July, 1931
IlVD USTRIAL AA-D ESGISEE'RING CHEMISTRY
763
Heating Asphalt by Diphenyl Vapor' G. H. Montillon,2 K. L. Rohrbach, and W. L. Badger DEPARTMEN OF T CHEMICAL ENGINEERING, UNIVERSITY OF MICHIGAN, A N N A R B O RMICH. ,
All the indirect methods of H E processing of asBoth the saturant and coating types of asphalt have heating used to date have been been successfully melted by means of diphenyl vapor. phalt from the crude rather unsatisfactory. The material to the finished A forced-circulation apparatus was used with an heat transferred has depended asphalt-velocity range of 2 to 13 feet per second. The product is carried on in the on the specific heat of the measphalt temperatures used were from 310" to 395" F., United States on a large scale. dium used, which is very low; and the diphenyl vapor temperatures from 490" to Over 5 , 5 0 0 , 0 0 0 t o n s were there is always a temperature 596" F. processed during 1926 (6). gradient along the heating' Of this amount 1,244,000tons The average heat-transfer coefficients were found to surface due to loss of heat from be: over-all, 30 to 45; asphalt liquid film, 30 to 55; and were used for roofing, waterthe medium; and the rates of proofing, impregnating, pipediphenyl vapor film, 225 to 400 B. t. u. per hour per heat transfer are very low. dipping, etc. hlanufacturing degree Fahrenheit per square foot. The liquid-film Any m e t h o d w h i c h will processes differ from plant to coefficients increased with increased velocity. Differovercome these objections by plant, but in general remain ences in viscosity had no effect. One batch had a eliminating the chance of cokbasically the same. The asviscosity of five to ten times that of other batches and ing or cracking the asphalt, by phalt, prepared to specificathe same average coefficients were obtained. allowing accurate and easily tion in the company's own No evidences of cracking or breakdown of the asphalt controlled temperatures, and plant or purchased outside, is or of carbon deposits on the heating surface were found by the use of a medium which m e l t e d in s o m e m a n n e r , at any time. One batch was heated continuously for will carry a large amount of heated to a temperature of 32 hours with an asphalt velocity of less than 2 feet heat in s m a l l v o l u m e with 350-415' F.; and in this state per second. The only changes in the asphalt were an is used to impregnats or coat the proper temperature drop increase in viscosity and melting point and a decrease for transfer, a n d p r e s e n t a roofing paper, cloth, felt, or in penetration due to vaporization of volatile matter. high heat-transfer coefficient p i p e s ; i n s u l a t e tubes; or Sufficient data have been obtained so that intelligent treat whatever weather- or would be a boon to the indesign of a commercial heating unit is possible. water-proofed material is bedustrv. ing made. The easiest and best medium known for the transfer of heat In making roofing, for instance, the asphalt is usually in large quantities has always been steam. The pressure, kept a t the proper temperature in dipping tanks, the felt and hence the temperature, can easily be controlled; the or paper strip is run or dipped into it, then is passed between temperature throughout the system is uniform; and the rate steam-heated rolls, surfaced with a mineral powder or sand, of heat transfer is high. The high vapor pressure of water at and rolled or cut to size. For pipe-dipping the same process higher temperatures, however, has prevented its use in the is used, except that the pipes are merely dipped into the tanks, present case. then hung to drain and to allow the asphalt film to harden. Any substance with thermal and physical properties similar Several methods for heating these melting and dipping to water, but with a lorn vapor pressure at higher temperatanks are used: direct fire without mechanical agitation, tures, would be valuable for this purpose. The recent availindirect methods such as circulating preheated oil through ability of diphenyl and diphenyl oxide in bulk a t low cost coils in the tank, or by forced circulation as in the pipe-still has given a decided impetus to their application for hightype of heaters. All these methods have certain faults which temperature heating. Their properties are such as to make it would be worth while to correct. their use advantageous. Work recently completed in this The asphalts used for roofing, impregnating, pipe-dipping, laboratory has shown that the use of diphenyl vapor is enetc., must have certain characteristics of purity, viscosity, tirely practical ( 2 ) . Diphenyl rapors as a heat-transfer ductility, durability, non-chipping or cracking, non-corrosire- medium are now being used commercially by a refining comness, etc. These properties, inherent in the asphalt when pany for oil distillation (8). Because a diphenyl boiler was put into the tanks, must be retained during the melting and already in operation in this laboratory and because the during use. This can usually be accomplished by careful various physical and thermal properties of diphenyl were at control of temperature and manipulation during heating. hand, it was selected as a heating medium for melting asphalt. However, the application of direct heating methods always The problem has been studied particularly from the asphaltinvolves the danger of overheating a t the point of applica- heating point of view rather than as a contribution to the tion. This induces a condition favorable to coking or crack- general field of theoretical work in heat transfer. Asphalt, ing of the asphalt, which not only is injurious to the equip- as a material for experimentation in the exact measurement of ment, but causes deleterious changes in the properties of the heat-transfer coefficients and their application to and correlaasphalt. Direct heat application also makes the control of tion by theoretical principles, is not an ideal substance. For temperatures within narrow limits very difficult. It also investigations of that sort other, more ideal fluids are available. involves the problem of very low coefficients of heat transfer in The first point of attack on this problem was a study of the most cases, thus making a large heating surface necessary. rate of heat transfer under varied conditions. Another and almost equally valuable point for investigation was the effect Received April 15, 1931. The material embodied in this article resulted from a research sponsored at the university by the Utilities Research of this type of heating upon the physical and chemical properCommission, Inc , of Chicago, and was under direct charge of a committee ties of the asphalt. The two problems were intimately interof that organization of which D W Chapman, manager, Industrial Deconnected. The attack was at first centered upon methods partment, of the Peoples Gas Light and Coke, was chairman. and procedure for measuring the coefficients from diphenyl 2 Associate professor of chemical engineering, University of Minnesota, Minneapolis, Minn. rapor into the body of the asphalt.
