gat)(general - defense technical information … the general american research division (gard) of...
TRANSCRIPT
GAT)(GENERAL AMERICAN TRANUPORTATION CORPORATION
FRICTION LOSS IN FLEXIBLE
S-ý PLASTIC AIR DUCT
by
R. B. NeverilH. F. Belils
Q9 OCD Work Unit ]1423A
GARD Report 1278-2 October 1965
Distribution of' this document is unlimited.
IL AND
GENERAL AMERICAN RESEARCH DIVISION
7443 NORTH NATCHEZ AVENUE. NILES. ILLINOIS 50648 312/847.400oO
Prepared forOffice of Civil Defense
Department of the Army, OSAunder
Work Unit 1423ASRI Subcontract No. B-70925(4949A-28)-US
FRICTION LOSS IN FLEXIBLE
PLASTIC AIR DUCT
by
F. B. NeverilH. F. Behls
0CD Work Unit 1423A
GARD Report 1278-2 October 1965
Distrioution of this document is unlimited.
Reviewed by: Approved by:
G. Engholm P7 Ro63nbergGroup Leader General ManagerEnvironmental Research
REVIEW NOTICE
This report has been reviewed in the Office of Civil Defense and a:•roved forpubli:ation. Approval does not tignify that the contenta necesaaril]y reflectthe views and policies ofi the Ot'tll"e of Civil Defenst.
FOREWORD
The General American Research Division (GARD) of General American Trans-
portation Coi-poration (GATX) was contracted by Stanford Research Institute
(SRI) for the Office of Civil Defense to design, fabricate, and test flexible
plastic tubing and fittings which would provide a system for handling venti-
lation air in fallout shelters when used with the shelte-r ventilator (shown
below) specified in MIL-v-40645., "Package Ventilation Kit, 20-Inch Fan, Modular
Drive (Civil Defense)". This program was performed under SRI Subcontract
B-70925(4949A-28).-US with Mr. C. A. Grubb serving as project monitor.
PACKAGE VENTILATION KIT IN OPERATION
0NWM AL AMittAN MONBA3M @VItStN
Il
'I
ABSTRACT
I I Tests were conducted to determine the pressure drop characteristics of
20-inch diameter, 4-mil thick, polyethylene tubing and both factory and.
shelter fabricated 90-degree elbows. The tests were performed at flow rates
Sranging from 1300 to' 4100 cubic feet per minute. These plastic components
are part of a portable ventilation system that has been developed for Civil
Defense fallout shelters, Specification MIL-V-40645.
5 Fully inflated 20-inch diameter plastic tubing has about t~hree-quarters
of the pressure drop of sheet-metal duct. However, the last fifty feet of a
I plastic duct system, which is not completely inflated, has 1-1/2 to 3 times theSduc
pressure drop per foot of fully inflated plastic tubing. The result is that
Sfor duct systems over 100 feet long th, pressure drops for sheet-metal and
plastic tubing are approximately the same.
'Me friction losses for both factory fabricated and shelter fabricated
elbows were established. A 40-inch, smooth radius, 90-degree factorya fabricated elbow is recommended for use with the Civil Defense Package
Ventilation Kit. This elbow develops a pressure drop equivalent to 50 feet
of straight tubing. The best shelter fabricated elbow is a three-piece elbow
with a radius of 60 inches that can be fabricated from the straight tubing
[ and tape stocked in the Package Ventilation Kit. This elbow develops a
pressure drop equivalent to 90 feet of straight tubing.
I
UNNIMAL AMERICAN REUHARMH OIVISION
' iii
TABLE OF CONTENTS
-SECTION Pag-
FOREWORD .. . . . . . . . . . . . ... . . . . . . .i.. . ii
ABSTRACT-. .... ....... ............. iii
1 INTRODUCTION.. ..... .... . 2
2 TEST PROUCFI)ES. . ....... . . . . ............. 3
2.1 Apparatus .............. ......................... 3
2.2 Methods ..................... ....................... 3
2.2.1 Tubing ........................................... 8
2.2.1.1 Duct Adaptor............................... 8
2.2.1.2 PVK Application........................... Q
2.2.2 Elbows .................. .... ............... 11
2.2.2.1 Factory Fabricated Elbows ................. 11
2.2.2,2 Shelter Fabricated Elbows............. 12
3 RFSULTS AND ANALYSIS .......................................... 19
3.1 Tubinrg...............................o. ......... 19
3.1.1 Duct Adaptor ................................ 23
3.1.2 Condition of Duct ........................ 23
3.2 Elbows. . . . .......... o ........................ o ........ o .o.. 25
3.2.1 Factory Fabricated Elbows ......... ...... 27
3.• 2 Shelter Fabricated Elbows ................... 9
4 SMM4ARY AND RECOMMENDATIONS.. . o.......... o .... o ............ 33
REFERENCES ........... oa.................... ........... 38
APPENDIX A - Test Data ........................ . ......... 39
APPENDIX B - Specification Used for Determining Cost ofFittings ........... ....... o................. o..... 49
GIENERAý, AMBRICAN REQEARC14 0IVIBIONiv
LIST OF FIGURES
I FIGURE NO.
1 Package Ventilation Kit (PVK) I2 PVK Duct Systems 23 Test Apparatus 54 Schematic Layout of Test Apparatus 6
I5 Friction of Air in Straight Spiral Conduit Duct 76 Test of the Tubing with the End Unrestrained (Free
Air Discharge)7 Test of the Tubing with the Duct Adaptor 98 PVK-Duct Test 10
9 Wire-reinforced Elbow 1310 Hand-tucked Elbow 1311 Shelter Fabrication of a 60-inch Radius, 90-degree,
Three-piece Elbow 1512 Shelter Fabricated Three-piece Elbow in Operation 1613 Shelter Construction of the Packing Box Elbow 1714 Packing Box Elbow in Operation 1815 Friction of Air in Straight Polyethylene Tubing 2116 Wrinkles in New Tubing 2417 Pressure Drop, Comparison of 90-degree Elbows 26.18 Instability in Miter Elbow 2819 Friction Loss of the 40-inch Smooth Radius Elbow 3020 S;helter Fabricated Elbows in Operation 3121 Friction Loss of the Three-piece, 60-inch Radius,
Elbow 3222 Factory Fabricated Elbow (Modified) 3523 Test Data -- 50 Feet of Tubing 4o24 Test Data 100 Feet of Tubing 4125 Test Data -- 150 Feet of Tubing 42S26 Test Data -- 200 Feet cf Tubing 4327 Test Data -- 250 Feet of Tubing 4428 Test Data -- 300 Feet of Tubing 4529 Test Data - 350 Feet of Tubing 46
30 Test Data -- 400 Feet of Tubing 4731 Test Data -- 450 Feet of Tubing 48
[EI:
GFOUVRAL AMCRICAN W9IUAPCH 01VISeON
v
I
SECTION 1
I INTRODUCTION
A Package Ventilation Kit (PVK) was developed (see Figure I and Ref. :)
for use as an inexpensive method of exhausting iftale, hot and humid air from
fallout shelters. This ventilator is intended for use with flexible plastic
duct systems (see Figure 2).and, therefore, flexible plastic tubing and fittings
are supplied with the Kit. The objectives of this program are to determine the
I tfriction loss of flexible tubing and fittings, and to recommend the best
fittings, based on cý.st and pressure drop, for use in fabricating shelter duct
systems.
F
I
.1
j
i3ttvmls Fa~uI~re 2 PKI• $YqlS~q•N•!
