{"title":"Effects of confined distance near floor and wire size on electrical wire flame spread behaviors based on heat transfer","authors":"Xinjie Huang , Meng Zhang , Hailong Ding , Peng Xu , Xinyi Zhang , Xinyi Li , Miaomiao Wang , Pengyuan Zhang","doi":"10.1016/j.ijthermalsci.2024.109173","DOIUrl":null,"url":null,"abstract":"<div><p>This paper aims to investigate the confined distance near the floor(0∼28 mm) and wire size (the ratios of copper core diameter to entire wire diameter are: 6mm/8 mm,6mm/10 mm,8mm/12 mm and 6mm/12 mm for type Ⅰ, type Ⅱ, type Ⅲ and type Ⅳ, respectively) on the flame spread over polyethylene (PE) wires. It is indicated that, when the confined distance is relatively small, the extinction occurs for all types.The typical parameters of flame shape including of flame width, flame height and flame area, flame spread rate and mass loss rate with the increase of confined distance s can be separated into continuous growth stage and stable fluctuation stage. At the continuous growth stage, the flame area shows an exponential relationship with s as: <span><math><mrow><mi>A</mi><mo>∼</mo><msup><mi>s</mi><mfrac><mn>5</mn><mn>2</mn></mfrac></msup></mrow></math></span>. And at the stable fluctuation stage, the flame width is larger than that at the unconfined condition accounting for a large portion.While, the flame height is always smaller than that in the unconfined case.In order to explicitly describe the heat transfer, the upward large main flame and downward small flame are firstly introduced in this paper. Correspondingly, the heat flux feedback of components to the preheating zone is established with the upward main flame flux <span><math><mrow><msubsup><mover><mi>q</mi><mo>˙</mo></mover><mrow><mi>f</mi><mrow><mo>(</mo><mrow><mi>u</mi><mi>p</mi></mrow><mo>)</mo></mrow></mrow><mo>″</mo></msubsup></mrow></math></span> [includes of <span><math><mrow><msubsup><mover><mi>q</mi><mo>˙</mo></mover><mrow><mi>v</mi><mi>f</mi><mrow><mo>(</mo><mrow><mi>u</mi><mi>p</mi></mrow><mo>)</mo></mrow></mrow><mo>″</mo></msubsup><mo>+</mo><msubsup><mover><mi>q</mi><mo>˙</mo></mover><mrow><mi>r</mi><mi>f</mi><mrow><mo>(</mo><mrow><mi>u</mi><mi>p</mi></mrow><mo>)</mo></mrow></mrow><mo>″</mo></msubsup></mrow></math></span>], the downward small flame heat flux <span><math><mrow><msubsup><mover><mi>q</mi><mo>˙</mo></mover><mrow><mi>f</mi><mrow><mo>(</mo><mrow><mi>d</mi><mi>o</mi><mi>w</mi><mi>n</mi></mrow><mo>)</mo></mrow></mrow><mo>″</mo></msubsup></mrow></math></span> [ includes of <span><math><mrow><msubsup><mover><mi>q</mi><mo>˙</mo></mover><mrow><mi>v</mi><mi>f</mi><mrow><mo>(</mo><mrow><mi>d</mi><mi>o</mi><mi>w</mi><mi>n</mi></mrow><mo>)</mo></mrow></mrow><mo>″</mo></msubsup><mo>+</mo><msubsup><mover><mi>q</mi><mo>˙</mo></mover><mrow><mi>r</mi><mi>f</mi><mrow><mo>(</mo><mrow><mi>d</mi><mi>o</mi><mi>w</mi><mi>n</mi></mrow><mo>)</mo></mrow></mrow><mo>″</mo></msubsup></mrow></math></span>], the conductive heat flux <span><math><mrow><msubsup><mover><mi>q</mi><mo>˙</mo></mover><mi>c</mi><mo>″</mo></msubsup></mrow></math></span> and the gypsum board heat flux <span><math><mrow><msubsup><mover><mi>q</mi><mo>˙</mo></mover><mi>g</mi><mo>″</mo></msubsup></mrow></math></span>. With the increase of s, <span><math><mrow><msubsup><mover><mi>q</mi><mo>˙</mo></mover><mrow><mi>f</mi><mrow><mo>(</mo><mrow><mi>d</mi><mi>o</mi><mi>w</mi><mi>n</mi></mrow><mo>)</mo></mrow></mrow><mo>″</mo></msubsup></mrow></math></span> shows an increasing and then decreasing trend, making it take a second role during heat flux feedback. Meanwhile, the analysis demonstrates that for the larger copper core (type Ⅲ) and the smaller of PE thickness (type Ⅰ), the ratio of heat flux of <span><math><mrow><mfrac><msubsup><mover><mi>q</mi><mo>˙</mo></mover><mrow><mi>f</mi><mrow><mo>(</mo><mrow><mi>d</mi><mi>o</mi><mi>w</mi><mi>n</mi></mrow><mo>)</mo></mrow></mrow><mo>″</mo></msubsup><mrow><msubsup><mover><mi>q</mi><mo>˙</mo></mover><mrow><mi>f</mi><mrow><mo>(</mo><mrow><mi>u</mi><mi>p</mi></mrow><mo>)</mo></mrow></mrow><mo>″</mo></msubsup><mo>+</mo><msubsup><mover><mi>q</mi><mo>˙</mo></mover><mrow><mi>f</mi><mrow><mo>(</mo><mrow><mi>d</mi><mi>o</mi><mi>w</mi><mi>n</mi></mrow><mo>)</mo></mrow></mrow><mo>″</mo></msubsup></mrow></mfrac></mrow></math></span> will be increased, which will enhance the heat transfer effect of downward small flame.