Ejector Performance in Refrigeration Systems

Ejector-based refrigeration systems employ a jet-pump principle to recover expansion work and drive secondary refrigerant flow without mechanical compressors. By converting a high-pressure motive fluid into a high-velocity jet in a converging–diverging nozzle, ejectors entrain cold vapour from the evaporator, compress it and deliver it to the condenser. This passive, single- or two-phase device can exploit waste heat, solar thermal energy or low-grade heat sources, offering a compact, low-noise alternative to conventional vapour-compression cycles. Performance is typically gauged by the entrainment ratio, critical back pressure and overall system coefficient of performance (COP). Recent advances have addressed challenges such as inefficiencies under off-design conditions, complex phase-change phenomena in CO₂ and steam ejectors, and the need for low-global-warming-potential refrigerants. Optimisation of geometry, novel materials and advanced computational methods have yielded significant gains in energy efficiency and operational flexibility. These developments hold promise for sustainable cooling in data centres, district heating integration and solar-driven air-conditioning, contributing to global efforts to reduce greenhouse-gas emissions in the refrigeration sector.

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Ejector Performance in Refrigeration Systems publication trend

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Technical terms

Entrainment ratio: The mass flow rate of secondary (entrained) fluid divided by the mass flow rate of primary (motive) fluid in an ejector system.

Coefficient of performance (COP): The ratio of useful cooling (or heating) output to the energy input required to drive a refrigeration or heat-pump cycle.

Two-phase flow: The simultaneous flow of liquid and vapour phases within the ejector mixing chamber, where interactions between phases affect momentum exchange and condensation processes.

Variable geometry ejector (VGE): An ejector design featuring adjustable internal geometry—such as nozzle exit position and throat area—to optimise performance under varying operating conditions.

Exergy destruction: A measure of irreversibilities or lost useful work potential within a thermodynamic process, used to quantify performance losses in refrigeration components.

References

1. A detailed review on CO 2 two-phase ejector flow modeling. Thermal Science and Engineering Progress (2020).
2. Energy, exergy, and environmental (3E) analysis of a compound ejector-heat pump with low GWP refrigerants for simultaneous data center cooling and district heating. International Journal of Refrigeration (2022).
3. Applying a variable geometry ejector in a solar ejector refrigeration system. International Journal of Refrigeration (2020).
4. Effect of area ratio of the primary nozzle on steam ejector performance considering nonequilibrium condensations. Energy (2021).