,I
SECTION 2
TEST PROCEDURES
2.1 Apparatus
The test apparatus consisted of an 80CO cfm centrifugal blower connected
by a flexible wire-reinforced cloth duct to a 47 foot long, 20-inch diameter
test stan. which was fabricated from "L U.S. Gage, zinc coated steel spiral
conduit duct with 6 inch seams (see Figures 3 and 4). The design of the test
stand is based on recommendations of the National Electrical Manufacturers
Association (Ref. 2). Air flow rates were measured with a lU-inch diameter
aperture sharp-edge orifice plate which was calibrated with a pitot tube five
feet upstream from the orifice. Two air straighteners were located approxim_.t: ly
14 feet and 28 feet upstream of the orifice plate to reduce turbulence. A
piezometer ring was located 14 feet downstream from the orifice and 5 feet from
the end of the test stand. Inclined manometers were used to measure the pre.-
sure drop across the orifice, and the static pressure drop of the test speci-!ne-s.
2.2 Methods
The specimens were first taped to the test stand. The blower was adjusi• i
to provide the desired flow rates, and the static pressure loss and flow rate
(orifice differential pressure) were recorded. Barometric pressure, dry-bulb
temperature, and wet-bulb temperature were recorded before each test to providt
the flow rate correction factor to standard air . = 0.075 lbs/cu ft). The
tare pressure drop of the test apparatusi.e., the pressure drop caused by th7
5 foot length of spiral. duct between the plane of the measuring station and
the plastic specimens,was suotracted frcm the test data after its correction t'*
GENERAL AMERICAN RESEARCH DIVISION
m
standard air. To establish the tare pressure drop, the friction loss for 100
1 feet of 20-inch spiral duct -- as measured from the static pressure measuring
J station -- was determined with the apparatus described above, and the results
are shown in Figure 5. The tare pressure drop for the leugth of spiral conduit
between the static pressure measuring station and the test apecimen was
calculated by multiplying the values of Figure 5 by 0.05 (see Table I); i.e.,
I Tithe ratio of the five foot length to the total 100 feet spiral duct tested.
lTable I
Tare Pressure Drop of the Test Apparatus
Air Flew Tare Pressure Drop(cfm)- (inches of water Lagej
1200 0.001014oo 0.00131600 ,o oo181800 0.00222000 . 002d2200 0.0033i4 2400 Q.0039260o0.0•
2800 0.00523000 0.0059I I3200 0.006634oo 0.00753•0 0.00633600 0.409.14W000 .000I I •4200• 0.0110
As shown in Figure 5 the friction ,r air Ir straight &piral duct, as
m.nutactured tq the Carrier Corporation. is approximately rive par cent lower
than tU theoretict& values r-4.-ea tnw t in the rrth-c1i chart of" tt* ARIUM
I ] Guide and Data Book (Ret. i).
II[I
04
cn
0 t4z
4.4E4 w
r.T4
E-i
(Y)
f AF-
44ýD 04
T11.4 fA
0 i-4 ýn1444
J.
GENERAL AMERICAN RESEARCM DIVIsioN
C;
2.2.1 Tubing
i I Plastic tubing lengths from 450 to 50 feet in increments of 50 feet were
tested at flow rates from 1.00 to 4100 SCFM (standard air) with the discharge
end of the tubing unrestrained (see Figure 6).
i Five high impact strength (Type II), untreated (Finish 1) tuuing specimens
were tested. Of these samples one was low slip* (Grade A), three were medium
slip (Grade B), and one was high slip (Grade C). The diame.ter is 19.75 + 0.25
jl inches, and tue thickness 0.004 (4-mil) + 0.0008 inches. The samples were
furnished by the Sinclair-Koppers Company, Inc. and the National Poly Produicts,
t Inc. Thin gage polyethylene films are classified as follows (Ref. 4):
L Type I Normal impact strength.
Type II High impact strength.
Grade A Low slip.
Grade B Medium slip.
SI Grade C High slip.
Finish 1 Untreated.
,I Finish 2 Treated.
ii 2.2.1,1 Duct Adaptor
l AftEr determining the friction loss ot' a plastic tubing specimen,
i the duct was %tQted vlth the duct adaptor attached to the free-end (see Figure 7).
*The test apparatus arid methods t',r determlnrWi the irpact, strenght it and slip
f!kinet~c cooEfi'cint of rricti~n) are preotnted in Federal SpecificationL-P-378. Finish 2 filLm is treaied t... aj e printinfý ink to adhere.
i|-_. LtIatIEAL AMIEPICAr- AEUEARNC~ OI;lVllISIO
Figure 6 TEST OF THE TUBING WITH THE END UNRESTRAINED (FREE AIR DISCHARGE)
Fi•.,urc 7 TEST OF THE TUBING WITIH THE DUCT ADAPTOR
GENERAL AMERICAN fIEUEAiICH ODVIBION
9
II
The purpose of' this test was to determine the friction 1bss of the system with
and without the duct adaptor for those duct systems where its use is optional.
"2.2.1.2 PVK Application
After determining the friction loss of plastic tubing specimens these
same specimens were attached tc a calibrated Civil Defanse Package Ventilation
Kit ventilator and the power input was measured (see Figure 8). Knowing the
wattage input to the system the air flow and pressure drop were determined from
the fan motor performance curve (Ref. 5). The air flow obtained by this meethod
agreed within three percent of the values obtained with the test set-up.
Therefore, the friction loss for tubing and fittings determined herein can te
applied to the Civil Defense propeller-type ventilator as s-pecified in MII-V-
40645.
I
I
3 Figure 8 PVK-DUCT TEST
IGENERAL AMERICAN RESEARCH OIVlIlON
1 10
2.2.2 Elbows
The friction loss of all fittings with 100 feet of straight tubing on the
downstream end of the system were ccmpar,-d tc each other. Testing with a duct
on the discharge end cf the elbcvs was necessary tc filly inflate the fittings,
and the results are thereforE only applicablt- tc fully inflated fittings. The
best factory fabricated and shelter fabricated elbows were then further tested
with duct lengths of 100, 200, and 300 feet to determine the effect of static
pressure on the elbow pressure drop cr equivalent duct length (EDL).
2.2.2.1 Factory Fabricated Eltows
A preliminary specification f,_r flexbtle: plastic elbows which might
be used in constructing a sh-lter ducc system to b- attached to a portable
ventilator was sent to eight fabricators. This specification is included aR
Appendix B. The temperature range, flow ra-e, and inrtrnal pressure were
specified to incorporate the most adverse conditicns expected during storage
and operation. Cost quotations were: requested for the fabrication of elbows
in seven configurations with varying centerlir. radii from 20-inches to 60-
inches. Table II shows the relative prcduction costs of' the 20-inch diame( r,
90-degree, smooth radius elboh with a 4C-inch centerline radius.
The majority of fabricators preferrti the us.- of polyvinyl chloride
(PVC) because it is easily heat stalrd and less expensive. All manufacturis
indicated that the smooth and miter -lbows were the siffpl~st and least
expensive to fabricat+ in. tlexiblt ;Iastir, 7Th- co -f tlii miter elbow
was essentially the same as a inrc17 '-!cw with a cr-nterline radius of 20
GENERAL AMERICAN RESEARCH OIVISION
3I
Table II
I- Costs of Smooth Elbow
I Manufacturer Material Thickness Quantity
mils 500 350,000 700,000 1,050,000
1-- Polyvinyl
1 Chloride 4 $2.00 $1.28 $1.26 $1.24
- Poly-2 ethylene 4 $15.35 $3.00 $3.00 $3.00
Polyvinyl3 bloride 8 $3.10 $2.75 $2.60 $2.55
X PolyvinylS4 hloride 4 $2.08 $0.43 $0.38 $0.37
*Outside seams of full production units would not be trimmed.
I inches. Therefore, 90-degree smooth and miter elbows of 4- and 8 -mil thick PVC
--I with centerline radii of 20, 30, 40, and 60 inches were selected for testing.