T
INDUSTRIAL AND ENGINEERING CHEMISTRY
764
Vol. 23, No. 7
distribution. It then enters the heating section, A , which is 9 feet 4 inches long, and goes from there to another mixing Diphenyl is a white solid with the formula CsH5.CeH6. unit for average temperature measurement and back to the I t s melting point is 156.6" F., and boiling point 491.5" F., a t receiving drum. 1 atmosphere pressure. Table I (9) gives an idea of its Just beyond the first mixing unit is a thermocouple for the physical and thermal characteristics. measurement of the temperature of the entering asphalt. It will be noted that a t 1 atmosphere pressure 1 cubic foot From this point to the next mixing box the asphalt flows of diphenyl vapor weighs 0.21 pound and carries as latent through a straight single piece of ordinary 1-or 11/4-inchpipe heat 0.21 X 138.2 = 29.02 B. t. u., whereas 1 cubic foot of (both were used in experimental work), thus insuring smooth steam under the same conditions weighs 0.03734 pound and flow throughout the heating section. The heating jacket carries 0.03734 X 970.0 = 36.22 B. t. u. Thus it will be seen around this pipe is a 4-inch pipe. One end is welded to the that diphenyl vapor, despite its rather low latent heat per inside pipe and the other joint is formed by means of a stuffing pound, carries about 80 per cent as much latent heat as steam box. The vapor jacket, B, has three thermocouple outlets, per unit volume under comparable pressures. T,for the wires from the pipe and vapor space thermocouples. Properties of Diphenyl
Table I-Physical TEMPERATURE
F. 156 200 250 300 350 400 450 491, 500 550 600 650 700 750 800 850 900
C. 69.2 93.3 121.1 148.7 176.7 204.4 232.2 255.3 260.0 287.8 315.6 343.3 371.1 398.9 426,7 454.4 482.2 O
,-----PRESSURE---I n . Hg oac. 29.9 29.8 29.5 28.5 26.2 21.4 12.3
0.0
1.6 13.8 32.3 58 9 95.4 143,9 207.1 286.2 386.0
Lbs. p e r sp. i n . abs. 0.015 0.060 0.227 0.701 1.83 4.20 8.64 14.70 16.3 28.5 47.0 73.6 110.1 158. 6 221.8 300.9 399.7
Properties of Diphenyl ----HEAT CONTENT---Liquid Latent B. 1. u. per lb. 0.0 190.9 17.7 175.0 39.1 161.5 61.9 154.0 86.3 150.0 112.6 148.0 140.9 143.5 165.8 136.5 171.0 135.0 202.5 126.0 234,s 117.0 267.9 109.5 301.5 103.0 335.4 96.5 91.5 369,6 82.5 403 9 438.4 67.5
The pressures may easily be compared by reference to the steam tables. For instance, a t 491.5' F. diphenyl has a pressure of 14.7 pounds absolute, steam, 628.9; a t 600" F. diphenyl has a pressure of 47 pounds, steam, 1540 pounds. T h e critical temperature of diphenyl is 980" F., while that of water is 706.1O F. The film coefficient for condensing diphenyl vapors ranges from 200 to 400 B. t. u. per square foot per hour per degree Fahrenheit, while the coefficient for condensing steam is 1500 t o 2000 (7). This difference is unimportant, however, for fhe coefficient of the film on the side of the heated liquid usually controls the rate of heat transfer. Apparatus
The apparatus consists, in the main, of an asphalt reservoir piped to a circulating pump, which forces the asphalt through a double-pipe cooling coil to a heating tube jacketed to form a vapor space and back to the reservoir. Drip tanks are provided for the measurement of the condensed diphenyl, and thermocouples are so placed that all pertinent temperatures may be recorded. The asphalt system particularly (Figure 1) consists of a melting tank, H , connected with the circulating system proper by means of a flexible pipe, R, and standing on a scale, P. The asphalt, once it has been placed in the system, is stored in tank G; from there it is drawn through pipe U , through the strainer, M , by means of the pump, J . The pump is a gearreduced positive-pressure pump driven by a direct-current motor so wired that exact speed control is possible. The pump forces the asphalt through a double-pipe heat exchanger, K , which is piped for both steam and water, to the mixer, N . At 2 is a compressed-air connection and an arrangement of valves to be used to blow out the asphalt in cases of plugged pipe lines or when cleaning the machine. At N is a mixing box for the purpose of obtaining an average temperature throughout the asphalt stream in case there is any non-uniformity due to its long cooling cycle. From here the asphalt flows through a long calming section, Ti, 8 feet long, to allow for the formation of a normal velocity
Total 190.9 192,7 200.6 215.9 236.3 260.6 284.4 302.3 306.0 328.5 351.8 377.4 404.5 431.9 461.1 486.4 505.9
----DENSITY-Liquid Vapor Lbs. per cu. f f . 60: 85 59.46 5 s . OS 56.65 55.24 53.81 52.59 52.32 50.73 49.04 47.30 45.38 43.28 40.89 38.10 34.58
o.ooios
0.0041 0.0117 0,0284 0.0616 0.1220 0.2100 0.236 0.445 0.750 1.185 1,730 2.400 3.355 4.690 6.850
Just beyond the second mixing box is a thermocouple connection, 0, for obtaining the outlet asphalt temperature. At 0 is a tee with a valve connection, W , for pumping the asphalt back to the melting tank. The reservoir G is vented back t o the melting tank by means of pipe S. The entire system except the heating pipe is made of ordinary 11/4-inch pipe and fittings. It is either steamjacketed or steam-traced to permit warming up before introducing the asphalt and to keep the asphalt melted when not being tested. Both the melting tank and the reservoir are equipped with high-pressure steam coils for melting the asphalt. The entire system is lagged with 2 inches of 85 per cent magnesia insulation. The diphenyl system consists of a boiler, vapor line from the boiler, vapor jacket, drip line to the drip tanks, drip tanks for measuring amount of diphenyl condensate, and return drip lines to the boiler. The boiler is the 100,000 B. t. u. per hour boiler described by Badger, Monrad, and Diamond (9). A I-inch vapor line connects it with the vapor space B. Just before entry to the space a thermocouple is inserted in the line to take entering vapor temperatures. The vapor jacket was described above. The condensate flows t o the drip tanks through the pipe D, in which another thermocouple is inserted for obtaining condensate temperatures. The drip tanks are made of welded iron pipe. Vent connections t o both the atmosphere and the boiler are provided. Sight glasses for reading the liquid level are placed on the front. The pipe F is the condensate return line to the boiler. Temperature Measurements
It was necessary to take the temperature of the diphenyl vapor, the incoming and the outgoing asphalt stream, and the tube wall (Figure 2 ) . Copper-constantan thermocouples were placed for this purpose. The temperature of the entering asphalt was taken a t a point about foot after passing the mixing box. The thermocouple was run directly to the center of the stream and supported by means of a small pipe. The temperature of the leaving asphalt was taken about a foot after leaving the mixing box a t the other end of the circuit.
