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Rating and Care
of Domesti.. Sawdust
Burners
By
E. C. WILLEY
Bulletin Series,
No. 15
July 1941
Engineering Experiment Station
Oregon State System of Higher Education
Oregon State College
THE Oregon State Engineering Experiment Station was
established by act of the Board of Regents of the College
on May 4, 1927. It is the purpose of the Station to serve the
state in a manner broadly outlined by the following policy:
(1)To stimulate and elevate engineering education by
developing the research spirit in faculty and students.
(2) To serve the industries, utilities, professional engineers, public departments, and engineering teachers by making
investigations of interest to them.
(3) To publish and distribute by bulletins, circulars, and
technical articles in periodicals the results of such studies, surveys, tests, investigations, and researches as will be of greatest
benefit to the people of Oregon, and particularly to the state's
industries, utilities, and professional engineers.
To make available the results of the investigations conducted by the Station three types of publications are issued.
These are
(1) Bulletins covering original investigations.
(2) Circulars giving compilations of useful data.
(3) Reprints giving more general distribution to scientific papers or reports previously published elsewhere, as for
example, in the proceedings of professional societies.
Single copies of publications are sent free on request to
residents of Oregon, to libraries, and to other experiment
stations exchanging publications. As long as available, additional copies, or copies to others, are sent at prices covering
cost of printing. The price of this bulletin is 25 cents.
For copies of publications or for other information address
Oregon State Engineering Experiment Station,
Corvallis, Oregon
Rating and Care of
Domestic Sawdust Burners
By
E. C. Wzuay
Assistant Professor of Mechanical Engineering
Bulletin Series,
No. 15
June 1941
Engineering Experiment Station
Oregon State System of Higher Education
Oregon State College
TABLE OF CONTENTS
I. Acknowledgments and Summary .......................................................................
1. Acknowledgments ....................................................................................
2.
Summary ....................................................................................................
Introduction ..........................................................................................................
II.
1. Domestic Sawdust Burners ...................................................................
2. Source of Fuel Supply ...........................................................................
3. Heat Value of Sawdust Fuels .............................................................
Domestic Burners ............................................................................................... 9
III.
1.
Types of Burners .................................................................................. 9
2. Differences in Design ..........................................................................
9
Rating the Burners .............................................................................................. 13
IV.
1. Rating Investigations ............................................................................. 13
2.
Rating Tests .............................................................................................. 14
3. Test Apparatus and Procedure ............................................................ 14
4.
Test Results .............................................................................................. 15
V. A Discussion of Test Results .......................................................................... 18
1.
Summary of Tests .................................................................................. 18
2. A Discussion of All Findings .............................................................. 18
Conclusions ............................................................................................................ 21
VI.
1.
Rating ........................................................................................................
21
2. Correcting Burner Troubles .................................................................. 22
VII.
References ............................................................................................................ 23
ILLUSTRATIONS
Page
Figure 1. Cutaway View of Typical Sawdust Burner ---------------------------------------- 8
Figure 2. Typical Sawdust Burner Installation on Hot Air Furnace ------------ 10
Figure 3. Sawdust Burner Installed on Steam or Hot Water Boiler
Figure 4. Typical Sawdust Hot Water Heater
------------
10
---------------------------------------------------- 11
Figure 5. Cutaway View Showing Cone in Fuel Hopper
---------------------------------- 12
Figure 6. Section of Burner Having One-Piece Feed Grate
Figure 7. Section Showing Typical Two-Piece Feed Grate
-------------------------- 12
------------------------------
Figure 8. Section Showing Typical Multiple Shelf Feed Grates
Figure 9. Domestic Sawdust Burner Rating Curve
13
--------------------
13
----------------------------------------------
20
TABLES
Page
Table 1. Lumber Production in Oregon
------------------------------------------------------------------
Table 2. Gross Heat Values of Sawdust by Units
----------------------------------------------
6
7
Table 3. Commercial Burner Output Rating ---------------------------------------------------------- 14
Table 4. Typical Laboratory Test Data
Table 5. Summary of Test Results
------------------------------------------------------------------ 16
-------------------------------------------------------------------------- 17
H
Li
Rating and Care of Domestic
Sawdust Burners
By
E. C. WILLEY
Assistant Professor of Mechanical Engineering
I. ACKNOWLEDGMENTS AND SUMMARY
1. Acknowledgments. The author of this paper wishes to take this
opportunity to express his indebtedness to W. L. Morrison for furnishing the
sawdust burners and grates that were used in the domestic heating research
laboratory in conducting tests; to A. P. Nicol and L. M. Klein (seniors in
Mechanical Engineering) for their work in the laboratory and recording of test
results; to E. G. Mason, acting Dean of the School of Forestry, for statistics
on wood utilization; to the engineers of the Western Foundry Company of
Portland for supplying information from their field installation notes; to W. M.
Martin, Professor of Heat Engineering, for helpful suggestions in arranging
data for the bulletin; and to S. H. Graf, Director of Engineering Research, for
counsel and editorial assistance in preparation of this bulletin.
2. Summary. The objective of this study was to arrive at some suitable
means of finding a more accurate method of rating the output of domestic
This investigation involved, in addition to laboratory experiments, a careful study of home installations. From the laboratory tests were
determined output ratings for various stack drafts and grate areas, while the
home installations furnished the data for determining a rating under average
sawdust burners.
field conditions.
After completing the foregoing study a final check was made with sawdust
burner manufacturers and a rating is recommended based on the correlation of
all the information at hand.
II. INTRODUCTION
1. Domestic sawdust burners. The burning of waste wood in the form
of sawdust is relatively new to the heating industry. Although crudely constructed equipment, mostly homemade, has been used for 10 or 15 years, it has
been during only the past 5 years that any attempt has been made to perfect
small domestic equipment to the point where it is commercially acceptable to
the general public.
The first attempts at constructing equipment for burning sawdust resulted
in devices that gave trouble in the form of excessive smoking, backfiring, and
creosoting. These difficulties were serious enough to discourage almost anyone
from using the devices even though the fuel was the cheapest on the market.
It was because of investigation into the causes of these burner troubles that the
writer discovered the importance of finding some standard method of rating
sawdust burners for output capacity.
The fact that so many of the installed burners were much larger than
necessary for the job gave a clue toward solving some of the troubles
encountered.
6
ENGINEERING EXPERIMENT STATION BULLETIN No. 15
An investigation disclosed the fact that most manufacturers of sawdust
burners knew little about the rating of their own product, were financially
unable to make an investigation, or were not interested in so doing.
