I&EC TRENDS
TODAY
Thermal properties of the solid surface have an important eject on the heat transfer coejicient for dropwise condensation. This conclusion was reached by P. Grfith and M . S. Lee of M I T who studied heatjuxes through gold-plated copper, zinc, and stainless steel plates on which water drops were condensing. A 0.005-in.-thick gold coating on the three dzferent substrates was used so that dropwise condensation occurred in the same way on each. Grzjith and Lee show that a 20-fold reduction in base material thermal conductivity can give a jivefold reduction in heat transfer coejicient. This dependence is shown to arise from the equation dejining the heat transfer coejicient (in which h is inversely proportional to the dtference between surface and steam temperatures) by postulating that the base material local surface temperature decreases with increase in thermal conductivity. This might occur by “crowding” of heatjux at certain points on the solid surface. Previous workers have not included substrate thermal conductivity as a variable in heat transfer correlations for dropwise condensation [Intern. J. Heat Mass Transfer 10,697 (1967)l. There i s no significant interfacial resistance at the phase boundary when mass transfer
occurs between phases in three binary liquid systems; to study the systems, T. M . Fosberg and W. J . Heideger of the University of Washington used the laminar liquid jet technique [Can. J . Chem. Eng. 45, 82 (1967)l. The possibility of an interfacial resistance-i.e., a departure from concentration equilibrium-was first noted by Higbie but is not considered in the familiar two-jilm theory. Scriven and Pigford [A.I.Ch.E. J . 4, 439 (1958)I have shown, by taking the j e t j u i d dynamics into account, that there is no interfacial resistance between COZ and a laminar water jet. Fosberg and Heideger measured the velocity at the liquid-liquid interface in the systems isobutanol-water, ethyl acetate-water and cyclohexanol-water; using a velocity projile equation developed by Garner et al., they afiplied unsteady-state di$usion theory. Their predicted rates of mass transfer agreed closely with experiment and verijied that there is concentration equilibrium at the interface in these systems. The laminar liquid jet technique is valuable in such studies because it involves short contact times between phases and low bulk phase transfer resistances. A jnite interfacial resistance is therefore not easily masked by other resistances, unlessjuid dynamics is unwisely neglected. This belief is the basis of a recommendation that scient@ writing be taught to all graduate students, so that they can make the future literature more comprehensible than today’s. F. P. Woodford of Rockefeller University, New York, who advocates adoption of a writing course [Science 156, 743 ( 1 9 6 7 ) ] ,thinks that the discipline of marshaling words into formal sentences, writing them down, and examining them is bound to clarify thought. Sometimes research workers who attempt to write a paper after a long period of researchJind that writing shows them that their research has found answers to scientijc questions which were never asked in thejirst place. Good writing at all stages of a piece of work is an essential weapon in the scientist’s arsenal, says Woodford. Bad writing, on the other hand, is not merely stylistically inelegant; it may be the outward manifestation of inward confusion of thought.
Writing clarifies thought.
VOL. 5 9
NO. 8
AUGUST 1967
7
STURTEVANT Pulver Mills Grind Without Heat Build-up
DmDP nu!!
Effectively Pulverize Soft, Non-metallic and Heat Sensitive Materials. Air-flow design of Sturtevant Pulver Mills eliminates heat attrition, makes them especially effective for fine-grinding soft, non-metallic and heat sensitive materials such as flour, DDT and insecticides to low micron sizes. In operation, rigid swinging hammers impact material between fixed wall hammers. Double hammer action creates fast, effective particle reduction. Air intake vanes whirl vertical air column through selector bars, precisely classifying end product to desired size, Inert gases or refrigerated air may be used for special applications, Replaceable, optional rubber grinding chamber liners permit pulverizi n g of steel-adhering material. Sturtevant Pulver Mills feature output capacities to 5 tons/hour and “0pen.Door” Construction.*
The addition of a Marasperse (usually in dry form) will make a thick aqueous slurry thinner and easier to handle. Or, if you are shooting for faster drying schedules of the slurry later in the process, you can cut back on the amount of water necessary to obtain a workable consistency.
Marasperse dispersants prevent flocculation of small insoluble particles in water suspensions. Usually less than 3 9% Marasperse (based on the weight of the solids in the aqueous system) will do the job. In some applications as little as 0.1% to 0.2% is enough. And the Marasperses are low in cost per pound.
AM ER ICAN
It’s easy to determine if a Marasperse w i l l be helpful to you. A f e w quick tests in your own laboratory or plant will p r o vide the answers. Tell us h o w you wish to test the Marasperse a n d w e will send samples f o r your evaluation together w i t h a copy of our current Technical Bulletin No. 130. Use the convenient coupon below.
For full information on Sturtevant Pulver Mills, write, phone or wire Sturtevant Mill Company, 15 Sturtevant Street, Boston, Massachusetts 02122. Phone (617) 8256500. Cable EMERYSTONE Boston.
CAN COMPANY M A R A T H O N PRODUCTS I CHEMICAL 1 0 0 Park Ave., New York, N. Y . 1 0 0 1 7
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AMERICAN CAN COMPANY, Marathon Productr/Chemicol 100 Park Avenue, New York, N.Y. 10017 Pleare rend i n f o r m a t i o n on the Marasperses for use i n
are accessible “By One Man in One Minute“ for easy inspection, clean. out, adjustment and maintenance.
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* * * *“OPEN-DOOR“ CONSTRUCTION * ‘ a The interiors of Sturtevant machines
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