INDUSTRIAL AND ENGINEERING CHEMISTRY
July, 1931
A
-
HEATING TUBE e -VAPOR SPACE C -DIPHENYL VAPOR I N L E T D -DIPHENYL DRIP OUTLET E -DRIP TANKS F -DRIP RETURN LINE G -ASPHALT RESERVOIR H ASPHALT MELTING & WEIGHING TANK
-
CIRCULATNG PUMP -- ASPHALT DOUBLE PIPE COOLER L - STEAM AND WATER INLET M - STRAINER N - ASPHALT MIXERS 0 - ASPHALT OUTLET THERMOCOUPLE P - SCALE J K
Figure 1-Diagram
765
P- ASPHALT INLET THERMOCOUPLE R - FLEXIBLE FEED HOSE
S - VENT LINE
T - VAPOR PIPE THERMOCOUPLE CUTLETS U - ASPHALT CIRCULATING LINE V - FLUID FLOW SMOOTHING SECTION ASPHALT DISCHARGE LINE 7.- COMPRESSED AIR CONNECTION
w-
of Apparatus
The temperature of the incoming diphenyl vapor was deter- just outside the vapor space by means of thermometer mined just before entry to the vapor space surrounding the wells. All thermocouple wires were carefully insulated, those from tube; of the outgoing condensed diphenyl temperature, just after leaving the vapor space. The average vapor tempera- the vapor space being brought out by means of an asbestosture in the vapor space was taken a t three points along the packed joint. They were all checked as closely as possible heating space, one about 4 inches from each end and one in place. The e. m. f. readings were taken with a Queen potentiometer and a galvanometer. directly a t the center. The heating-tube temperatures were taken a t three points Physical Tests on the tube with four thermocouple connections brazed to the tube a t each point-two a t the top and two a t the bottom, The following constants ( 1 ) were determined on the as2 inches apart. These were carefully checked until three were found which gave the best average increase in tube phalt for purposes of calculation of coefficients, and to trace temperature as the asphalt temperature increased along the any changes in the material due to heating: specific gravity, softening point, penetration, free carbon, and viscosity. tube. Specific gravity was determined by weighing an aluminum The arrangement of thermocouples is then as follows: (1) asphalt inlet, ( 2 ) asphalt a t C, (3) asphalt a t B , (4) asphalt a t A , ( 5 ) asphalt exit, (6) pipe surface a t C, (7) pipe surface at B , (8) pipe surface at A , (9) diphenyl vapor inlet, (10) diphenyl vapor a t C, (11) diphenyl vapor a t B , (12) diphenyl vapor a t A , and (13) liquid diphenyl a t exit to the drip tanks. The thermocouples were all made of No. 18 copper mire and No. 20 constantan wire, welded or brazed together. The same rolls of wire were used throughout, and couples made from different sections of the rolls were calibrated. The thermocouples were calibrated H - STUFFING SOX by means of Bureau of Standard samA p C -PIPE AN0 VAPOR THERMOCWPLE CMLETS 0 -INLET DIPHENYL d I %%$%:, THERMOCOUPLE WlRE CUTLET E -OUTLET OPHENYL . ples of pure tin and lead, and by means F -ASPHALT NLET p 1 %$' P,%&COUPLE ARRANGEMENT G -ASPHALT OUTLET of c. P. naphthalene. They were also Figure 2-Diagram of Heating Section and Thermocouple Connections checked by means of the vapor from boiling water a t atmospheric pressure, with a calibrated Corning thermometer to 352.0' F. An empirical ball, 11/* inches in diameter, in air, then in water a t 20" C. equation was derived from these data and a curve plotted (68" F.), and then in asphalt a t various temperatures from showing e. m. f. VS. temperature in degrees Fahrenheit: 300' t o 400" F. The specific gravity relative to water a t 20' C. is then equal to the weight of the ball in air minus its weight x = -0.71445 0.02199T 0 000010509T2 in asphalt divided by the result of its weight in air minus its The temperatures of the entering and leaving asphalt were weight in water. Expansion of the ball due to temperature also checked by means of thermometers placed in the pipe change was calculated and found to be negligible.
+
+
INDUSTRIAL A X D ENGINEERING CHEMISTRY
766
Vol. 23, No. 7
Table 11-Experimental Data RUN
ASPHALT TEMP.
VAPOR TEMP.
