Abstract
The selection of refrigerants for ejector refrigeration systems, within the broader discussion concerning refrigerant phase-out, is a cutting-edge and challenging research topic, owing to the multi-scale challenges in ejector performance. Indeed, it is known that the performances of ejector refrigeration systems depend on the local flow phenomena. For this reason, a precise selection of the refrigerant relies on the understanding of the fluid dynamic phenomena at the “componentscale”, and integrate such information within the so-called “system-scale”. This paper contributes to the current discussion proposing a screening of refrigerants based on an integrated Computational Fluid Dynamic (CFD) Lumped Parameter Model (LPM) approach. In this approach, ejector performances for the different refrigerant are obtained by a validated CFD approach, whereas the cycle is modelled by a Lumped Parameter Model. For the different refrigerants, the energy performances of the systems are evaluated and the effects of the “component-scale” on the “system-scale” are analysed.
Highlights
Ejector device is a static component, where an high-pressure stream (“primary flow”) accelerates till sonic/supersonic condition while flowing into a converging/convergingdiverging nozzle and, subsequently, expands into a mixing chamber while entraining a lowpressure stream (“secondary flow”); the primary and the secondary flows mix and are compressed in a diffuser [1]
This paper contributes to the current discussion proposing a screening of refrigerants based on an integrated Computational Fluid Dynamic (CFD) Lumped Parameter Model (LPM) approach
Ejector performances for the different refrigerant are obtained by a validated CFD approach, whereas the cycle is modelled by a Lumped Parameter Model
Summary
Ejector device is a static component, where an high-pressure stream (“primary flow”) accelerates till sonic/supersonic condition while flowing into a converging/convergingdiverging nozzle and, subsequently, expands into a mixing chamber while entraining a lowpressure stream (“secondary flow”); the primary and the secondary flows mix and are compressed in a diffuser [1]. For the sake of clarity, a discussion regarding ejector-component performance is proposed, based on the ejector operating curve (Figure 1b – note that Figure 1b is valid under the assumption of T3 in saturation conditions), which displays the relationship between the entrainment ratio (ω, Eq (1)) and the outlet boundary conditions (saturation T3). In on-design operation mode, ω is constant, as the primary and the secondary flows are in supersonic conditions [2]; when the outlet conditions reaches a critical point (T3 = Tcrit), the secondary flow is no more chocked, and ω decreases while T3 increases
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