Solid (:arbon Dioxide in I nctus trial Refrigeration D. €3. KILLEWER, 50 East (Ilst %reel, Xew York. h. Y. (Jf it has h e w dissipated at this puint :luring tlre melting of the solid. Tlie industrial operations rvliere tire use of solid carbon dioxide arc indicated fall natiirnlly into three classes: (1) a very low temperature (-70' to -185" F.) must be required; (2) t,he operation shall be on siicli a small scale or so intermittirnt as to make charges on ineclianical producing units proliibitive; or (3) tlie convenient,portability of tlic moistureless solid carhon dioxide unit must be a dominant factor. These tlrree criteria n ssarily limit the application of tliii; teclinic. It is of corirsc true that higher temperntnrps than those noted can be readily produced and controlled when solid carbon dioxide is used, bot within the range where other re,frigerating means are available, the item of economy I m comes a ruling factor against its use. Illiistrative of extreme low-tcmperature operation is tire application of solid carbon dioxide to replace or to supplement liquid air in tlre production of liigli vacuums. In the operaCompusitior, $i8.99% con tion of mercury diffusion pumps, cooling of the condenser by 90 Ib. DCP C U . It Density solid carbon dioxide prixiuces a result quite comparable with Sublinio. ternpeiaii~ia(ai one alrnoapiiarrl . 1119,O" F. that obtained with liquid air. Similarly comparable results 246 €3 f . / I . i'er 11, Iatont lieat ( a t subliming tempereturo) are to be had from its use for refrigerating tire absurptive o.loa spccifio boat "igas (auoraae) earl,on in the final evacuation of a tube by the Crookesmethod. Obviously, where extrcrnely luw teml it.urees a w required Tlie quantity consumed in tlie industry of high-vacuum tubes this material offers a ready means of gruducing tliem. A - for radio, illumination, and similar things is of considerable tiiougli the subliming temperature given nt a pressure of one conimercial magnitude and probably rehelm the extent of atmosphere pressure of carbon dioxide is well below most several tons per month. Kumerous operations are intermittent in tlieir character indnsbrial requirements, by causing the solid tu sublinie in a spacc where tlu: pressure is rcdoci:d below an atmosphere, and at the same time require very low temperatures, lower tlian can be conveniently produced without tandem refrigerat. r v e n Icwer timimatures may be pniduced. If, on the other iiand, a control of temperature at some higher valrie is re- ing installations. It is of course feasible to rcacli temperatures quired, a control of the pressure of gas over the d i d carbon down to the soiidifying point of the refrigerating fluid in a dioxide will within limits result in such a control. Tlie meclhanical refrigerating machine if the condenser temperapractical lower limit of ternperature uf sublimation is iii the ture is kept low, or if tlie capacity of tlie machine is sufficiently neighborhood of -165' F.,and tlie upper limit is tlrc triple larger than the required refrigeration load to permit it. Ordinarilv"tu imdiice noint of carbon di. temperatures below oxide where suhlima-ZOO" E'. refrigerating tion ceases and true machines are operated melting begiiis. This p o i n t is a b o u t 75 in tandem-i. e., one machine operates ixriinils pressure and -io0 13. In o t h e r solely to cool the conmordi, hy the use denser of tire other. m e m i n i a i d priwiiri' By using an ammonia thr siililinnition tenrinit to cool the condenser of a carbon diperatiire of solid carbon dioxide can Ije oxide machine, for inL-aricwI o v e r a low stance, it is possible range nf s m ~ 85' e F. to produce temperanil cxli !,e cnntrolled tures down t o the wit,li cansidcrable acfreezing point of carcuracy at any dcsircd bon dioxide. However, the cost of cnrrypoint within that ing sticli an installarange. Above -72" F., wlriere melting lietion Sor an int,erinitgiiis, tlie r o n i r u i uS tent ioad is o f t e n iiressiire is m l t nrr tictoo great i o make it cominercially fpnsihle. i: iirat e temimature controlexcept uf thehiling of tire liquid ineltcd from tlie soiid. In tliis field, solid carbon diuxide offiirs a reai1.v solution. Trinperat.ure of boiling of tlic liquid caii of course be readily In t.lie manufacture of perfume aimlutes from concretes, ouritrolled by pressure, but the latent heat of vaporization the odor is dissolved from tlie fat with alcohol, and in is much less than that of subiirnabion of thc solid, ami hence, order to remove dissolved fat from the absolute, the extracwliile part of the cooling poner can be crintr&d ivy tliis means tion must be conducted at as low a teinperatnre as possible.