A wire-reinforced elbow was also tested (see Figure 9). This elbow was
S constructed by inserting,- heliý.al coil of 0.072 inch.dia. tinned music wire
i inside u straight length of four-mil, 20-inch diameter, polyethylene tubijn,
The wire was taped to the inside of the duct every 90-degrees around t~hF
periphery of the tubing, and the distance between hoops was six inches.
2.2.2.? Shelter Fabricated Elbows
The shelier fabric-ated elbows that were t1estel were ,ri,-d-tucked,
I 3-pi .', and packi.,1,,, boxes taped t,. ier. The h - w U '20-
strumted by f'orring tucks )r p.1eat. l; ', r .'e s!ide &t he W'.d,' •wj aping the
I tu-.-s s that a gradual rad.iu, o1 ,urva, w.c ! eve l.p.I ( 'ee FiAr eure !,
SGENEIAL AMERICAN RESEARCH OIVISION
I!
The excess material inside of the duct, formed by the tucks, was placed down-
stream to reduce the resistance to air flow. This elbow is difficult to
.i construct, and in most cases requires a relatively large floor area when
inflated as compared to the other elbows.
mI A three-piece elbow was fabricated from polyethylene tubing by cutting
two 32 x 16-1/2 x 32 inch triangular-shaped sections 58 inches apart (see
Figure 11). The tubing was taped after overlapping the downstream seam
(relative to the direction of the air flow) approximately one inch. This
provided an elbow with an approximate centerline radius of 60 inches (see
II Figure 12). This elbow is easily constructed with a template.
1 A rigid elbow was constructed frocn a corrugated fiberboard box (see
Figures 13 and 14) and teýted. The packing box elbow, especially one less
I than 90-degrees, is very difficult to construct and requires materials which
in many cases will not be found in shelters.
LI3IIII3 r• W t• AL AP• CPCAN •g3A34Cw OIVISIOfu
off
Direct io
A.d 1 ro
Figur 1.1 HELTE WRISeION iOF 0-NrMI ~ I -IELW
GENF AL A URIC N P n1,A CM ý304!10'
I/ I
III,1�.
4
IFi�rure 11 SI-�LTEF C0NSTRLTC'TIOI�1 OF TI� PACKING BOX ELBOW
1
CIENENAL AMUNICAN NEUKANCS.4 OIVIUION
17
-w -� - -� - - ,� -�4:--,.-'� -
SECTION 3
RESULTS AND ANALYSIS
3.1 Tubing
The friction of air in straight polyethylene tubing for lengths from 50
to 450 feet are shown in Figure 15. These curves are bas0A on a least squares
regression of the test data as shown in Appendix A. The standard error of
estimate; i.e. the mean of the square of the differences between the data and
the fitted curve ranges from 0.007 inches of water gagt (iwg) for the 150 foot
length to O.02 iwg for the 4oe foot length. As indicated by the data presented
in the Appendix, the low slip zpecimen has the least friction loss for all
lengths except the 50 foot length. It was expected that this specimen would
hare the highest friction loss, and the high slip specimen the minimum friction
loss. It is felt that an insufficient number of samples were tested to establish
if friction loss can be correlated to slip since orly one lot of the low and
high slip specimens was uzed.
Figure 15 and Table 1II show that the pressure drop for the last 50 feet
of tubing in a duct system is from 1-1/2 to 3 times as great as that for duct
elsewhere in a system. As shown in Figure 6, page 9, the last 50 feet of
tubing in a duct system is not completely inflated due to the weight of material
and decreased static pressure in this part cf the system. The air velocity
in a partially deflated duct is greater than that in an infl&ted duct since
the cross-sectional area is leýs the.n that o' a ful.Ly inflated or circular
duct. Since the pressure drop due to frictlon is approximately proportional
to the vel.)city squared, the increase vel9ci!.y in partially inflated
UeN1,,AL AMERICAN ,•COARCM o,0,1,oA.
- --- - .~ -
I
Ij duct results in an increased pressure drl_. iii this section of duct. As the
flow -,te increases, the length of uninflated tubing in a system decreases.
As shown in Table lIT the friction loss for the polyethylene tubing other than
the last fifty feet in the system is approximately proportional to the length.
1 For example: at 1000 scfm the pressure dr-p increases 0.007 iwg (range:
0.006 to 0.007) for every fifty feet additional tubing; at 3000 scfm it
increases 0.049 iwg (runge: 0.047 to 0.05].) for the same length increments.
The friction losses of polyethylene tubing and sheet-metal ducts are also
compared in this table. In general, the friction loss of inflated polyethylene
I tubing is less than that fcl the same diameter sheet-metal ducts, whose pressure
drop is directly proportional to length. At 1000 scfm the friction loss of
inflated plastic Lubing is 0.007 iwg per fifty feet as compared to 0.008 for
the sheet-metal duct; at 3000 scfm the friction losses of plastic tubing and
sheet-metal ducts are 0.049 and 0.065 iwg per fifty feet, respectively.
I A mathen-atical expression derived from the least squares fitted curves of
a the data (see Appendix A) is:
p 1.915 x 10-6 [q1.349 + 0.01006 1) Ql. 8 33] (1)
I.where:
P = static pressure loss, inches of water gage
"IQ = air flow rate, standard cubic feet per minute (scfm)
L = tubing length (for lengths of 50 feet and longer)
The solid curves in the Appendix are based on the test data, while the dotted
Sportions ef the curves were generated with Equation 1.
[.
A C. AMC q!CAN PERVARCH DiVIHiON'
20
J_\ U'\
S-I 0. 0~ - "0 C-1 \0 0CoZ r C C C) c;
C'000 0 0 0 0
0 0 0
04 ~ C 01 0 0-0 0 0 0 0
C.4 0- c 0 0 0 C) C 0 0
040
0 c2 C1 C, 4-
;7 0 0 0 0C)1 4~-- -- )
0A 0j C~ Or\ o' 0 0 0
-4--- I il
GENRA A'ERCA REERH0VS
3.1.1 Duct Adaptor
The P•K includes a Duct Adaptor which is uved to seal the plastic ducting
to a window or doorway opening in, a shelter. This adaptor was tested with
plastic duct to determine if it could support the discharge end of the duct,
and thus reduce the high friction loss o; the final fifty feet of tubing in
a system. The Duct Adaptor increased the static prest:ure loes through the
duct system since a negative pres-cure occurs upstream of the adaptor. This
additional pressur- loss results from the converging and expanding air strean.
through the reduced flow area (see Figure 7, page 9), Therefore., the Duct
Adaptor specified for the Kit (YMI1-V-LO64c5) does not include legs., and is
intended for use in windows, doorways, or partitions cnly. When the air
supply for the shtiter enters the duct exit opening, or other r:Earby air
supply openings, the duct should extend at least 35 feet from the building,
and should not include the Duct Adapto:." (free air discharge).
3.1.2 Condition of Duct
Creases are formed in tht tubing during fabrication by rolling the tubing
on a cylindrical core. Tests with these creases in both the horizontal and
vertical positions produced the sam. static pressure losses. The tubing that
was walked on and crushes, howevtr, did indicate a decrease in static pressure
loss and less "whipping" and "flutter" at the discharge end. Ripples are
formed in new tubing when it is firsr irflated Tee Figure 16). After the
tubing is crushed, wri.nklti, aýJ g•nerally abused, these ripples diminish,
thus accounting for tnr- Ic,:, -as,- i. static ý :sui. .c-ss, s.
