Effect of Assumptions of Normal Shock Location on the Design of Supersonic Ejectors for Refrigeration
The complex oblique shock phenomenon can be simply assumed as a normal shock at the constant area section to simulate a sharp pressure increase and velocity decrease in 1-D thermodynamic models. The assumed normal shock location is one of the greatest sources of error in ejector thermodynamic models. Most researchers consider an arbitrary location without justifying it. Our study compares the effect of normal shock place on ejector dimensions in 1-D models. To this aim, two different ejector experimental test benches, a constant area-mixing ejector (CAM) and a constant pressure-mixing (CPM) are considered, with different known geometries, operating conditions and working fluids (R245fa, R141b). In the first step, in order to evaluate the real value of the efficiencies in the different ejector parts and critical back pressure, a CFD model was built and validated by experimental data for two types of ejectors. These reference data are then used as input to the 1D model to calculate the lengths and the diameters of the ejectors. Afterwards, the design output geometry calculated by the 1D model is compared directly with the corresponding experimental geometry. It was found that there is a good agreement between the ejector dimensions obtained by the 1D model, for both CAM and CPM, with experimental ejector data. Furthermore, it is shown that normal shock place affects only the constant area length as it is proven that the inlet normal shock assumption results in more accurate length. Taking into account previous 1D models, the results suggest the use of the assumed normal shock location at the inlet of the constant area duct to design the supersonic ejectors.
Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1316049Procedia APA BibTeX Chicago EndNote Harvard JSON MLA RIS XML ISO 690 PDF Downloads 559
 K. Cizungu, M. Groll, and Z. G. Ling, “Modelling and optimization of two-phase ejectors for cooling systems,” Appl. Therm. Eng., vol. 25, no. 13, pp. 1979–1994, 2005.
 C. Vereda, R. Ventas, A. Lecuona, and M. Venegas, “Study of an ejector-absorption refrigeration cycle with an adaptable ejector nozzle for different working conditions,” Appl. Energy, vol. 97, pp. 305–312, 2012.
 S. Elbel and P. Hrnjak, “Experimental validation of a prototype ejector designed to reduce throttling losses encountered in transcritical R744 system operation,” Int. J. Refrig., vol. 31, no. 3, pp. 411–422, 2008.
 K. Banasiak, A. Hafner, and T. Andresen, “Experimental and numerical investigation of the influence of the two-phase ejector geometry on the performance of the R744 heat pump,” Int. J. Refrig., vol. 35, no. 6, pp. 1617–1625, 2012.
 M. Nakagawa, A. R. Marasigan, T. Matsukawa, and A. Kurashina, “Experimental investigation on the effect of mixing length on the performance of two-phase ejector for CO 2 refrigeration cycle with and without heat exchanger,” Int. J. Refrig., vol. 34, no. 7, pp. 1604–1613, 2011.
 J. Chen, H. Havtun, and B. Palm, “Parametric analysis of ejector working characteristics in the refrigeration system,” Appl. Therm. Eng., vol. 69, no. 1, pp. 130–142, 2014.
 B. Gil and J. Kasperski, “Efficiency analysis of alternative refrigerants for ejector cooling cycles,” Energy Convers. Manag., vol. 94, pp. 12–18, 2015.
 S. Elbel and N. Lawrence, “Review of recent developments in advanced ejector technology,” Int. J. Refrig., vol. 62, pp. 1–18, 2016.
 J. Bao, Y. Lin, and G. He, “Working fluids comparison and thermodynamic analysis of a transcritical power and ejector refrigeration cycle (TPERC),” Int. J. Refrig., 2017.
 J. Lee, C. Lee, S. Baek, and S. Jeong, “Investigation of ejector-equipped Joule–Thomson refrigerator operating below 77 K,” Int. J. Refrig., vol. 78, pp. 93–107, 2017.
 Z. Ma, H. Bao, and A. P. Roskilly, “Thermodynamic modelling and parameter determination of ejector for ejection refrigeration systems,” Int. J. Refrig., vol. 75, pp. 117–128, 2017.
 G. Besagni, R. Mereu, F. Inzoli, and P. Chiesa, “Application of an integrated lumped parameter-CFD approach to evaluate the ejector-driven anode recirculation in a PEM fuel cell system,” Appl. Therm. Eng., vol. 121, pp. 628–651, 2017.
 M. Khennich, N. Galanis, and M. Sorin, “Effects of design conditions and irreversibilities on the dimensions of ejectors in refrigeration systems,” Appl. Energy, vol. 179, pp. 1020–1031, 2016.
 B. J. Huang, J. M. Chang, C. P. Wang, and V. A. Petrenko, “A 1-D analysis of ejector performance,” Int. J. Refrig., vol. 22, no. 5, pp. 354–364, 1999.
 Keenan, E.P. Neumann, and F. Lustwerk J.H., “An investigation of ejector design by analysis and experiment,” vol. J Appl Mech Trans ASME, 72 (1950), pp. 299–309, 1950.
 W. Chen, C. Shi, S. Zhang, H. Chen, D. Chong, and J. Yan, “Theoretical analysis of ejector refrigeration system performance under overall modes,” Appl. Energy, 2016.
 S. Croquer, S. Poncet, and Z. Aidoun, “Turbulence modeling of a single-phase R134a supersonic ejector. Part 2: Local flow structure and exergy analysis,” Int. J. Refrig., vol. 61, pp. 153–165, 2016.
 NIST-REFPROP, v9.1., “NIST (2013). NIST Reference Fluid Thermodynamic and Transport Properties -REFPROP, v9.1.” 2013.
 “ANSYS FLUENT 17.0.” ANSYS FLUENT Theory Guide release 17.0, ANSYS Inc., 2017.
 N. Galanis and M. Sorin, “Ejector design and performance prediction,” Int. J. Therm. Sci., vol. 104, pp. 315–329, 2016.
 Klein, S., “Engineering Equation Solver.(EES).” Engineering Equation Solver. F-Chart Software., 2011.