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SlICSTRIAI, rcSrigeriit,im lby solid cartxm dioxide Itas been limited by tire gractical i:orisidcration.; of rconoiny to the rclatively mall Init 1 iinpixtant field of w r y is quite aside irum its ervation uf perisliable fc stuffs, a field distinct from tlic present disciission. The with wliich estreniely low temperatures can be proclt ttirougli its use and the negligilrle investment required liave npened a number of promising applications of solid carbon dioxide in industry. 1t.s cost as cornparcd wit,li met:l,anical refrigeration is relntively high, hut tlic result,s to be secured tlirougli its use are inure strictly c~mgarable with t h e secured from much more expensive liquid air. Its present wide commercial dist,riliutinir niakrs it readily availaldc in all parts of tlic country. Its properties, on which its I I S ~is Iircdicateri, may br! tabulated as follows:
d i o v e the tripk, point, a I a r g part
materials of this sort by providing each rircter with a sriiall box refrigerated by solid carbon dioxide. The relative novelty even yet of this material in the indust,rinl field prevtxits a more complete survey of its possiliilitics, many of whiclr readily occur to one who studies it5 propcrties. The commercial development of large-scale ttiariirfacture of solid carbon dioxide has progressed to the point of providing nation-wide distribution on the basis of its iisc in refrigeration of perisliable proiluats in transit. Methods of shipment liy accirstorried incans with low eraporation losses permit supplies to be provided on short notice tlirouglioiit the country. R ~ - c e i v r oApril 15, 1932
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~1~'RIGEKATlU as~ applied to air i!onditi(jrrii,~ presents a distinctly different set, of conditions from those met elsewhere in refrigeration practice. Because the product of the air-conditioning process must primarily be free from any impurities, every effort in design must be directed toward making evcrytlrini: connected with i t safe beyond any possible question. This imsideration has led to the invt!stiga.tion of refrigerating systcnrs and to the desnlopnient of what is at Icast a unique type of r?irigerant and machine adnptcd for use wit,li it. The refrigerants, dichiorocthylenc (I)ii!liiic) and diehloromethane (Carrene), differ from the usual conirriercial cooling media in being liquid at ordinary temperatures aiid pressures, and the machine in wliich dliey are used is unique in operating always at pressures below atmospheric. The entire unit and the engineering behind it are sufficiently different from the ordinary to justify a rather full discussion liere. Aitt CosnImmIxG Ttre ~xocessof conditioning air, although aside frmi the rxirrciual objects of this discussion, must be s k e t c h i d lriefly here to form a proper basis for the discussion to follow. The phases of air conditioning pertinent to this paper are cooling and dehumidifying, other phases RS heating, h u m i d i f y i n g , ctr., being i r r e l e v a n t . The process consists essentially in filtering a i r , w a s h i n g it w i t h w a t e r cooled to a point which will fix it,s dew point at the desired level, and subsequently 11r i 11gin g to the required temperature for delivery to the space to bc mnditioried. In ordinary practice, a r e l a t i v e ti u m i (1it y of 45 to 55 per cent, requiring a dew point, 15" to 25" P. b e l o w tlie ultimate desired dry-ldk temperature, is cnnsidered b e s t f o r s p a c e s where summer cooling for comfort
of persons is involved. To attain this condition, the dew point is fixed by a tliorougli washing of the air with water i:ooled to the desired temperature to iusiire its dehumidifieation in Puminer to tile desired nioisture content. This air may then be mixed with other air until it has the desired dry-bulb temperature for introduction into the conditioned pace. This temperature will vary from 10' to 25" below that being niaintained in the occupied spaccs, depetending on the mctliod of distribution and other local factors. It is of prinrary importance that the mechanical equipnient arid tlie media or element employed in such air-conditioning offer no hasards t o the occupants within the building or space heirig conditioned. n'ot only must the danger from direct accident and hazard he entirely eliminated, but the more serious out,come of a pa& initiated by the most trivial muse must be scrupulously avoided. I n industrial air conditioning, the purpose of sui+ a systeni is to supply pure air of urriforni characteristics, and altliough a minor failure mag not involve such great hazards 5s in public Iiuildings, rii:\wtlielcss the objective of the system is defeated by any possible contamination that might get into the air from the failure of any part of the equipment.
REFRIGERANTS ClfoSEN FOB SYSTEM Xearing these points in mind, it was necessary to consider first the safety of t,he system and its ability to function properly inspite of possible errors on the part of operators. This led to the idea of a refrigerant of a relatively high boiling point operating u n d e r a s u b atmospheric p r e s s u r e , for under these coiidit.ions any leakage would necessarily be inward instead of outward. This required the development of a refrigerating machine to handle such a. substance under the prescribed conditions, which necessarily involved a relatively large-capacity compressor to handle the at-
