Unit Operations Review
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Evaporation by William G. Dedert, Swenson Evaporator Co., Harvey, Ill.
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Fresh water evaporation has become a world-wide technical endeavor Commercial evaporation advances are motivated by gains from increased steam economy, reduced downtime for cleaning, and improved product characteristics
T , E BEST PUBLICIZED evaporation field is centered around the world’s interest in production of fresh water from sea water. Evaporation, probably the best understood of potential methods, has advanced quickly to large-scale installations. The U. S. Department of the Interior, through the Office of Saline Water, has pursued a program of pilot plant trials followed by large demonstration plants. By the end of 1960, work was well along on the installation of a multiple-effect falling film installation at Freeport, Tex., and a multiple-effect flash evaporator at San Diego, Calif. The National Heat Transfer Conferences, jointly sponsored by A.1.Ch.E. and A.S.M.E., continue to contribute important knowledge of boiling concepts. Nucleate boiling, mechanically agitated film boiling, and falling film phenomena have received particular attention at these meetings. Investigations of vaporliquid flow and pressure changes within heated tubes are helping show the way to greater utilization of available surface through avoidance of “drying-out” of heat transfer surfaces. Rapid commercial application has been made of the numerous studies of mechanically agitated films in heat transfer equipment. Recent changes and emphasis in commercial evaporation technique are mainly concerned with reduced operating and maintenance costs and improved product characteristics. Generally rising fuel costs encourage more and more manufacturers to adopt the economies offered by multiple-effect evaporation. Growing awareness of the cost of evaporator shutdowns for removal of tube scale and other equipment fouling has resulted in substantial progress in this area. Techniques used to combat this 103s of production include controlled liquor film velocity and thick-
ness, suppression of boiling in the heat transfer surface, controlled temperature drop across the heating surface, and maintenance of crystal seed surface for preferential deposition of solids from the circulating solution. Skillful adjustment of these and other techniques has produced major improvements in the operating cycles for many applications. Improvements in product characteristics can be traced to use of new evaporator types as well as improved technique with older equipment. Increased use is made of thin and agitated film evaporators for heat sensitive and high viscosity liquors. Proper application of forced circulation evaporators now yields many crystalline products with uniform and controlled crystal size. The monetary returns from improved steam economy, reduced downtime, and improved product characteristics represent the main incentives to commercial evaporator progress at this time. This review covers the years 1959 and 1960.
Heat transfer Theory A number of investigators were concerned with the effect upon heat transfer of varying gas and liquid ratios in vertical tubes. An analysis of heat transfer behavior of climbing film evaporators by Doll-Steinberg (70) showed four regions of heat transfer values. The first two are the gradual increasing of the bubble population in the body of the liquid; the third is the region of linear fall-off; and the fourth is the region of constant value. This study by Doll-Steinberg was continued and reported by Turner (92). An analysis was made of the effect of liquid immersion and temperature differences on evaporation and liquid circulation rates for a naturally circulat-
ing evaporator. Tubes tested were 0.5 and 0.75 inch in diameter and 1.4 to 4.3 feet long. The data and graphs demonstrate the specific conditions which produce tube “drying-out” with this particular system. Vapor produced in a tube experiencing “drying-out” was independent of tube length above the wet zone. Changing only the immersion level and liquid circulation rate did not alter the over-all heat transfer coefficient when the entire tube was wetted. I t folloMed that either natural or forced circulation systems could be used without materially affecting the heat transfer performance if sufficient circulation is used to maintain a wetted tube. A correlation presented by Brown and others (5) would permit the prediction of flow pattern, hold-up, and pressure drop for the flow of immiscible gas and liquid phases in upward vertical flow. This work co,,ered average gas phase densities in the range of 0.092 to 0.552 pounds per cubic foot and tube diameters of 0.5 to 3 inches. Schrock and Grossman (57) studied the pressure drop in forced convection vaporization. They used a heat transfer system designed for the investigation of local heat transfer coefficients and local pressure gradients for water flowing vertically upward in a heated tube. Additional heat transfer measurements for the two phase flow of waterair and oil-air mixtures were made in a vertical tube bv Groothuis and Hendal (22). Values were obtained over a wide liquid mass piow range and a 200fold range of gas to liquid volume. The results were csrrelated over most of the range by interrelating the Nusselt and Prandtl numbers based on the physical properties of the liquid phase with a Reynolds number obtained by adding the liquid and gas Reynolds numbers, both VOL. 53, NO. 8
