Thermal Insulation with Aluminum Foil RALPHB. MASON,Aluminum Company of America, New Kensington, Pa.
T
HE principles governing heat flow by conduction, con- on aluminum foilair eell insulation introduce a variety of vection, and radiation have long been known, but experiments1 complications. After a careful survey of availtheir application in the production of aluminum foil.. able methods, the so-called guarded hot plate and the cold air cell insulation is a relatively recent development. By box methods were adapted to the problem a t hand. In combining the low thermal conductivity of air with the low the guarded hot plate method, a measured quantity of heat, emissivity or radiating power of bright aluminum foil in a developed electrically, is forced to flow through the insulsstructure designed to minimize air convection currents, there tion under test. By maintaining a guard ring around the has been introduced an insulation called Alfol, that l i a ~met hot plate and at the same temperature, the lateral flow of with commercial success (9, If). the measured heat outsidc of the test area is prevented. The guarded hot plate apparatus was constructed along Quiet air is one of the hest availilable mediums for preventing heat transfer, and the practical problem resolves itself into the lines suggested by Van Dusen (fd) and the National a determination of the best structure for confining the air in Research Council (7). The faces of the hot and cold plates cells so as to eliminate heat transfer by convection and radia- were made of heavy aluminum sheet. The hot plate, meastion. The most practical structure for any purpose may he uring 24 X 24 inches (61.0 X 61.0 em.) was so constructed a compromise het,ween maximum thermal efficiency and cost. that an inner square on each face, 16 X 16 inches (408 X 40.6 cm.), was isolated from the The p r e s e n t investigation has outer or guard portion by a '/e determined some of the fundaThermal insidation with a metal is made inch (0.32-cm.) slot. Alternat mental information necessary for ing current was used to heat the the commercial design and utilipossible by laking advantage of the low thermal hot plate, and the energy input zation of this type of insulation. emissivity of aluminum foil and the low thmnal WPS determined by means of a There are two general niethconductivity of air. The various factors deterods of using aluminum foil for Weston wattmeter. The temmining the qDiciency of aluminum foil-air cell insulation. One is to provide p e r a t u r e s were measured by insulation are analyzed, and the insulation values a f r a m e w o r k which supports means of copper-constantan the aluminum foil and forms a t h e r m o c o u p l e s . A Leeds & of a wriety of structwes determined experiNorthrup type K potentiometer series of air cells between the menlally in the guarded hot plate apparatus or b r i g h t foil s u r f a c e s ; in the a n d a sensitive galvanometer the cold bos upparatus. It is possible with this were used io conjunction with other, the foil is first crumpled type of insulation practically to eliminate heal the tliermocouples. and then partially s t r e t c h e d transfer by radiation and convection, and to upso that the resulting wrinkles The test panels were placed in in the foil separate the sheets the hot plate apparatus and the prmch the insulating value of still air. Thp wliole assembly well insulated when they a r c l a i d a g a i n s t aluminum foil-air cell insulations of the plain with alumina slag wool and cork each other and p r o v i d e t h e air-cell type are found to be better than strucn e c e s s a r y separation and air board. The conductance was tures with corrugated separators or crumpled cells. determined at three mean temfoil. The best results are obtained when the peratures. About 24 hours were METHong FOR DETERMINING usually necessary for the apis from 0.25 to 0.33 inch distance between foils THERMAL CONDUCTIYITY paratus to reach equilibrium for (0.64 100.84cm.). The light weight ofaluminum T h e a c c u r a t e measurement e a c h p o i n t determined. The foil-air cell insulation and its excellent insuhof t h e r m a l conductivity is a temperatures were determined tion properties make it especially suitable for difficult determination at hest, by means of the thermocouples use in the transportation industry. and thermal m e a s u r e m e n t s and the energy input read from 245
I 1\; D U S T R I A L A N D E N G I N E E R I Iu G C H E JI I S T R Y
246
the wattmeter. All measurements made in the guarded hot plate apparatus and reported here were made upon panels placed in a vertical position in the apparatus.
A I R SPACEWIDTH-INCHES.
FIGURE1. RELATIONSHIP BETWEEN CONDUCTAKCE AND WIDTHOF SINGLE ALUMINUMFOIL-AIR CELL INSULATIONS AT Two MEANTEMPERATURES
Vol. 23, No. 3
(16 X 16 inches) or measuring area occupied about 6.15 per cent of that area. Only one height of air cell was measured in these experiments-namely, 73/d inches.
