kn acknowledgment; the authors desire to express their · pdf filekn acknowledgment. the...

KN ACKNOWLEDGMENT .

The authors desire t o express their

grat itude t o Professor !oseph B. Finnegan

and Er . Hamilt on Allport , whose effort s and

co-operat ion make this report possible .

we also are indebt ed t o the staff

of the Underwrit ers ' Laborat or ies for helpful

sugge st ions made in this thesis and for the

use of Laborat ory equipment .

Kenneth V. Hall Frank !. Conway.

May 51 , 1917 .

Combust ion Retarding Apparatus .

TABLE OF CONTENTS .

Obaeot

Table of Cont ent s

List of Illust rat ions

Part 1

Int roduct ion

St at ement of Trade Cust oms

Part 2

General Survey of the Sub!ect

Methods of Using Screens

Part 3

Design and Const ruct ion of Apparatus

Cal ibrat ion of Apparatus

Part 4

Descr ipt ion of Test s

Re sult s

Curves

Part 5

Rest at ement of Problem

Discussion of Var iable Fact ors

14

16

65

66


LI ST OF ILLUSTRATIONS .

Figure

1- Fill and Vent Fit t ing

Combust ion, &pparatus

5- Observat ion Port s

End'

Flang es

Asp irat or

5- Relief valve

5- Spark Plug

6- Wiring Diagram.

7- Valve Layout

8- Screens

Introduct ion,and Stat ement

of Trade Cust oms in the Han_

ufacture of Wire Screens .


INTRODUCTION.

The first person t o employ the

known phenomenon,that combust ion will not

pass thru the mesh of f ine wire screens,was

Si r Humphry Davy. The Davy lamp consist sg es-

sent ially of a wire screen cylinder surrounding

the flame of an ordinary miners lamp . The gas

passes thru. the meshes t o supply the flame but

the flame does not flash out thru the meshes

when in the presence of explo sive mixtures of

gas and air . The presence of this mixture is

det ect ed by the sputt er ing of the lamp. Cl ose

observat ion will show t iny flames !ust inside

the screen which die out before passing thru the

mesh . The cooling propert ies of the wire screen

cool the flame below the kindl ing point and hence

the flame dies. The l imi t ing size of the Openings

and the size of wire have not been det ermined.

The mere stat ement of the mesh of a wire

screen will not ident ify it . There are certain


cust oms observed in this industry which we

will quot e from. the catalogue of the F.P.Smith

Wire Iron Works , Chicago , Illinois.


Terms and Cust oms of the Wire Cloth Indust ry.

Fill ing tarp wires are those which

run longitudinally in the cloth . Filling

wires run t ransversely in the cloth and cross

alt ernat ely over and under the warp wires . In

descr ibing cloth the warp mesh and wire precede ,

in their respect ive posit ions , the same element s

of the f illing . Thus 9 x 8 mosh'

No . wire

indicat es that the warp has 9 meshes per lineal

inch and is made from. No . 18 wire! and the f ill-

ing has 8 meshes per l ineal inch and. is made from

‘No. 19 wire .

The size of any mesh in wire

cloth is the distance from the cent er t o cent er

of it s parallel wires— not the clear space be—

tween these wires . The numeral which precedes

this word in the descr ipt ion of the cl oth in!

dicat es the number of Openings it has in one

lineal inch . Thus 4 mesh means that the cfloth

has 4 openings per lineal inch , each measur ing


from cent er t o cent er of it s parallel

wires.

The clear space between the wires is

det ermined by the size of the wire used in. the

cloth and is found by deduct ing the diamet er

of one of it s wires from. the size of the mesh .

Thus , if Hb .16 st eel wire !which is

diamet er! were woven int o 4 mesh cloth , it

would show inch clear space , or inch

!size of mesh! less inch !diamet er of

wire!.

The f illing meshes in many of the

very f ine grades,and also in some of the medium

ones made from. the largest wire that can be woven

in each,are somewhat larger than the warp meshes

because it is impossible t o force wire beyond a

certain point without straining it and impairing

it s eff ic iency.

Space This t erm, or as it is some-

t imes expressed "hole ' or 'Opening ", means clear

10

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t o which they are subg ected in the loom t ends

t o elongat e them and slight ly reduce their

diamet ers.

