820
T H E J O U R N A L O F I N D G S T R I A L A NU EliiG I ATE E R IiZ'G C H E M I S T R Y
and are made of wire mesh or of tinned metal perforated with numerous small holes, The size of the holes depends on the nature of the material to be extracted. Three strips of metal converge from the upper edge to the center, and a t the union there is a knob which serves both as a handle to pick u p the tray and as a spreader to distribute the extracting fluid as it drops from the condenser. The lid of the apparatus is of cast brass. This lid is seated on the cast brass i-ing which forms the top of the main body by means of a ground joint. It is held in place by six toggle bolts with wing nuts. There are two threaded holes through the lid. The central hole carries the autoclave attachment. The other is provided f o r a thermometcr. The autoclave attachment (Fig. 3 ) consists of a blox-off valve, G, which screws into hole 0, and also, attached by right-angle side arms to the central tube carrying the blow-off valve, a safety valve, H, and a pressure gage, I. A special fitting or stuffing box (Fig. 4 ) , with ground joint, of the same size and thread as the blowoff valve, can be screxyed in place of the blow-off valve when the apparatus is used as an extractor, still, or reflux condenser. The ground joint, J, of Fig. 4 is tapered and is female. Into this nut fits a connecting tube. This connecting tube (Fig. 5 ) is of brass, lined with block tin. I t has a ground male taper joint, K, at one end and a ground female taper joint, L, at the other, so that below it connects with the main body of the apparatus and above with the condenser. The condenser (Fig. 6 ) is a block-tin, coiled pipe surrounded by a copper cylinder wa;ter jacket. One end of the pipe, M, extends a short distance below the condenser, while the other end, N, extends ab0T-e the condenser in a rough semicircle. Both ends are tapered male ends. The
Vol. 13, No. 9
water jacket fits into a stand made of two bands of strap iron held together by and resting on three legs. The heating is accomplished by gas or by a n electric hot plate. When the stand supporting the condenser is placed upon the lid of the main body, the legs of the stand interlock their feet with three of the wing nut clamps and thus hold the condenser in position. By inserting tube (Fig. 5 ) , that is, fitting K into J and L into M, the apparatus is in position to be used as an extractor or as a reflux condenser. When the condenser stand rests beside the apparatus with the upper end of the congensing tube N fitted into the tapering joint J, the apparatus is in position to be used as a still. When the blow-off valve G is screwed into hole 0, the apparatus is ready f o r use as a n autoclave. The apparatus is most satisfactory for the extraction of material either in the dry, powdered state or in the fresh, moist state, with the different f a t solvents or with water. Without removing o r disturbing the material, the solvent can be drawn off and fresh solvent added for reextraction. Then without cooling the extract can be concentrated and the solvent recol-ered by distillation. Absolute alcohol can be made from ordinary alcohol by refluxing the alcohol over lime, and the absolute alcohol can then be distilled without exposure to the air. Extraction or distillation can be conducted under either positive or negative pressure. The advantages of this apparatus are that it is easily set u p and readily transported; it is easy to clean, and, above all, simple to operate. Its greatest value is that it allows a combination of procedures such as refluxing and distilling, or extracting and distilling, in a single piece of apparatus.
Radiation Effects in Thermometry By Clark S. Robinson] DEPARTMENT OF CHEMICALENGINEERIKG, MASSACHUSETTS IKSTITUTEOF TECHNOLOGY, CAMBRIDGE, MASSACHUSETTS
A thermometer, pyrometer, or other temperature measuring device, when inserted in a gas f o r the purpose of measuring its temperature, does not, except under unusual conditions, recorcl the true gas temperature, and the deviation may, in cases of high temperature, amount t o several hundred degrees, and a t ordinary temperatures it may be as much as ten or more degrees. It has long been known that heat is transmitted by radiation in a similar manner to light, and that it can be reflected, refracted, and absorbed. That different substances have different radiating as well as different absorbing powers has also been known, and as early as 1814 Dr. William Charles Wells performed many interesting experiments on these phenomena. However, while the effects of radiation on thermometer and pyrometer measurements of gas temperatures have been well known by physicists, it has not been common knowledge that thermometer o r pyrometer measurements are subject to such deviatiorls. Thousands of tests on furnaces, boilers, and the like have been made by engineers, in which gas temperature have been measured by the usual means, and furnace efficiencies calculated, when the temperatures thus measured may have been f a r from the fact, It is the purpose of this article to explain how true gas temperatures may be calculated, and to give the results of some experiments made by Xr. Goodman Mottelson in connection with his thesis on this subject a t the Massachusetts Institute of Technology during the past year. IReceived June 24 1921. An Essay on De$', London, 1914.