2. Source of fuel supply. Waste wood fuel is of two general types;
"sawdust," which, as the name implies, is a byproduct of the saw from the
lumber mills, and "hogged fuel," also a byproduct that is a much larger, coarser
The hogged fuel is obtained by putting the slabs and larger waste
pieces of wood into a machine having large rotating knives that cut it into
small pieces averaging one-half to one inch in diameter. This machine is
called a "hog," and hence the name "hogged fuel." The coarser fuel is used
mostly in large industrial plants, while the small domestic heating apparatus
uses the finer sawdust. In sawmills having planers, the planer shavings are
refuse.
also included in the hogged fuel.
Naturally the source of supply is at the location of our largest wooded
areas, which happen to be the northwest and extreme northeast portions of the
United States. Oregon and Washington have the largest stand of timber of
any of the states and are therefore the location of most interest in sawdustburning equipment.
The nearest estimate to the availability of wastewood fuel sources in
Oregon may be had from a study of a report compiled by the West Coast
Lumbermen's Association from reports of the United States Forest Service,
which is shown in Table 1.
This report represents a typical average cutting extending over a number
of years. According to authorities with practical experience in handling large
Table 1.
LUMBER PRODUCTION IN OREGON (1935)
By SPECIES
Million feet
board measure
1,855.1
64.2
52.5
72.5
13.1
31.6
1,028.3
Softwoods
Douglasfir
WestCoast hemlock
Whitefir
Sugarpine
Ponderosapine
Lodgepolepine
6.9
1.5
Hardwoods
*
5.7
3.2
*
Alder--------------------------------------------------------------------------------------------------------
*
Allothers----------------------------------------------------------------------------------------------- 10.7
Total-----------------------------------------------------------------------------------------------
3,145.3
By AREAS
Softwoods
East side
West side
1,036
2,089
Hardwoods
West side
20
Total
3,145
* Less than 50,000 feet
RATING AND CARE OF DOMESTIC SAWDUST BURNERS
sawmill waste, it is estimated that 60 per cent of the refuse is used to generate
power in the mill. The other 40 per cent has been disposed of by burning it in
large retorts.
The average sawmill will produce as a byproduct one unit of hogged fuel
for every thousand board feet of lumber sawed. (A unit of hogged fuel or
sawdust is 200 cubic feet.) This being the case and using the preceding report
as a basis for estimate, there would be available in Oregon enough refuse fuel
to heat 414,000 homes of average size east of the Cascade Mountain Range
and 840,000 homes on the coast side of the mountains.
3. Heat value of sawdust fuels. The heating value of wood as sold
varies greatly. This may be accounted for first by the physical structure and
content of resins, gums, oils, etc., and second because of the moisture content.
Because of the heat required to evaporate and superheat the moisture, there is
a very marked decrease in the heat available when wet fuel is burned. An
increase in the amount of moisture in a pound of fuel, therefore, causes a corresponding decrease in the heating value per pound of the fuel.
It is customary to refer to the amount of moisture in wood fuel as a percentage of either the oven-dry weight or the green or original weight. The
wood technicians or dry-kiln operators use the first method, while the second
method, basing calculations on the green weight, is often used by fuel
technicians.
The latest available data on Pacific Northwest sawdust heat values are
given in a report from the Forest Department of the Canada Department of
Interior laboratory at Vancouver, B. C., as follows:
Douglas fir ------------------------------------ 9,200 Btu/lb of oven-dried fuel
Western hemlock ------------------------ 8,500 Btu/lb of oven-dried fuel
Sitka spruce
-------------------------------- 8,100 Btu/lb of oven-dried fuel
*Westem red cedar ---------------------- 9,700 Btu/lb of oven-dried fuel
Western yellow pine ------------------ 9,100 Btu/lb of oven-dried fuel
The above report shows average heat values dry. These values are comparable to those obtained in tests to be discussed later, which were made in the
Oregon State College Domestic Heating Research Laboratory. These tests,
made by the calorimeter bomb method on Douglas fir sawdust, showed an
average dry value of 9,070 Btu per pound.
Average moisture contents of fir sawdust run arQund 42 per cent. An
average unit of fuel at this moisture content will weigh 3,700 pounds, which
makes available about 17 million Btu. The average installation using 50 per
cent excess air and 500 F stack temperature, however, will leave about 13
million Btu available for useful heat.
Table 2. Gsoss HEAT VALUES OF SAWDUST BY UNITS
105
Hemlock
Yellow pine
Red cedar
---------------------------
Sitka spruce -------------------------
84
77
92
51
45.3
44
48
4,300
4,050
2,700
3,320
3,440
3,268
4,930
3,605
14,800,000
13,200,000
13,320,000
11,970,000
'Although the calorific value per pound of oven-dried wood is high for western red
cedar, the low weight of this wood materially reduces its available heat per unit.
Figure 1.
CUTAWAY VIEw OF TYPICAL SAWDUST BURNER.
RATING AND CuE OF DOMESTIC SAWDUST BURNERS
9
I
From various field tests and laboratory data obtained, Table 2 has been
prepared, based on an assumed stack temperature of 500 F. In column "A" of
the table the percentage is based on oven-dry weight, and in column "B" it is
based on the original weight.
The gas analysis on field tests often shows from 16 to 18 per cent carbon
dioxide in the flue gas compared to 21 per cent under perfect conditions.
The greatest efficiency is generally found in large commrciaI plants where
trained attendants, using instruments, keep constant watch over the equipment
24 hours a day. As high as 65 per cent efficiency is sometimes attained under
these conditions, where the small domestic units will do well to get from 25
to 40 per cent.
III. DOMESTIC BURNERS
1. Types of burners. There is no great difference among the various
makes of sawdust burners on the market today. This is true not only of the
domestic type but also of the large commercial-type burners.
in general, the burners consist of a combustion chamber, sometimes called
a Dutch oven, in which are contained grates and refractory brick lining. On
the top of the oven is an opening on which is placed a hopper into which the
sawdust is fed. On the large commercial burners this opening is connected with
a chute into which a sawdust conveyor discharges.
A typical domestic-type burner is illustrated in section in Figure 1.
Note
that the grates are removable and adjustable. This feature is true of most
burners. The top and sides of the oven are protected by refractory brick
linings. In some cases there is provided space between the brick lining and
outer iron
is passed in order to keep an
excessive amount of heat from escaping from the oven.