ULNERAL AMERICAN RESEARCH DIVISION
2•I
- -~ .t
3.2 Elbows
Each of the factory and shelter fabricated candidate elbows was tested
by fastening it to the test stand and taping a 100 foot section of polyethylene
duct to the downstream end of Uhe elbow to assure that the elbow is fully
inflated. The pressure losses measured for these systems are presented in
Figure 17. Based on the results of this comparison of factory and shelter
fabricated elbows, a series of tests were conducted to determine the ien:gth of'
straight duct equivalent to the pressure drop for the recommended factory and
shelter fabricated elbows when fully inflated. These tests evaluated the
elbows with straight lengths of tubing. The tubing was attached directly to
the elbow by overlapping approximately one inch of the end of the elbow and
t. ,ing the seam. When inflated these elbows produced a total curvature or
bend of approximately 110 cegrees. This phenomenon is caused by stretching
of the plastic material due to the elbow internal pressure. Since the surface
at the outer radius of the elbow contains more material than the surface at the
inside radius, the effect of the stretching produced an angular bend of more
than 90-degrees. Prior to recurding data, all elbows were inflated and trimmed
to form a 90-degree angle. No attempt was made to determine the equivalent
duzt length for partially inflated elbows.
Of' o AMUPIOCAIU1 SUlUEimCH OIVotUUON
.60- -+4 F4-
t -ltý t k 444T 4-_44-i-ý ITTTT' i-i-4 4-4- i- 4 4+tAll elbows tested
*55 (see key below) t, . . - 1ý
with 100 feet oflow slip, NPP tubing
17 -1- _4_
-H-i-4-44i iý-_ P+ý 4- - +.504-
7-'-1 -4 Z4f-- H -t-4-4- 14
4
.45 + Recommended shelter _ýýt-+4- Zi _j t -I-I I-Pq fabricated elbow
-ý4# ++_60 I.nch radius7 3-piece miter. 4P f-L' 4-tr,
4T 47Ao +.7 _r -t4-_LLJ t104
-4-
7-r4-ý
.35 4-1 - -t4T. 4-
f_4_ IL4_7
X_ý-4.30 it -
I+41 1:7_+ 7, 4-- -44-4-4T
E-4
+CG.25 4- j L4 _4444-
ITT lRecommended factory'fabricated elbow
I JJ: ;+ 4 40 inch smooth radius.
T77ý-ý--+-4
ý7 -47" 4-- -
4-- -4--
f
100 feet of NPP tubing,
. . . . . . 7 low slip (see Appendix A, -7SYMLOI
.10
0% FWwry W, dowtAL ftjv* PW05 lowtur W 1446*6 Wtow 1.14. 4
0 rim %,wv "-no" " 1W W ý6.
a ft," PC ow-to Wt.* put00 ;-00 1(500 20010 2W 3000 35M 4M 7500Flow Rate, CFX OP 0.0175 LBS/CU FT
F.Ieu- 1ý PRESSUTE DRCT XMYARION OF ýKý-V&sREE ELBMZý
GENERAL AMIEnICAPY IM606464CO-4 0jVt8jCN
3.2.1 Factory Fabricated Fibotws
The elbows with thim lowest pr-,ssur- lo~ss-s art, factory fabricated smooth
radius elbows "see Figurte 17). F'or a giv~-r configuration. tht:m elbows fabricated
from four-mul plastic had low-.ýr prt.--surt- lo~s.s-ý than t~hose fabricated from
eight-mil plastic. The change in prt-:ssture los;s with c-ernt-erldirje radius decreased
as the centerline radius approached 60 inche-s. rh- lbows with ctnterline
radii of ~40-inches arid 60.inchims have neýarly ident~cal pressure losses,
indicating that the trade-;-off point fo7r c#-nterlinc radzius vErsus pressure loss
is approximately 40L inches. Increasing thi- cent,ýrlin-. radius beyond this point
provides only a minimal decre-ase in pr isvr,ý loss, and requires considerably
more shelter floor arta when; inflatt-J,
The mitered elbow had a considýýablt- prf:ssure- drop, even greater than
the shelter fabricated three-PIi~-Ce - lbicW, becauste of the extreme flutter and
vibration which developerd. Figurt- 18 is "stop-action" photographs of thr*
miter elbow illustrating the amiplit-.AdA -,f the pu.lsation in the tubing an"! elbow.
The wire-reinforced elbiow (sF~igiirý- 9,pagf-' 131 dev:i-oped excess!Ife
pressure losses. This tlbow had to tt aktare t Plow rate-s above 2000 cfm
to keep it from straightening out, W~thr thtm rý.ctraint, th- ~-1bow tended to
kink into a short. radius r-lbow' such as a miter ~1c.Thi instability
resulted in. the high preýsstur,: 'o~s
GENERAL AMERICAN REBEAPRCH CIVrnION
The four-mil polyvinyl chloride 40-inch smooth radius elbow is the best
factory elbow w"en cosidering pressure drop, space requirements, material and
-cost. Figure 19 shows the results of further rests performed on this elbow.
The soliA iVnes show the pressure losses for the elbow with straight lengths of
tubing attached to the downstream side, the broken lines show the pressure losses
for the straight lengths only, It can btý seern that the equivalent length of
stra-,ght tubing for the -O-inch smooth radius elbow is approximately 50 feet
when fully inflated. For the elbow to be fu.ly inflated fifty feet of straight
tubing must be on the downstream side.
3.2.2 Shelter Fabricated Elbows
Of the shelter fabricat•1 =-bcw ( •ur. -C', thý- three-piece elbow
results in the least pressur._ loss. The elbcw made from packing boxes produced
the largest pi essure loss. This elbow was extremely stable at all flow rates;
howeverthe exit and entrance losses of' the air -tream in the plenum-like
box produced the high pressure loss., The best hand-tucked t-!bow resulted in
pressure drops considerably higher than those shown in Figure 17. Since the
results were erratic (due to the elbow beng unstab_ý n! curve is presented.
Since the three-piece elbow has the least r(-ssure lost this elbow was
further tested with 100 t 20, and 300 fet of tubing (set Figure 21). it can
be seen that thepressure loas of the th.,--piect titovi with a centerline
radius of 60-inches is equivalent t, 90 f-ct of straight tubing when 'ully
inflated. For the elbow i.o v- L-l- :i fldt-] :'-v f--t of straight tubing
must be on the downstream Sl*:
IGEINER~AL AME£RIC:AN R•IUEARCH OIVI9ION
.60
55 --5
1.550(SEINGAPP INCILAIR S-MKOLPER)
II'.45 F
4.+4
.. 35 ....
II~.0IV
It.25
(a ----- 7F7
vI I
Three-piece, 60* Radius, ElbowI
Packing Box Elbow 1
Hand-tucked ElbowI
Figure 20 SHELTER FABRICATED ELBOWS IN OPERATION3
OWNRINAL AMERICAN 080EAU0C4 OIVtSOrv
31
SECTION 4
SUMMARY AND RECOMMENDATIONS
The friction losses of the 4-mil polyethylene tubing specified for the
Package Ventilation Kit, MIL-V-4O645, have been determined (sef- Figure 15 and
Equation 1), and have been incorporated into the FVK rating (Ref. 6). Fully
inflated 20-inch diameter plastic tubing has about three-quarters of the
pressure drop of sheet-metal duct. However, the last fifty ftt of a plastic
duct system which is not completely inflated has l-i/2 to 3 times the pressure
drop per foot of fully inflated plastic tubing. The result is that for duct
systems over 100 feet long the pressure drops for sht-:,t-metal and plastic
tubing are approximately the same.
The Duct Adaptor supplied with the PVK. should oe used to prevent re,.ir*.
culation in windows and doorways when the duct system terminates there, ind Iwhen necessary in corridors and partitions for developing systems which
control the flow or distribution of air. The Duct Adaptor should not be
used elsewhere, such as the end of the duct outside of a buildirg, since its Iuse increases the system pressure drop.
