Document Edr6meJgJK71wkD5REyXJ8joL

HEATING VENTILATING AIR CONDITIONING CUIDE 1942 Operation, Maintenance of Cloth-Screened Dust Collectors, by W. F. Terry (Heating, 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 Density,' 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). A.S.H.V.E. Research Paper--Comparison of the Weight, Particle Count and Dis coloration Methods of Testing Air Filters, by F. B. Rowley and R. C. Jordan (A.S.H.V.E. Journal Section, Heating, Piping and Air Conditioning, April, 1941, p. 246). A.S.H.V.E. Research Paper--Economical Air Velocities for Mechanical Air Filtra tion, by F. B. Rowley and R. C. Jordan (A.S.H.V.E. Journal Section, Heating, Piping and Atr Conditioning, August, 1941, p. 524). The Dust-Free Space Surrounding Hot Bodies, by H. H. Watson (Transactions of the Faraday Society, Vol. 32, 1936, Pt. 2, p. 1073). A New Electrostatic Precipitator, by G. W. Penney (Electrical Engineering, January, 1937, p. 159). 580 Chapter 30 FANS Classification, Performance, Fan Efficiency, Characteristic Curves, System Characteristics, Selection of Fans, Fan Designations, Control, Motive Power IN heating and ventilating practice, fans are used to produce air flow except where positive displacement is required, in which case com pressors or rotary blowers are used. All fans or blowers are classified according to the direction of air flow through the fan with relation to the axis of rotation and are either of the (1) axial flow or propeller type, in which the flow is parallel to the axis or (2) radial flow or centrifugal type, in which the flow is parallel to the radius of rotation. Axial flow fans are made with various numbers of blades, the latter varying widely in form. The blades may be of uniform thickness and made of cast or sheet metal, and either flat or cambered or of screw form; or they may vary in thickness, in the latter case usually being designed to conform to so-called airfoil sections of known characteristics, similar to those which have been developed for airplane propellers. Likewise, blade angle, or the angular relation of the blades to the plane of rotation, varies over a wide range. For operation against comparatively high pressures, it is customary to resort to enlarged hubs in proportion to fan diameter (large hub ratio) and correspondingly short blade length. The term disc fan has sometimes been loosely applied to such large hub fans, though it has long been generally used in connection with any propeller fan of comparatively short axial length whose blades are relatively flat; in other words, for fan wheels which occupy a space which is more or less disc-shaped. Radial flow or centrifugal fans include steel plate fans, pressure blowers, cone fans, and the so-called multiblade fans. All the foregoing types have variations which may be obtained by modification of the proportions or change in the curvature and angularity of the blades. The angularity of the blades determines the operating characteristics of a fan; a forward curved blade is found in a fan having slow speed operating characteristics, while a backward curved blade is found in a fan having high speed operating characteristics. A wide variation exists in the demands which have to be met by fan installations. A fan may be required to move large quantities of air against little or no resistance or it may be required to move small quanti ties against high resistances. Between these two extremes innumerable specific requirements must be met. In general, fans of all types in each 581