,

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~"~~ vl; .. ,01:= U

~---

'I THE LIBRARYFIRE Ri'5EAR,_H STATiON

nORt}-lf\i~1 WOOD

ItloF. R. I~~:: No. 419~960---Research Programme Objective E1/9

- DEPARTMENT OF SCIENTIFIC AND INDUSTRIAL RESEARCH AND FIRE OFFICES' COIdMITTE&JOINT FIRE RESEARCH ORGANIZATION

ROOF VENTING OF BURNING ENCLOSURES

PART III. VENTING FIRES OF CONSTANT HEAT OUTPUT

by-,P. H. Thomas, D. L. S~', P. L. Hinkley and C. R. Theobald

.-:.- .. -

This work has not been published andshould be considered as confidential advanceinformation. No reference should be made toit in any publication without the writtenconsent of the Director, Fire Research "Station, Boreham Wood, Herts.erelephone: Elstree 1341 and 1797).

This work has been done in conjunctionwith Messrs. COLT VENTILATION LTD.

Summary

Investigations using a 1/12 scale model representing one bay of afactory have shown that, where the area or the rire is small and its heatoutput is known, use can be made of Bernoulli's theorem and the theory ofturbulent Plumes to calculate the rates of discharge of heat-and air througha vent and beneath a curtain extending from the ceiling, the temperaturesnear the ceiling and the depth of the layer of hot air. Formulae are given-for the effect on these quantities of varying the size of the vent and _thedepth of the curtain. Some of the effects of the shape and position ofthe vents are also discussed.

February 1960 ­

F.1 000/1 2/346

Fire Research Station,Boreham Wood,HERTS.

© BRE Trust (UK) Permission is granted for personal noncommercial research use. Citation of the work is allowed and encouraged.

Notation and units used in this aerie.

Dimensions

C.G.B. unitsF.P.S. unitl

Conversion !I--------......,.--------t faotor used IP.P.S. unit.

toC.G.. S. unit.

MeaningSymbol

1

0.0160

1530.5

0.555

30.5

30.5

30.5

30.530.530.530.5

929929929

"

30.5

454­252~52

0.5550.555

2.84 ; 104

30.5

cm

cmcmcmcm

cm

cm

emem

'gm/s.C8.1/scal/s

OXOK8

cm3/ scm/s

it

it

ft/s2

itftft

, ft

--ftit

it

lb/sB.T.u/sB.T.n/s

OaOR

sft3/sft/s

-1 0 -1B.T.U Ib F

B.T.U.s-1 ft-1 °F-1 Hal '~:\iDi:10c:1~t om

Effective area of fire'Area of inletArea of ventCoeffioient ofdisoharge through thevent

Coefficient of dis­charge beneath thecurtain

Specific heat atconstant pressure

Depth of layer ofhot air

Depth of layer ofhot air beneathcurtain

Acceleration due togravity

Height of openingHeight of modelDepth of curtain

r-r:H + 1.5 l At,(effect~ve heightof model)

Thermal conductivityCharacteris ticheight dimension

Path length of airin model

Mass flow rateRate of flow of heatHeat output of fireAbsolute temperature

" ambient "TimeVolume flow rateVelocity of gas at lany given point in

'prototype and modelWidth of inlet "Distance measuredvertically fromfloor

Temperature aboveambient at any givenpoint in prototypeand model

Density

g

Cp

d

dc

'iC d

ws

1

AtQ

~T

TotVv

KL

hHHe'H~

Subsoripts

H = Near the ceilingc = Level with the bottom of the curtaino = Ambient conditions = Discharge under the edge of the curtainv = Discharge throUghtbe venty = At a distance, y, above the floorb = At the base of the hot layeri = Inlet

ROOF VENTING OF BURNING ENCLOSURES

PART III. VENTING FIllES OF CONSTANT HEAT OUTPUT

by,

P. H. Thomas, D. L. Simms, P. L. Hinkley and C; R. Theobald" ;" ':~'.

.,. : .r...... ,'; -,

1. Introduotion '

A previous note(1) desoribed the construction of'a 1/12 scale model ofa bay of a factory for use in studying the effect of venting burningenclosures. The present paper desoribes the experiments that have beenmade with this model to examine the infiuence of the"size, 'shape and posi­tion of the vent; the depth of' any auxiliary curtains and the'shape andarea of the heat source on the ,temperature ,distribution in :~the 1I10delandthe heat flow through it.: The results are shown to agree :wi,th c::alcula­tions based on a suplified theoretical approach to the ven,H~g of fif8S"derived from Bernoulli's theorem and the theory of turbulent plumes 2).

The application of the theory,·tolarger and differently shaped enolo­sures, larger fires and the design of venting systems ..Will. be discussed, inlater papers. ,.. ,';

; .: -:",

Experimental method and results

2.1. Apparatus and procedure

..:. ""

Tl).e model is shown in fig~ 1. Essentially it is an asbestosbox insulated on the outside with exfoliated vermiculite and linedon the inside 'with aluminium foil. Heat was supplied by varioustypes of' gas burner (rig. 2) the gas input being regulated to Jivea gross heat output of 2.37 B.T.U/s. The earlier experiments~3),show,ed that there were two time constants governing the equili~rium

temperature rise; a short one associated with the air flow and a 'long one of less importance associated with the walls. In eacjh 'experiment the walls were allowed to reach equilibrium. lIeasurementswere then made of the air temperatures at various points inside themodel and of the distribution of air velocity and temperature alongthe vertical centre line of the inlet. The temperatures weremeasured using ,44 S.W.G. chromel-alumel thermocouples distributed asshown in fig. 1A except for a ,few of the early 'experiments where theywere shown in fig. 1B. Air velocit:j.e(l were measured with a radia­tion compensated Simmonds anemometer\4). Since the horizontal dis.,.tributions of air velocity and temperature across ,the inlet were uni­form e~cept for some reduction in velocity within 2 in. of eithersideO), the air input to the model and the output of air and heatunder the curtain oould be obtained from the velocity and temperaturedistribution, along, the vertical c~ntre of the inlet.

2.2. Experiments ,and. results

Two series of experiments were carried out; inth,e first the ,shapes of burner and vent were varied; in the seoond the size and ,/position of, the curtain and the size of the vent were varied.

,... ; ';'"

"

2.2.1. Shape of burner and vent

Three types of burner and three' shapes of ,vent wore used in, these experiments. The burners (linear, circular and doubleline) are shown in figs. 2A, 2B and 2C respectively. , The ventswere rectangular haVing different proportions but the same areaof 24 in2• Details of these experiments are given in Table 1,whioh also gives the air temperature near the ceiling and therates of air input and disoharge under the edge of the curtain,which were obtained from velocity measurements, as explained'above. ,

,.