Most sawdust burners are built as individual units separate from the furnace and are intended to be placed in front of and connected with the furnace.
In most cases they are attached to the ash pit door after removing the coal or
wood grates and relining the furnace with firebrick. The firebrick of the
furnace is connected with the firebrick of the sawdust burner so that there is a
continuous sealed fire passage from the burner to the combustion chamber of
the furnace.
Contrary to an apparent misconception of the majority of laymen, the sawdust burner is applicable to most any type of furnace using solid or oil fuels.
The only problem is that of making suitable connection between the burner and
the combustion chamber of the furnace. Figure 2 shows a burner connected
to a gravity hot-air system. A forced hot-air system would look similar to this.
In Figure 3 is shown a connection made to boiler of the steam or water type.
In the case of the small domestic water heater it is customary to build the
burner and heater in one unit. Figure 4 shows a typical water heater. This
unit is built ready to make chimney and water connections. The burner is
essentially the same as the larger type burners. It is not unusual to see the
larger sizes of these water heaters used to furnish hot-water radiator heat for
small homes.
2. Differences in design. Although there is a striking similarity in the
general design of sawdust burners, the differences are mainly in shapes of
grates, shapes of hoppers, and methods of introducing secondary air to the
fuel bed.
10
ENGINEERING EXPERIMENT STATION BULLETIN No. 15
There has been considerable experimenting, mostly by the cut-and-try
method, to find the proper shape of hopper for best feeding of the sawdust.
The steepness of the side angles has been pretty well agreed upon, but there is
i
!I
L.
Figure 2.
TYPICAL SAWDUST BURNER INSTALLATION ON HOT AIR FURNACE.
Figure 3.
SAWDUST BURNER INSTALLED ON STEAM OR HOT WATER BOILER.
RATING AND CARE OF DOMESTIC SAWDUST BURNERS
11
still experimental work being done with devices to place on the inside of the
hopper to alleviate the packing of the fuel. The cutaway illustration in Figure
5 shows one method of attacking this problem.
Figure 4.
TYPICAL SAWDUST HOT WATER HEATER.
Not only is the shape of the hopper important but the shape and size of, the throat are of great importance to the proper feeding of fuel to the fire
grates. The inclined feed grates in the throat of the burner are probably the
most important contribution to efficient operation. One type of feed grate is
pictured and marked in Figure 1. Different types of feed grates are shown also
in Figures 6, 7, and 8. In each case illustrated there is possibility of movement or adjustment of these grates. Although the feed grate shown in Figure
8 is one that is made stationary, there are similar grates that have the steps
adjustable in respect to angle in order to accelerate or decelerate the fuel feed.
As a further check or control of the fuel feed, one manufacturer has provided
a cast-iron apron (Figure 7) which controls the forward movement of the fuel
on the main grate. This apron can be adjusted to any conditions of fuel or
stack draft.
The main grates are of two general types, the stationary or one-piece type
and the movable or shaker type. Figures 6, 7, and 8 show the one-piece type,
while Figure 5 pictures the movable shaker type similar to the old coal-type
In Figure 6 the main grate shows a raised portion at the front end.
Its purpose is to form a barrier to prevent the sawdust from covering the
grates.
entire grate. An exposed air opening to admit air for combustion at low firing
rates is thus obtained. It is the accidental covering of these air holes during
the inrush of fresh fuel over a bed of hot coals that results in an explosion
when the accumulated gas is finally ignited.
12
ENGINEERING EXPERIMENT STATION BULLETIN No. 15
The primary air supply is supplied to all burners alike; namely, through
the front draft door. The secondary air is brought in by methods as numerous
Figure 5.
Figure 6.
CUTAWAY VIEW SHOWING CONE IN FUEL HOPPER.
SECTION OF BURNER HAVING ONE.PIECE FEED GRATE.
RATING AND CARE OF DOMESTIC SAWDUST BURNERS
13
as there are makes of burners. Figure 6 shows one method used. In this
burner a short pipe just over the fuel bed is always open for auxiliary air regardless of shutting off the main supply at the draft door.
Figure 7.
Figure 8.
SECTION SHOWING TYPICAL TWO.PIECE FEED GRATE.
SECTION SHOWING TYPICAL MULTIPLE SHELF FEED GRATES.
IV. RATING THE BURNERS
1. Rating investigations. In 1928 the writer started an investigation
to determine, if possible, some basis for the rating of sawdust burners. At
that time there was no record of any research or investigation made by any of
the sawdust-burner manufacturers themselves, nor has any appeared up to the
present.
As a beginning, a letter was sent to every known sawdust-burner manufacturer in the Northwest, asking for a list of their burner sizes and output
ratings for each size. In the returns from this questionnaire, only one manufacturer submitted an estimate sheet showing sizes of burners and estimated
outputs. This material was to be used by their field dealers who made the
14
ENGINEERING EXPERIMENT STATION BULLETIN No. 15
4..
installations. Burners from 1.56 square feet to 26.05 square feet in area were
listed. Following is the information from the data sheet in condensed form.
As the burners with giate sizes larger than 8 square feet of area would
logically be classed as commercial sizes, they have been left out of this table.
Btu ratings for the following were calculated on the basis of 240 Btu per square
foot of steam radiation. The data have also been rearranged in order that
comparisons can be made later with information gathered in the research
laboratory.
Table 3.
COMMERCIAL BURNER OUTPUT RATING
Grate width
Inches
Grate area
Total
output
Output per
sq ft grate
Btu/hour
Btu/hour
162,000
194,000
259,000
389,000
518,000
648,000
972,000
104,000
107,000
124,500
113,000
123,800
127,000
119,000
Capacity
Square feet Square feet
steam cad.
10-3/4
11
12
16
18
21 ------------------------------------------------------28 -------------------------------------------------------
1.56
1.8
2.08
3.44
4.2
5.1
8.17
675
810
1,080
1,620
2,160
2,700
4,050
Through conference with the engineers who furnished the above manufacturer's data, facts disclosed that the data were not based on laboratory
research but on information taken from field installations. The engineers were
all agreed that the estimates were low and allowed a high safety factor for the
installing dealers.
Although there were no estimates on heating value of fuels or stack-draft
conditions, it is presumed that the high safety factor would allow for the poorest
conditions of either.
The main conclusion that can be drawn from an analysis of these data is
that the average output of the burners would be about 117,000 Btu per hour
per square foot of grate area.