THE CALCULATION OF TRUE GAS TEMPERATURES A thermometer or other temperature measuring instrument, \Then introduced into a gas, tends to approach the temperature of the gas. I n order to do this it must receive heat, if the gas is a t a higher temperature, o r it must lose heat, if the gas is a t a lower temperature. This flow of heat to o r from the thermometer occurs in two ways, by conduction and convection between the gas and the thermometer, and by radiation between the t.hermometer and the surroundings, usually the walls of the chamber o r flue. Imagine, for instance, a tube in a fire-tube boiler, through which hot furiiace gases are passing, giving u p p a r t of their heat t o the cooler walls of the tube. A pyrometer inserted in the tube, if a t the gas temperature, would radiate heat to the cooler tube, which would lower the thermometer temperature. Heat would then flow into it from the gas, and when equilibrium was reached the pyrometer would be a t a temperature sufficiently below gas temperature, yet sufficiently above tube temperature, so that its loss of heat by radiation to the tube would just compensate f o r the heat gained by conduction from the gas. On the other hand, a thermometer inserted in the a i r between the tubes of a steam coil heater for air, where the heating tubes are hotter than the air, would indicate a temperature hetween that of the air and that of the hot surfaces, the thermometer reading too high where in t h e former case it would read too low. The rate of flow of heat by conduction from the gas t o the thermometer can be expressed by the equation
Sept., 1921 9 = h c A (T-t,)
e
263
in suitable units, such as B.t.u. per O F . temperature differenca between gns and thermometer per hr. T = air temperature, in "F. abs. t, = thermometer temperature, in O F . abs. A =area of surface thermometer through which heat is Rowing. The rate of flow of heat by radiation from the thermometer to the surrounding walls can be expressed by the equation (in English units)
where R, = black hody coefficient of material from which thermometer is made. t,, =temperature of surrounding walls, in F. abs. At equilibrium Equations I and 2 are equal. Therefore,
261
265 267 266 269
-
C O P P F ~SHIELD
-
-
161.3
181.3
Aver. 261.6
S n y motion of the air about the thermometers was due in this case to convection currents alone. Calling tt the temperature o€ the unshielded thermometer, and t s that of the one with the silver shield, Equation 3 may be written f o r each as follows:
Eliminating t , and solving f o r T
(3)
From this equation it is possible to calculate the true gas temperature, T, from the thermometeia reading t t , if the values of ho, Rt,and t , are known. The heat transfer coefficient, hc, can be calculated from the Beclcett equation1 when the gas is moving under forced draft : 0.44 V@8To~oCp (m-0 081) h, = (4) MO"(?n -0.027) where h,=B.t.ii., hr./sq. it. of heating surface/OF. difference V=lbs. of gas/sq. f t . of cross section of gaspass./sec. T =temperatme of gas in O F . abs. C p =specific heat of gas at constant pressure m=mean hydraulic radius of the gas passage in ft. M =molecular weight of the gas When the gas is moving under convection currents only, Equation 6 is t o be used. The black body coefficient (Rt) for a number of substances are given approximately in the following table :
The ralue f o r iz, (English Units)
4f
EXAMPLES The following data were taken with a small electric furnace, 2-in. inside diameter, with the walls heated to approximately 725" C., as measured by a n optical pyrometer. Thermometers were suspended just at the level of the open top of the furnace. Three thermometers were used, all of the usual mercury-in-glass laboratory type, and calibrated against each other. One of these was used as such. while the second had the bulb covered with a tightly fitting, polished silver shield, and the third v a s shielded with polished copper. The following readings were made:
(6)
which is for use when the flow of gas by a surface is due to convection currents only, Equation 4 being used for forced draft. In this case A t is the difference in temperature between the hot walls and the thermometers, and must be calcnlated for each one separately. Under the conditions, Equation 5 must be rewritten, using h,t for the value of hc for the unshielded thermometer and h,, for the silver shielded one.
R,=0.03, R,=0.90. 2,=261.6- C:.=963O F. abs., t,= 161.3" C. =783O F. abs. (728 -261.6)-X 1.8 -2.9 h,,=0.7+
..... . . . . . . . . ...... ...... .... ............................. . . . . .............................. ................................. ................................ ............................... ..................................... ............................. .....