, " TABLE 1

:)~x~rl..ments'.' on eft'eot Or' shape or vent 8114 burper"r, , ,~ -. ., ,(Firat series) ,, •. ".' '. ."

c'

.\

','

. ..~: .·Obtained from 'meas~ments of'air velooities.';'''

'.' . .' ".

, ," .. c

- , ,, "

....'··Ra:tl' orVent ", ORate ordiBo~ee"

Vent position "Curtain ·Bate of disoharge or ,air ,·Jfeasurecl ,

dimensions H: over Heater., " depth air input or air thrOugh_'temperature '

he,"ter - under e~ - oeUbgin. in. " in.' ft3/ . ,vent, (by:'

, nearx "I,: ' ' Dear. ,. : of ourtain OF

inlet.. : ,

ft3/sdiff'erence)

- ' ' " "ft3/s ', - ,,-

ff ' ( ..4 x H -. Line 8 0.42 0.05 0.37' " 288

'Circular .;8 '" 0.41 0.10 ,0.31 270 ' ., , ....

- :

12 x ~ H, .. Line 8' 0.40 0.10 0.30 243.. Circlilar " 8, '0.42 0~15 0.27 243, •. ," .. -,. ,

22~571.': ', ,

. H ' Line ,8 0.39 0.13 0.26 , 288..,

1;1 Circular.

8 0.43 0.16 ,0.27 275.... - ","

. , :,

1: '"

,4.

H- Double .. 0.38 0.05 0~33x liDe 12 221" t -. e '.ft· ,12 0.38 0.05 0.33 220 ".. ,

": iI'-',', ',ft e "8 0.59 0.32 'O~27 ,,64- '.

" .- .. .I,:' - ,- 8, 0.64- 0.35 :0,,29 162", .. , -'.. - ! ' ..

~. r·"0 .. ".. . ,

"

........

••Volume meaaured at ambient temperature.

fThermooouples arrlUl8ed as in fig. 1B.

~ermooouples arranged as in fig. 1A.

..'- ,

t.

-,.',.1. ¥fest et peW.:!;;!.o,n o( unt,

2.2.2. Sise and psa;!.tioA o( vEl!!.t epA !l9RIib of S3iGI\1,nThe f'actors ~ild in thisseoom ·a«rias of' uparimeQta· were'

the poaition of the vent, the vent area and the depth of' the~Throughout, the ventwaa .approx1lllateJy square -and the oiroularheater was used. A sUlJllllBl"Y of results is given in fable 2. (pap 4).

,t. 't . • ~

The rate of disaliarg~ of' hOt air throush the vent (Table: 2), was,' ;', ';,:gena'fl.lly gt'ElBter when the ventoWas .over the heater than·when' it-was near':the inlet, althou,gh the differenoe ,was only important with the 1 in. Oul-',:tain. In that osse it Dan be explained by the hot gas having a veloaiV'" ;suffioie1'1t to oause a tendency to overshoot the vent when this ,W8,S. near ;the inlet (fig. ,) and to pass under the curlain. This resulted in ii -"" ~::

oorrespondill€ly high rate, of discharge under the ,ou.rteJ.xt.. ~:. . , .: "_";. • .: . ..1.. i» "'. • ~ .. ' :-: -. •

The position of the v~t had no Irl,gniticant ef':feot on' the, t~~~"~ :near the oeiliD€. ' "' .. :: ": ~, ,

•~. .,t··

"

'.2. J?¥!'!p::1buU0A of ye1°o1 t.y bea¥ta tRa i\tl1NJ!.In all the above experiments the rates of' air:flow -were ~ouiB.tea.

:from veloeity measurements; a typical distribution of velooii;y 'beneath"the curtain is shown in fig. 40, The velooity near the f'loor of' the, ,", ',:mpdel was 0.5 ft/s with the linear andoiroular burners'ana. 0.65, fila Withthe double line burner.

" t .

El:am1JIation of the air f'lew pattern in the inlet uaiJlg a BIIIOk:e trac"showed that in those experiments where there was a high rate, of dischargeof hot air beneath the aurtain a vortex existed between the inf'lowiJlg andoutflowing air streams (fig. 5). This sometimes led to an overestimateof the rate of flow of. air into the model as the non-direational anemametermeasured the speed of the air in the vortex instead of, the mean hor:l.llontalvelooity. '

The aoeural:\Y of the experimental measurements of air :flow and tlllllpera­ture may be estimated _by oompar:l.ng values of' the heat passing tbroush thevent oalculated in two different way.,.

,.' ..

(a)

(b)

From the net heat input to the'model (Qt) lass the heat dis­charged under the edge of the curtain ~Q); Q is obtained,:f'rom measurements of air temperature andSVelooi'-r beneath theourtaino

.9.v: = ~ - Qa ~__ ••••••••••• ( 1)r-

Prom the temperature and the mass of gas vented, obtained bysubtraoting the rate of discharge of air under the curtain f'rcmIthe rate of input of air (Tables, 1 and. 2). ."

Q' = 'l_ C (M - M)v'-lip is

"

•••••••• 0 •• (2)

In fig. 6, Q' is compared with~. The sOBtter is r",ther large,extending from aboi{t -25 per oent to + 50 per oento , "

The rate of flow of heat through the v-ent could. not be' obtained'fromthe temperature and velooity of the air flow through the vent because theanEllllometer calibration was uncertain at' the high air temperature existingthere. However, the above comp~n shows that the vent heat :flow Danbe obtained :f'rom measurEllllents of' a:!,ll! velooity and temperature beneath thecurtain without systematio error exoept that aome very high values of Q'were obtained. These are attributed to the difficulties in measuring tKeair input due to the vortex desaribed in the 'previous section. Beeauaethe first method ilWolves fewer measured quantities in the air streams, ithas been assumed that it is more reliable than the seoond method. :

1'ABLB 2

Be.u1ta of experi!!enta on aue and position of vent tD4 abe -of curtain(Sec0n4 aerieal -

'-,"

.,' '.: . ',

«: '.'

',: !,j,,,;"

" ,

~':' .\ .. :~z ,

',I: .' •.1 '

~f;

..'

"

-... roo:\' ," '

'" ~.: ';;.