The Wire-Cloth flanufacturers ' Asso-

ciat ion adopt ed the old English Gauge as the

Standard for all brass or copper wire cloth.

No . ofGaug e

20

21

22

23

24

25

27

28

29

30

31

32

33

35

36

OldEnglish

.035

.0315

.029

.027

.025

.023

.0205

.0188

.0165

.0155

.0138

.0123

.0113

.0103

.0095

.009

.0075

U.S.

.0375

.0344

.0313

.0281

.0250

.0219

.0188

.0172

01410125

0109

01020094

0086

0078

0070

Standard Amer ican

03200285

0253

0226

0201

0179

0159

0142

0126

0113

0100

0089

0080

0071

0063

0056

0050

COMPARISON’

OP VARIOUS HETAL GAUGES.

NO 0 0f

12

PART 2 .

A Survey Regarding the

General Principles and Important‘

ractors

Ent ering Int o the Study of Ret ardat ion of

Combust ion Thru l ire Screens in Closed Pipes ,

Together with a Summary of the methods of Using

Wire Screens Today.

13

Combust ion. Retarding Apparatus .

A STATEMENT OF THE PROBLEM .

The widespread use of Gasolene and

it s relat ed product s has built up the demand

for some safe way t o st ore these commodit ies .

It has been thought by invest igat ors that the

plac ing of a wire screen or a perforated. plat e

in the vent pipe would prevent the passage of

combust ion int o this st orage tanks . The

problem. then resolves it self around the law

of cool ing and radiat ion as applied t o the

screen and pipe it self . The probabilit y of

the combust ion flashing back is influenced by

the ignit ion t emperature of the gas , r ichness

of explosive mixture,calor ific value of the

gas , spec if ic heat of gas and air and the spea

cif ic heat of the product s of combust ion.

It is a well known fact that gases and

vapors in general are not actually explosive

except when mixed with air or oxyg en and then

only When the mixture is in def init e preport ions.

14

Combust ion’ Ret

arding Apparatus

FILL AND VENT FITTING AS USED ON STORAGE TANKS .

The fill pipe for an underground st orage

tank can not be opened without simultaneously

Opening the vent pipe . r111 and Vent openings

are provided with screens . Each f it t ing is

placed direct ly in a flange provided in the

underground st orage tank! the inner or f ill pipe

of the combinat ion fitt ing ext ends below the

out er or vent pipe so that the issuing vapor

will not t rap the incoming l iquid . Details of

construct ion are shown by f igure 1 for the com-

binod f illing and vent ing fitt ing which is used

when the tank is not permanent ly vent ed. If the

tank is permanent ly vent ed with a suitably'

pro—

t oot ed vent p ipe as required in some localit ie s ,

all that is necessary for the f illing pipe is a

properly locked and screened pipe , which is

accompli shed by having a simple two inch vent

provided with a locking and clos ing mechanism as

shown in f igure 1 and equipped with a screen as

16

Combust ion. Retarding A

shown by the same drawing with a wider

flange so that it will hang on the t op of

the out er pipe .

Combust ion Retarding Apparatus.

DESCRIPTION 0! APPARATUS.

The writ ers have endeavored in this

exper iment t o r eproduce condit ions which

would. most likely arise in standard pipe

lines .

The det ails of the apparatus are

shown by f igure 2 and consist s of two com-

bust ion chambers , two lengths of standard

pipe with flanged ends,for screen insert ion ,

two observat ion port s and flanges of spec ial

design , two specially designed and sensit ive

thermo-couples , two end flanges of special

design , containing taps for spark plugs , gas

and air vent s , relief valve,manomet er and

aspirat or connect ions.

The following is a list of the standard

pipe f itt ings used!

8- 4 ' Tees .4- 4 ' Flang e Couplin

gs .

2- Pieces 4 ' pipe 24 long .1- cross .1- 1 ' cross .2- 9 ' blind flanges with 2 ' t op .

2- 2' observat ion port s .

21


blind flange with taps .blind flange with and 1 " taps .

2 Thermo Couples .3 Millivoltmet er s .

Globe Valves .Pet cock .

adapt ers .l-l ' relief valve .

Globe Valve .

Gat e Valve .1-Aspirat or , 6 ' pipe .Gas Connect ions .Air Connect ions .