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based on superficial velocity. At higher gas to liquid ratios a maximum in the heat transfer coefficient was observed. A series of differential equations has been developed by Dukler (72) for the velocity and temperature distribution in thin, vertical films similar to those found in falling film evaporators. The results include laminar and turbulent flow conditions and account for different liquid properties and both concurrent and countercurrent gas flow. The values are said to provide reliable data in a commercially important region. Graphs present both local and average heat transfer coefficients and liquid film thickness for Reynolds numbers from 100 to 50.000 and Prandtl numbers from 0.1 10 10.0 for a wide range of vapor loadings. Investigations of the mechanism of boiling heat transfer were conducted by Ruckenstein (50). A new model was proposed, which accounts for the heat transfer from a heating surface to liquid layers by means of turbulent conductivity. Transfer is caused by mixing of the liquid layers by vapor bubbles which form and grow on active centers on the heating surface. The replacement of elements of the liquid at the surface caused by bubbles which separate from the active centers was also considered The hydrodynamic aspects of boiling heat transfer were discussed by Zuber (66). A theoretical analysis is given for five phases of boiling. The analytical model of Bosnjakovic for a bubble growing in a uniformly superheated liquid is extended to include a nonuniform field, and the growth is shown to be a function of the heat flux as well as the superheat. A theory for the diameter and emission frequency for bubbles a t a cavity shows both factors to be functions of the cavity diameter. A relation is derived showing the superheat and heat flux at which a cavity of stated diameter will nucleate. The maximum heat flux is shown to be caused by the same hydrodynamic factors that cause flooding in a perforated plate tower. The minimum flux in film boiling is derived from consideration of Taylor instability. Soviet literature is reviewed extensively with 115 references. Further studies on the mechanism of boiling water with emphasis on nucleate boiling were presented by Drew (77). The general relation between heating wall temperature and local heat fluctuation is illustrated and the variation of the peak heat flux with pressure and subcooling shown. The peak flux was in the range of 1 to 3 million B.t.u. per square foot per hour. As the peak heat flux from the normal nucleate boiling region is approached, a mixed regime of nucleate and film boiling takes place. It was observed that under certain con-
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ditions violent vibration can develop with subcooled liquid. Mixon (47) used electrolytically controlled bubble generation to stimulate nucleate boiling in the study of heat transfer of natural convection and surface boiling systems. Bubble formation produced a pronounced increase in natural convection heat transfer. Surface boiling conditions showed similar results. A surface blanketing by electrolytic bubbles under surface boiling conditions was indicated. A method of counting active bubbleproducing sites was developed by Gaertner and Westwater (79). The technique consists of plating a thin layer of nickel on a copper heating surface during the boiling runs and subsequently counting the number of pin holes in the plate. The numerous photographs presented reveal a random distribution of active sites. The heat flux was approximately proportional to the square root of the number of sites, which conflicts with previously suggested linear relationships between heat flux and number of active sites. An extensive study of the effect of transfer surface conditions upon nucleate boiling was presented by Griffith and Wallis (27). Various heat transfer mechanisms which have been previously proposed were analvzed by Engelberg-Forster and Greif (15) in light of recent experiments. Evidence is presented in favor of a vapor-liquid exchanqe mechanism which is shown to explain the insensitivity of boiling heat flux to the level of subcooling. A “Reynolds analogy” for nucleate boiling is presented in some detail. A procedure is given for calculating the superheat at which the liquid bulk velocity ceases to contribute to the heat flux. An expression for the growth of a vapor bubble in a highly superheated liquid is deduced. Wave theory of heat transfer in film boiling has been studied by Chang (7). This is the extension of a previous study in which heat transfer was analyzed by the wave theory for natural convection for nucleate boiling in detail and film boiling in principle. Heat transfer in saturated and subcooled film boiling from horizontal and vertical surfaces is analyzed from the viewpoint of the preA generalized vious presentation. Prandtl number is recommended. The predicted results agreed well with the experiments of previous investigators.