It was interesting to note from the estimate sheet that the capacity per
square foot increases quite perceptibly in the larger-sized grates. Ratings for
the four larger sizes of burners, taken from the same estimate sheet and not
included in the above, showed,
13.36 sq ft grate, estimated ............ 136,000 Btu/hr/sq ft grate
16.28 sq ft grate, estimated ............ 159,000 Btu/hr/sq ft grate
20.47 sq ft grate, estimated ............ 158,000 Btu/hr/sq ft grate
26.05 sq ft grate, estimated ............ 233,000 Btu/hr/sq ft grate
These higher ratings may justly be expected to be due largely to the fact
that the larger commercial-size burners are generally given constant personal
attention.
2. Rating tests. During the winter of 1938 a series of tests was made on
sawdust burners with the object of arriving at some method of rating them.
These tests were made in the Domestic Heating Research Laboratory of the
Mechanical Engineering Department at Oregon State College.
Before the recorded tests were made, a large number of tests were conducted to study the characteristics of the burners. It was soon determined that
the most important characteristics were: first, area of the grate; second,
stack-draft pressures; and, finally, the amount of opening available for the air
supply.
3. Test apparatus and procedure.
One 10-inch sawdust burner was
installed on a vertical fire tube steam boiler. This boiler was one that had been
RATING AND CARE OF DOMESTIC SAWDUST BURNERS
15
given a series of tests with solid wood fuel and that gave 143,500 Btu per hour
at 100 per cent rating. (See 0. S. C. Engineering Experiment Station Reprint
Series No. 7 for further details of boiler.) Extreme care was taken to seal
all cracks in burner connections so as to avoid any air leakage.
Water supply was taken from the city mains to a barrel on platform
scales.
An electrically driven gear pump forced the water from the barrel to
the boiler after it was weighed and recorded.
Fuel was weighed on a platform scale. In addition to the weighing of the
fuel, a representative .sample was taken at each run and analysis made of the
moisture content. With each new batch of fuel a test of heat content was
made also with the calorimeter bomb.
During the tests, various kinds and conditions of sawdust were used.
Douglas fir, red cedar, and hemlock mostly were used.
Most of the .sawdust
was regular run (not resaw) and fresh from the mill. Experiments were
made, however, using kiln-dried sawdust as well as old sawdust that had
become wet. One batch of sawdust (taken from under an old house) had been
stored for 6 years. Heating value of all these fuels showed a very small
degree of variation.
In preparation for each test, there was a warming-up period from I to 2
hours in duration.
Steam pressure was determined by a Bourdon gage, which was checked for
accuracy after each run.
Steam quality was determined by a steam separating calorimeter.
Stack temperature was determined by use of a high-velocity thermocouple
in conjunction with an electric pyrometer.
Stack pressures were measured with a standard 1-inch water draft gage.
Flue gas was analyzed with an Ellison gas analyzer.
4. Test results. Table 4, taken from laboratory data of No. 12 test run,
is typical of information obtained from each of the twenty-four tests. Table 5
is a condensed tabulation of data taken from all tests made in the laboratory.
It will be noted that these test results are compared on the basis of grate
area, stack pressure, and amount of draft opening.
As the following data are taken from tests on the 10-inch burner, it will
also be noted that the draft openings are recorded as 6.67 square inches, 12.37
square inches, and 80 square inches. The 80-square-inch opening was obtained
when the entire ash pit door was left open. This was, of course, the largest
opening obtainable. The small draft door when wide open gave 12.37 square
inches of draft area. When the small draft door opened 7/8 of an inch, it gave
a draft area of 6.67 square inches. This last opening had no special significance
except that it provided a point on a rating curve.
Included in the following pages are test data taken from 24 test runs as
follows
Tests No. 1 to 12 were made on a burner having 117 square inches of
grate surface.
Tests No. 13 to 18 were made using 43.5 square inches of grate.
Tests No. 19 to 24 were made using 70 square inches of grate.
Tests made with low stack pressure (0.02 inch of water and under) were
Nos. 6, 7, 8, 15, 21, and 22.
Tests made with stack pressure averaging 0.05 inch of water were Nos. 4,
5, 9, 14, 18, 20, and 23.
Tests with stack pressure of 0.1 inch average were Nos. 10, 11, 12, 13, 16,
19, and 24.
Tests with stack pressure of greater than 0.1 inch were Nos. 1, 2, and 3.
Table
Sawdust burner test
4.
TYPICAL LABORATORY TEST DATA
Test run No.
12
-
p5
Time
steam
ps
stack
T1
T2
T3
Steam
per cent
dry
Fuel
added
Water
added
COs
Per cent
C'
34
25
30
29
30
32
33
30
31
30
31
29
30
3:00
3:10
3:20
3:30
3:40
3:50
4:00
4:10
4:20
4:30
4:40
4:50
5:00
0_jo
0.11
009
0.10
0.13
011
0.11
013
011
0.11
011
010
0_li
51
51
52
52
52
52
52
52
53
53
53
53
68
600
490
445
460
600
600
560
575
530
580
560
570
690
69
574
72
72
72
72
69
68
68
68
68
68
67
68
O
Per cent
CO
Per cent
11.0
7.2
0
10.0
7.4
0
10.4
7.0
0
23
30
20
11.0
5.9
0
245
10.7
6.8
0
33
9858
52
25
9914
.
..
.
35
27
59
9878
59
------------------------------------------------
30.3
Average
and totals
-----------------------------------------------Ps = Steam gage
P2
Stack temp
T5 = Feedwater temp
T2 = Room temp
--------------- .
0109
52.2
98.83
118
= Stack temp
Bar, pressure = 2032 in. mercury
Sawdust used: Sample No. VI
Small draft door open 7/8 in.
T5
-h
Table 5.
Stack
draft
Run number
74.3
60.0
14.6
6.8
10.6
9.0
4.6
10.7
6.9
11.4
103,000
82,500
170,000
133,000
178,000
147,000
297,000
258,000
263,800
305,500
319,500
369,000
CO2
per cent
02
per Cent
Total
output
Btu
per hour
122.5
96.7
460
500
690
549
0.02
0.05
0.10
0.17
65.3
75.5
80.0
93.0
4,948
4,980
4,915
4,890
43.5
44.4
41.9
47.7
100.3
117.8
148.0
140.0
480
522
560
628
13.4
14.9
11.9
11.2
5.2
4.1
5.0
8.6
140,000
164,000
207,000
196,000
52.9
89.3
128.6
108.0
4,915
4,980
4,915
4,890
41.9
44.4
41.9
48.7
85.0
124.3
181.7
143.7
470
508
...............................
