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DIEF Dipartimento di Ingegneria Industriale

Supersonic Ejectors

           Ejector Prototype                                                                                                                                                                                                              

Supersonic Ejectors are passive compression devices that can be employed for a range of applications, from aeronautic high-speed propulsion systems, to nuclear reactor cooling, pumping of volatile fluids in power plants and compression of working fluid in refrigeration systems.

In particular, the use of ejectors in refrigeration applications discloses promising alternatives to standard vapor compression and absorption cycles. These alternatives constitute the subject of our research.



Check out our new book on Ejector Refrigeration!!!





1 – Development of a Supersonic Ejector Cycle working with Refrigerants, REC:

Scope and Goals: 

The aim is to develop and optimize a standard supersonic ejector cycle for industrial use. The system may operate on waste heat and solar power resources. The low production costs, simplicity and high reliability of the system may represent competitive features with respect to standard vapour compression and absorption systems.


Status of research and critical aspects:

Currently, a test bench of 40kW of cooling power is running at our laboratories. The plant was built in collaboration with Frigel S.p.a. (Scandicci, Italy) and its COP has reached 0.5. An optimization of the supersonic ejector design is required to increase the cycle efficiency and condensing temperature. Passive configurations are also attempted by substitution of the pump by means of injectors. Training periods within Frigel are available. In addition, possible partners on this research field may be Georgia-Tech (USA) and Politecnico of Milano (Italy).


Future research and thesis proposals:

a) Tests of new refrigerants inside the plant. Experimental and CFD analysis of alternative refrigerants on the existing geometry (BT, MT). Design of a new ejector profile suitable to the refrigerant properties (BT, MT).

b) Installation of injector to substitute centrifugal pump. Literature research on the method to design two-phase injector (BT). Selection of a proper design method, construction of the injector and experimental tests (MT). CFD analysis of the injector (MT, DT).

c) Optimization of the supersonic ejector profile. Entropy generation analysis using CFD (MT). Development of a theoretical 1D model of the supersonic ejector to give a first approximated profile (MT). Detailed numerical optimization by means of CFD analysis coupled with a suitable optimization algorithm (MT, DT).

Ejector Chiller Prototype - 40kW cooling power


Relevant publications:


  • F. Mazzelli, F. Giacomelli, A. Milazzo, CFD modelling of the condensation inside a Supersonic Nozzle: implementing customized wet-steam model in commercial codes, Energy Procedia, 2017

  • F. Giacomelli, F. Mazzelli, A. Milazzo, CFD modelling of the condensation inside a cascade of steam turbine blades: comparison with an experimental test case, Energy Procedia 126, 730-737, 2017
  • F. Mazzelli, A. Milazzo, CFD modeling of single-phase supersonic ejectors, Heat Powered Cycle Conference, June 26th – 29th, 2016, Nottingham, UK

  • Milazzo, A., Mazzelli, F., 2016. Ejector Chillers for Solar Cooling, in: Renewable Energy in the Service of Mankind Vol II, Springer
  • G. Grazzini, F. Mazzelli, A. Milazzo, Constructal design of the mixing zone inside a supersonic ejector, International Journal of Heat and Technology, Volume 34 (2016), Special Issue 1, pp. S109-S118
  • Mazzelli, F., Milazzo, A., 2015. Performance analysis of a supersonic ejector cycle working with R245fa. Int. J. Refrigeration 49, 79-92
  • Eames, I.W., Milazzo, A., Paganini, D., Livi, M., 2013. The design, manufacture and testing of a jet-pump chiller for air conditioning and industrial application. Appl. Therm. Eng. 58, 234-240
  • Grazzini, G., Milazzo, A., Paganini, D., 2012. Design of an ejector cycle refrigeration system, Energy Conversion and Management 54, 38-46



2 – Development of a Steam Ejector Cycle, StEC:

Condensing Isentropic Expansion

Scope and Goals: 

The aim is to build a new supersonic ejector cycle working with steam.

The system can operate with solar energy or waste heat from industrial applications. 

The absence of turbomachinery and the use of water makes the system extremely cheap, simple and reliable. These features may be ideally suited for use in developing countries.

Status of research and critical aspects:

Of importance in this research is the development of reliable numerical tools. In this respect, the prediction and analysis of the condensation shocks is a complex but fundamental aspect.

Furthermore, the description of the steam properties in metastable regions and the prediction of ice formation are critical for the correct operation of the system. Partner of this research are the Université Catholique de Louvain (Belgium) as well as the Ural Federal University (Russia).Exchange programs and International PhD degree are available.


