Multistage system include more than one compressor to raise steam pressure in the low temperature of the evaporator for condensing pressure to improve their performance. The capacity and efficiency of the refrigeration system quickly diminish as the difference between the suction and condensing temperature rises. These reductions as a result of die properties of refrigerants at low temperatures. As the temperature of the evaporator reduces the refrigerant vapour density is reduced, producing a large nonlinear increase in its specific volume. Thus, the volume occupied by each unit mass of the refrigerant increases the capacity of the compressor is reduced. Reduce the vapor pressure of low-temperature systems also increases the compression ratio, which raises the temperature of the discharge die units.
Conventional single-stage systems give satisfactory results with evaporator temperatures up 40F (40C) provided that their condensation temperatures are low. For evaporator temperatures below -40 F (-40C), some forms of multi-stage compression should be applied in order to prevent excessive discharge temperature and maintain a reasonable operating efficiency.
Multistage operation should also be considered to increase the capacity of the system, having evaporator temperatures below 0F (17.8C) to improve their effectiveness.
Multi-stage compression can be grouped into two categories, direct the formulation and the cascade of production. Direct the staging method uses two or more compressors piped in series with each other. In this layout, the extracts from the previous stage of the compressor enters the suction of the next stage compressor. This strategy reduces the degree of compression requires an individual compressors, which in turn increases productivity and efficiency in the work of subdivisions. The block diagram in three stages, in the direct setting of the system. In this scheme, I refrigerant vapor rose from the pressure evaporator in the condenser pressure in step three. Please note that there is only one evaporator and one capacitor in direct setting of the system.
Cascade staging involves the use of two or more independent refrigeration circuits, which are thermally connected by cascading condenser heat exchanger. Cascade condenser is used to die evaporator one step above for cooling gases in the condenser of the next stage. Each Shulbinskaya system uses refrigerant having to gradually reduce the boiling point. In this design, the compressed refrigerant vapor from the lower stage is condensed in a cascade capacitor. This component also serves as the evaporator to the next higher stage.
Both methods multistaging have relative advantages and disadvantages. In particular, the method that will produce the best results in the given application depends on the performance requirements, low temperature, which should be saved. In some cases, the combination of die cascade and direct the formulation of methods can be used to advantage for using the system exclusively. In these cases, compression components (direct formulation) is applied, as a rule, at the bottom of the higher step of cascade...