INDUSTRIAL A N D ENGINEERIJG CHEMISTRY
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T'ol. 22. KO.11
Ultra-Violet Radiation in Industry' M. J. Dorcas NATIONAL CARBON COMPANY, Ixc., CLEVELAND, OHIO
LTRA-VIOLET radiation is used in many industries because of its ability to cause chemical reactions t o take place. These photochemical reactions are at present important and the increasing quantity of research and development work in progress on the chemical reactions themselves and the equipment with which to accomplish them indicates that ultra-violet will assume a more important place in industry in the near future.
facture of chlorinated solvents from chlorine and hydrocarbons such as chloroform from methane. Many other laboratory reactions, most of which can be classed as oxidation, halogenation, or polymerization have been discussed as possible photochemical reactions having industrial application because they might then submit t o more accurate control of end point and proceed with formation of smaller quantities of undesirable side-reaction products.
Industrial Uses of Ultra-Violet Light
Importance of Selecting Proper Light Source
Ultra-violet, sometimes together with visible light, from the sun or artificial sources, is used a t present in the photographic industries such as photo-engraving, lithographing, and blue-printing; in the textile industry for the bleaching or grassing of the best quality of linen; in the leather industry
Selection of the proper kind or quality of light source is important for two reasons: (1) Different kinds or qualities or wave lengths of light often result in the formation of different products when the radiation is applied to a given reaction; (2) light or ultra-violet is a comparatively expensive form of energy and different wave lengths can often perform the same kind of action with different efficiencies. Most photochemical reactions are found to proceed with some wave lengths and not with others. I n general, photochemical reactions will occur in the presence of all wave lengths shorter than those represented by some particular figure and will not occur in their absence. This figure usually differs for each photochemical reaction. Further, most photochemical reactions have a uniform quantum efficiency; that is, a given number of molecules will react for every quantum of radiation supplied that has a certain minimum amount of energy. If a molecule will react when it receives a quantum with an amount ofoenergy corresponding to a particular wave length, say 4000 A, only the same amount of reaction will occur if the molecule receives a quantum supplied with a,," amount of energy corresponding to a wave length of 3000 A, provided that the energy corresponding to the shorter wave length is not sufficient t o cause the molecule to react in a different way. The amount of reaction is the same in the two cases, yet a third more energy is required to supply tohe quantum with energy corresponding to wave length 3000 A. compared with that quantumo supplied with energy corresponding to wave length 4000 A.
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I- Figure 1-Spectral-Energy
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Distribution Diagram of Sunshine
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Figure 2-Spectral-Energy
Distribution Diagram of Therapeutic D Carbon Arc
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for the final step in the manufacture of patent leather; in the food industry for increasing the vitamin D content of foods, for sterilizing water for public water supplies or for the manufacture of various beverages, and for sun-drying fruit; in the petroleum industry to remove the bloom from lubricating oils; and elsewhere artificially produced ultra-violet is used in accelerated tests of the durability of many articles. Many substances are subjected to such tests in the routine control laboratories in the course of manufacture. These include paints, varnishes, dyes, and dyed textiles, wall paper, and other colored printed matter, ink, rubber, laminated glass, and gasoline. Other uses of ultra-violet not yet extensive but which have been discussed in the literature include production of scrim oil in linoleum manufacture, the final treating of oil cloth to remove stickiness, as a supplement to sunshine to increase the amount of active principle in drug-containing plants such as digitalis, bleaching oils for food and technical uses such as for artists' oil colors, the synthesis of artificial rubber from unsaturated compounds such as vinyl chloride, and the manu1
Received June 9 , 1930.