Spark Plugs .l-fl ercury nanomet er .1 Pressure Gauge .Samples t est ed.


!Advanced wi re! and No . 35 copper wire . They

were fused in an elect ric arc . The sensit ive-

ness of the couples was f irst t e st ed by the

applicat ion of flame and a large deflect ion was

obtained on a millivoltmet er . They were then

t e st ed by the blowing of the breath upon the

couple , which produced an apprec iable deflect ion ,

thus assur ing their sensit iveness in det ect ing

combust ion in the clo sed pipe . The couples were

placed in a p ipe with a right angle bend at

out side end. The space not occup ied by the

thermo-couples thru the pipe was f illed with

plast er of paris . The ob!ect of the right angle

bend was t o avoid the blowing out of the plast er

of par is , by the force of the explosion.

The couples were placed two and one-

half f eet from. the fac es of the scr een , thus

_producing . a deflect ion only when they were in

actual contact with a flame , and not producing

a deflect ion by radiat ion of heat thru the sample .

combust ion Retarding Apparatus .

EndFlanges The end flanges were

or iginally two blind flanges . The head

flange was tapped for spark plug and

a tap for connect ions t o gas , compressed

air and manomet er . The rear end flange was

t apped for a spark plug and a 1 * tap for

relief valve , gas and aspirat or . The flanges

were bolt ed on air t ight . These are shown in

f igure 3 .

Insert ingScreens The problem of insert ing

screens was solved by the use of rubber gasket s

on each side of screen. Bolt holes were cut in

the scr een t o correspond t o bolt holes in 9 '

rubber gasket s. Great care was exerc ised in

insert ing screens so that the mesh would not be

dist ort ed. In this manner an air t ight !o int

was easily obtained.

Asp irat or The aspirat or as shown in

f igures 4 and 5 ,consist ed of a 6 ' standp ipe ,


were used as a source of ignit ion for the

gaseous mixture . The spec ially designed

spark plug is shown in figure 5 .

ReliefValve The relief valve was used

t o take care of the excess pressure produced

during the combust ion. Drawing of the relief

valve is shown in detail in f igure 5 .

The valve employed was made Of brass.

It consist s Of a conical valve , seat ing int o a

valve Opening , and. held closed by a spring. The

t ension Of the spr ing could be regulat ed by a

knurled plug at the t sp of the valve . The

valve ficrewed int o a l ' standard. pipe tap in

the rear flange .

Manomet er A 24 ' U shaped manomet er was

used. The liquid was mercury. With this mano-

met er , the difference in. level of the two legs,

and by reference t o curve no .5 the desired per—

centage of gas was obta ined , and by referring t o

50

Combust ion. 3etarding Apparatus.

curve no .5 the desired volume Of air could be

expelled by not ing the manomet er reading . It

was also feasible t o a scertain the air t ight—

ness Of the syst em by int roducing a difference

in. pressure between the syst em and the atmos-

phere and Observing how much l ess in pressure

would take place in a given t ime . One leg Of

the manomet er was connect ed t o the apparatus and

the other leg left Open t o the atmosphere . The

difference in reading on the manomet er shows the

difference in pressure Of the combust ion chamber

and atmospheric pressure .

Induct ionCo il in induct ion co il as shown in

figure 6 was connect ed t o a st orage batt ery thru

it s pr imary coil and the secondary t o the spark

plug .

32

Combust ion Retunding Apparatus .

CALIBRATION’

OP APPARATUS.

VO lume The volume of the apparatus

was det ermined by wat er displacement . The

!oint s were paint ed and made t ight , and the

blind flanges bolt ed on the ends . Wat er was

pour ed int o the Observat i on. port with a standard

U.S.Gallon measure and a graduat ed flask . The

apparatus was found t o contain

Gas— air

Mixture Assuming that gas and air are

chemically inert,the following method was used

for det ermining the p ercentage mixture !

Let VI- Velume Of syst em in c .c . below

atmospheric pressure .

P1- Pressure of‘

V below atmospheric .

2- The volume Of air plus gas in

subaect ed t o pressure ,P3 .

Pza

Atmospheric pressure .

vs! vz

avl or volume Of gas in c .c . tobe added t o the syst em.