...............................
0.02
0.05
0.10
0.17
600
644
13.4
14.5
14.7
13.3
6.7
4.7
2.3
1.8
117,000
174,000
256,000
200,000
................................
0.08
0.05
0.02
81.6
71.0
58.2
4,560
4,560
4,560
47.4
47.4
47.4
65.0
51.4
33.0
350
390
250
7.9
8.2
7.0
12.2
11.9
13.4
Draft opening 80 sq in.
211,500
95,000
362,200
141,000
515,000
208,000
429,000
163,100
Draft opening 12.37 sq in.
150,000
182,000
73,300
117,000
158,500
57,300
75,000
130,000
36,800
.................................
...............................
...............................
0.09
0.05
0.02
100.0
75.5
53.0
4,560
4,560
4,560
47.4
47.4
47.4
90.0
45.0
44.0
380
350
220
9.8
8.2
9.2
10.1
11.8
11.2
206,000
103,000
100,000
...............................
0.08
0.05
89.3
83.0
4,830
4,830
44.4
44.4
44.0
38.0
250
200
7.8
6.8
12.2
13.4
Draft opening 6.67
162,000
130,000
141,000
120,500
...............................
0.09
0.05
0.02
184.0
109.0
76.0
4,830
4,830
4,830
44.4
44.4
44.4
75.0
56.0
42.0
506
217
223
6.2
8.2
9.3
13.9
11.7
10.9
280,000
208,000
157,000
------------------------------...............................
5
...............................
8
4
11
Grate area 70.5
19
sq
Overall
eff
per cent
Draft opening 6.67 sq in.
43.5
41.8
44.2
53.3
6
20
21
Stack
temp
F
4,948
4,915
5,033
4,166
10
2
Total
input
Btu
per hour
Steam
total lb
per hour
44.3
36.9
72.6
76.4
9
12
3
Output
Btu per hr
per sq ft
of grate
Moisture.
per cent
by weight
0.02
0.05
0.11
0.17
7
1
Fuel lb
per hr
Heat per
per sq ft lb fuel as
fired
grate
Grate area 117 sq inches
in. of
water
SUMMARY OF TRST RESULTS
inches
83,000
67,000
138,000
108,000
Draft opening 12.37 sq in.
113,600
133,700
168,000
159,000
47.0
45.5
46.7
42.1
43.1
43.8
52.6
43.1
44.9
39.0
40.4
38.1
40.3
36.2
28.3
Draft opening 44 sq in.
24
23
22
Grate area 43.5 sq inches
16
18
223,000
168,500
111,500
Draft opening 12.37
13
14
15
269,000
159,000
111,000
101,000
50,300
49,000
sq
in.
49,000
42,700
sq
45.0
29.8
41.4
37.8
35.4
in.
85,000
62,000
47,400
31.6
39.5
42.6
18
ENGINEERING EXPERIMENT STATION BULLETIN No. 15
V. A DISCUSSION OF TEST RESULTS
1. Summary of tests. Results of all the laboratory tests are shown in
condensed form in Table 5. It is interesting to note that regardless of draft
conditions, sizes of grates or draft openings, the efficiencies nearly all fell within
a range of 30 and 50 per cent. The average efficiency was 40.6 per cent. Also
with the varied ages, moisture content, and kinds of sawdust fuel, there was an
average heat content per pound as fired of 4,790 Btu. The average output per
square foot of grate area was 158,000 Btu per hour.
Analysis of test results also shows that the intensity of draft is a most
important factor. It will be noted that the highest output rating in nearly all
cases was obtained when the draft was around 0.1 inch. Even in the case of
the largest draft opening, the output was maximum at 0.1 inch draft pressure
and decreased at higher draft pressure.
Not only were the outputs higher but the efficiencies showed the same trend.
The highest efficiency was obtained when the draft pressure was around
0.1 inch.
Segregating the results of the tests into groups of stack pressure intensity
it was found that all those tests having 0.1 inch stack pressure averaged 204,000
Btu per hour output per square foot of grate, while tests made with the 0.5
inch draft gave 141,000 Btu per hour and the 0.02 inch drafts gave an average
of 132,000 Btu per hour per square foot of grate area.
2. A discussion of all findings. There was no estimate made in the
commercial rating sheets to show the amount of fuel consumption for the
burners per square foot of grate surface. During the laboratory tests, however,
83.5 pounds of fuel were burned per hour per square foot of grate surface on
an average. Of course this was during continuous and supervised firing. If a
burner were being used intermittently and were subj ect to dirty grates, this
rate would be somewhat reduced.
Using the results of the laboratory tests s a basis of comparison, it is interesting to note the difference between these and the commercial rating mentioned in the first part of the paper. In these commercial ratings, the average
output per square foot of grate per hour was 117,000 Btu. No mention was
made in the estimate sheet about draft or the Btu content of fuel as fired.
Assuming that these commercial burners had used fuel with average, as fired,
heat value of 4,025 Btu per pound (see Table 2, average fir and hemlock mix)
and the average fuel burned was 80 pounds per hour per square foot of grate,
then to attain 117,000 Btu per hour the burner would have been giving only 36.5
per cent efficiency.
It is reasonable to expect at least 80 pounds of fuel consumption per square
foot of grate on any of the small domestic burners. The average of 83.5 pounds
obtained in laboratory tests was an average for all the test runs including those
with a very low stack draft. The average of tests where the stack draft was
0.1 inch of water showed 105 pounds burned per square foot per hour. Also
investigations of burners in home installations during the past 5 years disclosed
the fact that there are few small domestic burners with less than 0.1 inch water
stack draft available. The average home with a well-constructed smoke stack
25 to 35 feet high will give 0.15 to 0.19 inch of water draft.
This burning rate may seem abnormally high when comparison is made
with the results of tests made by Henry Kreisinger (Combustion Engineering
Company, New York) in the Bureau of Mines Laboratory in Pittsburgh,
Pennsylvania. These tests, as reported in the magazine Mechanical Engineering
of February 1939, were made on large 500 to 1,000 hp steam boilers in which
RATING AND CARE OF DOMESTIC SAWDUST BURNERS
19
hogged fuel (waste wood of much larger size than sawdust) is used. In these
large burners the fuel is fed to the Dutch ovens by means of chutes over the
grates. The fuel piles up in cone shape on the grates and the air is admitted
for combustion, 10 per cent through the fuel bed and 90 per cent over the top
of the fuel bed. The fact that a top rate of combustion was shown to be only
60 pounds per square foot per hour may be accounted for from a quotation in
the article entitled "Effect of Size of Fuel Particles" as follows
"The surface of a freshly fired fuel receives heat by radiation and convec-
tion from the already burning volatile matter.