Most measurements of air cell insulation reported in the literature have been made on single air cells. It is much easier to construct panels of this type, but the thermal insulation of narrow air cells is low, and the energy input to the hot plate is small for temperature differences of 10' or 20" F. (5" or 10" C.) between the hot and cold plates. It was also considered best to make the measurements with multiple air cells, since single cells are seldom used. The first series of measurements with the 2-inch (5.08cm.) panels but with varying numbers of air cells is shown in Table I. The thermal conductance of each panel was determined a t three different mean temperatures. The temperatures of the hot and cold plates are reported in the table, as a knowledge of these factors is essential in air cell insulation. I n thermal measurements of this type, the common practice is to hold the cold plate constant and increase the temperature of the hot plate. It proved to be impractical to hold the cold plate a t the same definite temperature for all the experiments. It was also difficult to construct panels exactly 2 inches in thickness, and because of slight variations
SPACIKG OF FOILIN PANELS
I
3 Air Spaces
One of the objects of this investigation was to determine the optimum spacing for air cells bounded by bright aluminum foil which would give the maximum heat insulation for a given thickness. A series of panels was prepared, each approximately 2 inches
(5.08 cm.) in thickness, which contained two, three, four, five,
six, seven, and eight air cells, respectively, bounded by aluminum foil. The panels were made 24 X 24 inches in area to fit the hot late apparatus, and were similar in construction except for t&e number of sheets of aluminum foil dividing the 2 inches of thickness into air spaces. The sheets of foil were separated and supported by strips of Masonite of the requisite thickness to give the desired number of air cells per 2 inches. The con-
3
4
5
6
7
8
A I R SPACEW I D T H - INCHES I6 ri
FIGURE3. RELATIONSHIP BETWEEN CONDUCTANCE OF 2 INCHES OF ALUMINUM FOIL-AIR CELL INSULATION AND WIDTH OF INDIVIDUALAIR SPACES
.I5
'I ;.14
2
2
.'3
m LL
.I2
z
2
II
0 z
0
u
.IO
60
80
100
120
I40
IN
180
200
MEANTEMPT.
FIGURE 2. CONDUCTANCE VALUESOF ALUMIFOIL-AIR CELL INSULATIONS 2 INCHES IN THICKNESS
NUM
struction of the Masonite separator frames was somewhat complicated because of the fact that the guarded hot plate had a measuring area of 16 X 16 inches. The outer shell of each separator frame was made from strips of Masonite 1 inch (2.54 cm.) wide. Crosspieces of the same separator material I/? inch (1.27 cm.) wide were used to form an inner square 16 X 16 inches, which coincides with the hot plate in size and position and is the area of insulation actually under test. This central s uare was divided into four smaller cells, each of which was 7 3 7 4 X 7 3 / 4 inches (19.7 X 19.7 cm.). The purpose of the crosspieces in the center area was t o support the aluminum foil and insure good contact with the hot and cold plates in the test apparatus. The aluminum foil was fastened to the separator frames with a rubber resin cement. The Masonite used in the inner square
in thickness the data are not directly comparable. To make comparisons easy, the data of Table I were first plotted for a fixed cold-plate temperature of 40" F. (4.44' C.). To do this, small corrections were applied to the measured conductances in order to adjust the data for a cold-plate temperature of 40' F. These corrections were small, being less than the probable error in thermal measurements of this type, except in the case of the insulations containing three air spaces per 2 inches, where there is considerable convection and where differences in temperature play a more important role. From these corrected values the conductances of single air spaces were calculated for mean temperatures of 100' F. (37.8" C.) and 150" F. (65.6" C.) as shown in Figure 1. For example, the average width of each air space in the insulation containing six air spaces per 21/8 inches (5.4 cm.) was 0.354 inch (0.899 cm.) (allowance was made for the aluminum foil). The conductance of this insulation a t a mean temperature of 100" F. was 0.100 B. t. u. (0.488 kg.cal.), and the conductance of a single air cell would be 0.600 B. t. u. (2.929 kg.-cal.) a t the same mean temperature. The relationship between conductance and width of single aluminum foil-air cell insulations a t mean temperatures of 100' and 150" F. is shown in Figure 1. I n drawing smooth curves through the points, a minimum conductance is indicated as
247
C"N""CT*XCS-
.