Test The apparatus was t est ed

for leakage by f illing with wat er and admit-

t ing compressed air . Where any Of the wat er

leaked out , marks were made , the apparatus

drained , all leaky !o int s were paint ed and

t ight ened. The syst em was f inally t e st ed by

the use Of the manomet er and asp irat or . All

the valves were closed. The asp irat or was

turned on and a difference of level of mercury

was Obtained. The asp irat or was then shut Off

the difference of mercury in the two manomet er

arms remained constant,thus showing that the

syst em was air t ight . This proceedure was

carried out at each insert ion of a new screen.

56

4 .

DESCRIPTION OF TESTS .

58


DESCRIPTION OF TESTS .

All of the valves connect ed with the

syst em are closed t ight ly at the start . First

Open the exhaust valve leading t o the aspirat or

then Open the gas inlet , shown in f igure 7 ,

allowing the gas t o run for one minut e . This

will clear out any air that may have been in the

gas lines attached t o the syst em. Close the gas

inlet . The aspirat or is now f illed with wat er

from. the cit y main , and all Of the gas that is in

the syst em may be removed by f illing the asp irat or

several t imes . To fac ilitat e the replac ing of

the gas by air , the observat ion. port on the head

end is removed.

The syst em is now ready for the int roduct ion

of an explosive mixture . The Observat ion port is

replaced in it s original posit ion and all valves

closed. The valve t o the manomet er is opened and

the aspirat or allowed t o drain unt il a difference

in reading of in . Hg . is observed , by referring


t o curve no .3 shows a mixture of The

aspirat or valve is now clo sed and the Operat or

on the rear end allows gas t o ent er the syst em

unt il the pressure difference is r educed t o

in . Hg . Then the operat or on the head

end admit s gas int o the combust ion chamber unt il

the manomet er shows no difference in pressure

This indicat es the syst em is under atmospher ic

pressure . All valves are now t ightly closed and

the gas allowed t o diffuse for f ive minut es.

The gas at the head end i s ignit ed by

means Of the spark plug . The combust ion may be

not iced thru the observat ion port and also be de-

t ermined by the galvanomet er deflect ion.

If the combust ion. pasees thru the scr een ,

the galvanomet er on the rear end will show a de-

flect ion and the combust ion. may be seen thru the

observat ion‘

port .

If the combust ion does not pass thru

the sample , the spark is applied on the rear end ,

40

Combust i on Retarding Apparatus .

as shown in f igure No .7 , and the com—-

bust ion can be observed thru the port hole

and the presence of flame also indicat ed by

a deflect ion of the galvanomet er .

If we secure no combust ion on this

second t rial , then it is readily known that

there was not an explosive mixture in that

port ion of the p ipe . Whenever this occurs

another t est should be made using the same

p ercentage mixture.

Aft er the combust ion , the manomet er

valve is Opened and a reading taken of the

decreased volume by reference t o curve No .4 ,

this amount may be ascertained. This reading

will show if complet e combust ion t ook place .

It s reading should always be great er than the

amount of gas put int o the syst em as a per-

centage of the oxygen in the air is consumed

during combust i on.

41


The manomet er yalve is now closed,

the pet cock on the spark plug Opened , the

aspirat or and compressed air valves Opened.

The aspirat or should be filled and drained

three or four t ime s t o insure the complet e

removal of all burned and unburned gases .

If the sample proves effect ive in

retarding combust ion a richer mixture is

int roduced int o the system. and the sample

t est ed as above .

When the screen fails t o retard at

a certain percentage mixture , a t est using

this same mixture is repeat ed t o make

reasonably sure at what mixture the screen

has failed. Then a new sample i s installed

and the process repeat ed as above .

By finding at what percentage mixture

the different samples prove ineff ect ive and

compar ing these values with those found for

the other screens and plat es , a relat ivit y

FIG . 8 AFTER TEST .


The following samples were t e st ed ,

a. p icture of these i s shown in f igure 9 ,

with their respect ive numbers !

Screen No . Mesh

l 20 50

2 16

5 20 50

4 50 57

5 4 ” German Silver Corrugat ed Coil

6 6O 56 Copper

7 40 55 Brass

8 60 56

9 24 55 Copper

45

Mat er ial

Cu .Plat e

Brass


DATA .