Thin Films There has been a continued interest and pursuit of technology involving thin film evaporation equipment. This has involved both mechanically formed thin
INDUSTRIAL AND ENGINEERING CHEMISTRY
films as well as other techniques aimed at maintaining a thin or agitated iilm on the heat transfer surface. An important report by Lustenader and others (38) presents over-all heat transfer coefficients utilizing thin films both in evaporation and condensation. Coeffi ients were as high as 8000 B.t.u. per hoursquare foot per ’ F with Tvater and much higher when dropwise condensation was promoted. The films were obtained by wiping the evaporating surface and utilizing surface tension effects on the condensing surface. Desirable surface and wiper designs were evolved. The result. were considered applicable to compact process equipment. Tests on sea water showed the slowly rotating wiper retards scale formation and the absence of bubbling in the thin film minimizes brine carryover producing high purity condensate. The evaporator was a 3-inch inside diameter copper tube 24 inches long with a 0.035-inch wall enclosed within a 6inch-diameter borosilicate glass tube which was heated to prevent condensation. The rotating wiper was constantly supported on a fluid film to minimize friction and wear. Water wettability of the wiper blades was found to be of considerable importance. The advantages, performance, and applications of a wiped film type evaporator were described by Jones (28). An analysis is presented of hinged blade us. fixed blade wipers. Increased feed rate was found to provide an increased coefficient until the feed rate provided a film thick enough to be picked u p by the wipers. I t is suggested that the wiped film evaporator is particularly suited for applications requiring short time exposure to heat and the processing of very viscous materials. Urea is given as an example, since it demands a relatively high temperature to avoid solidification yet will suffer degradation if held a t these temperatures. Experimental concentration of streptomycin solutions in a thin film evaporator was reported (26). The effects of temperature difference, flow rate, boiling tcmperature, and viscosity on the heat transfer coefficient are reported. The temperature difference was found to have the greatest effect, with the boiling temperature the next most important variable. Results on the processing of protein and egg albumin are also reported. An analysis of film condensation on a rotating disk was presented by Sparrow and Gregg (54). The laboratory disk was placed in a large body of pure saturated vapors with the centrifugal field associated with the disk rotation sweeping the condensate outward along the disk surface. Results are given for the heat transfer as well as the condensate layer
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Unit Operations Review
Here are two examples of evaporator equipment. On the left, a triple-effect forced circulation evaporator used on neutral sulfite paper mill pulping liquor. On the right, a scale model of a specially designed quintuple-effect long tube vertical evaporator
thickness, torque moment, and temperature and viscosity profile. The values cover a Prandtl number range of 0.003 to 100. Kreith and others (37) developed an analogy between heat, mass, and momentum transfer in a similar rotating disk system. They compared experimentally measured mass transfer values under laminar and turbulent conditions. The experimental analog was shown to eliminate difficulty associated with accurate measurements of heat transfer coefficients. A study of film coefficients for scraped surface exchangers by Harriott (24) includes consideration of the techniques as applied to evaporators. Over-all heat transfer coefficients were determined for water, oil, and earrot puree. Leniger and Veldstra (35) ran experiments on the evaporation of water with a wiped film evaporator. Variation in heat transfer coefficient is reported as a function of boiling temperature, temperature difference, liquid flow rate, and the speed of the rotor. A design analysis for mechanically aided heat transfer units was presented by Kern and Karakas (29). Relationships are established involving the heat transfer coefhient, power requirement, throughput, and hold-up functions of the equipment geometry and fluid properties. Frequently, it is the quality or effect upon properties of concentrated materials that determines the type of evaporator equipment to be used. An examination (47) of film type evaporator
influence upon these factors has been reported for operation with proteins, fruit juice, sugars, and vegetable extracts. Lorens (37) discussed methods for preventing chemical reactions which often accompany evaporation by control of boiling time and temperature. The temperature would be controlled by vacuum level and the time would be held to a certain maximum through the use of modern rapid evaporation equipment requiring only a single pass of the feed material. Three types of European rapid evaporation equipment are discussed. A wetted wall column has been used as an evaporative crystallizer (6) for the production of pure fine grained salt from crude salt solutions. Advantages cited are high mass transfer rates and low power consumption. Capacity and cost factors are Five,. Several patents have been issued involving equipment designed to produce a thin film on the evaporating surface. One of the wiped film designs (76) is based upon a rotating cylinder within a chamber, with the rotating cylinder acting as the evaporator surface. Uniform film is established on the rotating cylinder and removed after a controlled interval of time. This design attempts to avoid any accumulation of liquor within the equipment in order to avoid deterioration from oxidation or temperature effects. Another patent (48) combines this same basic design into multipleeffect evaporator systems. Bechtler (Z), Feres (77), and Obr and Kubik (45)
have patents covering mechanically formed film evaporators. A falling film evaporator patent has been issued to Vasil'ev (67).