From the surface the heat
travels by conduction to the inner parts of the piece. Large pieces of fuel have
a comparatively small surface and a large interior mass to which heat must be
transferred by conduction. Inasmuch as the heat conductivity of wood is low,
it takes a longer time to drive off the moisture and the volatile matter from a
single large piece of fuel than several smaller pieces of equal total weight. A
bunch of excelsior or wood shavings burns in a few seconds because they have
a very large surface to receive heat and practically no interior to which heat
must be supplied by conduction. A stick of wood takes several minutes and a
log in a fireplace takes several hours to burn, because they have a small surface
to receive the heat and a large interior mass to which heat must be transferred
by conduction to drive off the moisture and the volatile matter. The surface at
first receives heat by radiation and by convection. After the volatile matter
has been distilled from the surface layer, the temperature of the layer is raised
and the surface begins to glow. If oxygen has access to the surface, the fixed
carbon burns and heat is generated at the surface and transferred to the inner
parts. As the fixed carbon burns off, a layer of fluffy ash is left at the surface
of the piece of wood or log. This fluffy layer of ash is a hindrance to heat
transfer and also to the heat generation because it prevents the oxygen making
contact with the fixed carbon underneath the layer of ash. If there is an intensive turbulence of the gases and air above the fuel bed, the layer of ash may
be torn off and carried away by the gases, and expose the fixed carbon to contact with oxygen, or, absorption of heat by radiation and convection. In an
open-grate fire, where no turbulence is provided to remove the layer of ash, the
latter accumulates on the surface and unless it is scraped or shaken off with a
poker the fire goes out.
"Therefore, the size of the pieces of fuel has a marked effect on the rapidity of combustion. Wood-waste fuel should be chopped up into reasonably
small pieces to increase the surface and to reduce the amount of combustible
inside of the pieces to which heat must be transmitted by conduction for driving
off moisture and volatile matter, and to which oxygen must be supplied through
a layer of ash to burn the fixed carbon."
This article also states that the average moisture content is about 50 per
cent. This does not agree with our findings, which averaged 42 per cent moisture found in testing the sawdust fuel. The difference may be accounted for
from the fact that the sawdust is largely taken from the inside wood while the
bark and sapwood that go into the hogged fuel refuse would probably give a
much higher moisture content.
In further justification for the higher burning rate of the small domestic
burner, it should be pointed out that the method of introducing the air to the
fuel bed is of much importance.
In the large-size industrial burners the fuel is piled on grates in a large
conical pile; 90 per cent of the air for combustion is taken in through draft
doors over the top of the fuel bed. On the other hand, in the small domestic
burners the air is taken in through the fuel bed almost entirely.
20
ENGINEERING EXPERIMENT STATION BULLETIN No. 15
Consequently the smaller burner not only has better control of the excess
air, but by taking the air through the fuel bed there is better and quicker
absorption of the moisture in the fuel, the air currents help to keep the fuel
bed moving, and there is better control of the grate temperatures.
For the purpose of more clearly comparing the results of these investigations, Figure 9 has been prepared to show the laboratory rating results with
the results obtained from the commercial burner company.
A study of many home installations during the past 5 years shows that
other burner companies are underrating their burners as much or more than
the one from which these data were obtained. Referring to the curve of Figure
9, the commercial field rating shows an average heat output of 119,000 Btu
per hour per square foot of grate area.
The curve (Figure 9) indicating the output of burners plotted during the
stack pressure of 0.1 inch show an average output of 200,000 Btu per hour per
square foot of grate. This was obtained while using all types of fuel and for
various draft openings.
Two ratings that are not shown but that should be mentioned at this time
are, the average rating for all the tests made in the laboratory, which included
the very high and very low stack pressures, and the tests with the very lowest
stack pressures. The average for all conditions showed an output of 158,000
Btu per square foot of grate per hour while the very lowest stack pressure
(0.02 inch) averages 132,000 Btu per hour per square foot of grate.
It does not seem unreasonable to say that any good well-constructed burner
should be able, even under poor conditions, consistently to produce 150,000 Btu
per hour per square foot of grate area. This rating, which is shown on the
u..UUU.U..UUflU..UflflUUuflflflfl'aflUflflUUflu.u.
UUUUUUIUUUUUUUUU4UUUUUUUU
.UUUUU.IUU..IU.U..I...I...UU.UU..UI.I.IuUuuu.UuUUu..uuu.Uu.JL.U!luu....
nnnnnnnnnnnnnnnnnnnSS4nunnnnaThkanunn
nnn.nnnunn.uuunnnnnnn.nnn.fls'Annnnnar4nnnnan.
................................m........ .dUUUPUUUU
nlW'4uun9y1rdNnuns
4Oflfld0UUUUU
UUUUUUUUUdUUUUU
AUUUUUPUUPdUUUU
flUUUUUU
.....................fl 4UUUUUUUSUt4UUUUUIUU
ufluuuuUu'aUUt4USflUUuuUuUuuuuU
UUUUUUUUUUUUUUI,UU4UPUUUUUUUUUUUUUUSUUU
UUUUUUUUUU!
l.I..uuuu.uuuu.uu.uI
.UUUUUUUUU'4UcUflUPdUUUUUUUUUUIMURUflU
..u.........ra..r4n.n..................................................flfl.
UUUUUUUáPdINUUUUUUUUUUUIIUIIIIUUU
.uu.a.uuu'4uuflauUUUU.UflUuuufluuu
flUrAUdaUUUUUUUU.NU
.......tra............fl.....................................................
.2r.....................................................fl....................
4....................U..........................U...........U.U...........U..
GRATE AREA IN SQUARE FEET
Figure 9.
DOMESTIC SAWDUST BURNER RATING CURVE.
I '
RATING AND CARE OF DOMESTIC SAWDUST BURNERS
21
curve of Figure 9, would make ample allowance for poor draft, poor fuel, and
to some extent dirty grates, and still it would be much higher than the rating
that is now given by one commercial manufacturer and that is followed by the
majority of the present manufacturers.
VI. CONCLUSION
1. Rating. This investigation has been made with a view to formulating
a definite standard rating for the output of domestic sawdust burners. Investi-
gational work was carried out in home installations as well as in a series of
tests made in the research laboratory.