2
(5.08)
I
(2.54) (2.64)
1
2J/n ( 5 . 3 2 ) I > & / , *(4.82) 2
(5.0s)
2a/a
(5,401
85.4
41.2
112.3 40.6 132.3 40.3 . .. ,,
44.2
71.7 92.0 ., .
03.3 76.5 86.3 86.0
.
B.
t. zi. (K#.-cd.) 0.142 (0.693) (24.71 0.144 (0.703) (30.2) 0 . 1 4 5 (0.708) 130.01 0.302 (1.4741 0.419 (2.046) 0.600 (a.W211) 0.050 (3.173) 0.123 (O.RO0) 0.145 (0.70s) 0.15s (0.771) 0.112 (0.547) 0.117 (0.671) 0 . 1 3 0 (0.035) 0.110 (0.537) 0.1111 (O.SS1) 0.126 (0.615)
(17.4)
0.101
(0.493)
0.10S (0.527) 0.116 (0.566) 0.106 ( 0 . 5 1 7 ) 0.115 (0.561)
l~a/,'(4,92)
0.119 ?'/XI
(5.16)
(0.5811
0.103 (0.503) 0.110 (0.537) 0.117 (0.571)
ciccurring fur air spaces betwen 0.6 tmd 0.7 inch (152 and cell insulation and the width oS iridividual air cells. The in1.78 cm.) in t,hickncss. Tising approximately the same sulation containing eight air cells per 2 inches gave the lowest height air cell, Dickinson and Van Dusen (S) fonnd a mini- value in this series OS measurements. If the conductance of 2 inches of insulation containing ten air spaces is calculated mum condiictance at ahout 0.03 inch (1.6 cm.). Using the curves of Figure 1, a derived series of curves from Lhe curves of Figure 1, it will be found to have ap(Figure 2) w ~ plotted s for exactly 2 inches of insulation, and proxirnatcly t.he same value as the one containing eight. for the condition where the mold face of the insulation is st air cells. Ilovever, no measurements were made in this 40' F. For example, the. conductance of a single air space region. inch in width a t 100' F. may be taken from the curve in The curve shown in Figure 3 is similar to that obtained Figure 1. The conductance of four air spaces (2 inches in by Cregg (4),but the conductance values reported by him total thickness) will be onefourth the conductance of a single Sor aluminum foil-air cell insulation are slightly higher than air cell. The dotted portion of the curve for the insulation those given here. However, the material used for the containing three air spaces is uncertain, since the conduo- separator Srames in this investigation has a lower conductance tance measurements in this region were erratic, as a result, than the wooden separator frames used by Gregg, and, if no doubt, of the increased effect of convection. As the num- allowance is niade for this difference, the results check in a ber of air spaces in 2 inches of insulation is increased from very satissactory manner. Most of the oonductance values four to eight, a decrease in conductance is noted. The differ- reported by Queer (8) are somewhat hialter than the results ence bet&een the conductgiven here. ance of the insulation conThe curves of Figures 2 taining seven air spaces and and 3 show that the inthe one containing eight air sulation with the '/Xnch spaces is small; the one ex(0.63-em.) spacing gave the tra foil adds to the insulalowest conductance of the tion value by decreasing i n s u l a t i o n s measured. slightly the small fraction After allowing for the small of h e a t t r a n s m i s s i o n b y amount of heat transferred radiation. by radiation, it was