FILM TEMP.
F.
F.
F.
ATV
VAPOR ATU OVER-ALL FILM
F.
F.
ATL
ASPHALT
FILM
U OVER-ALL
hV
VAPOR FILM
hL
ASPHALT FILM
S
SP. GR.
zf
U
0.860 0.855 0.86 0.856 0.859 0.855 0.854 0.875 0.872 0.868
21.14 14.96 21.14 15.85 13.5 14.5 13.7 73.0 57.5 43.6
Fl./sec. 6.55 6.55 6.04 6.05 6.54 6.06 6.06 5.91 6.05 5.92
CP .
1 2 3 4 5 6 7 8 9 10
352.4 363.5 348.6 356.0 357.5 360.4 360.5 307.0 321.3 313.0
528.8 543.6 533,6 545.8 550.0 545.2 550.0 490.0 492.4 518.0
427.7 439.5 427.95 437.6 442.9 441.1 442.5 386.0 394.4 403.1
176.4 180.1 185.0 189.8 192.5 184.8 189,5 183.0 171.1 205.0
23.2 25.6 23.6 24.2 20.0 21.6 23.3 23.4 23.4 22.8
F. 150.6 152.1 158.8 163.3 170.8 161.5 164.1 158.0 146.2 180.2
11 12 13 14 15 16 17 18 19 20
319.5 315.3 323.6 316.8 349.8 354.0 355.5 332.2 331.7 335.5
508.0 495.2 497.0 490.0 533.6 532.0 532.0 498.8 497.8 510.0
403.0 395.1 401.8 391.6 430.1 432.0 433.8 404.5 403.6 413.2
188.5 179.9 173.4 172.0 183.8 178.0 176.5 166.6 166.1 174.5'
20.0 18.4 15.0 23.2 21.0 19.6 17.6 19.4 20.2 16.6
167,O 159.6 156.5 147.2 160.6 156.1 156.7 144.6 143.8 155.4
25.5 34.1 34,76 28.7 38.4 40.7 40.3 49.8 40.0 45.0
215.2 298.0 359.0 190.5 300.0 330 0 362.0 384.0 294.0 422.0
32.5 43.1 43.2 37.6 49.2 51.9 51.0 64.8 51.9 56.5
0.868 0.871 0.869 0.873 0.859 0.8.58 0.857 0.868 0.868 0.865
43.6 56.0 45.5 61.7 20.0 18.7 17.67 41.7 43.0 32.0
6.05 6.05 6.48 6.13 6.26 6.27 6.27 5.51 5.51 6.46
21 22 23 24 25 26 27 28 29 30
359.4 366.6 369.5 370.1 371.6 374.4 339.7 341.5 340.1 338.1
548.0 554.6 563.0 669.0 576.4 586.0 533.0 534.0 535.0 528.0
439.9 447.0 452.4 455.8 458.2 464.0 423.1 426,9 424.9 419.2
188.6 188.0 193.5 198.9 204.8 211.6 193 3 192.5 194.9 189.9
25.0 24.6 24.8 25.0 28.8 29.4 23.8 19.6 23.0 26.0
161,O 160.9 165.9 171.4 173.3 179.3 166.8 170.8 169.6 162.2
43.2 42,75 46.9 39.6 42.3 44.3 44.6 34.8 37.04 28.0
291 0 292.0 327.0 281.0 278.6 285,O 324.0 305.4 280.0 182.8
56.6 55.9 61.3 51.5 56.1 58.7 58.1 43.9 47.75 36.7
0.855 0.852 0.85 0.849 0.848 0.846 0.861 0.860 0.860 0.862
15.0 12.2 10.4 9.7 9.1 7.7 24.1 21.7 23.0 26.7
6.55 7.09 7.91 6.06 7.09 7.63 6.56 5.88 6.56 5,88
31 32 33 34 35 36 37 38 39 40
340.0 359.8 365.5 335.8 344.1 364.2 366.9 370.9 372.4 383.5
535,O 558.0 -576.0 510 0 523.0 546.6 569.8 577.0 576.0 582.0
424.8 445.5 457.3 411.7 421.7 443.3 455.4 460.6 462.4 469.9
195.0 198.2 210.5 174.2 178.9 182.4 202.9 206.1 203.6 198.5
23.0 24.0 24.0 20.0 21.0 21.6 23.2 24.2 21.4 23.4
169.6 171.5 183.6 151.8 155.25 158.1 177.0 179.4 180.0 172.9
38.7 42.85 43.7 44.6 47.2 47.1 42.6 39.2 34.04 34.74
293.4 317,O 343.0 348,O 358.6 355,O 333.0 299,O 289.0 264.0
49.8 55.6 56.2 57.5 60.9 60.8 54.75 50.6 43.2 44.75
0.86 0.853 0.848 0.866 0.861 0,854 0,849 0.847 0.847 0.844
23.0 12.5 9.: 33.0 25.0 13.5 10.0 8.5 8.2 6.8
5.88 6.56 6.56 5.525 5.77 6.63 6.63 6.63 6.69 8.06
41 42 43 44 45 46 47 48 49 50
383.5 384.3 372.5 380.8 380.2 379,7 358.5 356.5 361.9 367.0
584.6 588.6 542.0 546.0 547.6 542.0 542.8 544.0 546.4 547.2
471.6 472.8 447.4 454.1 453.3 452.3 441.2 439.5 444.45 446.0
201.1 204.3 169.5 165.2 167.4 162,3 184.3 187.5 184.5 180.2
22.6 25.0 18.0 16.8 19.0 15.4 16.8 19.6 17.4 20.2
176.1 177.1 149.6 146.5 146.3 145.2 165.4 165.9 165.1 158.0
37.4 36.2 33.6 33.8 37.0 31.0 35.1 32.1 31.7 32.6
296.4 265.0 289.0 304.0 298.0 298.0 338.0 281.0 308.0 267.0
47.75 49.1 41.8 42.0 46.7 38.1 41.2 39.9 39.1 41.1
0.844 0.843 0.852 0.850 0.850 0.85 0.854 0.855 0.853 0.853
14.5 14.2 12.3 10.23 10.3 10.9 14.2 15.0 13.0 12.5