F o r the wall temperature, t,, when the malls are incandescent, the optical pyrometer may be used, or, f o r lower temperatures, thermocouples may be immersed in the wall surface. Where the wall temperature cannot be measured, another method, to be described below, may be used.
may be calculated from the formula h, ~ 0 . 7 --375
S_f_i R_ S_T_.A R. ...N C E , .., , , . , ,.....,. 1.0 Absolute black body.. Highly oxidized i r o n . , , ..........., , . . . . . . . . . . . 0.90 Polished copper. , . O . @ i to 0.10 Oxidized copper Monel metal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gpld, polished Silver polished N i c k d polished Platinhm
T. Thesis 1920.
162 162 158 160 161 162 165 163 162
252
e
lM. I.
C. 188
26;
h, = coefficient of heat transfer by conduction, expressed
h , ( T - 1 , ) = R , x o . 1 6 2 ~100 [ ( ~ ) ' - (100 ~)*]
S I L V ~SHIELD R
UNS~IELDED C. 256 265
(1)
where Q -=heat flow per unit time
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T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I S G CHEMISTRY
375 (726-161.3)X1.8 = 3.4 ha, = 0.7 375 0.03 0.03 X 0.162 l(9.63)' - (7.S3)4] + 963 X2.Q-783 X3.4
+
' (
...
T=
0.03 -X2.9 0.90
-3.4
T =772" F. abs. = 155' C. I t will be noted that the silver thermometer under these conditioizs read 6°C. t o o high, while the plain glass one read 107°C. too lwgla. The copper covered thermometer gave an intermediate reading, since its value of Rt is between that of silver and glass, that ii, 0.07 to 0.10. Another experiment was made with the same electric furnace t o show the effect of various shields f o r thermometers. Unshielded Theyometer C. 272 281 275 279
284 -
Aver. 278
S i l v y Shield C. 169
Black Iro? Shield C. 313
Glass Shield
-
-
-
174 171 164 166 169
316 316 312 316
OC. 292 297 299 299 297
315
296
The silver became tarnished during the test, and its reading fell off somewhat, as is shown in the following table:
The shields were then removed, giving the following readings, the thermometers remaining in practically the same Dositions as before. 290 291 290 293 292
287 277 281 281 281 I
-4ver. 281
282 280 293 284 293
........ . ...
292 Silver Plain . . . . . . . . 276 Difference 16
272 260 266 263 263
-
-
-
291
286
266
h, =
293 278 15
266 247 9
253 240 8
251 243 8
248’C. 241°C.
7“.
274
280
278
278
286
287
288
CONCLUSIONS 1-Thermometers for measuring gas temperatures must have their readings Corrected for the effect of radiation t o the surroundings. 2-For measurements permitting small errors, a silver shield will give fairly close approximations if uncorrected. It is necessary, however, to correct the silver thermometer reading in order to get accurate temperatures. 3-For corrosive gases monel metal can be used in place of silver, but the reading should be corrected except for \.err approximate work. 4-Where gas is moving a t very high velocity, any thermometer will read practically the true temperature, the large deviations occurring where the gas velocities are very Iom. 5-Thermometers vi11 read true gas temperature exactly only when the surrounding walls are at the same temperature as the gas.
[( X (762 - 7 15 X 3 .O
>
292 278 14
The silver shield was then polished and compared again with monel metal, the gas velocity having changed. Polished silver . . . . . , . . ,174 176 177 1 7 8 177 178 170 16t, Average = 173OC. Monel metal . . . . . . . . . . 1 9 6 199 204 204 204 205 201 204 Average = 202OC. Plain glass , . . . . .... . , 2 8 3 285 283 277 290 282 287 287 Average = 284OC.
using for T the value 716 obtained from the reading of the silver thermometer as being near the true temperature, a small error in this temperature being negligible. Csing Equation 5, I i=
290 278 12
. .=’ . ikiic,. . 2 7 6
P l a i n glass Average -
0.44X (2.3)0’8 X (715)0’5X0.24X (0.25 -O.OSl> =3,0 (30)0’1X(0.25 -0.027)
0.03X0.162
292 277 15
The tarnished silver was then compared in a heated pipe with a thermometer shielded with polished nionel metal Tarnished s i l v e r . . . . . . .188 188 183 185 187 189 189 192 Average = 188°C. JIonel metal .. . . . . . . . .156 185 150 170 179 182 156 189 -4verage = 183OC.
