Surface-cooled motors

Free circulation of the coolant from the machine to the surrounding medium 0 Free convection No external power source is essential. Fleat dissipation is achieved through natural convection like a surface cooled motor... 

Figure 7.10 Approximate output of a surface-cooled motor...

Table 7.2 Approximate output of surface cooled motors...

Textile motors Crane motors Determining the size of motor Sugar centrifuge motors Motors for deep-well pumps Motors for agricultural application Surface-cooled motors Torque motors or actuator motors Vibration and noise level Service factors Motors for hazardous locations Specification of motors for Zone 0 locations Specification of motors for Zone I locations Motors for Zone 2 locations Motors for mines, collieries and quarries Intrinsically safe circuits, type Ex. f Testing and certifying authorities Additional requirements for ciritical installations Motors for thermal power station auxiliaries Selection of a special-purpose motor... 

Caution needs to be taken with local pressure variations of the environmental atmosphere. A well-known example is the outlet side of an external cooling fan of a surface-cooled motor or generator (see Fig. 6.15). At this point, the environmental potentially explosive atmosphere shows an increased pressure, which shall be overcompensated by an adequate internal overpressure. The p-standards ask for a minimum overpressure of 50 Pa (=0.5mbar) for Group I p-apparatus or Group II p-apparatus in zone 1. 

Frame surface cooled (using the surrounding medium) The primary coolant is circulated in a closed circuit and dissipates heat to the secondary ccxilant. which is the surrounding medium in contact with the outside surface of the machine. The surface may be smooth or ribbed, to improve on heat transfer efficiency (as, in a TEFC or tube venulated motor (Figures 1.19 and 1.20) 4 ... 

Figure 7.1(a) Surface cooled loom motor, without fins... 

In addition to fan speed, the operating temperature of the motor is determined by how effectively the heat generated in the motor can be conducted to surfaces that are in contact with the cooling medium (generally air) and the ability to transfer this heat via convection to the cooling medium. In a conventional totally enclosed fan-cooled motor the heat must be transferred from the laminated steel... 

Vo/r SPDP motors also have a cooling fan bul their surface is plain, whereas TEFC motors have fins on their housings that add to their cooling surface. Refer to Figures I.l8(a)-(c) and 1.19(a)and (b). 

A form of cooling, and the one of prime interest, concerns ablative cooling. It is essentially a heat and mass transfer process in which mass is expended to achieve thermal dissipation, absorption, and blocking. The process is passive in nature, serves to control the surface temperature, and greatly restricts the flow of heat into the material substrate. As a result of these desirable attributes, ablative cooling (includes use of plastic compositions) has been widely used for thermal protection of solid propellant motors and less extensively in liquid propellant motors. 

Air-moled h.Mlamxir—As used in the petroleum industry, air-cooled exchangers normally comprise two headers joined h> a horizontal bank ol tinned tubes. Usually two motor-driven fans located above (induced dralii or below (forced draft) the tubes are used lo circulate the air over the tinned surface. 

Molybdenum disulfide is dispersed in greases and oils for lubrication in volatile carriers it is used to form dry coatings of lubricant. Sodium molybdate is an especially effective corrosion inhibitor on aluminum surfaces and is dissolved in cooling solutions to protect aluminum motor blocks in automobiles. 

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