Volume of Syst em 6 gallons pint s .

x

1 gallon 251 cu .i n.

1 pint cu .in .

6 x 251 cu .in

09 cu .in 0

Volume cu .in.

1 cu . ih .— 5 0 0 0 0

x c .c . volume of syst em.

Gas

7

8

9

10

11

12

15

14

15

16

17

x Volume

.07

.08

.09

.10

.11

.18

.15

.14

.15

.16

.17 N

fl

N

H

H

H

M

H

N

N

N

a

46

Gas , c .c .

1720

1955

2200

2445

2685

2950

5180

5420

5660

59104150

Air ,


DATA .

Lo ssGas x P

3sq.in .

7 .07 x

8 .08 x

9 .09 x

10 .10 x u

11 .11 x

.12 x

15 .15 x w

14 .14 x

15 .15 x

16 .16 x

17 .17 x

in .Hg .

1% sq.in

x

48

Manomet erIn .Hg .

sq.

in .Hg .

2 0 1 in .Hg .

P1In .Hg .


DATA .

TEST OF SCREEN #6- FIGURE 9 .

60 fl esh #56 Gaug e Copper Wire Screen.

GasMixture

Observed Combust ion .

Head End

Yes

SCREEN #8- FIGURE 9 .

Rear and

NO

Yes

60 Mesh #56 Gauge Brass Wire .

Yes Yes

when Combust ion appears at both head

rear ends , it means the sample proved ineffect ive .

P

T5.Hg .


DATA .

TEST OF SCREEN #5- FIGURE 9 .20 Mesh #50 Gauge Brass Tire Screens .

When Combust ion appears at both head and rear

2 Gas Observed Combust ion .

hixture Head Ind Rear End .

Yes No

Yes

SCREEN FIGURE 916 Mesh #28 Gauge Brass Wire .

Yes No

Yes

ends it means the sample proved ineffect ive.

58


DATA.

TEST OF SAMPLE #5- FIGURE 9 .

German Silver Corrugat ed Co il .

P1 Gas Observed Combust ion .In . Hg . Mixture Head End Rear End .

Yes Yes

This coil failed t o retard combust ion

at the lowest percentage mixture obtainable .

This may have been due t o the fact that it was

diff icult t o secure a t ight f itt ing of the co il

int o the p ipe wall.

60

5

A RESTATEMENT OF

PROBLEM AND .A DI SCUSSION

LE EACTORS.


air , the flame from the spark produces

ignit ion at the point of contact, i .s .

incit es chemical react ion . This combust ion

proceeds t owards the c ent er of the apparatus

and thereby forms a plane of combust ion which

divides the gaseous mixture int o two part s! on

the one side are the highly heat ed product s of

combust ion , and on the other is the st ill una

consumed gas . The dimensions of the two part s

vary in proport ion as combust ion moves from. the

consumed t o the unconsumed. port ion.

The veloc it y at which this plane advances

is different for each gaseous mixture , and de-

pends both on the composit ion Of the mixture and

on the pressure t o which it is sub!ect ed , the

higher the velocity the great er the rise in tame

parature , and this latt er in turn direct ly in—

fluences the expansion of the gas and the pnoduct s

of combust ion,which thereby exert such a st rong

pressure on their environment !air , walls , et c .!

66


Screen #5- figure 9- a 20 mesh 50

gauge brass wire was second in retarding value,

failing when the percentage mixture reached the

value of

Screen #9- f igure 9 a 24 mesh , 55

gauge copp er wire retarded the combust ion up

t o

Plat e #1- 20 mesh , 50 gauge copper

plat e r etarded the combust ion up t o

Screen #6- 60 mesh , 56 gauge copper

wire failed when the mixture was

Screen #2— 16 mesh , 28 gauge brass

wire retarded the combust ion up t o

Screen #5- 50 mesh , brass wire and

#8 a 60 mesh,brass and the German Silver Cbil

did not retard any combust ion . The flame burned

away that part of screens #4 and #8 which were in

actual contact with the flame .

From. the foregoing result s , it is

indicat ed that the f ineness of the mesh alone will


mot ion and the sample placed on the down-

st ream. port ion of the Therefore,all

of these samples would hold up much bett er in

actual field work,but the ir relat ive values

as found in these t est s would not be alt ered.

68

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