, ,

"

,;:

,I

! "

~~~~'_f~ 1IIll~UI:ements of-~ ve1ocit,-.

ho1~e ..,uured at8lllbie~t temperatUre.

..:. , -,

hate or ,'- " Te.p,rature, "'teof, 41s~~'

~

- Veftt poeitioft ' *Rate' of 41scltarp,..-

of air \..'", DearCurtain Vent area' ceili.DBdepth H: ever boater air~t

,

of air -. thrOu&hta2 • .:j -~';;_::,"'"- ,

in. I:near in1et n/ts, uD4ercurtain vent (bytt3/s: din'erence) , :.' s :".:,-.'

", wi. ,: ._.·,~:p:·.::'l, ." ,~

"

16 H .-0~29

.. 0.01 " 0.28 340'I

.,~" 0.26 0.03 0.23 j 354:

24..

H ' ; 0.36 0 0.36f _

28612 .. " ' '

I .. 0.29 0.01 0~28 283;40 H • 0.40 0.03 0.37 '243..

I 0.35 0 , 0.35 24.8 I"

16 H 0.4-1 0.15....

0.26 ~ 299I 0.4-2 0.22 , 0.20, ' 308

8 24- H 0.4-9 0.13 0.36 279,I 0.4-2 0.05 0.37 262

• 40 H 0.4-6 0.03 0.4-3 232I 0.4-8 0~07 • 0.4-1 241

"" 16 H 0.85 0.51 0.34- 183:.1

I 0.67 0.53' -, 0.11. 183:I 24- H 0.75 , 0.4-6 0.29 -, 191, I .. 0.93 0~74- 0.19 180

40 H 0.75 0.34- , Q.4-1 165 " ;.

I '0.80 0~55" 0.25 176 ..- ,

,.: "

. ,

,',.:- ;.

..,,'

- ,

r c,

,.." ,

3-:40 .Distribut;i.on ot, ~e.mppWe ;la Sie fII238l,• , '. _ J . .. . ... ' o. ~ '~~

v • • : _ A.-:·,typioal vertical temperature distribution 8S reco~' ·b;y-~.tliermooouple8

1'-12 (figo rs). is shown in fig. 7. There iSQ layer ofhot'atr"beneath theoeiling, a layer of cool air near the floor ·-ends .central,. layer'where the hotand cold layers are JIli#ng. The variation in tempera.ture! ~v~ any horizontalplane',ll the mooel was found 'to be small compared W;~ .the, vert:L~ variation it

" temp.era.'ttJ.re& -. -, ; •• ' -. '

. ". ."

3.. ,5. Ef't"ect .otabape~-am.j?08it.iQA, of vgnt'. '..

Both~ -shap&.&Jd poaiti~n.-Of the· vent had _op:).:y ~..aliiht effect on thetemperature -within the enolosure'"-ana. the heat,·vented from it; 'there tended tobe sli-gh~mor-e discaar-ge beneath the curtain-when' the ,v~nt '·was near(itO'These results are very-similar to those obtained in other experiments 1 -' 5).

4. Calcu:I.a;t!0BS of ,air flow-a,n,d tsnm~

The foregoing experiments have. determined the heat-and air flow through thevent and under the curtain.and the temperatures near ,the roo~ for ~ous oonfigura­tions of vent ·and curtain in a small scale -modelo In this section a simple tbeor.Y'is developed which enables these quantities to be predioted, i.l?- 'certain cases, fromthe dimensions and geometry of the model and the size of the fire, and it is shownthat the experimental results are oonsistent with this theoryc> .

- .

4.10 Co'efficients of disclJ,a.rfl~"

;' ..In the following argument the pressure drop due to the loss of velocity

head of the inlet flow ·beneath the ourtain is negleoted.. This is juatif'iedsinoe the layer of hot air beneath the gailing was at least· 4 in. thick andits temperature was of the' order of 180 F while the pressure drop across theinlet was equivalent to a head of only about Oa2 in. of air at this temperature.

The rates of discharge of hot gas through the vent and under the curtainmay be calculated from the vertical distribution of temperature in the model.by using Bernoulli's Theorem (Appendix I).. It is, however, found that thea.ctualdiacharge' measur-ed experim~tally is less than the theoretical by afactor whj.g{l is known as the coefficient of discharge. . This is usually0116 - 0 0 7l 6 ) but may vary with the size and shape of the orifice and thevelocity and orientation of the tlowo

4.2. Determipation of coefficient of discharge through the vent

It is shown. in the appendix that

00 •• 0 •••••

To, . 9

may be evaluated gra~hically by plotting 'IT

. '. .. Vv =A" - 't/(:. Cd

. The integral (H 9/T~ I • .)0

against y. This was done for several different conf'iBurat1ollBof vent andourtain (fig. 8), and by inspection of the graphs, it was found that to a firstapprox:ima.tion

. '.

" 0 •• 000 ••• 0, (4)

where d was measured to the Pj)int of in.f'lea:tion of the temperature distributioncurve, ioe. the shaded area 'in fig. 8 is approximatel.y equal in area to therectangleo Hence .~guatio~ (3) simplifies to ,

V"C=

d0&0000000. (5)

5

VJ(' as oaloulated from equliUon. (5) is plotted against the measuredrlteJ.of c11scharge of gas through the vent (fig. 9) (obtained fran the'subtraotion of the meas~d mass spilled under the ourtain 'frOm the .measured mass input (Tabl~ 2».' The results for those l;lXp8riments'where the disorepancy between Q.. 'and Q' 'exceeded 25. per oent are" .omitted. Lines oorresponc11ng ~o ooeft'IoientB of disoharge of 0.6 and0.7 have been drawn on this graph. . AJ.though there' is a large soatter,the experimental results are consistent with the assumption that the.'ooefficient of c11soharge is about 0.6 and this value .is assumed in allsubsequent caloulations. In applying the theory to full scale 'builc11ngs and to vents c11ffering great],y in shape from any discussed .in this note, other values. for the discharge coefficient may be ~quired.

4~3. Determination of coefficient of c11scharse under. the curtain

It' the velocity head of the gas in the upper part of the enolosuremay be neglected the ourtain behaves as an inverted weir. (Appendix)

;..-10 ~tl, ~) di ....,..... (6)

This equation was evaluated graphioally for a few. oases from' theexperimental temperature c11stributions and it was found that a s1a11arapproximation to that given in the previous seotion,oould be uaed,if .the bottom of the hot layer extended at least about· 2 in~' beloW .the

. bottom of the ourtain. Then as a first approximation .equation (6)reduoes to . .

(7)" f. ' , . ".

. : ,:. ~ .:,....•..•.~. ,

. ,.' 3 . .. .v« = 2 'd' ~2 /2g "H'·_ .. -w - /'C~ . 3. o·,.~.d'" <v 0

V . .S/C'a was plotted against the measured volume disoharged over the edge

of the ourtain (fig. 10)•. Again there is a large soatter, but there ,is no systematio variation about a line correspcinc11ng to a value of 0~6"