The smooth 40-inch radius plastic elbow is the best of the factory
fabricated elbows, This elbow when fully inflated results in a pressure
drop equivalent to 50 feet of straight tubing. For thte elbow to be fully
inflated at least 50 feet of tubing must be on its downstream side. Since.
this elbow must be cut at 75-degrees whin uninflateA so that the resulting
inflated elbow is 90-degrees, it is rt_-c,mmtrjd-d that ",Figure 8 of MLL-V-
GENERAL AMERICAN RL•SARCH UIVISION
S- -n
o40615" be modified as shown in Figure 22.. The cuffs have been rem-wed since
Sthey are of no value for taping the tubing to the elbow, and in most cases
j produce wrinkles and dis'-ortion. Since polyvinyl chloride material is easily
heat sealed it is recommended that tris material be specified in paragraph 3.7.3
1 of MIL-V-L0645; therefore, the second sentence of this paragraph should read
as follows:
- "The elbows shall be !'abricated from 4-mil thick polyvinyl chloride
h or type II, grade C, finish 1 polyethylene conforming to Specification
L-P-378 with a minimum flat dimension of 31 inches."
The most efficient shelter fabricated elbow is the 60-inch radius three-
piece elbow. This elbow when fully inflated produces. a pressure drop
equivalent to 90 feet of straight tubing. For the elbow to be fully inflated
3 at least 50 feet of tubing must be on the downsticam side.
Factors that should be considered in the selection of elbows for use in
shelters are the simplicity of assembly, floor space required when inflated,
"3 stability in operation, ana cost. Assembly of the factory fabricated elbow
in a duct syLtem is a simple matter of cutting straight lengths of tubing
at the appropriate length, inserting the elbow, and taping the components
* together. Any angle between zero and ninety degrees can be obtained by
cutting the elbow at the angle desired. The shelter fabricated elbow can
be fabricated from materials in the PVK, and the required number of 90-degree
elbows can be fabricated to develop a suitable ventilation duct system for
any shelter. The three-piece, 90-degree, elbow can probably be constructed
by the shelterees with a template and instructions; however, fabrication
( GENERAL AMERICAN RESEARCHl OIVIUIOJ
34
73
It
�E..
I1III.
I-,
'IE4 I'U
CJ I0dp
.3' 1c�J D's
C,, 1+1H -
IIII
SENUmAL AMUPUCAN *UACE D�VIUSON 335
of an elbow with angles other than 90-degrees would most likely be difficult
and confusing. Therefore, it is recommended that:
1) One factory fabricat•ed elbow be furnished with the PVK. One
elbow should-satisfy the majority of shelter duct systems.
2) A 90-degree elbow template should be included with the PVK
for those systems requiring more than one elbow. If a system
requires elbows with an angle less than 90-degrees a factory
fabricated elbow should be cut for the desired angle, thus
eliminating most cases of shelter fabrication of an elbow other
than 90-degrees.
The equivalent duct length of any plastic tubing system can be determined
by adding the total length of straight tubing plus the number of elbows times
their respective equivalent duct length (see Equation 2) -- 50 feet for the
factory fabricated elbow and 90 feet for the shelter fabricated elbow.
EDLs = L + 50 Nf + 90 N (2)
where:
EDL = Equivalent Duct Length of the system, feets
L - length of straight duct in the system, feet
Nf - number of factory fabricated elbows, dimensionless
N = number of shelter fabricated elbows, dimensionless
The pressure drop of these systems my be determined using the following
equation.
6 1.349 EDL ) 31 (3)
RPNENAL AMIAI *USUAPCH OIVlIe•36
where:
AP a static pressure drop, inches of water gage
- air flow rate, standard cubic feet per minute (scfm)
FPDL - Equivalent Duct Length of the system (for lengths of 50 feet8 and longer), feet
Equations 2 and 3 have been experimentally verified for straight tubing,
and for elbows located anywhere in a duct system except within 50 feet of the
discharge end. Future tests should be performed to verify the generality of
equations 2 and 3 to a system with the elbow(s) partially inflated (within
the last 50 feet of a system). Tests on other diameter plastic ducting and
ducting fabricated from different thicknesses of plastic should also be per-
formed to establish a general relationship for plastic duct pressure drop in
order to evaluate the performance of shelter ventilators of other diameters.
37
REFERENCES
1. B. A. Libovicz and H. F. Behls, "Shelter Package Ventilation Kit",prepared for the Office of Civil Defense under Contract OCD-PS-64-22, OCDWork Unit 1423A, General American Transportation Corporation (GARD Report1244), Niles, Illinois, October i965.
2. National Electrical Manufacturers Association (NEMA) Standards PublicationNo. FM1-1955, "Electric Fans", 155 East 44th Street, New York, New York.
3. ASHRAE (American Society of Heating, Refrigerating and Air-ConditionitigEngineers) Guide and Data Book, 1965 and 1966, New York, Chapter 31,Figures 2 and 3, PP. 562-3.
4. Federal Specification L-P-378, "Plastic Film (Polyethylene Thin Gage)".
5. Libovicz, op. cit., Figure 36, p. 65.
6. Libovicz, op. cit., Figure 31, p. 55.
INnLAeA ,•s•:•ovmDI9Ia m m m mun n In n
I 44-
-~~~t A--- I-
U.Ul-
-4-I --
Ir 0___ __ _
c- -1 0:T
L- _ 7 1;AaL
*1nC ~ .-.,
-4 .4 0L ~ ~;~ o U.pU~ aznua.4
I GEN RAL MERI AN R SEAR H ONISIO
iiT
+ ~ -r, 7
4-' -i~~ C
.. 4-i 44
4Fz
:4 0
co ,- ' rr \-~.4
1 ~4.
I~~ ~~~~~~~ oh ZI o ePu ýnusz ~
U GEERALAMEICANRESERCH~IVI~4+
t+-, jw it; 4 T- 4 t l 4
F". + J-,
41 . - i 4 iý I
Ej 4 ýii4It+
i+4
f t -HI 44
-f--- T-1:i 14
K 41 +4ý 1-L J-
1 k7`j;,I T
4.4
j*,4±- -441
-4,+ - 41
-Ei 4
#
I q I cqf4-
Of
-4 -7 +
00 E-iAl
V34+
.... ... ....4-1. . ! I "I'll - . 0S. ýam, E - I I -ý+ . - -. 11 i _;_ I = _L-- - -- "" I I , . 1 (Y)-14
2F A
43 42
-j-4-j-4,- 4-14+ 9 E-4+
F4 m o fr4-T- 'T T'-7ý - -Ij
T+ 4ýT
-7- tý
+-'T
'A 40 14 1441
4A0 0------- ILI it 1ý ILI f
bD0 4J
410T, Hr
0 0 0-H v ý4 14
+H1 -H-Hý+_rm14- .,t!-:
T ..:;-r +
Tt 11H-4
T If 44
4 ýýl44 H! 14+H4P4- III' T, TF+ -t+
IAH t I i ll r 7-r I444 -
144 4;
-141,44#
XW%UN
ofto zo,4vlA jo vatiouj loarveoij oTjvýp
GENERAL AMERICAN RESEARCH CIVIVION
45
a I4--.
4-4
-.. ' o4 .4 .41L 4* 4 -
. .... 4 41 a .4 4 - 4 R --.
+2 -4. 4
~ 4- 4.1,
I ~ ~ ~ o '4..-r 44
4~o 6 --- *.
L'-44,-
-4--
-~-7 142K 4II T 0
-:T.
ji4ii +
j 1 r ~ ~ 1 .trv
i4ig j euo J~UA O IS4~UZ~O~3SJT 1UT
GENEAL AERICN REEANC4 DIISI1+ +T
UA
.. .... f2
u t .4-4O -
7777-
-_4 ... .. ... . .. ... ,. .4 .
02. 43 0 0
II
4 4444- i4
M..