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Figure 3-Spectral-Energy
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Distribution Diagram of Therapeutic C Carbon Arc
If cost of energy is an importanb factor in the process, efficiency demands that the energy be supplied with radiation of the longest wave length capable of causing the reaction Source of Radiation
Radiation of many different qualities is available. The sun as a source of radiation for industrial applications is handicapped because of its variability and its limited range of
November, 1930
INDUSTRIAL A X D EYGINEERILYG CHEAMISTRY
wave length. Artificial sources are more reliable and more capable of producing a greater range of wave length. The carbon arc is the most versatile of these light sources, since by varying the chemical composition of the electrodes which
Figure 4-Hand-Operated
Bare Carbon Arc a s Is Used i n LanternSlide Projection
support this arc the radiation can be varied between wide limits. Figures 1, 2 , and 3 show the spectral-energy distribution diagrams of the sun and two different kinds of carbon arcs, respectively. I n these diagrams energy is plotted against wave length. Many other different spectral-energy distributions are available from other kinds of carbon electrodes and other sources. The carbon arc is especially suitable for research work, since an inexpensive yet versatile light source can be obtained by use of a small carbon arc lamp of known spectral energy distribution. Figures 4 and 5 show inexpensive lamps that are useful for experimental work. Inadequacy of Lamps Previously Available
Carbon electrodes capable of producing the required quality of radiation have been available for many years. They were not used in many industries, however, because there were no suitable lamps in which to burn them. Most of the lamps heretofore available have been of two types: (1) those of small capacity which were satisfactory for giving a small amount of light to test samples of material, or (2) those, such as the photo-engraving lamps, that could give large amounts of energy but required some attention, such as replacing or readjusting the carbon electrodes, each hour or so. The small lamps gave a satisfactory quality of Figure 5-Table Model light and many of them would burn Lamp for long periods without attention. Khen applied to large-scale industrial processes, however, large numbers of these small units were required. This involved large initial investment, their relatively low efficiency resulted in high switchboard power costs, and the operating difficulties of dealing with large numbers of small delicate units of apparatus were considered prohibitive by many plant superintendents. The larger photo-engraving lamps, while thoroughly satisfactory for the work for which they were designed, could not be used in many other industrial applications. They gave large quantities of radiation, but required
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the frequent attention of an operator. These interruptions and the high cost of the labor required to operate them prevented their widespread use. Furthermore, these lamps would fluctuate several per cent in current consumption and output of radiation. New Lamp for Industrial Use For industrial applications it is necessary that large quantities of energy of proper wave length be supplied by rugged apparatus that is not too complicated or fragile for plant operation and that will operate with a steady output a t minimum attention. Such a light source has recently been developed. The lamp shown in Figure 6 is a powerful, rugged arc lamp that will supply commercial quantities of radiation, will operate for 10 hours or more without attention, and is capable of remote or automatic control. Batteries of these have been installed in industrial plants where each unit of the process was receiving 5 kilowatts of energy of wave lengths shorter than 4000 A. with a total switchboard drain of 40 kilowatts. This is a production of ultra-violet in commercial quantities with a switchboard efficiency of over 12 per cent. An important feature of these new lamps is that they are controlled by small motors on a simple electrical circuit so that the power consumption and the radiation are constant at all times. These arcs are capable of considerable variation in size, but a typical medium-sized one is 50 volts, 60 amperes, using 3 kilowatts directly from a 220-volt a. c. line t h r o u g h transformers. Such an arc, if burning the “C” c a r b o n whose spectral-energy diagram is shown in Figure 3, would give about 50 X watt per square millimeter at 1meter horizontal distance from the arg of radiation s h o r t e r than 6500 A. $bout half of this is visible and about half ultra-violet radiation. Thus each square meter of surface 1 meter from an arc of this size can be irradiated with 25 watts of ultra-violet. There are about 12.5 such s q u a r e m e t e r s about the arc. If it is not possible to use the radiation a t the surface of this theoretical sphere. it can be collected by suitable reflectors to Figure 6-skeleton Me&give most of the radiation on any p :;a& ’ FA;*trial Type area required. Such data enables preliminary calculations for design of almost any installation to be made. The cost of operating such lamps varies with the cost of power. Carbon electrodes and power usually would cost less than 20 cents per hour. Industrial Uses of New Lamps
Various features of this new type of lamp have made some large-scale irradiation processes possible. The constancy of output has enabled its use in the activation of some food products where the concentration of activated substance varies greatly with total quantity of the proper kind of ultra-violet supplied. Constant and reproducible output of ultra-violet a t all times without deterioration has resulted in improved yields and less expenditure for control testing in this industry.
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Groups of such lamps can now profitably replace sun exposure of patent leather, making this process independent of the variations of the weather. Some mineral waters are about to be sterilized by exposure in thin films to this light. Accelerated tests are now made more rapidly than before because of the greater intensity of these long burning lamps. Sometimes a material catalyst will supplement the radiation, giving yields and products hitherto unknown, as demonstrated recently by Gardner in his researches on the solidifying of drying oils. Such researches now make possible a new
Vol. 22, No. 11
quick method of scrim oil manufacture. The dehydration of animal and vegetable food products in the presence of bright sunlight to prevent mold and bacteria growth is now commonly dependent on the weather. The artificial sunshine now makes possible continuous operation of this dehydration. A great number of reactions a t present known only as laboratory curiosities no doubt will eventually become industrial processes with this development of more powerful and convenient light sources.