Steam Coefflcient A study was made by Birt and others ( 4 ) of the change in steam side heat transfer coefficient h, arising from mechanical or chemical removal of water from the steam condensing surface. Using a laboratory rotating cylinder evaporator, they found h, increases directly with motor speed under filmwise condensation conditions. Tetrakis(dodecylthi0)silane (1% solution in CC14) was used as a dropwise condensate promoter in a 25-ton-per-day sea water double-effect evaporator. When the chemical was added at the rate of 50 ml. per hour initially, followed by 50 ml. every 8 hours, the over-all heat transfer coefficient increased from 480 to 650 B.t.u. per hour-square foot per F. Further work on dropwise condensation was reported by Kullberg and Kendall (32) who reported improved heat transfer coefficients using silicone resin coatings on a copper tube. The heat transfer equipment is described, and coefficients are presented graphically. The coating applied proved durable, at least with low pressure steam.
Scale The literature for the period reviewed contains less reference to scale and scale VOL. 53, NO. 8
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prevention of evaporator equipment than in previous years. Sea water evaporation represents one of the fields in which scale prevention has been of great importance. The U. S.Department of the Interior, Office of Saline Water, has extensively pursued this subject and published a review of the literature on formation and prevention of scale ( 7 ) . This is a general treatment of the subject of scale formation with emphasis on sea \rater scaling. Morgan and Wasserman ( 4 2 ) have reported on control of fouling associated with tomato paste evaporation. A patent (25) devoted to evaporation of spent paper mill sulfite liquors is claimed to avoid scale formation through circulation of C a s 0 4 crystalline sludge. The concentration of the recirculated liquor reaches 50 grams of C a s 0 4 per kilogram of solution. Another patent (46) on spent paper mill sulfite liquors proposes to avoid scale through treatment of the aldehydes in the vapors. T h e vapors are scrubbed countercurrently by a cooler liquid steam consisting of subsequently condensed vapor. T h e temperature level of the total condensate is raised to preheat the liquid feed.
trainment studies, and decontamination factor values were established for each system. A vapor mass velocity of 2000 to 3000 kg. per square meter per hour was recommended for a high decontamination factor in an industrial scale evaporator using the glass fiber-packed entrainment separator. Recent tests (34) show that properly designed and operated evaporators can produce vapors containing less than 0.01 p.p.m. total dissolved solids. The effecx of entrainment separators and liquid level upon vapor purity was also investigated. A patent (36) covering baffled vapor drums is designed to reduce entrainment by forcing vapor and entrained droplets to change direction by 90" to 180". The equipment is proposed for flashing hydrocarbon oils at reduced pressure, dehydration of feed products, and evaporation of various solutions or suspensions. Entrainment in boiling sugar solutions has been studied (20) in a pilot plant evaporator operated at 250 mm. of mercury absolute. The experiments were designed to check the influence of evaporation rate, liquid concentration, and liquid level on amount of entrainment. The pilot evaporator was a natural circulation calandria.
Corrosion
Fresh Water
An investigation of corrosion from paper mill black liquor vapors (62) resulted in determination of the H2S concentration in these vapors. Some mercaptans and traces of COa were identified. The HZS concentration was independent of temperature between 90" and 130" C. and directly proportional to liquor concentration; HZS concentration increased with rising sulfidity of the liquor. With 28 to 33% sulfidity the steam contained 0.5 and 1.5 grams of H2S per kilogram of water at 18 and 58% total solids, respectively. Evaporator corrosion in paper mill evaporator equipment was discussed by Jacoby and Lankenau (27). Turnbull (58) has reported upon the effect of temperature and operaling conditions o n corrosion in multiple-effect IYaCl evaporators. Monel, copper alloys, stainless steels, and other metals were studied. A comparison between neutral brines and highly alkaline brines indicates that large differences in corrosion can be expected with varying p H c o n 5tions.