found The optimum spacing for that the ratio of heat transferred to the conductance the air cells with a given number of aluminum foils of still air was practically would be about 0.6inch (1.5 constant for 2 inches of insulation c o n t a i n i n g s i x , em.), as is shown in Figure 1. However, where maxiseven, and eight air spaces, mum insulation must be which mould indicate that obtained in any givenspace, the effect of convection was t h e m i n i m u m conductconstant and, as will he ance is obtained by using shown, probably negligible. The experiments of Creregg more foils with closer spacing. Figure3, whichis from (4)have shown that the the data of Figure 2, shows conductances of air cells inch (1.27 em.) in width do the relationship between the not vary, when measured in conductance, at a mean temperature of 60" F , of 2 the vertical position and in a inches of aluminum foil-air COLDBox APPARATUS horizontal position. with the I
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 25, No. 3
TABLE11. THERMAL COXDUCTIVITY ASD CONDUCTANCE OF ALUMINUMFOILAND PAPERINSULATIONS (Plain air-cell type) Av. WIDTHTOT.AL THICKOF EACH A-ESS OF High Low PANEL DESCRIPTION OF INSULATION AIR SPACE INSULATIONaide side Inch (cm.) Inch (em.) F. O F. Center baffled Masonite frames black 0 . 3 4 ( 0 . 8 6 ) 2 . 0 9 (5.31) 1 0 5 . 1 7 8 . 0 paper (0.0095-inch or 0.0241-cm.): 6 166.8 78.2 air spaces 214.4 7 8 . 8 C. B. Masoniteframes aluminum0 . 3 4 (0.86) 2.06 (5.23) 120.8 7 2 . 3 painted paper; 6 air spaces 181.3 7 3 . 2 251.4 73.0 C. B. Masonite frames 0.0006-inch 0 . 3 4 ( 0 . 8 6 ) 2 . 0 6 ( 5 . 2 3 ) 133.2 7 6 . 7 (0.0015-c,m.) lacquered foil (thin coat198.3 7 6 . 2 ing) : 6 air spaces 276.5 76.1 Masoniteframesfromcoldbox 0.00035- 0 . 4 4 ( 1 . 1 2 ) 0 . 8 8 ( 2 . 2 4 ) 109.2 4 0 . 2 inch (0.00089-cm.) plain foil: 2 air 176.4 4 1 . 3 spaces 234.6 4 1 . 8 Masonite frames from cold box 0.00035- 0 . 4 4 ( 1 . 1 2 ) 0 . 8 8 ( 2 . 2 4 ) 9 7 . 2 4 2 . 0 inch lacquered foil: 2 air spaces 155.8 4 2 . 5 204.0 4 2 . 0 a All values for thermal conductivity are in B. t . u./hour/sq. ft / " F./inch of thickness,
+
+ +
+
+
-.
TEMPERATURE
Difference Mean CONDUCTIVITY4 CONDUCTANCE O F. O F. (" C.) B. t. U. (Ku.-cu~.)B. t. U. ( K g . - ~ d . ) ... 2 7 . 1 9 1 . 6 (33.1) 0 . 4 7 0 (0.0583) ... 8 8 . 6 1 2 2 . 5 (50.3) 0 . 5 1 0 (0.0632) ... ,., 135.6 146.6 (63.7) 0 . 5 5 2 (0.0684) ... ... ... 4 8 . 5 9 6 . 5 ( 3 5 . 8 ) 0 . 2 7 0 (0.0335) ... 1 0 8 . 1 127.2 ( 5 2 . 9 ) 0 . 3 1 1 0.0386) 1 7 8 . 4 162.2 ( 7 2 . 3 ) 0 . 3 3 4 10.0414) ... ... ... 5 6 . 5 104.9 (40.5) 122.1 1 3 7 . 3 (58.5) ... 200.4 176.3 (80.2) 0 . 2 1 7 (0.0269) 6 9 . 0 7 4 . 7 (23.7) 0 . 2 4 7 (1.206) 1 3 5 . 1 108.9 ( 4 2 . 7 ) 0 . 2 4 6 (0.0305) 0 . 2 7 9 (1.362) 192.8 138.2 ( 5 9 . 0 ) 0 . 2 7 5 (0.0341) 0 . 3 1 2 (1.523). 5 5 . 2 6 9 . 6 ( 2 0 . 9 ) 0 . 2 5 6 (0.0317) 0 . 2 9 1 (1.421) 1 1 3 . 3 9 9 . 2 ( 3 7 . 3 ) 0 . 2 9 5 (0.0366) 0 . 3 3 5 (1.635) 1 6 2 . 0 1 2 3 . 0 (50.6) 0 . 3 2 8 (0.0407) 0 . 3 7 3 (1.821) and kg.-cal./hour/sq. meter/O C./meter of thicknesa.
... ...
...