+2
L I'P4
OUNERAL AMEUSICAN 049UEARCH OIVOIdON'48
II Spec. No. 1278-1
Date: 13 April 1965
3 General American Transportation Corporation
S2ecification for Plastic Duct Elbows1 1. S cpe
A study is being conducted to determine the type, quantity, material,and configuration of plastic duct fittings which will be required in aportable Package Ventilation Kit suitable for Civil Defense fallout shelters.At present it is anticipated that at least tt':ee 900 elbo'is or three 45*elbows will be required per kit. This study will include fabrication ofvarious 45e and 9Q0 elbow confifurations with subsequent tests and analysisof each configuration. Selection of the optimum zlbow will be based onefficiency (low pressure drop), stability, and production costs. A productionrun of the package ventilation kit will be on the order of 350,000 units inwhich at least three of the selected elbows will be supplied per unit.
3 2. Requirements
2.1 Description
The elbows are to be fabricated from 4 mil (.004) niini•aum pial"1c filmsuch as polyethylene or polyvinlychloride, etc. with a 20 inch ncrrnialdiameter (equivalent to tubing 31 x .004). The maximum stati pressurewithin the elbows will be 1.0 inches W.G. The maximum air velocity withinthe elbow will be 2000 feet per minute. The elbows must be capable ofbeing stored (but not necessarily operated) at ambient temperatures of-60*F to 120*F and relative humidities of 0 to 100%. Operational temperatureof elbows in a ventilation duct will be approximately 85*F. The cuffs ofthe elbow will be assembled to straight lengths of polyethylene tubing31 x .004 by means of a coupling to form the ventilation duct. Materialfor the elbows must be flexible, unsupported plastic film in natural colorand odorless. Type, grade, and finish of plastic material can be specified
* by the fabricator. The method of sealing or bonding the seams is left tothe discretion of the fabricator.
2.2 Elbow Configurations
Seven elbow configurations under consideration are shown in zrawl-ti gnumber Spec. 1278-1. Each configuration is dimensioned In respect to aradius R, nominal diameter D, and a cuff length C. Preproduction modelsof each configuration are required for testing and will have the followingdimensions.
C a 4"; D -20"; R = 20"C a 4"; D 20"; R 0 30"
4"; D 20"; R a 40"C w 4"; D 20"; R a 60"
1 e~aft L AMGIClAN IIN.ARN@ DIVIGIOS
Spec. No. 1278-1
900 3-piece elbow (4 elbows in total)
C = 4"; D = 20"; R = 20"C = 4" D = 20"; R = 30"C 4"; D = 20"; R = ho"C = 4"; D = 20"; R = 60"1
9g0 5-piece elbow (4 elbows in total) [C = 411; D = 20"; R = 20"C =41"; D = 20"; R = 30"-C =4"; D = 209"; R = 40C =- 4"; D = 20"; R = 60"
90* mitered elbow (1 elbow in total)
C = 6"; D = 20"1
45° smooth elbow (4 elbows in total)
c, = 4": D = 20"; R = 20"1C = 4"; D = 20"; R = 30"C = 4"; D = 20"; R = 40"C = 4"; D = 20"; R = 60" Ii
:-05° 3-piece elbow (4 elbows in total)
C = 4"; D = 20"; R = 20"C = 4"; D = 20"; R = 30'" -
C = 14"; D = 20"; R = 40"c 4"; D = 20"; R = 60"1
450- mitered elbow (1 elbow in total)
C 6"; D = 20"
The dimension: D is nominal and is equivalent to the diameter of extruded Utubing 31" x .004.
3. Quantity
Preproduction elbows for testing purposes will consist of one elbowper size per configuration or a total of 22 elbows. After testing a cost versus -performance analysis will be conducted to determine the optimum elbow configurationand size. A production run of the selected elbow will then be made in quantityof 500 units. A follow-up production run will consist of either 350,000, 700,000,or 1,050,000 units to be fabricated over a two year period. Cost estimates of [preproduction elbows as well as estimates of each size and elbow configurationin quantities of 500, 350,000, 700,000, and 1,050,000 should be submitted by I"the fabricator.
GENERAL AMERICAN RESEARCH DIVISION
51
low" AWN G- F -i -
IJNCIA2$I6FIED
DOCUMENT CONTROL DATA - R&DfSeaaefty .Ie..Li1eatla, W1 tgpI. e4* of abuenceOWtowsid anndeaad uatn amunt be antmen attn w N.oveoait apoai Ia clasaaffled)
I. ORIGINATI:4 0 ACTIVITY (Cau~t.~t aulber', a RULPOR7 SECURITY C LABRIFICATION"
General American Transportation Corporation I UN~CLASSIFIEDI 7i449 North-Natchez Avenue [z.6mouP
Niles, 1P'inois _______________g S. REPORT Y!Ti.C
Friction Loss in Flexible Plastic Air Duct-
< 4. DECIPTIVE NO-Tag (T#111 of tgmlt a" 610111011 dot")-
Neveril., R~obert B.
Behls, Herman F.
__._REPORT__________7a__ TOTAL NO. OPPA 7b. No. OP REFS
Ib H Pont-40) (Anly adwrnue mbs that may be aselndmo
~1 10. AV A IL ADILITY/LIUITATION NOTICES
Qualified requestors may obtain copies of this report from DDC.'Distribution of this report is unl imited.
I1I. SUPPL EVEN TARY NOTES 12. SPONSORING MILITARY ACTIVITY
Office of Civil DefenseF I Departmrent of the Army_____________________j Wav-hingtor, D.C. 20310.
IS. ANSTPACT
The friction losses for 20-inch diameter, 14-mil t hick, flexible polyethylene-tubing and plastic elbows are presený;ed in this report. This type of ducting
L is intended for use with the Civil Defense fallout shelter ventilatorspecified in MIli-V-406L45, (U)
L
[ DD I JAN$ 1473 UNCLISS rFTHESecurity C!flsaiflcation
UIMCLSSLIEiDSecurity ClassificationLNKALN *
KEY WiROS- - -
ftor- Wi' fOLS Wi' no' WT
CIVEL L"F'9ENSE SS?,F4V'S -r1Z-F FALLOU7 ST~UiTIFFSSPECIF [CAT FON'SCOOL~iGG & VENTT 1IAýTING EQUIPMENTVEN'TEIATIGIN
E-IRONMENT IMATTIB ALSPIASTICS
INSTRUCTIONS
I. ORIGINATING ACTIMVTY Enter the name and address io AvAILABILIT V/LIMITATION NOTICES: Enter any lrn-of the contractor. subcontractor. grantee, Department of De. -iain oni further dissemination of the report, other than thosefease activity orote organization (corporate uhr sunth. reort. 0ato)Isig mpsech by security classification, using, standard statements
2& EPOT SCUITYCLASSIFICATION: Enter the over. (1) "Qualified reqwvesý may obtaini copies of this91 security classification of the re'port. Indicate whetherance with appropriate security regulations. (2) "Foreign announcement and dirsmemination of this1
2b. ROU Auoma'- dwngadig i upeifid ~DeDreport by DDC is not authorized."
