Hermetic compressor

Using other criteria, compressors are classified as open, semiher-metic accessible), or hermetic. Open type is characterized by shaft extension out of compressor where it is coupled to the driving motor. When the electric motor is in the same housing with the compressor mechanism, it could be either hermetic or accessible (semihermetic). Hermetic compressors have welded enclosures, not designed to be repaired, and are generally manufac tured for smaller capacities (sel-... 

Those lubricants marked M easily absorb moisture and great care must be taken to prevent exposure to air when adding new oil. The moisture in the air will be absorbed into the oil and will lead to contamination of both refrigerant and oil. With hermetic compressors this can lead to motor winding failure. 

There is a need for small compressors to be driven from low-voltage d.c. supplies. Typical cases are batteries on small boats and mobile homes, where these do not have a mains voltage alternator. It is also possible to obtain such a supply from a bank of solar cells. This requirement has been met in the past by diaphragm compressors driven by a crank and piston rod from a d.c. motor, or by vibrating solenoids. The advent of suitable electronic devices has made it possible to obtain the mains voltage a.c. supply for hermetic compressors from low-voltage d.c. 

Figure 4.11 (a) Semi-hermetic compressor (Courtesy of Dunham-... 

Centrifugal machines can be built for industrial use with ammonia and other refrigerants, and these mayhave up to seven compression stages. With the high tip speeds in use, it is not practical to build a small machine, and the smallest available centrifugal compressor for refrigeration dutyhas a capacityof some 260 kW. Semi-hermetic compressors are made up to 7000 kW and open drive machines up to 21 000 kW capacity. 

For hermetic and semi-hermetic compressors, it must have a high dielectric strength. 

Moisture in halocarbon circuits will be indicated by the colour trace on the sight glass, where this is fitted. Immediate action is required, especially with a hermetic or semi-hermetic compressor, before damage is caused. The drier should be changed and the... 

Example 35.3 A hermetic compressor is rated at 18.2 kW for R.22 when evaporating at 7°C, suction superheated to 35°C, condensing at 54°C, and with 8 K suhcooling of the liquid. Assuming that the inlet gas picks up another 30 K as it passes over the compressor motor, estimate the change in capacity if the suction is superheated to 12°C. 

HERMETIC COMPRESSOR - Compressor which has the driving motor sealed inside the compressor housing. The motor operates in an atmosphere of the refrigerant. 

The first hermetic compressor was invented by a French Abbot, Abbe Audiffren, in 1905 and manufactured by Singrun at Epinal, also in France. Later manufactured by major refrigeration companies, the machine, shown schematically in Figure 1.13, had many innovative features (Cooper, 1990). A sphere formed the condenser and an oval-shaped cylindrical vessel the evaporator, these were connected by a hollow shaft and the whole assembly was rotated by a belt drive. SO2 was the working fluid. 

For the actual systems, compressor work will be higher than for ideal for the isentropic efficiency and other losses. In the case of hermetic or accessible compressors where an elec trical motor is cooled by the refrigerant, condenser capacity should be ... 

It is common that compressor manufacturers provide data for the ratio of the heat rejected at the condenser to the refrigeration capacity as shown in Fig. 11-89. The solid line represents data for the open compressors while the dotted hne represents the hermetic and accessible compresors. The difference between sohd and dotted line is due to all losses (mechanical and elec trical in the electrical motor). Condenser design is based on the value ... 

Commercial refrigeration - Alternatives to CFCs for new commercial refrigeration equipment include HCFCs (including HCFC mixtures) and HFCs and HFC mixtures. Retrofit of existing equipment is possible by using both HCFCs and HFCs, in conjunction with reduced charges and more efficient compressors. Hydrocarbons are, to a limited extent, applied in hermetically sealed systems. 

Small compressors will have motor overheat protection adjacent to the hermetic shell or built into the winding (see Section 4.8) and larger motors will have contactor-starters with overcurrent devices. Overheat protection is also fitted on many machines, to guard against high motor winding, cylinder head or oil temperatures. These usually take the form of thermistor detectors, connected to stop the motor. 

Manufacturer four Danfoss hermetic scroll compressor rated power of electric motor... 

Vane compressors are used in small, hermetic units, but sometimes as booster compressors in industrial applications. Two basic types are fixed (roller) or single-vane type and the rotating or multiple-vane type. In the single-vane type the rotor (called roller) is eccentrically... 

Vane compressors are used in small, hermetic units, but sometimes as booster compressors in industrial applications. Two basic types are... 

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