TABLE111. DESCRIPTION OF IXSULATIONS WITH CORRUQATED ASBESTOSSEPARATORS >fAX. TOTAL THICKNESS THICKNESR WIDTH THICKNESS OF OF EACH OF CORRUQATED RADIATION BIB SPACE INKLATION SEPARATORS SEIELD OF
PANEL
COABTRUCTION OF INSCLATION~
PITCHOF CORRUQATIONB
WEIQET
Lb./ Inch (cm.) Inch (cni ) Inch (cm.) I/ls-inch (0.48-cm.) corrugated asbestos separators 0 . 1 6 ( 0 . 4 1 ) 1 . 0 0 ( 2 . 5 4 ) 0 . 0 1 8 (0.046) asbestos sheet; 5 air spaces B l/r-inch (0.64-om.) corrugated asbestos separators 0 . 2 1 ( 0 . 5 3 ) 1 . 1 3 ( 2 . 8 7 ) 0 . 0 1 8 (0.046) aluminum foil: 5 air spaces C '/a-inch (0.95-cm.) corrugated asbestos separators 0 . 3 5 ( 0 . 8 9 ) 1 . 1 9 ( 3 . 0 2 ) 0 . 0 1 8 (0.046) asbestos sheet; 3 air spaces aluminum D '/pin& corrugated asbestos separators 0 . 3 3 ( 0 . 8 4 ) 1 . 0 6 ( 2 . 6 9 ) 0 . 0 1 8 (0.046) foil; 3 air spaces E l/pinch (1.27-cm.) corrugated asbestos separators 0 . 4 6 (1.17) 1 . 0 0 (2.54) 0 . 0 1 8 (0.046) asbestos sheet; 2 air spaces aluminum F l/pinch corrugated asbestos separators 0 . 4 8 (1.22) 1.00 (2.54) 0 . 0 1 8 (0.046) foil; 2 air spaces 4 Sodium silicate was used as adhesive: insulations were baked before measuring thermal conductivity.
A
+
+
+ + +
+
To demonstrate the part played by radiation in heat transfer, various materials such as black paper, aluminumpainted paper, and lacquered foil were substituted for the aluminum foil in the Masonite frame panels containing six air cells per 2 inches. The results are shown in Table I1 and Figure 4. For purposes of comparison, the results obtained with the bright foil (D) are also included. The panels containing foil covered with a very thin coat of lacquer tC) were only slightly inferior to the bright foil, showing that the emissivity of the foil
0 . 0 2 2 (0.056)
Inch (cm.) cu. ft.
(Q./cc.)
0 . 4 8 (1.22) 12.3
(0.197)
0.0006 (0.0015) 0 . 5 0 (1.27)
7.3
0 . 0 1 8 (0.046)
1 . 2 5 (3.18)
6.7
(0.117) (0.107)
0.0006 (0.0015)
1.25 (3.18)
4.5
(0.072)
0 . 0 1 8 (0.046)
1 . 0 6 (2.69)
6.4
(0.102)
0.0006 (0.0015) 1 . 0 6 (2.69)
4.4
(0.070)
had been only slightly increased by lacquering. The conductance of the panels constructed with aluminumpainted paper ( B ) was approximately what one would expect with a material having an emissivity of about 30 to 40 per cent. The substitution of black paper ( A ) for the foil decreased very markedly the heat-insulating properties of the air cells. White paper gave results which were practically the same as those obtained with the black paper, showing that the long heat rays are absorbed and emitted as readily by the white paper as by the black. Another comparison between bright foil and lacquered foil is shown in Figure 5. In this case a heavy coat of protective lacquer was applied to the foil, and the conductance has been increased more markedly (about 25 per cent) than in the case where there was only a thin coat of lacquer. These curves were not included in Fievre 4. since the seuarator frames were of different consiruction and were only 0.88 inch (2.24 cm.) in thickness. The separator frames were made from Masonite strips, but instead of isolating an inner square 16 X 16 inches (40.6 X 40.6 cm.) from the 24 X 24 inch (61.0 X 61.0 cm.) frame, crosspieces inch (1.27 cm.) wide were used to form nine air cells approximately 7 x 7 inch (17.8 X 17.8 cm.). When these frames were placed in the hot plate apparatus, the air cells overlapped the guard and test portions of the hot plate. The results plotted in the usual way indicate that steeper curve8 Oligher temperature coefficient) are obtained ALUMINUMFOIL-AIRCELL PANEL where this condition exists. Type measured in hot plate apparatus; Figure 4 shows that a very thin outer foil removed to show inner construccoat of lacquer on the aluminum foil' tion of panel.