for the' discharge coefficient, though two reSUlts in 'particular are ofdoubtful value.

4.4. Rate of entrainment of air

,. ,

The air flow through the vent and under t;he curtain may be oal-.culated from equations (5) and (7) respectively provided that· Qg and dare known. These latter quantities may be'calculated by oonsideringthe rate at whioh the hot air ·layer is replenished by the rising plumeof hot gas and entrained air from the burners (fig. 1.1)" The effectof the rate of input of coal gas in these experiments (0.0175 ft3/s) maybe negleoted, in oomparison with the muoh' greater rate of fJ,ow of airinto the hot layer.

The mass of air (14) entrained in a distanoe (H' - d) by hot gases.riSing(ffOm a point source of heat may be obtained from a f01'l!liUa givenby Yih 2) which in our notation may be written . ".

Il = 0.153 fH r Qe g 1i (H(-d/h (8). ~ C T J .{fH p 0

Sinoe the fire is not a point source a correotion may be introduoed '(')based on the angle. of spread of the plume' as' suggested by .G,' I. Taylor 7 •

H~ = H +1.5 .;-;:; •••.••••••• (9)

The evaluation of Af, the effective area of the fil-e, 'ilic11soussed inthe following seotibn. . .

6

1+.5. Caloulation of temperature beJieatb, the oeji .. "

The temperature beneath the oeiling can be oaloulated by 8U~Stitutin8

(11) .•• 0.000 •••

. i'

. ! .in equation (8)

6 .,'i'\I ..l = ,~? ?t

(9u + T ).. c.2. T 1- ( .,2o (~o p)"3 (gl' 0)"3 (H .a:)~ .

Since the effective area of the fire in these experiments was nOt oertain,values of 9u calculated from eqy.ation (11) were plotted against a for anumber ofailbitrary values of H' and compared with the'experimental points

.plotted in the same graph (fig. 12).· .:The most satisfactory agreeaent. between theory and experiment was found if HI,. was. taken to be 25 in~, which

gives At ,;, 21 'in2 from equation ·(9)."

Aa the vaiues of both ev and 9H obtained using the ciroular burner didnot differ significantly from. those obtained using the linearburne~with.the same Vllnt and curtain, it fol,lows.,that the ~ear burner had approximatelythe same effective area as the cirCular one. .

The values of d and 9H obtained experimentally using the double lineburner were put into equation (11) and it was found that this burner had aneffective area of 100 iJi2 0 -:', .

J+~6. ,.Calculation of depth 'of la.yer of hot 8as

The depth' of the la,yer cit 'hotgas be!1eath the, ceiling is obtained by ,equating, the mass of hot il.irentering ·the ·layer. to that disoharged thrOughthe vl)nt and under the curtain (fig. 11). " "

.When there is nodisc~rge under; the ourt81n11=11. ,. •••••••••• (12)

hom equation (5)

. 11,/ =cd

fRy?g d~,i" . To,'.,

and from equatio~ (8)~ (10), (12)'imd (13)

. t . f iCdAv d =.0.043 (H-d)2

•••'••••••• (13)

.11 = ~ + lis' ..

. . . .' ".

Th~ relevant experiaientiu.result~are oOllpared with equation (1J+) iD fig. 13."Equation (14) will not apply if d}:1Io sinoe therato .of discharge of hot " .il.ir beneath the ourt&1nJlust then be t8keninto·ii.ocoUnt~ , , "

., :' . - ,,\....:.. ". . .' . : " .

............ (!,s)

. ..~ .. ...... . ~ .

" "

, ,7'

and from equations (8), (10),(13), (15)8.nd(16)

, ,", ~ "",2 ~' ~ 2

Cd AV

d i + 3 Cd w (d - HO) '= 0.043 (H,-d)

The relevant experimental results are oompared with equation (17) whend).Ho and with equation (14-) when d(H in t'ig~ 14-. The agreement1:ie_n th~ory and praotice is very sa~isfaotory in view of theapproximatiom made. '- ,

I:t there is no ve'nt open and all the heat is disoharged beneath,the ourtain equation (17) reduoesto ' ': ' "

l " 2-C~'W (d:- Ho)2 = 0.065 (H~od) 2

4-,7. ,Rates of .disoharm of air

r. •"(;,,.

4-.7.1,' Throufsh vent - no spill under 'ourtain

'The theoretical rate of disoharge th1-oughthe 'Vent when-;;'" ,:;there is .no spill under the ourtain is obtained by putting the',- values of d and Qj{ obtained from aqUationa (W) and (11) in aqua';';,<­

tion (5). ' The variation in rate of'disoharge with, ventaroa ''oaloulated in this w8J and, oorreoted for disobarge ooeffioient,is oompared with the experimental points in fig. 15~,' ' , ,

4.7.2. upder,ourtain- no vent

,The theoretioal rate of disoharge una.er the curtain when,there is no vent is obtained by putting the values of -d and 9Hobtained from equations (18) and (11) iD. equation (7)~ Thevariation in rate of discharge nth ourt&1ndepth oaloulated inthis W8J and oorreoted for disohargeooet:rioient is oompared withthe experimental points ,in fig.',16. In'both figs 15' 8.nd16, theagreement is, satisfaotory.

4.8. Rate of disoharm of heat through the ventThe theoretioal rate of disoharge of heat throil.gh the vent is

, obtained, by putting the values of d and Qj{ obtained from equations (17), and (11) in the equation (19) below whioh is derived from equation (5),

Qv = Cd ~, eH fH C/'26 d 9H" P. T

. ' 0

The variation' in the theoretioal value ~ heat disoh~rged with ventarea is oompared with the experimental points ,for two ourtBJ.n depthsin tig. 17.' Again, the agreement between theory and practioe issatisfaotory. " '

4.9. Summsl'V of Seotion 4',,It has been shown in seotion 4 that it is 'possible to oaloulate a'

, number of quantitiell allsooiated with the heat and ,mass flow in the,Ilodel and, although there ill in some oases a wide sOatter in the"data,the faot that no signifioant systematio differenoabetween,observed andmeasured quantities has been found shows, that the methods ~ oaloula­ting thelle quantities, based only on the heat and mass, bal&noe usingelementary buoyancy oonllideratioas and plume theory, are satiBfaotory. \,

8

. 5. Applioations of theoq..

A th~ory was developed. in the previous section ·.and it was ":fQ~nd, by experi­ment to apply to a particular model" This section shows tha~ the theory may beexpected to apply to larger scales of the 'same mode1 and, in some. cases, to other