The. following data were obtained in a heated galvanized pipe 1 2 in. in diameter, through which a warm mixture of air and burner gases was passing at the rate of 2.3 Ibs. per sq. ft. of cross-section of the pipe per second. Silver thermometer = 1 2 3 ” , 126’, 124” C. Aver, = 124’ C . P l a i n thermometer = 15Z0, 150”,140” C. Aver, = 150° C. Using Equation 4, h, was found to be 3.0 in English units.
r
Vol. 13, No. 9
T H E J O U R N A L O F I N D U S T R I A L A N D ElVGINEERIhTG C H E M I S T R Y
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0.03 -XX3.O -3.0 0.90 T = 712” F. ab^. =122 C.
I n this case, the silcer thermo?nete?-read 2” G . t o o h i g h , a n d the glass o n e 28’ too hic/h.
TWOthermometers, one silver and the other plain, were inserted in the intake manifold of a gasoline engine whose intake gases had been previously heated, and which were moving at a high velocity, 7.5 lbs. per sq. ft. per see. LTnder these conditions, the value of lz, was great enough nearly to overcome the effect of radiation, and the two thermometers read the same a t 60°C. Tests were made in a galvanized iron pipe 7 in. in diameter, in which burner gases containing some sulfur dioxide were flowing at the rate of 0.125 lbs. per sq. f t . per see.
BIBLIOGRAPHY Henry A. Hazen, “Thermometer Exposure,” U. S. Army, Signal
corps.
Le Chatelief;, “ High Temperature Measurements.” Steinmet?: Radiation, Light, a n d Illumination.” Tyndall, H e a t a Mode of Motioq;” R’ C. Wells .4n Essaj- on Dew W: IC. Lewlb, ‘’ Chemical Enaineerinr. Kotes.”
ADDRESSES AND CONTRIBUTED ARTICLES The Chemistry of Acenaphthene and Its Derivatives By Dorothy A. Hahn and Harriet E. Holmes M T . HOLYOKE COLLEGB, S O U T H
The purpose of this imper is to present an outline of the chemistry of acenaphthene, accompanied by a fairly coinplete bibliography of the substance. Such an outline has not a s 5-et been attempted, and it seems desirable because of the fact that it may serve to call attention to the many gaps which exist in the chemistry of this very interesting substance and thus may lead to a thorough and systematic investigation of its derivatives. In this connection it may be pointed out that within recent years methods for s e p nrating acenaphthene from coal tar have been perfected so that it is no longer the rare and expensive preparation rliich it was when the first systematic inrestigation of its derivatives was undertaken by C. Graebe3 and his coReceived June 20. 1921. The work repreaented in the compilation of this material WRS done in partial fulfilment of the requirements for the degree of M . A . a t Mt. Holyoke Collrge. Acknowledgment must be made to Dr. C . C. Baile>-, Director of Orgllnic Research a t the Research Laboratories o€ The Barrett Company, for the suggestion that such a summary might he of value a t this time. SC. Giaebe, Ber., zo (1887), 657; C . Graebe and E. Gfeller, Ber. 11892), 652; Ann., 376 (1893), 12; 9.Craebe and J. Jequier, Ann., z g o (l&f?$ 195; C . Graebe, Ann., 327 (1903), ( 7 . x
3
~~
~~
HADLEY,
MASSACHCSErlS
workers in Germany and by T. Ewan and J. B. Cohenl a t about the same time in England. The research initiated by thcse inen was neglected f o r a period of seven years, when F. Sachs and G. Mosebacli2 entered the field with the avowed purpose of systematically filling in the gaps in the chemistry of aceiiaphthene. These investigators point out in the introduction to their second paper that the extreme meagerness of the information which exists in regard to the cheniistry of acenaphthene is very surprising in view of the fact that the chemistry of napthalene, to which it is so closely related, has been brought to B state of dazzling completeness, The very fact that so many derivatives of naphthalene have been prepared and their constitution exactly determined is, however, of the greatest importance for the future development of acenaphthene chemistry. This faet mill be referred to again later in this paper, but at the present time it need only be pointed out that by the appliJ Chem Soc , 5 5 (1889), 578. * Ber., 43 (1910), 2473; 44 (1911), 2852