Extensive activity throughout the world on production of fresh water from sea water and brackish waters is evidenced by a substantial number of publications in this field. C'ne good source of information is the U. S. Department of the Interior 1959 annual report (60). This publication reviews progress made in all proposed schemes for production of fresh Lvater. Besides the evaporator activity, it also described work in the fields of electrodialysis, freezing. solvent extraction, osmionics, ion exchange, and others. The review for 1959 describes the evaporation progress in terms of long tube vertical (LTV) multiple-effect systems, forced circulation vapor compression stills, vapor compression with rotating heat transfer surface, flash distillation, and wiped film evaporators. Note is made of success in avoiding scale with the LTV multiple-effect evaporator a t temperatures u p to 250' F. through operation with proper seeding procedures and a "sludge recirculation" technique. The 1960 annual review has not yet been issued. Four 630,000-gallon-per-day flash evaporators (56) are in operation in Kuwait, Arabia. The equipment is described and operating experience noted. This report also includes a discussion of the use of flash evaporators for boiler feed water production in power plant
Entrainment
Entrainment of liquid in evaporators and its control are subjects of a report by Mitsuishi and others (40). Both a mechanical cyclone and a glass fiberpacked column were used in the en-
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cycles. The use of single-stage flash evaporators (55) in steam power plant cycles is claimed to improve the heat rate as compared to cycles using submerged tube evaporators. Experience cited indicates the equipment does not require descaling whether the feed is fresh water or sea water. The distillate is of extremely high purity-0.05 p.p.m. of total solids from fresh water feed (concentrated to 3000 p.p.m.) or 0.25 p.p.m. from salt water feed (concentrated to 70,000 p.p.m.). Flash evaporators (39)have been in successful operation aboard the Point Barrow U S X S Supply Ship. This is a two-stage flash evaporator, and data reported indicate no scale after six months ofoperation. Numerous patents have been issued covering various types of sea water evaporators. Among these are patents (73, 53) on flash evaporators and a patent (64) on a recompression evaporator. Special Types and Processes
The thermodynamic principles on which the flash evaporator operates were described by Frankel (78), together with some of the reasons for the recent emergence of this type of equipment. I t is shown that the performance of a flash evaporator is much less dependent on the number of stages used than is the case for a submerged coil unit. The thermodynamic losses involved in using a finite number of stages and the influence of other losses which are unavoidable in practice are described and assessed. The actual design of flash evaporator vessels is described, showing means of avoiding interstage piping despite the use of a large number cf stages. Test results from scale deposition and entrainment separation studies are included. The use of ultrasonic waves of 200 to 500 kc. ds an aid to increased heat transfer coefficients has been reported by Nakai (34) The effect on scaling, bumping, and foaming at rhe heating surface is described. The evaporation of neutral sulfitr paper mill pulping liquors in a forced circulation evaporator using an external heat exchanger was investigated by Han and others (23). The data simulated quadruple-effect operation, with tube liquor velocity the principal variable studied. Over-all heat transfer coefficients as well as liquor and steam coefficients were presented. The results of this work have subsequently been successfully applied in commercial installations. Rottenburg (49)investigated the relative merits and physical properties of 20 different heat transfer media. This presentation includes 72 references on the subject. Coates and Pressburg ( 8 ) described how heat transfer occurs in
