Abstract
Enclosure fire fighting by finely-dispersed water capability without direct water droplet flow effect from a sprayer upon a fire is shown. Fire fighting requirement droplet flow investigation experience points at successful application of Zauter’s diameter (volume of all droplets to their surface relation) while describing the results of experimental studies and theoretical calculations. With presence of enclosure eddy medium motion on account of ascending combustion product flow and interaction with a sprayer droplet flow in a finely-dispersed droplet ensemble there appear eddy diffusion, migration, deposition, and Magnus effect phenomena. With turbulent gas flow mode the particle deposition velocity on pipe and channel walls in most cases surpasses Brownian deposition velocity of the same particles in eddy-free motion. The above phenomena are typical of fine droplets up to 150 μm in Zauter’s diameter. Droplets of 200 μm and larger diameter are not subjected to eddy gas motion effect, just depositing under force of gravity and initial impulse. A particle motion in gaseous medium follows its pulsations with this or that phase or amplitude lagging, i. e. asymmetrically, but with certain velocity excess to the side of lower magnitudes of pulsating medium velocity. Fine water droplet motion study in eddying gaseous medium allows to reveal processes facilitating fire suppression in the whole enclosure without direct water droplet flow effect from a sprayer upon a fire. The experimental studies performed on enclosure Class A and B fire suppression have demonstrated enclosure fire suppression capacity by finely-dispersed water with droplets of up to 50 μm in diameter that was predicted under theoretical consideration of fine droplets motion in eddying gas medium.
Highlights
Experimental study of suppressing effect of fine water droplets on propane/air premixed flames stabilized in the stagnation flowfield // Fire Safety Journal. — 2013. — Vol 58. — P. 84–91
The above phenomena are typical of fine droplets up to 150 mm in Zauter’s diameter
The experimental studies performed on enclosure Class A and B fire suppression have demonstrated enclosure fire suppression capacity by finely-dispersed water with droplets of up to 50 mm in diameter that was predicted under theoretical consideration of fine droplets motion in eddying gas medium
Summary
Ñâÿçàííûå ñ âîçìîæíîñòüþ îáúåìíîãî ïîæàðîòóøåíèÿ òîíêîðàñïûëåííîé âîäîé. Ïîêàçàíû îñíîâíûå îñîáåííîñòè äâèæåíèÿ ìåëêèõ êàïåëü âîäû â òóðáóëåíòíîé ñðåäå ïðè íàëè÷èè â îáúåìå ïðîäóêòîâ ãîðåíèÿ îò î÷àãà è êàïåëüíîãî ïîòîêà îò ðàñïûëèòåëÿ. Ïðèâåäåíû âûðàæåíèÿ äëÿ òóðáóëåíòíîé äèôôóçèè è ìèãðàöèè ìåëêèõ êàïåëü â òóðáóëåíòíûõ ïîòîêàõ. Äëÿ ÷àñòèö äèàìåòðîì d = 100 ìêì âðåìÿ ðåëàêñàöèè t = 2,55·10–2 ñ è ïðè òîé æå íà÷àëüíîé ñêîðîñòè äëèíà ñâîáîäíîãî èíåðöèîííîãî ïðîáåãà Lp ñîñòàâèò 2,55 ì. Êàê ïîêàçàíî â ðàáîòå [4], íàëîæåíèå ïóëüñàöèé íà ãàçîâóþ ñðåäó ïðèâîäèò ê çàìåòíîìó óìåíüøåíèþ ñêîðîñòè îñàæäåíèÿ íàäñòîêñîâñêèõ ÷àñòèö, êîãäà àìïëèòóäà ïóëüñàöèîííûõ ñêîðîñòåé ñðàâíèìà ñî ñêîðîñòüþ îñåäàíèÿ. Ì. Ëèôøèöà [12], ìîæíî ïîëó÷èòü óðàâíåíèå äëÿ ñìåùåíèÿ ÷àñòèöû, êîòîðîå ñîäåðæèò, êðîìå ãàðìîíè÷åñêèõ ñîñòàâëÿþùèõ, íåïåðèîäè÷åñêóþ ñîñòàâëÿþùóþ, îïðåäåëÿþùóþ íàëè÷èå äâèæåíèÿ ÷àñòèö (ìèãðàöèè) â íàïðàâëåíèè, ïðîòèâîïîëîæíîì çíàêó ãðàäèåíòà ïóëüñàöèîííîé ñêîðîñòè ñðåäû. Ðàññìîòðåíèå çàêîíîìåðíîñòåé äâèæåíèÿ ÷àñòèö ìîæíî èñïîëüçîâàòü äëÿ îöåíêè ñêîðîñòè ìèãðàöèè çà ñ÷åò ïóëüñàöèè ñðåäû. Ãäå Vs — ñêîðîñòü îñàæäåíèÿ ÷àñòèö; U* — ñêîðîñòü ãàçà â ìàêðîâèõðÿõ (äèíàìè÷åñêàÿ ñêîðîñòü ãàçà), ñì/ñ
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