8.0 8.0 3.94 3.89 4.77 3.68 4.19 4.19 4.19 3.89
51 52 53 54 55 56 57 58 59 60
363.3 363.0 348.3 350.0 375.0 377.0 370,4 358.9 361.5 379.3
560.0 564,6 539.0 548.0 565.0 572.6 571.0 546.0 544.0 574.0
452.7 453.4 435.6 439.0 458.8 462.7 459.2 443.0 442.8 464.6
196,7 201.6 190.7 198.0 190.0 195.6 200.6 187.1 182.5 194.7
16.0 18.6 14.4 18.0 20.2 22.0 21.0 17.0 17.4 22.0
178.8 180.8 174.6 178.0 167.6 171.4 177.6 168.3 163.2 170.6
28.1 32.3 26.1 30.6 35.1 33.6 30.4 29.4 31.02 32.5
332,O 319.6 316.0 308.0 301.0 274.0 266.0 296.0 298.0 263.0
35, s 39.6 31.4 37.5 43.8 42.2 37.8 36.0 38.2 40.8
0,850 0.85 0.857 0.856 0.849 0.846 0.848 0.854 0.854 0.846
10.5 10.2 24.7 23.2 17.3 16.3 9.0 21.7 21.8 15.9
3.92 4.67 3.94 3.64 5.2 5.72 4.71 3.95 4.45 5 74
.
O
The melting point was determined by the ball-and-ring method; the penetration, by the needle penetrometer a t 77" F.; free carbon, by means of a benzene extraction apparatus. The viscosity was determined with the hlacMichae1 viscometer. This was standardized against a Bingham viscometer (S),a pipet viscometer (4), and a falling-sphere viscometer (5) by use of castor oil, heavy mineral oil, and No. 6 and Xo. 10 Transil oils. The viscosity of the asphalt was determined between the temperatures 370" and 500" F. Calibration of Drip Tank
The drip tanks were calibrated by adding to them a weighed amount of water whose volume could be calculated from its weight and temperature, and reading the height in centimeters. This was done several times with each tank, and the results were averaged. The two tanks were found to be so nearly alike that the results could be used interchangeably. The expansion of the drip tanks with temperature was calculated, and the pounds of diphenyl per inch in height calculated from this. The drip tank calibration curve was drawn from this table.
47.3 41.7 45.7 39.5 27.7 30.3 34.8 27.64 27.5 31.2
321.2 263.0 318.0 276.0 238.2 231.4 257.0 193.5 180.5 251.6
62.2 55.6 59.75 51.4 34.96 38.8 45.0 35.9 36.2 39.9
Procedure
The asphalt was removed from the drum in which it was received and placed in the melting tank. Steam was then turned into the heating coil and the asphalt melted. The steam was also turned into the tracing lines throughout the asphalt circulating system and the apparatus well heated. The diphenyl vapor was turned into the vapor space surrounding the heating section. When the entire system was hot and the asphalt melted, the valves were opened, the pump started, and all the asphalt circulated through the apparatus and into the receiving tank. The asphalt was then circulated around the system and heated to the required temperature by means of the diphenyl vapor, and the boiler pressure allowed to rise to the point required. If the temperature of the asphalt tended to rise farther than planned, it was controlled by turning steam or water into the double-walled cooler. When everything had been brought to equilibrium, the velocity was set and measured, the drip tanks were changed so that a t the beginning of a run drips were run into an empty tank, and a run was started. A run covered the length of time necessary to fill one drip tank with condensed diphenyl.
7 67
INDUSTRIAL AND ENGINEERI,VG CHEMISTRY
July, 1931
Table 11-Experimental
577.0 585.0 578.4 536.0 546.0 547.5 569.0 572 5 574.0 526.5
FILM TEMP. ' F. 469.0 477.5 473.6 435.2 438 85 443.75 461.5 462.6 464.75 442.62
ATU OVRR-ALL ' F. 191.7 190.7 185.9 185.6 195.4 189.5 192.0 195.5 193.75 179,5
VAPOR TEMP.