source of heat either above or below; this would indicate that there was no convection present. The value given in the International Critical Tables for the conductance of air is a mean value. When the somewhat higher values for the conductance of air, as given in the literature, are used, and when corrections made for the conductance of heat by the Masonite strips included in the measuring area are considered, it is found that the conductivity of still air has been very closely approximated in this form of insulation. Considering the various factors involved, it appears that very little could be gained by using closer spacings than inch in the aluminum foil-air cell form of insulation. When the width of the air space exceeds ' / z inch, convection starts to play an important role, and the greater the thermal head (temperature difference) between the foils, the greater will be the amount of heat transferred at a given mean temperature.
EFFECT OF EMISSIVITY ON CONDUCTIVITY
Inch (em.)
Y
I N D U S T R I A I.
March. 1933
A N 1)
ENGINEER I N G
c 11 E M 1 s'r H Y
249
GUARDED HOT PLATE. APPAEUTW did not appreciably increase tile coiiductivity of the ilksulation in which the foil was incorporated. A very tliick lacquer coating, however, resulted in a larger increase in conductance (Figure 5). These facts are of importance where the insulation may be used under corrosive conditions and where a thin coating of lacquer wilt maintain the brightness and low emissivity of the foil and yet give satisfactory protection against corrosion. PANELS
WITH
CORRUGATED
SEPARATolLs
tlie ~iaiiei,the iiurnber of Njr cells, and the thickness of the rndiatiori shields, and from these data. the maxkium width of each air cell was computed. The results of tests on these panels are shown in Table IV and Figure 6. The substitution of aluminum foil for the asbestos sheet used between the corrugated separators causes a marked decrease in the thernial conductivity. The panels with the '/&ch (0.63-cn1.) corrugated separators were not as efficient insulators as the panels with t.he 3/&ch (0.95-em.) corrugated separators. Asbestos has a higher thermal con-
For many purposes there are advantages in the use of thin corrugated asbestos or paper structures separating the aluminum foils. A series of panels was constructed in which the foil layers were separated by corrugated asbestos, and,
5 BO
MtANTiMP'f.
i56 t
52
p 46
z :; 32
E .28 2 0
0 z
.21(
sa
iw
izo
140
so
180
0
MLANTIMP'f.
FIGURE4. EFFECTOF E M ~ I V I T01'Y AIR-CELLPhanTioNs ON C o ~ ~ u c ~ t v r n (SIXAm SPACES PER 2 INCHF-R AWIIOXIMATELY)
for comparison, panels were iiicludcd in wlrich asbestos sheel WES substituted for the aluminum foil. A brief description of a e h set of panels is given in Table 111. The depths of corrugation in the original separators are given in Tablo 111, but, during assembly and clamping into the hot plate, the separator is compressed somevhat and the width of the air cell is changed. The table contains the total thickness of
ductaiicc tlran air, and considerable heat passes through the separaton. The presence of more asbestos in the '/&nch corrugated structure than in the 3/s-inch structure probably explains the poorer insulating value. The panels containing the '/r-inch corrugated separators were measured with the corrugations in a vertical position and also with the c o r n Rations in a horizontal position. S o difference was noted in tlie conductivity values for the panels as measured in the difiercnt positions. Since asbestos is E fairly poor beat insulator, more heat than usual passed through these panels. On account of this, no conclusions will be drawn from these measurements as to the relative merits of vertical and horizontal corrugat,ions. Panels with various types of corrugated papor separators were constructed and are described in Table V. The thermal conductivities o i these insulations are shown in Table VI and Figure 7. In general, the panels constructed with GOITUgated paper separators were somewhat better thermal imulators than those containing corrugated asbestos separators. The paper had a higher thermal resistance and was considerably thinner and lightor in weight. 111 addition, the
INDUSTRIAL AND ENGINEERING CHEMISTRY
250
Vol. 25, No. 3
TABLEIV. THERMAL CONDUCTIVITY OF AIR-CELLINSLJLATIONS WITH CORRUGATED ASBESTOSSEPARATORS POSITION OF CORRUGATIONS MAX.WIDTH TOTAL THICKNESS IN OP EACH OF Hi h PANELS HOTPLATEAPPARATUS AIR SPACE INSULATION si8e Inch (ern.) Inch (em.) O F. A Horizontal 0.16 (0.41) 1.00 (2.54) 70.5 148.4 222.4 B Horizontal 0 . 2 1 (0.53) 1 . 1 3 (2.87) 99.4 198.5 276.1 B Vertical 0 . 2 1 (0.53) .13 (2.87) 105.8 198.8 262.2 C Horizontal 0 . 3 5 (0.89) .19 (3.02) 84.6 200.5 255.7 D Horizontal 0 . 3 3 (0.84) .06 (2.69) 104.0 222.3 311.8 E Horizontal 0.46 (1.17) .oo (2.54) 75.1 164.2 251.0 F Horizontal 0.48 (1.22) 1.00 (2.54) 83.6 200.8 257.2 Described in Table 111. I
Low side O
F.