.shapes of.model~ .

The~·. 18 nothing in the foregoing theory that restricts it to any particularscale, provicied .that the scale 'is large eno.ughtor·the flow to be tur~ulent andthat external wind conditions do not influence the flow. There is a restriotionon the shape of the enolosure beoause the·experiments. have been oarried out witha flow which is essentially two-dimensional, 1 0 e . the- gases flow along the modelox:'. in" a vertioal direotion, but there .is.no radial tlow.,;

.This is because the assUmption was made.in the .theory that the temperatureis a funotion ,of the height above the floor but is '~therwise, independent of .position; i.e. no mixin~ ~ccurB between' the hot and cold laYers. . Work on two-'~mensional flow systems~8} has' shown that .little:niixing "would be expected to .ooour even when .eaoh of the layers is t.urbulent unless the relative velocity isquite high. Consideration ~llbe given·to the.problem of radial flow in futurework. .

-5.1. 'Soaling

,For geometrically similar enclosures of "linear dimension L, the velooityof the ex!t hot gases due to th~ buoyancy of the, hOt layer is of the form

, .

:;·.-v /TtL" ".. ..; '; ..:X .. ',.'.:.' .,.' ',

, ..~ 1~.. ".:. . .' . : .. ~. :~.' .. .i,e •••' ,* ••• (20) .

.. '

,and' the heat' balanoe is ·:of··the form.-·',"-, -,

......

• ••• 0'•••••

.. ,.

Examples of equations similar to equatd.on (20r are (1) - (6) and similar t'o(21) is (19). Other equations can readi~'be shown to .be combinations.ofthese two types.

From equations (20) and (21),.• \.' <.' • \ .~'

Q . (J".:J -x ~T L3

Equation (11·) is of this type

.00.0. ,••••• (22)

x,.oc. i! 0 •••••• 0 •• (23)TI Li

Equation (8) is of this type .(strioe M(~:v L2)0 .

These., ~J.ations have been confirmed for. the' present modei'-u~ing different heatinput8~3).; they can be used to ex·tend the .range of equations, ,(8) - (18) whenthe linear scales are varied.

c I ' .... \r,.-' - •I .....~~ .•9

l' ~, r .

·These. soaiing laws are derived for' an enc.Iosure: in:'wMch the exit .is the majorresistance to flow. For more general systems the .relations between L, ,~, g andQarethe same but their dependanoe on T will be different and usually less.~o avoid this complication it is desirable to keep the .. temperatures ina model thesame 808 in the prototype which is b~ing modelled. . . ~,:.-:. ,~.,

~. ~.r ~~: :~ .....

. '.:.::. I:

'5.2. Fioor are!~ ..

, ...

, "

"

'Bquationa (1-13) do not oontain the term ,"floor area", so that noll1­nally they m~, be applied to buildings of an:y si.e.. However, as t11e,floor area 1.nonIases, mixing of' the hot and, oold laYers inofOases ~dve~ts u.v be ilJ.ightly less effeotive as their distanoe from the ftieinoreallell(1.51. A similar etfectmust be expectedU heat losses byconduction and ,radiation through the walls and oeilings are' ot, ~;Lativolygreater iIIIportance than in this, model. In general, on lal"ge bUildings.,one needonJy oonsider the oeiling. This problem has yet to be 'investigated.

5.3. mect of area of fire

, The depth of the hot layer hlis been caJ,culatedtrom equation C14-) asa f'unC1;ion of the ettecUve area of' the fire, assWlling no discharge"bei1eaththe ,curtain and is shown iil fig. 18, for. various vent areas.

, Asth~ ettectiTe area ot the tire increases' the depthof' the layerof'hot air :1l1creases" and if discharge beneath' the curtain is to be pre-

'vented, larger vents are required. With fires of' large area the ventarea required m~ become impractically large; and the discharge of' hotgas can onJybe prevented by restricting the air inlets. ~",

5.4-. Bttecit of inlet openiIl§s of' limited sizeoD temperature and air flow, '

Under the oonditionsOf' the experiments desoribed in this paper, itis possible to,negleot the ettect of the pressure drop across the inlet,and therefore to regard the neutral pressure plane as coinoidiilg withthe bcittom ot the"hot gas layer. In generaJ.., ,hoWever, the, neutral, 'planel!ill be higher than the bottom of the hot' gaB l8yer in order to

.'. l'rorlde &buoyanoy head to balance the velooity headaorossthe iDlet .',{fig.19). ' ,Equations to allOw for this cianbe easily derived, but are '" generally dit't'ioult to solve. There is a simple solution when the

bottom .of'the hot air layer is above the bottOm: of, the oUrtain and there 'is no spill under the ourtaiD; ,the mass rate of' flow of gas through themodel is thenl (See A~enciix 2h__'_, f 2", cll~ ,

II=CdA;.d A.2~H · ·(24), ' - o;~ T

H(1 +~ T)

Av 0

Equati:on (14-) then becomes

'.1. ".,' ~.. f 1Cd d =0.04-31c--2

, "", , ....1, ..•••••••••• .,(25)

" , " ,To 1 ,,' ,Thus, it the size of the ,inlet is reduced so that TH' ~ cannot be neg-

, lected inoomparison with # the l~er of hot , 'air will be ,inoreaaod in thickness and hence from equation (11) its temPeraturewill be higher. A simple solution is also possible ,when it can ,beassumed that,theCmQciol is fullCOf)hotgas at~'i. Thip Q~se has,bee~'treated by Yokei 9) and Dyakov 10 • There is ..vidence'11} that this "approxi.mation can be used when a fire covers most of tho floor areaof',the model although it did not appear to hold for' the lf~rtmentsreportedolsewhere with a large coal gas fire ,in a model\5)., Theseexperiments, therefore require some future 'oonsideration and this willbe:reported later.

6. Conolusions

, The eiperiJllents .have shown that, the ehape of theverit is not importantand that it~poSiticnwithin a small curtained area is' oJu,y of aiilor iltPor,o,tance 'provided that the hot lrlr does not have a suf'ficiently:highhon-'Bonta! velooi1;y to cause e. tendoncy to overshoot the 'vent. These quanti­~ative resultsoolltirm. the qualitative results obtained by earlier experi_ments using a',smoke tracer, and it can therefore be inferred that a Uletulguide m~"be obtained from simple experiments with a smoke tracer.,