Data (Continued)
hV ATL ATV VAPOR U VAPOR ASPHALT FILM FILM. O V E R - A L L FILM
hL ASPHALT FILM
61 62 63 64 63 66 67 68 69 70
ASPHALT TEMP. P. 385.3 394.3 392.5 3.50.4 350.6 358.0 377.0 377.0 380.25 347.0
71 72 73 74 75 76 77 78 79 80
349,75 342.0 344.0 344.0 351.5 362.75 355.5 351.5 348.0 351.25
527.5 530.0 533.0 525.5 539,O 546.0 548.0 552.0 554.5 563.0
430.75 429.4 431.75 427.2 430,6 437.5 443.45 447.0 446.0 449.76
177,75 188.0 189.0 181.5 187.5 193.25 192.5 200.5 206.5 211.75
14.0 11.5 11.5 13.5 17.5 22.0 15.0 8.0 9.0 13.0
162.0 174.8 175.5 166,4 168.2 169.5 175.9 191,o 196.0 197.0
29.35 26.95 26.15 25.5 28.9 27.1 24.9 22.7 20.7 19.6
341.0 402.5 393.5 314.0 283.0 217.5 293.0 520.0 434.0 294.0
35.45 31.9 34.1 30.6 35.4 34.0 30.0 26.2 23.95 23.35
0.8545 0.860 0,8575 0.86 0.862 0.855 0.854 0.8505 0 8525 0.85
26.6 27.5 26.25 28.5 26.75 29.0 21.75 20.05 21.0 20.0
81 82 83 84 85 86 87 88 89 90
358.75 370.0 371.0 371.75 373.0 376.25 376.0 379.5 380.0 379.0
569.5 564.0 566.5 565 0 563.0 563.0 566.5 564.5 567.0 567.5
454.67 454.4 455.8 455.625 454.2 459.25 459.5 459.5 461.6 460.5
210.0 194.0 195.5 193.25 190.0 186.75 190.5 185.0 187.0 188.5
17.5 24.0 24.0 24.0 26.0 19.0 21.5 23.0 22.0 23.5
191,85 168.7 169.6 167.75 164.0 166.0 167.1 160.0 163.2 163.0
19.9 20.6 21.2 23.5 25,s 29.9 30.1 32.2 29.6 33.2
219.5 153.0 155.0 173.0 173.0 268.0 244,O 206.0 230.0 244.0
24.1 26.2 27.0 29.8 32.9 37.0 37.8 41.0 37.2 46.5
0.85 0.85 0.85 0.85 0.85 0.848 0.848 0.849 0.847 0.848
18.75 18.75 18.3 18.0 18.7 17.4 17.4 17.4 16.8 17.2
91 92 93 94 95 96 97 9s 99 100
379,75 390.25 391.5 392.0 392.5 354.5 356,5 357,s 35S, 0 358.5
573 0 580.0 5S3.0 581.0 582.0 523.5 530.0 540.0 549.0 552.0
462.26 471.09 472.9 473.0 473.5 431.45 434.7 440,95 445.5 445.1
193.25 189.75 191,5 189.0 189.5 169.0 173.5 182,5 191 0 193.5
26.0 26.0 26.5 25.0 25.5 13.0 15.0 13.5 14.0 18.0
165.0 161.68 162.9 162,O 162,O 154.0 156.4 166.9 175.0 173.2
34.8 32.7 33.2 31.2 32.4 36.9 36.8 33.8 31.4 35.5
238.0 218.0 252.0 214,O 220.0 438,O 390.0 418.0 392.0 349.0
45.0 42.3 42.7 40.2 41.7 44.5 45.0 40.2 37.8 43.7
0.8475 0.844 0.844 0.844 0.847 0.883 0.851 0.855 0.851 0.851
16.6 14.6 14.3 14.25 14.2 25.28 25.0 22.6 21.0 21.2
101 102 103 104 105 106 107 108 109 110
366.75 370.0 352.7 361.1 365.45 358.45 365.0 368.35 373.9 378.4
556.0 558.5 526.9 538.7 546.9 543.4 551.7 556.7 563.5 568.2
449.2 451.75 429.6 440 1 445.9 438.8 448.3 451.9 458.2 462.2
189.25 188.5 173.2 177.6 181.4 184.9 186.7 188.3 189.6 189.8
22.0 22.5 17.4 17.4 18.6 22.1 18.1 19.2 18.9 20.1
164.85 163.5 153.8 158.0 160.8 160.5 166 5 166.9 168.6 167.6
37.8 39.0 35 0 36 5 33 2 38 0 35 0 34 8 33 1 33 6
298.0 299.5 320.0 341.0 296.0 290.0 330.0 311.8 303.0 289.0
47.8 49.6 43.5 45.2 41.3 48.2 43.2 43.3 41.0 41.8
0.852 0.85 0.86 0.855 0.853 0.855 0.852 0.851 0.850 0.848
20.0 19.5 177.0 142.0 125.0 144.0 118.0 111.0 99.0 92.0
9.9 11.65 4.59 4.58 4.59 5 1 5,1 5,l 5.52 5.52
111
384.9 349.9 359.5 357.0 344.7 346.5 367.9 368.9 372.6 372.3
569.2 594.7 586,2 589,9 542.5 538.3 535.7 540.5 548.2 551.7
467,3 459,7 464.3 461.3 434.3 432,9 443.8 445.9 451.6 463.5
184.3 244.8 226.7 232.9 197.8 191.8 167.8 171.6 175.6 179.4
17.6 22.7 14.7 22.2 17.5 17.3 14.0 15.5 15.8 15.4
164.7 219.6 209.5 208.6 179.2 172.8 151.7 154.0 158.0 162.4
32.9 30.9 32.7 27.4 28.1 27.1 38.1 35.8 30.9 27.3
316.0 305.0 460.0 263.5 290.0 274.0 417.0 362.5 314.0 292.0
40.7 38.0 39.0 33.7 34.1 33.1 46.4 43.9 37.8 33.2
0 846 0.85 0.847 0.841 0,857 0.858 0.884 0.853 0.851 0.851
85.0 95.0 87.0 92.0 144.0 148.0 142.0 137.0 124.0 120.0
5.1 5.1 5.35 5.4 5.6 5.6 3.91 5.7 5.5 5.5
Viscosity : 338' F. 392' F. 415' F.
....... ......
....... ...... .......
RUN
112 11B 114 113 116 117 118 119 120
F.
I4
Zf
P.