an evaporators, and the same authors (9) reviewed how to analyze and calculate the performance of multiple-effect evaporators. A graphical method for calculation of the performance of multipleeffect evaporators was presented by Wise (65). A review of HdPOd evaporation by Bennett ( 3 ) covers materials of construction, flowsheet, and operating experience. The flowsheet and physical arrangement of the natural circulating L T V rising film evaporator provides controlled supersaturation levels to minimize scale formation and salt deposition within the equipment. Operating experience with these techniques demonstrates reduced tube plugging and scaling. T h e equipment is readily adapted to the recovery of fluorine. The textile industry continues to install caustic recovery systems based on evaporation of recovered liquors. The systems yield an important reduction in stream pollution plus the value of recovered caustic. The double-effect LTV rising filmevaporator at theNorth Carolina Finishing Co. was described by Wilkerson and Rochelle (63). Another article (57) describes similar equipment in the Fruit of the Loom, Inc., plant a t Warwick, R. I. This installation concentrates recovered caustic from 5 to 40Yo NaOH. The evaporator surface condenser also provides hot water for general plant processing. The performance of a falling film evaporator concentrating milk was presented by Keville (30). Murch and Ziemba (43) explained the use of radioactive isotopes as the density measuring device on a grape juice evaporator. Discharge concentration of 72' Brix is maintained to within 10.5a/,. The source of gamma radiation is mounted on one side of a short section pipe and the radiation detector on the opposite side of the pipe. T h e detector converts the amount of radiation (dependent upon density) into an electricaI signal. Plate-type heat exchangers (33) are used in evaporator systems for various food processing applications. The plate exchanger is claimed to offer space saving, reduced cleaning time, and simple modification for changing capacities. A Florida installation concentrates orange juice, containing pulp, to 65" Brix in a double-effect evaporator. Total retention time is about 1 minute. This is a short-time, high-temperature vacuum evaporator operating a t 170' F. in the first effect and 120" F. in the second effect, with single pass climbing and falling liquor flow in each effect. A patent (74)was issued on an evaporator using vapor as the heat transfer medium. The vapor is heated indirectly in an external exchanger and
returned to the evaporator where it contacts incoming fresh liquid dispersed by sprays or baffle plates. The vapor is circulated with a fan mounted on top of the evaporator and may be passed through an entrainment separator. A portion of the vapor is withdrawn, and it could be used as the heating medium for another stage. Advantages claimed are low temperature and pressure differences and establishment of a maximum temperature based on saturation pressure, with a resulting reduction in overheating and fouling of heating surfaces. Increased heat transfer rates and reduced corrosion in multiple-effect evaporators are claimed by a patent (52) suggesting feed de-aerating and separate heating of the make-up and recycled liquid feeds. The flowsheet proposed is specifically pointed to sea water applications.
