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738 CHAPTER 33 1952 Guide range is extended appreciably beyond that of the conventional cyclone. Pressure losses of collectors in this group range from 3 to 8 in. water, colujnn. 3. Dry Type Dynamic Precipitator. In this type, dust is precipitated by centrif ugal force upon specially shaped blades of an exhauster:wheel,.and then conveyed through a dust, circuit in the fan casing to the dust storage-hopper. - 4. Cinder Catching Fan. This is a special type of collector in which removal of solids is effected by a slotted scroll. - It is a fan unit which is often used for the dual purpose of dust' removal and induced draft service. SETTLING CHAMBERS While it would be possible in theory to remove dust by settling in a large chamber when conveying velocities "are reduced, to the point where the. particles would no longer be held in suspension,' such devices have little practical application in dust collecting equipment. Extreme. space re quirements and the. presence of .eddy currents1 may nullify the effective velocity. The settling chamber type of collector can therefore'be used only for removal of extremely coarse particles. Pressure' drop should be % to in, water, column, plus that necessary, to accelerate the air motion to the required conveying velocity at discharge of. the settling chamber. SONIC AGGLOMERATORS . Sonic agglomerators, now in an early stage of development, may prove to be valuable accessories in the dust collecting field. " High-intensity sound can be utilized to coagulate low-micron and sub-micron sized aerosols such as smoke, fumes, or -very fine dusts into resultant particles which are large enough to be collected efficiently with several of the'types of dust collecting equipment previously described. . This high-intensity sound can be created by various means such as piezo-electric crystal: generators, magnetostriction units, or-high-powered sirens which are practical at present for units with greater air flow ca pacities. For effective coagulation, a minimum sound level of 155 to 160 de cibels6.- 7t 8 is required. . The sound frequencies used are dependent on the size of the particles to be coagulated, and may vary from 1000 cycles-per second for larger particles to far into the ultrasonic region for smaller parti cles. Fairly high dust concentrations, on the order of one grain per cubic foot of gas, are required for effective coagulation. Neither operating temperatures in the range of O F to over .1000 F, nor electrical properties of the aerosols,6 have any apparent effect on agglomeration efficiencies TESTING METHODS Methods pf determining the performance of industrial air cleaning de viceswill depend upon-the nature of the air contaminant, its quantity, the required accuracy of the test, and the type of air cleaning device. .The technics used in collecting the samples are the same'as those utilized in the field of industrial hygiene. ' ' ": The tests may be facilitated by feeding, uniformly, a known amount of the material to Se-removed. The performance efficiency may be calculated from the amount of material introduced, the quantities of air involved, the amount of material intercepted, and the quantity that escapes. When it is necessary to test the device under actual use, the material entering and leaving must be sampled simultaneously over a sufficiently long period of time to collect ati adequate amount for analysis. If feasible, the quantity Air' Cleaning 739 of material removed by the cleaning device during the test/period should. also .be determined. ,. . Unusual care must-be exercised in collecting the samples to- insure that the sampling areas selected are actually representative of the' material entering and leaving the Cleaning device: With gases; vapors-and fresh fumes, this problem is not great: On' the other hand, mi^ts, dusts and aged fumes may present considerable trouble. When the material is .confined' in a duct system, it is common practice to collect the sample along the center line. The sampling tube is located .parallel with, and facing, the flow. The sampling velocity should be approximately the same as the air velocity in the duct.' With large ducts it may be desirable to make traverse tests to locate an optimum sampling position. REFERENCES `Bronchial Asthma.and Allied Allergic. Disorders, by S. S. Leopold and'C: S- Leopold (Journal of the American Medical Association, March 7, 1925) Vol. 84, p. 731- 734). ' Dirt Patterns on Walls, by R. A. Nielsen (A.S.H.V.E. Transactions, Vol. 46, 1941, p. 247): '' ' - ...... ' ; ......... - * Industrial Dust, by Philip Drinker and Theodore Hatch (McGraw-Hill Co., New York, N. Y.). ' ' -- :1 ' 4 A.S.H.V.E. Standard Code for Testing and Rating Air Cleaning Devices Used in General Ventilation Work (A.S.H.V:E. Tbansactions, Vol. 39;T933, p. 225). ' ' 5 A Test Method for Air Filters, by Richard S'. Dill (A.S.H.V.E.'Tbansactions, Vol. 44, 1938, p. 379). . : - .-- . '" ' Industrial Sonic Agglomeration and Collection Systems, by H. W. Danser and E. P. Neuman (Industrial and Engineering Chemistry, November, 1949): ' 'Sonic Agglomeration of Fumes'in Ferromanganese Blast Furnace,' by A. H. Briscoe {Heating and Ventilating, June 1950). 8 Elements of Ultrasonics; by S. Young White (Audio Engineering, February, 1948). '" BIBLIOGRAPHY . . Design, and Applicatipn of Oil-Coated Air Filters; by H. C. Murphy (A.S.H.V.E. Transactions, Vol. .33, 1927, p. 73). . :' Operation and Maintenance ;of Air, Filters, by W. G- Frank. {Heating, Piping and Air Conditioning, May, 1931; p. 378).. , i Size and Characteristics of Air-Borne Impurities, .by W. G. Frank (Heating, Piping and.Air Conditioning, January, 1932, p., 35): , <.' Fundamental^ Principles in the Design, of Dry Air Filters, by Otto Wechsberg (A.S.H.V.E. Journal Section, -Healing, Piping and Air Conditioning, April, 1933,' P- 217). .- ,. . _ ' ;- The Economic Factors in Converting Recirculated.Air for Ventilation, by H..E. Ziel and Henry Sleik (A.S.H.V.E. Journal Section, Heating, Piping and Air Condi tioning, July, 1943, p. 367). Operation, Maintenance of Cloth-Screened Dust Collectors, by W. F. Terry (Heal ing, Piping and Air Conditioning, May, p. 259, June, p. 304, 1933). Testing and Rating of Air Cleaning Devices Used in General Ventilation Work, by Samuel R. Lewis (A.S.H.V.E. Transactions, Vol. 39, 1933, p. 277). A.S.H.V.E. Research Report No. 1094--Air Filter Performance as Affected by Kind of Dust, Rate of Dust Feed, and Air Velocity Through Filter, by F. B. Rowley and R. C. Jordan (A.S.H.V.E. Transactions, Vol. 44,1938, p. 415). A.S.H.V.E. Research Report No. 1122--Air Filter Performance as Affected by Low Rate of Dust Feed, Various Types of Carbon, and Dust Particle Size and Den sity, by F. B. Rowley and R. C. Jordan (A.S.H.V.E. Transactions, Vol. 45, 1939, p. 339). A.S.H.V.E. Research Report No. 1145--The Effect of Lint on Air Filter Perform ance, by F. B. Rowley and R. C. Jordan (A.S.H.V.E. Transactions, Vol. 46, 1940, p. 25). A.S.H.V.E. Research Report No. 1169--Comparison of the Weight, Particle