22.0 22.0 21.4 14.0 16.8 16.0 21.0 21.5 22.5 13.5
167.5 166.4 162.2 169.6 176.5 171.5 168.85 171.8 169,O 137.2
35.1 36.4 36.5 32.1 31.9 32.25 33.55 33.75 34.75 29,35
279.0 288,4 291.0 388.0 339.0 349.5 280.1 281,O 274.0 357.0
44.2 45.9 46.1 38.6 38.9 39.2 42.0 42.3 43.8 42.3
0.844 0.841 0.842 0.857 0.855 0,8505 0.8475 0.8475 0.840 0.854
15.0 13.5 14.1 24.6 23.2 21.75 16.75 16.5 16.6 24.0
Ft./sec. 6.34 7.7 7.7 3.85 4.79 4.71 5.21 5.74 6.33 3.91 3.95 1.955 1.955 2.635 4.575 4.72 3.74 1.91 1,955 1.955
The follon ing data were taken : thermocouple readings over all the thermocouples, drip readings each 5 minutes to ascertain their constancy, and pump r. p. m. or, in other words, asphalt velocity. At the end of a run the drip tanks were changed and a new run was started. Two types of asphalt were tested. One was a saturant and the other a coating type. The coating type was No. 15, R. S.A. Parolite (Brand 6810) with the following characteristics. Melting point (ring and ball) Penetration (77' F , 100 grams, 5 sec \ Free carbon v*scos1tr 320' F 365' F 392' F
SP. G R .
F.
176 2 ' F 83 3 0 25% 210 cp 60 cp 33 cp
One batch was used in making runs 1 to 69, and a fresh batch for 70 to 102, inclusive. The saturant type of asphalt was Standard Oil Company S o . 80-90 Flux air blown to the following constants: Melting point (ring and b a l l ) , . . . . . . . . . . . . . . . . . . 232' F. Penetration (77' F., 100 grams, 5 sec.) . . . . . . . 17 Free carbon.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.36 t o 0.39%
CP.
.......
2.64 6.29 6.29 7.55 7.55 8.25 8.24 10.54 11.27 10.55 11.35 12.7 12.8 13.3 13.3 4.14 4.14 4.14 4.14 7.0
. . . . . . .. . . . . . 4820cp. . . . . . . . .. . . . . . 545 cp. .., 115 cp. . . . . . .
This sample was used for runs 103 to 120, inclusive. Runs 1 to 102 are primarily heat-transfer runs using a variety of asphalt and diphenyl vapor temperatures and asphalt velocities. Runs 103 to 120 are also heat-transfer runs, but the investigation during that period had the equally important purpose of studying the effect of extreme conditions of temperature and velocity on the asphalt. B continuous run was instituted during which the temperature of the diphenyl vapor was allowed to rise, that of the asphalt was kept at approximately 375' F. and the velocity of the asphalt was held at less than 2 feet per second. At the beginning of the run and at the end of each 8 hours the velocity was increased, heat-transfer data were recorded, and a sample of asphalt was obtained. The constants on these samples are listed in Table 111. Operating Difficulties
Because of the variable characteristics of asphalt, it was found extremely difficult to check any of the results obtained for the heat-transfer coefficients. Another reason for this is
~
-
INDUSTRIAL AND ENGINEERING CEIEMISTRY
i68
hlanicd on tbc difficulties wtiich arose in the h a n d h g of the material. Each time the material was brought to temperature, and even while being held at temperature, tbc physical constants were found to have changed. Volatile matter was constantly being driven off and therefore the viscosity was constantly changing, and of course vith it the specific heat and specific graT7ity. Because of the high viscosity of the material at the lower temperatures, it was hard to place thern~ocouplesin the exact center of the stream. The asphalt came through the tube in slugs at times because of the release of volatile matter, and the tliermocouples presented a higher temperature reading than the actual temperature of the asphalt was known to be. The last batch of asphalt actually from in the apparatus owing to the increase in viscosity while beating the asphalt ovcr such a long period of time. The large amount of heat lost by radiation from the machine, owingto the high teniperature and thelarge surface exposed in comparison with the amount of heat taken up by the asphalt, made it extremely difficult to make runs with any predetermined conditions without wasting considerable time waiting for equilibrium. The total heat used by the machine, both for heating the asphalt and for radiation, was almost equal to the total output of the diphenyl boiler, so that each return of drips to the boiler set up new pressure and temperature conditions. It therefore became necessary to make rnns under whatever conditions obtained a t the moment, at the same time keeping the general conditions pretty well under control. Results
A large number of runs were made ami data recorded for them. Of these 120 were considered accurate enough to calculate and report (Table 11). The average heat-transfer coefficient was found to lie between 30 and 50 B. t. u. per square foot per degree Fahrenheit for the asphalt film. The diphenyl-vapor film coefficient was found to be from about 200 to above 400, the general average being about 320 B. t. u. Tliese values lie in the same a v m g e range as those reported by
Vol. 23, No. 7
Badger, Monrad, and Diamond (2) for the coeficientv ou vertiea1 tubes. This average is so much higher than the values of the coefficierit tbrough the asphalt film that the rat,e of heat transfer is controlled by the rate through the asphalt film. Considerable effort was made to correlate the data. obtained. General trends could he traced, hut all attempts to arrange the asphalt film coefficients in definite mathematical or grapbical form met with failure. The coefficients sliowed a very definite tendency to increase with increasing liquid velocity. At 2 feet per second the coefhients were about 25, and at 11 to 13 feet per second ttiey were 45 to 50 B. t. u. per hour per degree Fahrentieit per square foot. There was, however, no appreciable effect on the coefficient due to change in viscosity. The last batch of asplialt run (Table II), with a viscosity from five to ten times that o l any of the previous samples, gave practically the miue results for heat-transfer coefficients. There was no indication of breakdown iu the asphalt a t any time. One hatch was heated discontinuously for over 200 hours. The last batcti was processed continuously for 32 hours under the most extreme conditions obtainsble, The only changes noted were an increase in viscosity and melting point and a decrease in penetration, due to the removal of liigldy volatile materials. There was no nieasurable change in fixed-carbon content. A careful microscopic examination of sections of the heating tube showed no carbon deposits on the walls and no indication of coking. ?%e changes in hotli types of asphalt during prolonged treating were due mainly to the evolution of volatile matter. This is clearly illustrated in Table 111. I n bot,h types the viscosity increased considerably, as did the inelding point, while the penetration value decreased. At the same time the fixed-carbon percentage remained so small as to make measuring difficult. Acknowledgment
Tbe authors wish to express their indebtedness to W. L. McCabe, of the Chemical Engineering Department of the
INDUSTRIAL AND ENGINEERING CHEMISTRY
July, 1931
Table 111-Changes TINEOF HEATING FIXEDCARBON Hours % b y wt.
in Asphalt during Heating
___-
MELTINGPOINT PENETRATION320° F. a
C.
