Fans, Ventilation and Heating

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Read Books, 2008 - Education - 52 pages
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CONTENTS Centrifugal and Disk Fans - - - - . - 3 Heaters for Hot Blast and Ventilation - 25 Heating and Ventilating Machine Shops - - 39 Copjrigbt, 1010, The Industrlal Press, Publishers of Nrcn xxar, 49-55 LaLayette Street, Sew Tork City CHAPTER I CENTRIFUGAL AND DISK FANS Tbere are ta-o types of fans in common use, known as the centrifugal fan or blower, and the disk fan or propelier. The former consists of a number of straight or slightly curved blades extending radIalIy from an axis as shown in Fig. 1. When the fan is in motion, the air in contact with the blades is thrown outward by the action of centrifugal force and delivered at the outer circumference or periphery of the wheel. A gartial vacuum is thus produced at the center of the wheel, and air from the outside flows in to take the place of that which has been discharged. Ffg. 3 illustrates the action of a centrifu gal fan, the arrows showing the path of the air. This type of fan is usually enclosed in a steel plate casing of such form as to provide Fig. 1. Centnfvffal Fan Flg. 2. Cestrlmgal Fan n C d a s h for the free movement of the air as it escapes from the periphery of the wheel. An opening in the circumference of the casing serves as, an outlet into the distributing ducts which carry the air to the various rooms to be ventilated, or to the furnaces in the case of mechanical draft. h fan with casing is shown in Fig. 2. The discharge opening can be placed in any position desired, either up, down, top horizontal, bottom horizontal, or at any angIe. Where the height of the fan room is limited, a form called the threequarter housing may be used, in which the I o e r p art of the casing is replaced by a brick pit belowMICHISEBT, October, Sorcrnber and December, 1903. the floor level see Fig. 4. Another form of the centrifugal fail is shown in Fig 6. This is known as the cone fan and Is commonly placed in an opening in a brick wall and discharges alr from its entire periphery into a room called a plenum chamber with which the various distributing ducts connect. This fan is often made double by placing two wheels back to back and surrounding them with a steel casing in a similar manner to the one shown in Fig. 2. Cone fans are very efficient and are capable of moving large quantities of air at moderate sDeeds. Fig. 5 show a form of smalI directconnected exhauster colamonly used for ventilating toilet rooms, chemical hoods, etc., and for furnishing a forced draft for forges and small boilers. Centrifugal fans are used almost exclusively for sup- - G w l 3 r, x . r . Flg. S. Direction of Flaw in Centrlfigal Fen plying air for the ventilation of buildings, for forced blast heating and for mechanical draft. They are also used as exhausters for rernov-Ing the air from buildings when the resistance is considerable and the quantity of air to be handled is large. Tle disk fan is similar in construction to the propeller of a vessel and moves the air in lines parallel to its axis. This fan is made In various forms wfth both flat and curved bIades. Fig. 7 shows one of the various designs arranged either for belted or direct-connected motor. This type of fan is light in construction, requires but little poser at low speeds and is easily erected. Zt is especially adapted to exhaust ventilation when the resistance is, small, being conveniently placed in the attic or upper part of a building and driven by an electric motor. Disk fans are Iargely used for the ventilation of public a toilet rooms, smoking rooms, restaurants, etc....

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