40.9 40.7 41.8 48.6 60.0 50.4 56.5 56.8 58.9 40.9 40.7 41.4 42.5 42.9 44.4 41.1 41.4 41.3 41.3 41.9 41.6
TEMPERATURE Difference O
CONDUCTIVITY B . L. w. (Kg.-caZ.)
Mean
F.
F.
29.6 107.7 181.1 50.8 148.5 225.7 49.3 142.0 203.3 43.7 159.8 214.3 61.5 179.4 267.4 34.0 122.8 209.7 42.3 158.9 215.6
55.7 94.6 131.9 74.0 124.3 163.3 81.2 127.8 160.5 62.7 120.6 148.5 73.3 132.6 178.1 58.1 102.8 146.2 62.5 121.4 149.4
(" C.)
(13.2) (34.8) (55.5) (23.3) (51.3) (72.9) (27.3) (53.2) (71.4) . . (17.1) (49.2) (64.7) (22.9) (55.9) (81.2) (14.5) (39.3) (63.4) (16.9) (49.7) (65.2)
0.459 0.495 0.528 0.365 0.384 0.400 0.373 0.394 0.405 0.443 0.534 0.580 0.298 0.325 0.348 0.482 0.581 0.688 0.386 0.450 0.476
(0,0569) (0.0614) F.0655) 0.0453) 0.0476) 0,0496) (0.0463) (0.0489) (0.0502) (0.0549) (0.0662) (0.0719) (0.0370) (0.0403) (0.0432) (0.0598) (0.0720) (0.0853) (0.0479) (0.0558) (0.0590)
TABLEV. DESCRIPTION OF INSULATIONS WITH CORRUGATED PAPERSEPARATORS Max. TOTAL THICKNESS WIDTH THICKNESS OF EACH OF CORRUGATED AIR SPACE INSULATION SEPARATORS OF
PANEL
CONSTRUCTION OF INSULATION"
Inch (cm.) Inch (em.) '/,-inch (0.64-om.) corrugated kraft paper separators aluminum foil; 9 air spaces 0.19 (0.48) 1 . 7 5 (4.45) 6/1o-inch (0.79-cm.) corrugated paper separators aluminum foil. 7 air spaces 0 . 2 7 (0.69) 1.94 (4.93) */a-inch (0.95-cd.) corrugated kraft paper separators aluminum foil: 6 air 8 aces 0 . 2 8 (0.71) 1 . 7 2 (4.37) :/a-inch corrugated chestnut Zber separators aluminum foil. corrugations crossed a n d sprayed with alurninuA paint. 6 air 8 aces 0 . 3 2 (0.81) 2 . 0 0 (5.08) E s/s-inoh corrugated chkstnut h e r separators aluminum foil. 6 air spaces 0 . 3 1 (0.79) 1 . 9 1 (4.85) F */a-inch corruga'ted chestnut fiber separators aluminum foil. crossed corrugations: 6 air spaces 0 . 3 0 (0.76) 1.84 (4.67) corruiated strawboard separators G '/a-inch 0.32 (0.81) 1 . 9 7 (5.00) aluminum foil: 6 air spaces H '/%-inch (1.27-cm.) corrugated kraft paper separa0 . 4 3 (1.09) 1.72 (4.37) tors aluminum foil: 4 air spaces idium silicate was used as adhesive except for panel Cp , where r u b t,er cement was 5 s