10

/!I

I

The layer of hot gas beneath'the oeiling 'can be, regarded as uniform intemperatu~ and Bernoulli's ,theorem, together with' the theory of turbulentplumes}oan be applied tO,estimate its depth and temperature. This leads tothe following formulae for predicting the efficiency of a vent when the pres­sure drop across the inlet is negligible and the air flow 'is linear in ahorizontal plane!

(fig. 13)

hot air (d)

(H!'';'d)~Depth of layer ,of

i0.6 A d2",0.043, v

d (H

O.~Ac dt + O.4'd(d:'H )~ '" 0.043(Hic.)~(fig. 14), v c' -',,'

(a)

when

.:

(b) 'Temperature of hot air layer~IlH)2 '

6.5 Q,~3= . I

(foCr)¥(gTsrt (HI-d)~ (fig. 12)

,(c) Rate of discharge of heat throughthe vent,

may be ,

(fig. ,17)

. . . .," "

, There is ,satisfactorY agreement', betweerime~ureci:and calculated dataand it is therefore possible to design' a,ventiD:g system provided the heatoutput of the, fire and the, ,various dimensions ,of ·the building are known.Conside'rationwill be given to s.ome problems..of de'sign' in a later paper

.uafng .the' methods given here. ' '

," '-'-~''''' ,"

'Q" '06'" 6 .. / " To \~ ',!2g ,d~Il,H }l,ov'" ,'fo "r \T +9 I "H • !lV

.' . O. HI. :) . To .... . ..

When the mOdelis:fu~10~hoig;;:~tli.e ari~lySiS~f'YO~Oi(9)":" used, .....-, ,,;,-, . "'.'

~.

:\ .

•• • 1 " ••

.. ' ..

. ' ." ,"

AoknOwledgment

The authors would liketo'thanJiMr;', R. ,W. Olaridgefpr his v8.luableassiStanoe with the experiments' and 'Miss V. 'MoNaughton for undertaking the

. oalcuia~':i.ons~,.,- .. ' . ..... ' . <, .

'," ;

1. 'SIMMS; D. L., HINKLEY, P.L., EindBisSETT, A;' ,Roof venting of burning, Elnolosures,'Part 1. Joint Fire Research Ore;lmization., F. R. 'Note No.'390/1959. '. ' ."

. -.,' .~ .2.' YIH, C; S; , 'Free conveotion due, to a point

, U.S. Nat. Congr.Appl. Meeh, 1952, 941\-7;sourceof"heat.

..,:,Froc. 1st

3. SIMMS, D. L., HINKLEY; P.L; and BISBFrT, A. Roof venting of burningenclosures Part II. '. Joint Fire Research Organization. F.R. Note No.391/1959; ,

4~ ~IGMORE, R. H. Aradiation' compensated anemometer.Ore;anizatiori. F. R. Note No; 297/1957. ,

Joint Fire Research

5. THOMAS, P. H. and SIMMS, D. L. on the prevention of flame spread beneathceilings in fUlly developed fires' by roof vents. Joint Fire ResearchOre;anization F. R., Note No. 376/1959.

, , ,

6•. LEWITT,~. H. Hydraulics and the mechanios,of riuid8; London, 1958,( 10th Edition), Sir Isaao Pitman and Sons 'Ltd. " ,

11

TAYLOR, G. I.'WALKER, E. G.et seq.

The dispersal of fog from airfield runwil,ys.· ed.and FOX, D. A. Ministry of SupplY. London, 1946, p.230

8. BAKKE, P. Some Interim Notes on Methane Roof ~rs. Safety in MinesResearch Establishment Research Report No. 164 Feb. 1959.

YOKOI, S. Aconstruction.No. 29, March

10. DYAKOV, N. M. Influence of area and space layout of building" ,construction in relation to direction of fire spread. Collected,information on fire resistant'building construction. "'Central ResearchInstitute for Fire Protection, Moscow, 1958.

11. SIMMS, D. L., HINKLEY, P. L.burning enclosures, Part IV.Note (in preparation).

",' .

and THEOBALD, C. R. Roof venting ofJoint Fire Research Organization; F. R.'

.:

_:'.3 ._

12

') -, v. ....._' ~ • i . . •

Appendix I .

Derivation of formulae for rates of flow of air 'under the curtain

,', • ,I ' .. " and through the vent' , .., _'0'. " .... "

1. 'Disoharne ·of·hot'air through the vent (equation ·3)i

:~...~ .'.

The' 'air .'is' regarded 'as being stationw.7 inside the '·model. :The ';p~iB'~'re' .beneath the ceiling (PH) differs only slightly fro,m that. outs.ide ,the JI104el,.:{po}so that it is possible to negleot the change in density of the air with 'pressureon passing through the vent. Bernoulli's ~quation (whioh.is given together withexamplfi)8' of. ·its . use in m8J'137 text books{6)} may then be ~itten in a simplifiedform.

,•••••••,.:••, (26). . .. .'.

. . : .r'. -~, ~.' . ,'';'~.'~ -: :. ..

To obtain (% - p ) it is assumed that the temperat~, and hence the density,of the air in the°model is a funotion of the height above the floor (y) but isothetrwiae indepel1dent ,of position. Then (referring to fig. 20)

. "~ -.

••••••••••

~~ e doc-" ,

.) R Ceiling

't~f;:

rl e:i .PH

iI

l~jJ .. ' ~ ],

j

But pr r: 'oTo == P.a Ta'and T - T =,Go

-:"1--- _

,.;.

Floor

Fig. 20

1

Column ofair of ~toross section

:. <, •", ' ..

~.~' ~ •,. ~ .'• • • . (28)

••••••••••

._. :.::. ~ •• "\ .':10:

Then from equations (26, 27, 28, 29)

Now

. .~ ::,~ ," .\:~J ,. .:~ ..,r:,·

• •. - . ,'.. "'~ "~"'''~r ........

', •••••••••• (30)"".~ .. """' '-_-~I' - .... ".

_ (~1>, .c.. . .~_ ~

.•.~! ••• " ••.•

&llowiD6. tor the coeffioient of discharge as explain~d ip. sectioJ1 4.·1 •.

Bquation (3) can be derived from (30) and (31)

v• .- Cd ~.);;:f9/T<\Y

• To

Disoharge of hot air beneath the ourtain (equation 6) .i . i . i

',t ••

. .. .....

Consider a horillont8.l strip of the opening beneath the curtain at 8

distanoe, r, above the floor and having an area Wdy (fig. 21)... .

Ceilins

Curtain'(width w)

Outside air

p T(,.) :')

. '.'" .,...- - - - - - - - - - - - ~ v - +...- ~.•". I r. -

II

I

Floor

l'i6. 21

........... ·(32)

'nUs may be regarded as a vent at a height, y, above the floor andt"rom equation (3) the disoharge (dV) thrOUgh the strip will be .

I . (1. dV = Cd W dyI-g i'i "" WT dy

\I To

and the disoharge ~hrou~~ the ~ntire opening (Vs) will beH HI' ~ r-

'i." r. 0 . ~ i ai /2 g ~t '&~ itT & 'Vi' = CdJodV .. C~ w' 0 (J .To .. )dy

. This 1s equation 6~

2..

,"

"• •••• 1'. Appendf!II .. ... , ...

" p;privation of formula for mass flow 'of air through the model '

, (e9uati~n 24-) ,- ,

