucleation site density, and bubble terminal velocity are measured from the monochrome movies, which have been recorded at 8000 frames per second with a digital CCD camera and magnifying lens. Results are compared to predictions from existing models of bubble nucleation behavior in the literature. Wall superheat, heat flux, and heat transfer coefficient are also reported.     

Visualization of pool boiling on enhanced surfaces

This work reports experiments to visualize nucleate boiling on an enhanced tubular surface having sub-surface tunnels and surface pores. The finned copper tube had 1575 fins/m (40 fins/in.) and 0.8 mm fin height. The fins are covered by a thin foil sheet having 0.23 mm pores at 1.5 mm pore pitch along each interfin region. Data are provided for two foil cover sheets, one copper and the other a transparent plastic. The uniqueness of this work is that the visualization method allowed direct observation of the boiling process in the subsurface tunnels. Use of a high speed camera with 30 × magnification allowed detailed observation of the evaporation process in the tunnels and of the vapor bubbles emerging from the pores. The experiments were conducted for saturated and subcooled boiling in the horizontal and vertical orientations. For the vertical tube, the saturated boiling experiments showed that all of the tunnels were vapor filled except for liquid menisci in the corners. This was also true for the horizontal tube at high heat flux. For the horizontal tube at low heat flux, portions of the tunnel length was liquid filled. A large portion (70–90%) of the region was vapor filled except for liquid menisci in the corners, and the remaining part of the region had oscillating menisci. These experiments provide conclusive proof that the heat transfer mechanism in the subsurface tunnels is evaporation on the menisci in the corners.     

Bubble growth in saturated pool boiling in water and surfactant solution

The presence of surfactant additives in water was found to enhance the boiling heat transfer significantly. The objective of the present investigation is to compare the bubble growth in water to that of a surfactant solution with negligible environmental impact. The study was conducted at two values of heat fluxes to clarify the effect of the heat flux on the dynamics of bubble nucleation. The bubble growth under condition of pool boiling in water and non-ionic surfactant solution was studied using high speed video technique. The bubble generation was studied on a horizontal flat surface; and the natural roughness of the surface was used to produce the bubbles.