Future research and thesis proposals:

a) Construction of a new Steam Ejector Cycle inside the ICE-Lab. Project and sizing of the main components of the system as well as the measurement apparatus (MT). Design of the Two-Phase steam ejector by testing and comparison of various design techniques (BT, MT). Study of the possibility of removing the pump by use of a steam injector to feed the generator (MT, DT).

b) CFD analysis of the supersonic steam ejector. Literature research on the modelling of condensation shocks and prediction of ice formation (BT). Extension of the steam property libraries inside the meta-stable region (MT). CFD analysis of various ejector profiles (BT, MT).


Relevant publications:

  • F. Giacomelli, F. Mazzelli and A. Milazzo, CFD Modeling of High-Speed Condensation in Supersonic Nozzles, Part I: Steam, 4th Thermacomp Conference, June 6th – 8th, 2016, Atlanta, U.S.A.
  • G. Biferi, F. Mazzelli, A.B. Little, S. Garimella, Y. Bartosiewicz, CFD Modeling of High-Speed Condensation in Supersonic Nozzles, Part II: R134a, 4th Thermacomp Conference, June 6th – 8th, 2016, Atlanta, U.S.A.
  • F. Mazzelli, D. Brezgin, I. Murmanskii, N. Zhelonkin, A. Milazzo, Condensation in supersonic steam ejectors: comparison of theoretical and numerical models, 9th International Conference on Multiphase Flow, May 22nd - 27th, 2016, Firenze, Italy.
  • Milazzo, A., Rocchetti, A., 2015. Modelling of ejector chillers with steam and other working fluids. International Journal of Refrigeration, 57, 277-287
  • Milazzo, A., Rocchetti, A., Eames, I.W., 2014. Theoretical and experimental activity on Ejector Refrigeration. Energy Procedia, 45, 1245 – 1254
  • Grazzini, G., Milazzo, A., Piazzini, S., 2011. Prediction of condensation in steam ejector for a refrigeration system, International Journal of Refrigeration 34, 1641-1648.
  • Grazzini G., Rocchetti A., 2008. Influence of the objective function on the optimisation of a steam ejector cycle, International Journal of Refrigeration 31, 510-515
  • Grazzini, G., Rocchetti, A., 2002. Numerical optimisation of a two-stage ejector refrigeration plant, International Journal of Refrigeration 25, 621-633.




3 – Development of an Ejector Expansion Cycles, EEC

Goals and Scope: 

The aim of this research is to exploit the simplicity and reliability of supersonic ejector to replace the expansion valve without recurring to complex rotary and turbo-machinery solutions.

The recover of expansion losses inside conventional refrigeration systems can lead to COP increase of the order of 5 to 20% depending on the specific application and refrigerant. This may produce a substantial impact if applied on a worldwide scale.

Partners in this research are Frigel S.p.a. (Firenze) and Université Catholique de Louvain (Prof. Bartosiewicz, Belgium). In addition, collaborations may be found with Dorin Compressori (Firenze) and REASE research group (Prof. Ferrara, Unifi).


Status of research and critical aspects:

Currently, the group has a research contract with Frigel Spa (Italy) to study the use of ejectors on a train of compression chillers working with R410a. Thermo Group will conduct both CFD simulations of the flash expansion ejector as well as experiments on the complete refrigeration system.

Past research activity in this field has mostly concentrated on a CFD modeling approach. An Homogeneous Equilibrium Model (HEM) for a commercial CFD code has been developed for this purpose with fluid properties of carbon-dioxide taken from REFPROP database.

The most critical aspect of this activity is the lack of detailed experimental data for the tuning of numerical models. Moreover, numerical difficulties are connected to the modeling of flow at supersonic speed with phase change. 

Density map of CO2 in the supercritcal and Two-Phase region

Future research and thesis proposals:

a) Experimental and Numerical activity on the flashing of synthetic refrigerants inside an ejector expansion cycle working with R410a. This work is partly financed by Frigel S.p.a. (BT, MT). Literature research on design procedures for the ejector (BT). Design, construction and tests of the supersonic flashing ejector (MT).

b) CFD analysis of the two-phase flashing flow inside the ejector. Literature research on the physics and models of the high speed cavitation and related fields, like supersonic propulsion (BT, MT). Development of new numerical procedure by means of open source software, like OpenFoam or dedicated software from aerospace research (MT, DT).


Relevant publications:

  • Giacomelli F, Mazzelli F, Milazzo A, Evaporation in supersonic CO2 ejector: analysis of theoretical and numerical models, International Conference of Multiphase Flow, Firenze, May 2016
  • A. Milazzo, F. Mazzelli, Future perspective in ejector refrigeration, Heat Powered Cycle Conference, June 26th – 29th, 2016, Nottingham, UK.



** BT – bachelor thesis,  MT – master thesis,  DT – doctoral thesis

ultimo aggiornamento: 20-Apr-2018
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