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Comparison of various motive flow control methods to implement capacity modulation in HVAC&R systems using two-phase ejectors.

Number: pap. F16

Author(s) : ELBEL S., LAWRENCE N., ZHU J.

Summary

Recent studies have shown that expansion work recovery by use of a two-phase ejector offers significant opportunity for improving the COP of HVAC&R systems, especially for transcritical CO2 systems. Nevertheless, consistent system efficiency improvements across a wide range of operating conditions require adjustment of the motive nozzle geometry to modulate mass flow rate and control high-side pressure. There are various ways of implementing motive nozzles with adjustable restrictiveness that can compensate for different ambient conditions or varying evaporator load. The methods considered in this paper are a needle control mechanism to change the effective cross-sectional area of the throat of the CD nozzle, and the use of parallel, fixed-geometry ejectors that can be activated with shut-off valves. A low-cost ejector control option is also presented. That option allows capacity modulation through the use of a conventional expansion valve that can be used in series or in parallel with a fixed-geometry ejector. Finally, a novel method called vortex flow control is introduced that allows variation of nozzle restrictiveness without variation of physical nozzle geometries. In this case, the capacity modulation effect could be achieved by varying the ratio of axial to tangential flow mass flow rates entering the motive nozzle. This paper describes and compares the different nozzle control mechanisms. Experimental data are presented to compare the various concepts.

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Pages: 12

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Details

  • Original title: Comparison of various motive flow control methods to implement capacity modulation in HVAC&R systems using two-phase ejectors.
  • Record ID : 30022108
  • Languages: English
  • Source: 8th international conference on compressors and refrigeration, 2017.
  • Publication date: 2017/07/20

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