-rective 520010 and Armed Forces Industrial Manual. Enter (3) IOU. S. Govermnt agencies may obtain copies ofthe grouli numb~er. Also, when applicable, show that optional thi report directly from DDC, Other qualified DDC
markings have been used for~ Group 3 and Group 4 -as author. users shallI request 'through
3. REPORT-TITL- Eater the complete report title in all (4) IOU. S, military agencies may obtain coie of thiscapital letters Titles in all cases should be unclassified, report directly from DDC. Other qualified usersIf a meaningful titlv cannot he selected vwithout classificap *Wti request throughtion, show title claisit'catiou In all capitals in parenthesisimmediately following the title.________________
4. D)ESCRIPTIVE NOTES: It appropriate, enter the type of (5) "All distribution of this reprt is controlled. Qual-report. eg.. Interim, progress, summary, annual, or final. Iifid DDC users shall request through
Give the Inclusive dates when a specific reporting period Is
5. ATHO(S):Entr te nae~s of uthr~s as how on If tAe report has been furnished to the Office of Technicalor In the report. Enter last name, first name, middle initial. casv, Deps actmadente ofe Comrice, if kowr.sl otepbimIf military, show rank and branch of service. The name of ctehifatndnerhepcifkosthe principal author is on absolute minimum requirement. IL SUPPLfEMENTARY NOTES. Use for additional explana-6. REPORT DATE. Ente~r the date of the report as day, tory notes.month, year, or month. yeas If more than one date appears 12. SPONSORING MILITARY ACTIVITY: Enter the name ofon the report, use date of publication, the departmental project office or laboratory sponsoring (pt ?I
7a. TOTAL NUMBER OF PAGES;- The total page count ing for) the research and development. Include address.Ushould follow normal pagination procedures, Lo., enter the 13. AEUSTRACT; Enter an abstract giv'ing a brief and factualnumber of pages containing information, summary of the document indicative of the report, even though
it may also appear elsewhere in the body of the technical re-76. NUMBER OF REFERENCE&: Enter the total number of port. It additional space is required, a continuation sheetreferences cited in the report. shadl be attached.I&a. CONTRACT OR GRANT NUMBER. If apprwpiate, enter It is highly desirable that the abstract of classified re-the applicable number of %&e cor2ract or grant under which Iports be unclassified. Eat-h paragraph of the abstract shallthe report was written, end with an indication of the military security tblassificationSb, 8c, & Gd. PR~OJECT NUMBER: Rnter the appropriate of the irformation in the paragraph, represented as (TS), (S).military department kdontification, such as project mumber. (C), or (U).subproject number, system numbers, task number, etc. There Is no limitation on the length of the abstract. How-9.. ORIGINATOR'S REPORT NUMBER(S): Enter the offi. ever, the suggested length is from 150 to 225 we-ds.cial report number bi' which the document will be identified 14. KEY WORDS: Key words are technically meaningful termsand controlled by the, originating activity. This number must or short phrases that characterize a report and may be used asIbe unique to this Mejomt index entries for cataloging the report. Key words must be
96. OTHER REPORT NUMBER(S): If the report has been selected so th.: -urity classification is required. Iden-
assigned any othe report numbers (either by the originator tiers, suciý as oe, it model designation, t.rade name, mili-or by the aponeor). also enter this number(5). tary proj,,ct code name, geographic location, may be used as
key words but will be followed by an indication of technicalIcontext. 'rhe assignment ol links, rules, and weights inoptional.
UJ
Sacilly Classification
(D 1.421
-H ) (DW H ( )
4-) r HO 4:) "4 (aO
r-4r- (A 4-
N- aH~- 'I4 - rlH0 ~OZ
U . E-4 4. 400 4-)4-30W
V 4 10r 4. _2*f-rE2 -4
"EI IHr 940-0 0 ri4i4 F4 ca~00 ~O3.'
4X) 0*'4 cu# HQ0 V(
VCI 2G F-4vo a 14 4)H t 4.).e K'E1HH+
m to 4. 0 044C f+ C'I 0 00 P44 C-w 0 W~ 4.) rO) v.d 4) 4,~. -1).024 H M2H N1~. m0'
4+)'U 0H0.c 0 .V, -4 U3cuco 0 o > CH.Q 2 14k34 CO. \ 00 4 -T J\ t-r4 04I:" )"
~H 43t.UN0 4GJ V.r t ~ J (a toC H 4-) > UN W r4 r4
0 -1P40 O " P f+G43
1.4 U2P) 1.4 C12+4) W) o )0)' Jv) H HO P4 H 1 HOI4 04 4 ) aE.-or- 4 %-r a * r.4~ Iai M
V4 4J 0E- 2) 00
CI2H H
CD0 00 P
*- 0Q V4I H(O H (D 0 04. -H4 0)
4- * ~ O r4 I 0
H)
0
Prepare6 forOffice of Civil Defense
Department of the Army, OSAunder
OCD Work Unit 1423ASRI Subcontract No. B-70925(4949A-28)-US
SUW_ -LR~ yOF
RESEARCH REPORT
FRICTION LOSS IN FLEXIBLEPLASTIC AIR DUCT
GARD Report 1278-2 October 1965
by
General American Transportation CorporationGeneral American Research Division
Environmental Research GroupNiles, Illinois
REVIEW NOTICE
This is a summary of a report which has been reviewed in the Office of CiviDefense and approved for publication. Approval does not signify that thecontents necessarily reflect the views and policies of the Office of CivilDefense.
GENUR\L AMEJRICAN RESEARCH OIVISION
I1TRODUCTION
A Package Ventilation Kit (PVK) was developedI for use as an inexpensive
method of exhausting stal.e, hot and himid air from fallout shelters (see
Figure 1). This ventilator Is intended for use with flexible plastic duct
systems (see Figure 2) and, therefore, flexible plastic tubing and fittings
are supplied with the Kit. The objectives of this program are to determine
the friction loss of flexible tubing and fittings, and to recommend the best
fittings, based on cost and pressure drop, for use in fabricating shelter duct
systems.
Fi.3ure 2 PYK DUCT SYSS71M
B. A. Liboviez '11. F. Bels, "St~heiter Pat:-a. Ventilation Kit", prepcred
ror the Offtice ;f Civil Litfenae under Cct.ract OCP-PS-64-22, OCD Work Unit.
Illinois, ioiber1
mHBM MAL AMOOMSO AMMNW OAW NVUS@
TEST PROCEDURES
P" .aratus.--The test apparatus consisted of an 8,000 cfi centrifugal blower
connected by a flexible wire-reinforced cloth duct to a 47 foot long, 20-inch
diameter- test stand which was fabricated from 24 U.S. Gage, zinc coated steel
spiral conduit duct with 6 inch seams (see Figures 3 and 4). The design of the
test stand is based on recommendations of the National Electrical RManufacturers
2Association. Air flow rates were measured with a 14-inch diameter aperture
sharp-e•dge orifice plate which was calibrated with a pitot tube five feet
upstream from the orifice. Two air straighteners were located approximately
14 feet and 28 feet upstream of the orifice plate to reduce turbulence. A
piezometer ring was located 14 feet downstream from the orifice and 5 feet from
the end of the test stand. Inclined manometers were used to measure the pres-
sure drop across the orifice, and the static pressure drop of the test specimens.
Methods.--The specimens were first taped to the test stand. The blower was
adjusted to provide the desired flow rates, and the static pressure loss and
flow rate (o'.ifice differential pressure) were recorded. Barometric pressure,
dry-bulb temperature, and wet-bulb temperature were recorded before each test
to provide the flow rate correction factor to standard air (P = 0.075 lbs/cu ft).
The tare pressure drop of the test apparatus, i.e., the presbure drop caused by
the 5 foot length of spiral duct between the plane of the measuring station and
the plastic specimens, was subtracted from the test data after its correctio.i to
standard air.
2 National Electrical Manufacturers Association (NEMA) Standards Publication
No. FMl-1955, "Electric: Fans", 155 East 44th Street, New York, New York.
GENERAL AMERICAN REDEARCF 0,1VISION
4
Tubing.--Plastic tubing lergths from 1450 to 50 feet in increments of 50 feet
were tested at flow rates from 1300 to 4100 SCFM (standard air) with the
discharge end of the tubing unrestrained. Five high impact strength (Type II),
untreated (Finish I) tubing specimens were tested. Of these samples one was
low slip* (Grade A), three were medium slip (Grade B), and one was high slip
(Grade C'. The diameter is 19.75 + 0.25 inches, and the thickness 0.004
(4-rail) + 0.0008 inches.