From these tests and investigations the following conclusions are indicated:
1. Domestic sawdust burners should be rated for capacity according to the
size (projected square feet area) of their grates. For all general purposes it
is found that a rate of 150,000 Btu per hour per square foot of grate surface
output will meet all general conditions.
2. The intensity of stack-draft pressure is a very important factor in the
rate of burning and the stability and smoothness of operation of combustion.
A minimum of 0.1 inch of water stack draft should be available at the
smoke connection of the furnace. In cases of higher draft conditions a draft
regulator should be provided in the smoke connection.
3. Oversized burners; that is, burners that have a capacity for more than
is needed to supply the normal heating demand of a residence, are the source
of much trouble and inconvenience. For example, when a burner has been shut
off it is necessary to carry on some combustion in order to keep the fire from
extinguishing. An auxiliary air intake is provided for this purpose, and if the
burner is of excessive size this auxiliary burning will cause an overheating of
the living quarters. On the other hand, if the auxiliary air is reduced it will
cause the fire to smoulder and unburned gas to fill the combustion chamber of
the burner and furnace. This unburned gas is a potentional source of the much
dreaded backfiring. Also when the smoke connection is cooled there is a tendency for the cool pipe to condense the vapors of the unburned gas, and this
results in creosoting.
4. Domestic size sawdust burners are very well adapted to automatic control.
By having thermostatic controls on the draft doors of the burners as
much as 25 per cent of the fuel may be saved over the hand regulated method.
Also a much more even temperature may be obtained by the automatic control
method.
5. A general rule for calculating sawdust burner capacity may be taken
from the following equation:
A=
Q
R X H X Eff
When, A = The area of the burner grates in square feet.
The total Btu output of the burner.
Q
R The rate of burning in pounds of fuel per hour per square
foot of grate.
H = Heating value of fuel per pound as fired.
Eff = Overall efficiency of the burner.
22
ENGINEERING EXPERIMENT STATION BULLETIN No. 15
From the evidence gained in this investigation it is pointed out that for all
general purposes this equation can be written,
Q
A=
150,000
When the specific heating value is known or the output rating or efficiency
are known to be different than those found in this investigation, however, then
application to this equation will give the desired area of grate or output of
burner. For example, by using a heating value of 5,000 Btu per pound, which
is not uncommon for pine wood sawdust, and by using a firing rate of 80
pounds of fuel per square foot of grate along with a 40 per cent overall
efficiency and applying this to the formula, the result would be:
A=
or A =
Q
5,000 X 80 X 0.40
Q
160,000
2. Correcting burner troubles. The most frequent troubles encountered
in sawdust-burner installation are: (1) backfiring and smoking, (2) burning
back into the hopper, (3) creosoting in the smoke connection and around an
intake door.
The first condition to investigate when there is excessive smoking and backfiring is the draft pressure. If the stack does not give at least 0.1 inch of watergage pressure, then investigate to see if the stack is obstructed, has loose joints
or connections, or if the top of the stack is lower than the highest point on the
building. In this latter case there would be down-draft currents when the wind
is in the right direction. It may also be due to faulty adjustment of the feed
throat or grates of the burner. In some cases the feed is not regulated and too
large a body of fuel feeds down over the burning fuel bed, which smothers the
blaze temporarily. A good many times this occurs when the draft door of the
burner has been closed for long periods. In this case the chimney cools and
the draft is reduced.
When the ash pit is allowed to fill with ashes, or clinkers are allowed to
form on the grate, it sometimes restricts the air to such an extent that it causes
smoking or backfiring.
Burning up into the hopper is caused by poor feeding down of the fuel.
Any poking down into the hopper will cause arching of the fuel and in consequence the fuel will burn up into the hopper to the point of the fuel arch. Condition of the fuel sometimes causes this. Light dry shavings or old very dry
sawdusts have a tendency to arch over more than the fresh green and heavier
kind. For this reason it is found that dampening the sawdust lightly will help
to give a more even flow through the neck of the feed hopper. Uneven feeding
will also cause smoking and backfiring.
Another cause of poor feeding is insufficient fuel in the hopper. When
there is not enough weight to force the fuel down on the grates, the burned
ash will arch and cause burning into the upper portions of the hopper.
Where there has been repeated burning of the fuel up in the throat of the
burner there is formed a rough clinker-like deposit on the throat walls. This
should be cleaned off thoroughly. After smoothing these walls it sometimes
helps to rub them with some powdered graphite.
L
RATING AND CARE OF DOMESTIC SA\VDUST BURNERS
23
Creosoting is caused by the condensing of vapors from the smoke-laden
gases. Types and conditions of sawdust fuel determine largely the degree of
creosoting. Green woods having a large oil and resin content will of course
give off more creosote in the condensation process. When air to the burner is
shut off and very little combustion is taking place, there is not enough heat
passing up the smoke connection to keep the chimney warm, and certain constituents of the smoke-laden gases will then condense on the cold sides-of the
pipe. Enough combustion should be taking place to keep the chimney warm
without causing too much heat being supplied to the house.
Creosoting in the flue connection may be lessened by covering the pipe with
a good asbestos insulation. Mere asbestos paper will not do. Either an asbestos
cell covering or a i-inch thick covering of asbestos and magnesia will be needed
to make proper insulation.
When creosoting takes place in the draft door on the front of the burner,
the only way to correct it is to leave the door open a very small crack so that
enough air may pass through to keep the fire burning. Naturally if the burner
is too large for the house, this will cause overheating during the period when
there is no call for heat. That is one of the disadvantages of having oversize
burners, however, and one that the writer found so prevalent when making this
investigation of rating burners.
Overheating; that is, uncontrolled heat, is generally due to oversized
burners. If the chimney gives an unusually high.draft, however, and the draft
doors do not fit snugly, or there are cracks in the burner that allow excessive
air leakage, this will of course cause uncontrolled combustion. The first correction in this case is to seal all cracks in the burner and grind a smooth surface
on the draft door so that it closes properly. If the draft is iz excess of 0.1 inch,
it will prove economical to have a draft regulator placed in the smoke connection.
Underheating is a rare thing with sawdust burners. If it occurs, it is
generally caused by poor draft conditions of the chimney. The writer has yet
to see a burner installed in a home that was too small for the house.
VII. REFERENCES
Utilization of sawmill waste and
Vancouver Laboratory of the Forest Products
1. JENKINS, J. H., and GUERNSEY, F. W.
sawdust for fuel.
Laboratories of the Department of Mines and Resources, Canada. Forest Service Circular No. 48, 1937.