Thermal Conductivity of Liquids' J. F. Downie SmithZ E S G I N E E R I I G SCHOOL, H A R V A R D U N I V E R S I T Y , C A M B R I D G E , XIASS
H E thermal c o n d u c tivity of liquids is a subject on which virtually no theoretical work has been done. Weber (3) derived an empirical expression for thermal conductivity,
The thermal conductivities of several liquids, many of which are new, are tabulated. A general equation is proposed for the thermal conductivity of all non-metallic liquids at 30" C. and atmospheric pressure. This equation is: kzO.12 - - - 8.1 X 10+ (pCXM'!6)1'15
Lees used a modification of his method for solid nonc o n d u c t o r s . A correction has to be made for the heat conducted through the walls of the containing vessel. p CQ.4 Goldschmitt used a modiUnfortunately, this equation does not give the temf i c a t i o n of t h e h o t - w i r e perature coefficient. method of S c h e i e r m a c h e r . k = 0.00359 Cp ?! x 3 A graph is included which may be used instead of the The liquid is contained in a where m = molecular weight of equation to determine conductivities. small-diameter tube with the liquid heated wire in the center. C = specific heat p = specific gravity Callendar measured the heat carried away by a current of liquid flowing through an electrically heated tube. This equation is satisfactory for some liquids, but for others Bridgman used two concentric cylinders with the liquid it does not give accurate results. For water the agreement contained between them, heated a t the center of the apparatus with observation is closer than 5 per cent. For some liquids by an electrically heated high-resistance wire. the agreement is not so close. It is this last method which was used by the author in his Bridgman (1) suggests as a formula for the approximate determinations. Indeed, the copper-cylinder assembly which determination of thermal conductivity of electrically non- was made by Bridgman in 1923 was kindly loaned by him to conducting liquids the author. This saved considerable time, for great skill was required in the fashioning of this very delicate piece of equip k = 2ao/d2 ment. where a = gas constant = 2.02 X D = velocity of sound in liquid d = mean distance of separation of centers of molecules, Apparatus assuming an arrangement which is cubical on the . average, and calculating d by the formula d = Two copper cylinders, A and B , Figure 1, are assembled ( M / p ) 1 I 3 where , M is the absolute weight in grams concentrically. The outside diameter of the inner cylinder, of one molecule of liquid A , is "8 inch (9.5 mm.) and the inside diameter of the outer rllthough this formula is interesting from a theoretical cylinder is 13/32 inch (10.3 mm.), so that there is an annular standpoint, it does not help much if we need an accurate space 1/e4 inch (0.4 mm.) wide between the two cylinders. value for thermal conductivity, for in some cases the values This annular space contains the liquid to be tested. Heat is supplied to the inner cylinder, A , by passing a current of obtained are more than 30 per cent off. These two formulas seem to be the only ones for the deter- electricity through a high-resistance wire, H , in the center of the cylinder. A number of flat copper strips, C, ensure good mination of thermal conductivity of liquids in general. Experimentally not much work has been done in this field thermal contact between cylinder B and the thick cylinder, either. A few of the investigators are Milner and Chattock, X . The heat from the wire H passes radially through cylH. F. Weber, Jakob, Chree, Wachmuth, Lees, R. Weber, Gold- inder A , the annular layer of liquid D, cylinder B , the copper strips C, the steel cylinder, XI and out to the oil bath, which schmitt, Graetz, Winkelman, Callendar, and Bridgman R. Weber supplied heat to the top of a column of liquid from is stirred rapidly and kept a t a fairly constant temperature by a vessel kept a t a certain temperature by oil which was elec- thermostatic control. The temperature difference of the cylinders A and B is trically heated, while the bottom of the column was cooled by a horizontal copper plate standing in ice. The tempera- determined by three thermocouples T (only one shown). It is ture difference was taken a t two points 1 cm. apart by copper- assumed that the temperature of the copper cylinder A at constantan thermocouples. The heating from the top was the diameter of the inner thermocouple junction ring is the same as that a t the inner face of the liquid; and that the done to avoid convection currents. temperature of the other cylinder, B , a t the diameter of the 1 Received August 8, 1930. outer thermocouple junction ring is the same 8s that at the 2 National Research Fellow, Harvard University Engineering School.
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