</p></div>","PeriodicalId":341,"journal":{"name":"International Journal of Thermal Sciences","volume":null,"pages":null},"PeriodicalIF":4.9000,"publicationDate":"2024-05-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"International Journal of Thermal Sciences","FirstCategoryId":"5","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S1290072924002953","RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"ENGINEERING, MECHANICAL","Score":null,"Total":0}
引用次数: 0
Abstract
This paper aims to investigate the confined distance near the floor(0∼28 mm) and wire size (the ratios of copper core diameter to entire wire diameter are: 6mm/8 mm,6mm/10 mm,8mm/12 mm and 6mm/12 mm for type Ⅰ, type Ⅱ, type Ⅲ and type Ⅳ, respectively) on the flame spread over polyethylene (PE) wires. It is indicated that, when the confined distance is relatively small, the extinction occurs for all types.The typical parameters of flame shape including of flame width, flame height and flame area, flame spread rate and mass loss rate with the increase of confined distance s can be separated into continuous growth stage and stable fluctuation stage. At the continuous growth stage, the flame area shows an exponential relationship with s as: . And at the stable fluctuation stage, the flame width is larger than that at the unconfined condition accounting for a large portion.While, the flame height is always smaller than that in the unconfined case.In order to explicitly describe the heat transfer, the upward large main flame and downward small flame are firstly introduced in this paper. Correspondingly, the heat flux feedback of components to the preheating zone is established with the upward main flame flux [includes of ], the downward small flame heat flux [ includes of ], the conductive heat flux and the gypsum board heat flux . With the increase of s, shows an increasing and then decreasing trend, making it take a second role during heat flux feedback. Meanwhile, the analysis demonstrates that for the larger copper core (type Ⅲ) and the smaller of PE thickness (type Ⅰ), the ratio of heat flux of will be increased, which will enhance the heat transfer effect of downward small flame.
期刊介绍:
The International Journal of Thermal Sciences is a journal devoted to the publication of fundamental studies on the physics of transfer processes in general, with an emphasis on thermal aspects and also applied research on various processes, energy systems and the environment. Articles are published in English and French, and are subject to peer review.
The fundamental subjects considered within the scope of the journal are:
* Heat and relevant mass transfer at all scales (nano, micro and macro) and in all types of material (heterogeneous, composites, biological,...) and fluid flow
* Forced, natural or mixed convection in reactive or non-reactive media
* Single or multi–phase fluid flow with or without phase change
* Near–and far–field radiative heat transfer
* Combined modes of heat transfer in complex systems (for example, plasmas, biological, geological,...)
* Multiscale modelling
The applied research topics include:
* Heat exchangers, heat pipes, cooling processes
* Transport phenomena taking place in industrial processes (chemical, food and agricultural, metallurgical, space and aeronautical, automobile industries)
* Nano–and micro–technology for energy, space, biosystems and devices
* Heat transport analysis in advanced systems
* Impact of energy–related processes on environment, and emerging energy systems
The study of thermophysical properties of materials and fluids, thermal measurement techniques, inverse methods, and the developments of experimental methods are within the scope of the International Journal of Thermal Sciences which also covers the modelling, and numerical methods applied to thermal transfer.