2. KREISINGER, HENRY. Combustion of wood waste fuels. Mechanical Engineering, voi. 61, No. 2, February 1939.
3. THOMAS, C. E., and KEERINS, G. D. A discussion of the economies of fuels
used in Oregon. Engineering Experiment Station, Oregon State College. Circular Series, No. 1, September 1929.
I,.
OREGON STATE COLLEGE
ENGINEERING EXPERIMENT STATION
CORVALLIS, OREGON
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and C. D. Adams. 1930.
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Optimum Power and Economy Air-Fuel Ratios for Liquified Petrolemn Gases,
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Rating and Care of Domestic Sawdust Burners, by E.
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24
A
RATING AND CARE OF DOMESTIC SAWDUST BURNERS
25
Reprints
No. 1. Methods of Live Line Insulator Testing and Results of Tests with Different
Instruments, by F. 0. McMillan. Reprinted from 1927 Proc. N. W. Elec. Lt.
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26
ENGINEERING EXPERIMENT STATION BULLETIN No. 15
Research Papers
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No. 1. Electric Fish Screens, by F. 0. McMillan.
Bulletin of the U. S. Bureau of
Fisheries, vol. 44, 1928. Also in pamphlet form, U. S. Bureau of Fisheries,
Document No. 1042.
No. 2. Water Control of Dry Mixed Concrete, by G. W. Gleeson. Concrete Products,
December 1929.
No. 3. High-voltage Gaseous Conductor Lamps, by F. 0. McMillan and E. C. Starr.
Trans. American Institute of Electrical Engineers, vol. 48, no. 1, pp. 11-18,
1929.
No. 4. The Influence of Polarity in High-voltage Discharges, by F. 0. McMillan and
E. C. Starr. Trans. American Institute of Electrical Engineers, vol. 50, no. 1,
pp. 23-35, 1931.
No. 5. Progress Report on Radio Interference from High-voltage Transmission Lines
Pin and Pedestal Type Insulators, by F. 0. McMillan. Trans. 8th annual
general meeting, Engineering Section, Northwest Electric Light and Power
Assoc., 1931.
No. 6. Aggregate Grading for Tamped Concrete Pipe, by G. W. Gleeson.
Concrete,
June 1932. Rock Products, 1932. Concrete Products, June 1932 and MayJune 1934.
No. 7. Water Control of Dry Mixed Concrete, by G. W. Gleeson. Concrete Products,
September 1932, and Rock Products, November 1932.
No. 8. Litliarge and Glycerine Mortars, by G. W. Gleeson.
Paper Trade Journal,
October 13, 1932.
No. 9. Radio Interference from Insulator Corona, by F. 0. McMillan. Trans. American
Institute of Electrical Engineers, vol. 51, no. 2, pp. 385-391, 1932.
No. iO. The Coordination of High-voltage Transmission Lines with Radio, by F. 0.
McMillan. Trans. 9th annual general meeting, Engineering Section, Northwest Electric Light and Power Assoc., 1932.
No. 11.
Asphalt Emulsion Reduces Insulator Radio Troubles, by F. 0. McMillan.
Electrical World, vol. 102, no. 6, August 5, 1933.
No. 12. Silicon, a Major Constituent of Boiler Scales in Western Oregon, by R. E.
Summers and C. S. Keevil. Paper presented at annual meeting, American
Society of Mechanical Engineers, 1933. Abstracts published in Mechanical
Engineering, vol. 55, p. 720, November 1933; Power, vol. 77, p. 687, midDec. 1933; and Power Plant Engineering, vol. 37, p. 519, December 1933, and
vol. 38, p. 219, May 1934.
No. 13.
Study of the Frequency of Fuel Knock Noises, by W. IT. Paul and A. L.
No. 15.
Siliceous Scales in Boilers of Western Oregon and Washington, by R. E.
Albert. National Petroleum News, August 9, 1933.
No. 14. The Pollutional Character of Flax Retting Wastes, by G. W. Gleeson, F. Merryfield, and E. F. Howard. Sewage Works Journal, May 1934.
Summers and C. S. Keevil. The Timberman, vol. 35, p. 30, May 1934.
No. 16. How Much Phosphate? by R. E. Summers. Power, vol. 78, p. 452, August
1934.
No. 17. The Carbon Dioxide-Hydrogen Ratio in the Products of Combustion from
Automotive Engines, by G. W. Gleeson and W. H. Paul. National Petroleum
News, September 15, 1934.
Exhaust Gas Analysis, by G. W. Gleeson and W. H. Paul. Parts I, II,
and III. National Petroleum News, September 26, October 3 and 10, 1934.
No. 19. Simplified Measurements of Sound Absorption, by A. L. Albert and T. B.
No. 18.
Wagner. Electrical Engineering, vol. 53, no. 8, p. 1160, August 1934.
No. 20. Treatment and Recovery of Sulfite Waste, by F. Merryfield. Civil Engineering, June 1936.
No. 21. Industrial Wastes in the Willamette Valley, by F. Merryfield. Civil Engineer.
ing, October 1936.
No. 22. Flow Characteristics in Elbow Draft-Tubes, by C. A. Mockmore. Proc.
American Society of Civil Engineers, vol. 63, no. 2, pp. 251-286, Feb. 1937.
No. 23. Some Simple Experiments Dealing with Rates of Solution, by G. W. Gleeson.
Journal of Chemical Education, vol. 15, no. 4, April 1938.
No. 24. Heat Transfer Coefficient in Boiling Refrigerant, by W. H. Martin. Refrigerating Engineering, vol. 36, no. 3, September 1938.
No. 25. Kiln Drying Guaranteed Moisture Content Spruce Lumber, by Glenn Voorhies.
West Coast Lumberman, vol. 66, no. 1. January 1939.
No. 26. Steam Demand in Drying Douglas Fir Lumber, by Glenn Voorhies. The Tim.
berman, vol. 40. no. 4, February 1939.
No. 27. Aircraft Precipitation-Static Radio Interference, by E. C. Starr. American
Institute of Electrical Engineers, Preprint, May 1940.
I
RATING AND CARE OF DOMESTIC SAWDUST BURNERS
I
27
'
No. 28. High-Voltage D-C Point Discharges, by E. C. Starr.
Electrical Engineers, Preprint, May 1940.
American Institute of
No. 29. Humidity in the Freezing Chamber, by W. H. Martin.
Foods, vol. 1, no. 7, May 1940.
Western Frozen
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