P.
7fi9
Mm.
VISCOSITY----365’ F. 392’ F.
SPECIFIC GRAVI ry 347’ F. 374’ F.
CP.
CP .
210
60
33
0.89
0.88
835 475
140 120
64 55
0.888
0.882
CP.
S A T U R A N T TYPE
Original 100 2;:
0.25 0.38-0.18 0.062-0.03 0.061
80 109 111 108
176.2 228.2 231.8 226.4
83.3 70.4 64.6 66.5
106.9 108.6 110.5 117.0 115.5
223.4 227.6 230.9 224.6 239.9
16.8 18.85 15.5 16.6 15.1
COATING TYPE
Original 8 16 24 32
0.36-0.39 0.337 0.274 0.265 0.335-0.294-0.296
University of bxickgan, for valuable assistance in supervising the work and interpreting the results. Literature Cited (1) Abraham, “Asphalts and Allied Substances,” Van Nostrand, 1929. (2) Badger, hfonrad, and Diamond, IND. ENG. CHEM.,22, 700 (1930).
(3) Bingham, “Fluidity and Plasticity,” p. 76, McGraw-Hill, 1922. (4) (5) (6) (7) (8) (9)
Ferris, IND.E N G .CHEM.,20, 974 (1928). Gibson and Jacobs, J . Chem. Soc.. 117, 973 (1920). Mines, Bur., Mineral Resources, P t . 2, Non-metals, 29-37 (1928). Monrad and Badger, IND.E N D . CHEM.,22, 1103 (1930). Othmer, I b i d . , 22, 988 (1930). S w a m Chemical Co., “Physical Properties of Diphenyl” (Bulletin).
Spectroscopic Studies of Engine Combustion’ Lloyd Withrow and Gerald M. Rassweiler GENERALMOTORSRESEARCH LABORATORIES, DETROIT,MICE
flame across the combustion Separate spectrographic studies made of the flame HIS paper describes a chamber with the very rapid fronts and afterglows of explosions produced with preliminary s p e c t r o several fuels in a gasoline engine, and covering the burning of the last part of the graphic study of the charge which constitutes the physical and chemical procspectral range 3500 to 6500 A., indicate that the reknock. Accompanying the esses which take place in the actions accompanying the afterglows are different rapid p r e s s u r e rise d u r i n g gasoline engine. The specfrom those taking place in the flame fronts. The each explosion is a marked ret r o g r a p h i c method of apvisible afterglow spectrum is emitted by the same i l l u m i n a t i o n of the gases proach was chosen because by molecules which give off light during a reaction bethrough which the flame has this means it is possible to tween carbon monoxide and oxygen, while visible passed, which phenomenon is investigate these p r o c esses light from the flame fronts of hydrocarbon fuels in herein designated as the afterwithout disturbing the envinon-knocking explosions comes largely from CH and glow. A similar re-illuminaronment in which they norCz molecules. The gasoline flame fronts in the detotion has been observed in mally occur. Although this nating zone during knocking explosions show CH experiments with bombs by fact has been pointed out preand C z bands only faintly, but flame fronts outside of Maxwell and Wheeler (8) and viously by a number of workthe detonating zone exhibit both sets of bands with others, and has s o m e t i m e s ers, the method has not been intensities comparable with non-knocking explosions. been called the a f t e r b u r n . used extensively in the study Addition of lead tetraethyl to the gasoline removes the Considerable confusion has of e n g i n e combustion. To knock and reestablishes the CH and Cz bands in the existed as t o the source of this the writers’ knowledge the light from the detonating zone. Lead is present in light, some investigators beonly i n v e s t i g a t i o n s of this the flame fronts as atomic lead and molecular lead lieving that it was due simtype which have appeared in monoxide. ply to a continuation of the the literature are those by oxidation of the original hydrocarbons. Visual observations G. L. Clark and his eo-workers (d,S, 4) and by Thee (11). Since these researches were published, rapid strides have in the engine showed that the afterglow was frequently of a been made in advancing the knowledge of the general char- different color than the flame front and should therefore show acter of engine combustion and in explaining the nature of a different spectrum. knock in an engine. To this advance this laboratory has To make a thorough survey of the spectra of flames in an recently contributed work with the sampling valve (14) and engine, and particularly t o study the origin of this afterglow, with the combustion camera ( I S ) , the latter of which has it seemed necessary so to arrange the apparatus that the been of particular importance in determining the most fruitful light from various portions of the flame and from various method of carrying on this spectrographic study. parts of the combustion chamber could be studied separately. For convenience, one of the pictures taken with the com- In this important respect the present work differs from that bustion camera is reproduced in Figure 1. It was taken on a of previous investigators. I n all the earlier work described film moling from right to left on which was focused the in the literature, the observation window appears to have image of a narrow window running the full length of the ceiling been so located that the spectra of the flame fronts and of the of the combustion chamber of an engine. The image of the afterglows were superimposed upon the spectrograms. For flame moved a t right angles to the film motion-that is, from this reason the interpretation of the data has been exceedingly bottom to top. This picture is a record produced by a difficult. The present paper contains spectrograms taken single knocking explosion and clearly shows the motion of the during separate preliminary studies of the light emitted in 1 Received April 22, 1931. the visible spectral region by the flame fronts and the after-
T