densi~~Pu;~ depth ,'"i:

The restUof. the .odel '

" ..... .'.' ....

Ceiling

-r.~) . ~ ....\,.;, <.;

~oin'l-

~ '. .J, " c;. . ,

!' ",' - H' '

. .~..~. . -.''~. ~

. ~ .., r"·" , .-- - ,--'1,.- -'''ri ~_ .... ~-!-- -_:.-.;..---~ ,U ' . " ,

Outside'air

I. "

"

, '. A ~Pr.1I1~~~~ ..~~er~ ot)~ot air of. tempera:ture Ta,a <.(H - .ao> i8 assumed to exist be~eath 'the ceiling.,'90ntains UJ" at T and D (Fig. 22).' "

. 0 ~o '......;~'; • ~:~,~.;~. ·~·..:·,:i:- ,- :- '. ". '.

Fis.'22

Bernoulli I 8 equation m~ be written

I

I,Par the disoharge through the vent,.,

, l' +'H 1V<,>. t,0, '2g =ta

, .: . '.: ..,,' . - ~.- ---.0-1...........;._'--

'f1 t1Pressuredistribution~sid8model'

....,_ .and tor air entering through the inlet beneath the ourtain

, ..., ....

t) ~d) + (J .3!L: 0 I h 0 2g

ITo. (33) and (34).2 ,?.

,ftJ -fl, = ~H.lL + eo '*'~2g 2g

But PH ~Ft ~ (.eo - eH)d

eo,To = ,~ TH'

'9, =TH - To

~n trom equations (35, 36, 37, 38)

•••••••••• '(3~)

•••••••••• (35)

........... (36)

•••••••••• (37)

•........, (8)

.~.~ .1

Vi 8D~ Vv OaD Qe obtained in terms .of:~~he·,~&88 flow (M) and the area, of ~vent and i~et (A", and Ai)' s~poe._, .".. I .: _ _, " • ,.' . ,": .' •

~ - ,~.::. " _.~. .•••;,. -a_;; .~'. :.:~ ~'.

:f

II = Ca" Ai fa "i. .:.'_...._. _<' •••_ : ••••• ~ .. ~. (4-9)

. ,. ..,~. 'c' J, A,; fa:~' =C 'Av" Po '!2'l'v (fram 37)""" ~'~. '.~ .:.;.'-' (41:) !L. d ,d .-, 0 TH. ...':' ::,', ,..' )J -t r"; ",

:

Provided tha~ ~he shapes aJl.d areas of the vent, ~d ,"nle~ .40 D9t cUttergreatly trolD e~oh other,

• ,.: >

C~ .A., Cd·. ~- a

and tro. t39, 4-0, 4-1, '4-2) equati~n .(24) oan be derived

••.••• e-.-. ~ (~)

28 :49ft

.- 2 '\{1 +!L TH ~"-.. A 2-To.'".. V

••••••••••

,I ....

(2;)

;L'. "

+,." .v .

. . ,

-,

" . ": ~ . ~ .

{ ,1. •

" .

: ." '\ ...... I

2

.~. -! . :

.. " . r '.~:"

.; .''''

........ .; .

. '.:" .

-1/3578 F.R.419

x I(

x 1 8,1110

x90x eo)(6

xl2

)(5 xl4

ELEVATlON

Roof tray

Depth I

of curtain I.1

I1.l

t -

1,90,100,1102 34 .

-56 7

910 II

ELEVATION

Roof tray

r1-----1...~----------JProbe

Depth I

of curtain II

II

t

IIII

'II1I

I

x "90

x 100

x r -'11

x 110

PLAN

I-thick glass fibre

-151J

I .~ 90-12 )(10-x2 J ,

I)(14"x -VentJ 5

!I

x4-x )(6

I I

-I

1-j

I

PLAN

FIG.IA. DIAGRAM OF MODEL SHOWINGPOSITION OF THERMOCOUPLESFOR MOST EXPERIMENTS

FIG.IB. DIAGRAM OF MODEL SHOWINGPOSITION OF THERMOCOUPLESIN SOME EARLY EXPERIMENTS

aN

II1t

FIG.2A. LINEAR BURNER

0'

o

o ~G"~ CI5 Jets

FIG. 2B. CIRCULAR BURNER

~l!,

. +t + -+ + + + + + + +! \

------. 2' ------

I

; __\Lrantail burners

1\.+ + ,..... + 4- ... + .... + ...

FIG.2C. DOUBLE LINE BURNER

Shallow curtain -vent over hecter (Notendency to "ov~rshoot" vent)

'" " ----..-...----.,..-.-.-,.-~~~C"~--.·R.~Pidiy movin~~ Olr "

• ' I I' •

Shallow curtain - vent near inlet" .""...(Considerable tendency to 'oversnoot vent)

Slowly movingair

" I

Deep curtain ~vent' near inlet' (No"tendency to ·ov~r5hoot· vent) ,.' - .

F'IG.3. TO ILLUSTRATE TENDENCY OF AI"R STREAMTO ·OVERSHOOT THE VENT

. .

11358 1 F.R 419

--" .Cold .oir&--..... Hot air:e

2~ 1·5

OF AIR -It/s

o 0·5

VELOCITY

-ln -Out0·5

----:l----:::::::::::===-EE:ddiOcgeZ"Oiof curtain~

~ol!J

UJe> .-~I<{~

·llJ~...J

IZ,,-UJU­IO

FIG.4. TYPICAL VELOCITY DISTRIBUTIONIN INLET (CIRCULAR BURNER)

FIG.S FLOW INSIDE MODEL WITHGAS HEAT1NG

'W I'I-

~>""0 2-~ ........O~0: 0lJ..~

~a:LLl <t:'>lLIOl?::>LLl I'

" 0 a::c!=>J:~.... 0::

.~ ~- 0g~ Ill!

'LLuJ"r~=

I-<to =!WZ~I«dJ

---+ l11'0 + ...

-:["T"

+

'5 +

l/$

•

---0

.V \Dill

.5

1

/

() 0·5 r-o 1-5 2·0 2· 5-2 -I

HEAT FLOW THROUGH VENT MEASURED BY DIFFERENCE 0v-B.tu. ft s

CURTAIN DEPTH -in VENT AREA - sq in.

Circular Distributedburners burners

16 24 40 16 24 40

r • - -8 + + + Ii

12 t + + +

FIG.6, COMPARisON OF Ov WITH, O~

c .18 /' czillng

16 J. --_._--

I Hot layer

12

/a EdglZ of-/' curtain---- - - - - - - - ---.- -

8 ~

.: Mixing layer

~ -I- -- - -- -I,

ICold loverI

- j

c

I0::

§lL.

IJ.J

()co«l­IowI

100 200 300 400o

AIR TEMPERATURE ABOVE AMBIENT(9) - F

FIG.7 TYPICAL VERTICAL TEMPERATURE DISTRIBUTION

Coldlayer

Mixingloyer

Hotlayer

2

~r

a:......'-'

q CO<;~~~*~~~~~~~~~~4L~----JLEdge of~ I cu rtoin

l.1J

beo«I­J:ollJ::r

·c

0'1 0·5

FIG.8. TYPICAL VERTICAL DISTRIBUTION OF ~

/' -+-.~6 /'-- ,.~V -it-51- /'

I-/ A *+ /. +

0.> +

+ --3r:-/'

.r>2

V ,

/'

·1.- /

i/ I I I I Io 0'/ 0·2 0·3 0'4 0'5 0·6 '0·7 0·8 0·9 .',0

C;:ALCULATED RATE OF DISCHARGE THROUGH VENT- ft 3/5

(UNCORRECTED FOR DISCHARGE COEFFICIENT)

CUR.TAIN DEPTH -in VENT AREA - sq in.16 24 40

I • -- -8 • + -+12 f + '+

~ Discharge coeticient of 0'6 - - - Discharge coeficient of 0·7

~ FIG. 9· c;oE;:FFIC1~NT OF DISCHARGE THROUGH THE VENTC""J<,

'-'-1'

woa:~U(J')- III IO~ ....ll--

°1Wz~-

~~tr: 0 ·5.----.,.--+-­

O~wU0:::Jet(J')LLJ

iJ50~5

o S 1-0 ---05CALCULATED RATE OF DISCHAR<;;E UNDE~ CUP.TAIN _ft

J/s

(UNCORRECTED FOR' DISCHARGE COEFFICIENT)

BURN~P. CURTAIN DEPTH ""':'in VENT AREA ~ sq in.

16 24 40CIRCULAR I

.• -4;- ---._- 1-----

DOUBLE LINE B e, . , .

FIG.IO· COEFFICIENT OF PISCHAR~E UNDEREDGE OF CURTAIN

Hot air dischargedthr:qugh vent (Mv )

---H

~~ entrolned byrising column ofhot gas (M)

\

Burner. \ I\ I\ I

Effective /'W' ---1

point source

RIG. II. TO ILLUSTRATE PROCESSES MAINTAININGCONS~ANT DEPTH, OF HOT AIR UNDERCEILING

Lines are of equation

.~

I26 "':r

t24

8b 2/. = 375 °

(8h+500) 3 (HI_d)~3

where HJ-H+!-S fAf

CURTAIN DEPTH-in VENT AREA -sq in.

16 24 40I • -- --8 t + -4-

12 t + +

O''------;;-----~:-----~

r-%

<D"-"f­ZWdJ~ 300l-------t------t---~~«w>odJ<{

19Z 2001t--- - --:--- -t---'7"--7""0-"----:*":.......-7""'-- - ...,....-l:JwuWIf-

a::~ IOOI~-----+-------t----____jZ

wa:

~c!WQ.~Wf-et«

FIG,12°, TEI\~PERATURES NEAR THE CE!LING

o

c -.x 0 r-,

8

