Thermocompressors Fixed nozzle

Thermocompressors can be of two basic types fixed nozzle types or units with a reguiating spindle. Fixed-nozzle thermocompressors are more efficieni and are used when the thermocompressor can be operated under steady-loac conditions. Thermocompressors with regulating spindles are designed for use when performance approaches critical conditions and changes in suction loac and suction and discharge pressures are expected. 

The prime advantage of a single fixed-nozzle thermocompressor is its compactness. Single nozzle units are preferred when large compression ratios are required. Single nozzle units are used for small capacity application and when several parallel units are needed to provide some degree of control. 

For spindle operated thermocompressors, shown in Figure 18-2(b), the nozzle design is quite different from that of fixed nozzle units. The nozzle and spindle assembly combines a rounded entrance orifice with a straight section into which a tapered spindle is guided. Operation is much like that of a needle valve. The length of the spindle travel is based upon the design requirements. 

The construction of a multiple-nozzle fixed-orifice thermocompressor is the same as that of the single nozzle unit, except that it employs several steam nozzles as shown In Figure 18-2(c). The usuai configuration has one nozzle on center with the remaining nozzles equally spaced peripherally around it. This type of unit can be used for both critical and noncritical applications. Its characteristic performance curve is similar to that of a single nozzle fixed orifice unit. 

Figure 18-5 and Figure 18-6 show typical capacity rates and sizing curves for fixed multiple nozzle and regulating spindle thermocompressors, with steam as both motive and suction fluids. These curves should be used to approximate thermocompressor size and performance. The ectual efficiency can vary with the size of the thermocompressor, the control variability, the system, and the manufacturer. 

Figure 18-7 can be used to estimate the purchase cost for fixed-multiple-nozzle and automatically-controlled-spindle thermocompressors. 

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