Literature Cited (1) Badger, W. L., and Associates, Inc., U. S. Department of the Interior, Office of Saline Water, Research and Develop. Progr. Rept. No. 25, 1959. (2) Bechtler, H. C., Ger. Patent 1,019,642 (Nov. 21, 1957). (3) Bennett, R. C., Chem. Processing 23, No. 7. 123 11960). (4) Birt,' D. C. P.,' Brunt, J. J., others, Trans. Znst. Chem. Engrs. (London) 37, 289 (1959). (5) Brown, R. A. S., Sullivan, G. A,, Govier, G. W., Can. J . Chem. Eng. 38, 62 (1960). (6) Chandler, J. L., Brit. Chem. Eng. 4, No. 2, 83 (1959). (7) Chang, Y. P., J . Heat Transfer 81, 1 (1959). (8) Coates, J., Pressburg, B. S., Chem. Eng. 6 6 , No. 4. 139 (1959). (9) Zbid., No. 6, p. 157. (IO) Doll-Steinberg, A., Brit. Chem. Eng. 3. 536 (1958). (1 lj Dre;, T. 'B., Trans. A'. Y. h a d . Sei. 20, 733 (1958). (12) Dukler, A. E., 3rd Natl. Heat Transfer Conf., Am. Inst. Chem. Engrs., Am. SOC.Mech. Engrs., Storrs, Conn., August 1959. (13) Ebner, K., Ger. Patent 1.018.025 ' (Oct. 25,. 1957). (14) Edling, G. E., Swed. Patent 163,225 (May 13, 1958). (15) Engelberg-Forster, K., Greif, R., J . Heat Transfer 81, 43 (1959). (16) Farbenfabriken Bayer, A.-G., Brit. Patent 830,940 (March 23, 1960). (17) Feres, V., Czech. Patent 90,376 (May 15, 1959). (18) Frankel, A., Proc. Znst. Mech. Engrs. (London) 174,No. '7, 312 (1960). (19) Gaertner, R. F., westwater, J. W., 3rd Natl. Heat Transfer Conf., Am. Inst. Chem. Engrs., Am. SOC. Mech. Engrs., Storrs, Conn., August 1959. (20) Garner, F. H., Ellis, S . R. M., Shearn, D. B., Trans. Znst. Chem. Engrs. (London) 37, No. 5, 246 (1959). (21) Griffith, P., Wallis, 3. D., 3rd Natl. Heat Transfer Conf., Am. Inst. Chem. Engrs., Am. SOC.Mech. Engrs., Storrs, Conn., August 1959. (22) Groothuis, H., Hendal, W. P., Chem. Eng. Sci. 11, 212 (1959). (23) Han, S. T., Andrews, B. D., Dedert, W. G., 2nd Natl. Heat Transfer Conf., Am. Inst. Chem. Engrs., Am. SOC. \
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31, 1959). (26 Hua Hsiieh Shih Chieh 1959, p. 231. 1271 Jacobv, H. E., Lankenau.' H. G., ' Tafifii 42;.168A (July 1959). (28) Jones, H. H. M., Znd. Chemist 36, 599 (December 1960). (29) Kern, D. Q., Karakas, H. J., 2nd Natl. Heat Transfer Conf., Am. Inst. Chem. Engrs., Am. SOC.Mech. Engrs., Chicago, Ill., August 1958. (30) Keville, J. F., Chem. Eng. Progr. 54, 83 (October 1958). (31) Kreith, F., Taylor, J. H., Chong, J. P., J . Heat Transfer 81, 95 (1959). (32 Kullberg, G. K., Kendall, H. B., i h e m . Eng. Progr. 56, No. 1, 82 (1960). (33) Lawler, F. K., Food Eng. 32, 60 (March 1960). (34) Lawrence, H. R., Ziobro, R. J., Am. SOC. Mech. Engrs. Meeting, Paper No. 58-A-237,November 1958. (35) Leniger, H. A., Veldstra, J., Chem.Zngr,- Tech. 31, 493 (1959). (36) Little, D. M., U. S. Patent 2,875,139 (Feb. 24, 1959). (37) Lorens, C.,Geniechim. 80, 57 (1958). (38) Lustenader, E. L., Richter, R., Neugebauer, F. J., J . Heat Transfer 81, 29'7 (1959). (39) Marine Eng./Log 64, 96 (August 1959). (40) Mitsuishi, N., Yamamoto, Y., Oyama, Y., Kagaku Kogaku 23, 648 (1959). (41) Mixon, F. O., Chon, W. Y.,Beatty, K. O., Chem. Eng. Progr. 55, No. 10, 49 (1959). (42) Morgan, A. I., Wasserman, T., Food Technol. 13, 691 (1959). (43) Murch, A. F., Ziemba, J. V., Food Eng. 30, 81 (November 1958). (44) Nakai, S., Japan Patent 2421'(59) lAoril 14). (45') b b r , k., Kubik, T., Czech. Patent 88,183 (Jan. 15, 1959). (46) Ramen, T., U. S. Patent 2,896,705 (July 28, 1959). (47) Reavell, B. N., Goodwin, G. A., Chem. @? Znd. (London) 1958, p. 1450. (48) Rodenacker. Mi., Ger. Patent 1,005,042 (March 28, '1957). (49) Rottenburg, P. A., Trans. Znst. Chem. Engrs. (London) 35, 21 (1957). (50) RAuckenstein, E., Acad. rep. fiofiulare Romzne, Studii cercetari chim. 7, 117 (1959). (51) Schrock, V. E., Grossman, L. M.. Nuclear Sei. @? Eng. 6 , 245 (1959). (52) Silver, R. A., Brit. Patent 829,852 (March 9, 1960). (53) Zbid., 828,819. (54) Sparrow, E. M., Gregg, J. L., J . Heat Transfer 81, 113 (1959). (55) Stalcup, E. F., Coit, R. L., Power Eng. 64, 60 (May 1960). (56) Stalcup, E. F., Coxe, E. F., Coit, R. L., Mech. Eng. 82, 84 (1960). (57) Textile Znd. 123, No. 7, 71 (1959). (58) Turnbull, J. M., Corrosion 16, 11 (July 1960). (59) Turner, J. C. R., Brit. Chem. Eng. 5 , 857 (December 1960). (60) U. S. Department of the Interior, Saline Water Conversion Rept., 1959. (61) Vasil'ev, B. M., Russ. Patent 119,518 (May 10, 1959). (62) Venemark, E., Svensk Papfierstidn. 61, 881 (1958). (63) Wilkerson, V. F., Rochelle, M. D., Textile Znd. 123, 120 (February 1959). (64) Williamson, W. B. (to Emhart Mfg. Co.), U. S. Patent 2,885,328, (May 5, 1959\.
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