~~~.

6 <,

I'--

I ~

~O'6 Av - O' O~% (H -d) 2 where H'-25 in,

x Experi mental points2

0 10 20 30 40 s

a:wja:«~oJ:I..LoI

b:w-0

0"

VENT AREA (Av) - in2

ttla>.t.n('t')

FIG.13. DEPTH OF HOT AIR LAYER(1\.1("\ r't1c.rI-JAor::c- 111\.1r'tl:'D rIIDT!l.II\.I\

.='U

8 :I:-J:

ti:wo

Iz

~c::~u

5020 30 40'VENT AREA (A..,)- in 2

10o

cr<.,, ---~~ ~dge of 8 in. c urto: n0

8 ", ......9 I'- -,

<, D........

.............. ~~6 ...... ......--

x--- x.- x

4 .

2

a:«oI

-'0-

\J..o

'0:w~...J

U.oI~0­Wo

-...,...-- Bottom of hot Jover below edge of curtain.

0·6 Ayd} +9(d-Hc)~ =0'043(25-d)~"'

-:' - - - Bottom of hot layer above edge of curtain0·6 Av d~ =0'043(2S-d)51

x Curtain depth Iin. 0 Curtain d~pth 8 in.

FIG,14. DEPTH OF LAYER OF HOT AIR (GENERAL CASE)

504020 30

VENT· AREA" (Av)-in2

10

~~B

.»>: j .~

00

,

,

o

9. 5

0·25

0·75

,......-:t~

~ZW>Io::J

~I~

woa:.~

'U!J1o

o Experimental points

-- Theoretical line (see section 4:S)

FIG.15. QISCHARGE' OF AIR THROUGH. VENTS(NO SPILL UNDER CUR.TAIN ')

~.~. 0·75

z::>

c!<{

u, ' O'~-----+-----'''''''-:---+---e-o

5 '. 10

CURTAIN DEPTH ( He) -, in

II,

15

o Experimental point,

-- Theoretical line (se~ section 4- 8)

FIG.16. DISCHARGE OF AIR UNDER EDGEOF CURTAIN (NO VENT). ,

5020 30 40, '

VENT AREA (Av) - i,,~

10o

,..,.., ...,. - -;- 1"'" -:- - - -. '/~

0 .d "-

/ 0

0 1/

II

-5 ~

/

//

~/ ->0 I"

V/ /x

// //

)(

'5 . ' V,x ' ,

/

PI

0,

CURTAI~ EXPEP..IMENTAL THEORETicALDEPTH ~in POINTS LINES

(see section 4-9),

I x

8 0 - ----

FIG. 17 HE:AT VENTED

Vtr:t area ". ". ". .. l~ I.•._- ..,. "~'--'-- .. ·.1

I

i--,..-~._---. -I

I,-t-----+---- --I

t-----t-------

?CO '250

EFFECTIVE' AREA 9F FIRE (Afr..- inl

Lines ore obtained from equation (14)

FIG.IB, E:FFECT OF FIRE ARq:A ON DePTH',OF LAYER OF' HQT AIR. (NO SPILL

UNDER CURTAIN)

-1/3589 F.R 4f9

- T - - - .- - -

Vent

..'

o

in 0 out

VELOCITY

Theoretical velocitydistribution in inlet

F1G.I9. VELOCITY AND PRESSURE DISTRIBUTION

-~ 0 +PR.ESSURE (qbove otmospher!c)

Theoretical pressure distri but ionaway from inlet and vent

IN MODEL