Elbows.--The friction lcss of the fittings listed below were tested with 100
feet of straight tubing on the downstream end of the sy3tem and the results
were compared to each other. Testing with a duct on the discharge end of the
elbows was necessary to fully inflate the fittings, and the rpsults are
therefore only applicable to fully iflated fittings. The be:.t factory
fabricated and sheltcr fabricated elbow,- were then further tested with duct
lengths of 100, 200. and 300 feet to determine tho effect of static pressure
on the elbow pressure drop or equivalent duct length (EDL).
K•. t• • h•Lt, St• Material
1F-i•1C&UnM Ma Mrs ___ " Table IM INtily 60 smooth Madlsn PC~i% Pector o0 ftoth Radius PVC
0 ?actw 6C 0mUI % Rat d min PCFacto" Smooth 8 Summary of Elbows
0 ftelte 60 3-F P07- TestedFatr 0 sot ethyleneP
Factory - 7- M Our WtWa lter. -I Pecking Do cmawetd -
OFnetor 20j Smoth Namaln PYC
*The test apparatus and methods for determining the impact strength and slip(kinetic coefficient of friction) are presented in Federal SpecificationL-P-378, "Plastic Film (Polyethylene Thin Gage)". Finish 2 film is treate&to allow printing ink to adhere.
GENERAL AMERICAN RIEiUEAPCH DIV1lION
5
24
__________________ 2T IUdi
o i-i
N
I
i________________________________ U
�.0
o
4
-1---� *1iE
41-
I-U
�o E-4-j
4
U
40 -J C0 z
U UI,_ £ p___ U 21N. 2 0N 4jN 0 �-
Hi
UI-h'2U
g______f C12
II.
____________________ ivrrri-r-- 111111.iJ...LE
Fri -
I I I I
L.LLLLLJ2)i U I.
- .1IA0a N
4
OENU�AL 1 �43NICAPd �E��ANCH DIVtUeON
7,
RESULS AIMf ANALYSIS
Tubing.--The "'rictLon of air in straight polyethylene tubing for lengths fro.m
50 to 450 feet are shown in Figure 5. These curves are based on a least
squares linear logarithmic regression of the test data. The standard error
of estimate; i.e., the mean of the square of the differences between the data
and the fitted curve ranges from 0.007 inches of water gage (iwg) for the
150 foot length to 0.023 iwg for the 40O foot length. Fully inflated 20-inch
diameter plastic tubing has about three-quarters of the pressure drop of
sheet-metal duct. However, the last fifty feet of a plastic duct system
which is not completely inflated has 1-1/2 to 3 times the pressure drop per
foot of fully inflated plastic tubing. The result is that for duct systems
over 100 feet long the pressure drops for sheet-metal and plastic tubing
are approximately the same.
A mathematical expression derived from the least squares fitted curves
of the data is:
P = 1.915 x 10-6 Ql.349 + 0.01096 (L (I)
where:
P = static pressure loss, inches of water gage
q - air flow rate, standard cubic feet per minute (scfm)
L = tubing length (for lengths of 50 feet and longei')
GSlNgPA'. AMGF410AN ... ARCMH DIVISION
8
H tN t I ;4i
Trl tJ4.
4-7,14 i;!
J44-
fli ft-t4
! l i t .4i-14 +.iýi
4
TIt
+T r. T :p
4-ý i
-tH+ lwý1ý
-4 - -- ý- 1-1 . " I - -1 -1 -L1A
_LL 'i, H-::L it
1 F
+; 44-" -+N
i I I T i
4+
4-::
-7tlrr-7
-H4 4
I T
Tr -- 1. . .. ......
rý 7 4
44., T 0
44
E-4T I I
444-
TTI Ft-1--44+
+
iý, I-M 14H-
is
+
+
2 E I .. .. . . .
4-
TV I
...... 44; loj+
.44
vs
*ýVok jo *4q=l "W"Imm anon
Faztory Fabricated Elbows.--The elbows with the lowest pressure losses are
factory fabricated smooth radius elbows. The elbows fabricated from four-
mil plastic had lower pressure losses than those fabricated from eight-mil
plastic. The change in pressure loss with centerline radius decreased as the
centerline radius appro- J 6 .0 inches. The elbows with centerline radii of
40-inches and 60-inches have nearly identiLcal pressure losses, indicating
that the trade-off point for centerline radius versus pressure loss is
approximately 40 inches. The mitered elbow had a considerable pressure drop,
and the wire-reinforced elbow developed excessive pressure losses.
The four-mil polyvinyl chloride (PIC) 40-inch smooth radius elbow is the
best factory elbow when considering pressure drop, space requirements, material
and cost. Pigure 6 shows the results of tests performed with this elbow.
The solid lines show the pressure losses fur the elbow with straight lengths
of tubing attached to the downstream side, the broken lines show the pressure
losses for the straight lengths only. It can be seen that the equivalent
length of straight tubing for the 40-inch smooth radius elbow is approximately
50 feet when rully inflated. For the elbow to be fully inflated fifty feet
of straight tubing must be on the downstream side.
OGNEMAL AMaNICAN NSUBARCH CIVISION
10
Shelter Fabricated Elbows.--Of the shelter fabricated elbows (see Table I)
the three-piece elbow results in the least pressure loss. The elbow made
from packing boxes produced the largest pressure loss. This elbow was
extremely stable at all flow rates; however, the exit and entrance losses
of the air stream in the plenum-like box produced the high pressure loss.
The best hand-tucked elbow results in pressure drcps considerably higher than
any of the other elbows, and the results were erratic.
Since the three-piece elbcd has the least pressure loss this elbow was
further tested with 100, 200, and 300 feet of tubing (see Figure 7). It can
be seen that the pressure loss of the three-piece elbow with a centerline
radius of 60-inches is equivalent to 90 feet of straight tubing when fully
inflated. For the elbow to be fully inflated fifty feet of straight tubing
must be on the downstream side.
A•plication.--The equivalent duct length of any plastic tubing system can be
determined by adding the total length of straight tubing plus the number of
elbows times their respective equivalent duct lengti: (see Equation 2) -- 50
feet for the factory fabricated elbow and 90 feet for the shefter fabricated
elbow.
FDL L + 50 Nf + 90 14 (2)
where:
,DL Equivalent .uct Lenith of thc system, ftets
L - Lentth -' stralt'ht du,:, 1i T'lhe system, feet
N r number of factory rabri•,nted eL,!ws, ýimensL,ý,ajc.s
N tmi C,S
@SNIUUIAL AMSIIIvCANd *3SSACI•',4 [email protected]
rod| •' 1•' i ' • I~lmli mlmlami| • nilam alll lal I~ll • '' m ml mr 4-
A I I I I I I I I I
DUCT LENGTH. I
51 AIR FLOW 20"
+ Ifif I
I IF 6 # -1604
goo"*
TUBING - SINCLAIR -KOPPERS i
MEDIUM SLIP I J-
(SEEAPPENDIX A, SYMBOL 0)Ac
ft+++
T4_4-
.30IWO
.3( ---- ----I I t
T I
.2!
I I - i tI I
7 1 1 1 +I I -A LL-
t+t+- i
ELL
1.44 7 +
4444ý
Ac ýjt4-i -
+
4_4If pr 1
t
i-ii 4- i,t
J, 4 - 64-
:A
A 6pw 4000
Flow Rate CPU 4 p 0. 075 taB./CU
- ~ERRATA i-Subject Report: R. B. Neveri). and H. F. BehJ~s, "Friction Loss i
in Flexible Plastic Air Duct", -OC Work Unit
- 1423A, GARD Report 1278-2,. October, 1965.
Pa~ge 26, Fig"'.e 17
IThe ordinate scale of Figure 17 which ranges from 0 to .60 inch
of water gage, static pressure is double the actual value and A
H 'should be changed to indicate a scale range of 0 to .30 inch of
water gage. A
J
GEEAKMRCNREERHDVSO