Conference article

Experimental comparison of the dynamic evaortor response using homogeneous and slip flow modeling

Martin Ryhl Kærn
Technical University of Denmark, Department of Mechanical Engineering, Denmark \ Danfoss A/S, Refrigeration and Air-Conditioning, Denmark

Brian Elmegaard
Technical University of Denmark, Department of Mechanical Engineering, Denmark

Lars Finn Sloth Larsson
Danfoss A/S, Refrigeration and Air-Conditioning, Denmark

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Published in: Proceedings of the 8th International Modelica Conference; March 20th-22nd; Technical Univeristy; Dresden; Germany

Linköping Electronic Conference Proceedings 63:28, p. 246-255

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Published: 2011-06-30

ISBN: 978-91-7393-096-3

ISSN: 1650-3686 (print), 1650-3740 (online)


The dynamic response from an evaporator is important for control of refrigeration and air-conditioning systems. Essentially; the prediction of refrigerant charge inside the evaporator is crucial for the dynamic behavior. The prediction of refrigerant charge follows from suitable void fraction correlations from the literature. A chosen set of void fraction correlations (slip flow) and the assumption of homogeneous flow will be investigated in this paper and compared to experiments on a simple coaxial type evaporator. The numerical model of the evaporator is a dynamic distributed mixture model; where different void fraction correlations can be applied. It is shown that the dynamic response of the homogeneous model is too fast; whereas the slip flow models agree well with the experiments. Another difference is that the charge prediction of the homogeneous model is approximately 2-3 times less than the slip flow models.


refrigeration; air-conditioning; evaporator; two-phase flow; modeling; Modelica; transient; dynamic; simulation


[1] M. A. Woldesemayat; A. J. Ghajar; Comparison of void fraction correlations for different flow patterns in horizontal and upward inclined pipes; International Journal of Multiphase Flow 33 (4)(2007) 347 – 370. doi: 10.1016/j.ijmultiphaseflow.2006.09.004.

[2] G. E. Dix; Vapor void fraction for forced convection with subcooled boiling at low flow rates; Tech. rep.; General Electric Company Report NEDO-10491 (1971).

[3] A. Premoli; D. D. Francesco; A. Prina; A dimensional correlation for evaluating two-phase mixture density; La Termotecnica 25 (1971) 17–26.

[4] X. Maa; G. Dinga; P. Zhanga; W. Hana; S. Kasaharab; T. Yamaguchib; Experimental validation of void fraction models for r410a air conditioners; International Journal of Refrigeration 32 (2009) 780–790. doi: 10.1016/j.ijrefrig.2008.12.009.

[5] G. Mader; L. F. S. Larsen; G. P. F. Fösel; Low charge system behavior - interactions of heat exchanger volumes and charge; in: 2nd Workshop on Refrigerant Charge Reduction; IIR; KTH; Stockholm; Sweden; 2010.

[6] L. Wojtan; T. Ursenbacher; J. R. Thome; Measurement of dynamic void fractions in stratified types of flow; Experimental Thermal and Fluid Science 29 (3) (2005) 383 – 392. doi: 10.1016/j.expthermflusci.2004.05.017.

[7] D. Steiner; Heat transfer to boiling saturated liquids; VDI-Wärmeatlas (VDI Heat Atlas); Verein Deutscher Ingenieure (Ed.); VDI-Gessellschaft Verfahrenstechnik und Chemie-ingenieurwesen (GCV); Düsseldorf; 1993; (Translator: J.W. Fullarton).

[8] L. Wojtan; T. Ursenbacher; J. R. Thome; Investigation of flow boiling in horizontal tubes: Part i - a new diabatic two-phase flow pattern map; International Journal of Heat and Mass Transfer 48 (2005) 2955–2969. doi: 10.1016/j.ijheatmasstransfer.2004.12.012.

[9] S. M. Zivi; Estimation of steady-state steam void-fraction by means of the principle of minimum entropy production; J. Heat Transf. 86 (1964) 247–252. doi: 10.1115/1.3687113.

[10] J. Antonius; Distribuerede fordampermodeller på flere detaljeringsniveauer; Master’s thesis; Technical University of Denmark; Department of Energy Engineering (1998).

[11] Cullimore & Ring Technologies Inc.; Littleton; Colorado; USA; Sinda/Fluint user’s manual; General Purpose Thermal/Fluid Network Analyzer; version 5.2 (2008).

[12] A. Jakobsen; J. Antonius; H. J. Høgaard Knudsen; Experimental evaluation of the use of homogeneous and slip-flow two-ophase dynamic models in evaporator modelling; in: 20th International Congress of Refrigeration; IIR/IIF; Sydney; 1999.

[13] Dynasim AB; Research Park Ideon SE-223 70; Lund; Sweden; Dynamic Modeling Laboratory; Dymola User’s Manual; version 7.4 (2010).

[14] J. Eborn; H. Tummescheit; K. Prölß; Airconditioning - a modelica library for dynamic simulation of ac systems; in: 4th International Modelica Conference; Hamburg; Germany; 2005; pp. 185–192.

[15] C. C. Richter; Proposal of new object-oriented equation-based model libraries for thermodynamic systems; Ph.D. thesis; Technische Universität Carolo-Wilhelmina zu Braunschweig; Fakultät für Maschinenbau (2008).

[16] M. J. Skovrup; Thermodynamic and thermophysical properties of refrigerants; Department of Energy Engineering; Technical University of Denmark; Nils Koppels Allé; Building 402; DK-2800 Lyngby; Denmark (2009).

[17] VDI Wärmeatlas; Berechnungsblätter für den Wärmeübergang; Springer-Verlag; Ch. Lab.; 9th Edition; Dd 20; (2002).

[18] S. M. Ghiaasiaan; Two-phase flow: Boiling and Condensation in Conventional and Miniature Systems; 1st Edition; Cambridge University Press; 2008.

[19] S. V. Patankar; Numerical heat transfer and fluid flow; Taylor & Francis; 1980.

[20] O. Bauer; Modelling of two-phase flows with modelica; Master’s thesis; Lund University; Department of Automatic Control (1999).

[21] A. F. Mills; Heat Transfer; 2nd Edition; Prentice Hall; 1999.

[22] E. J. Dittus; L. M. K. Boelter; Publications on Engineering; Vol. 2; University of California; Berkeley; 1930.

[23] V. Gnielinski; New equation for heat and mass transfer in turbulent pipe and channel flow; International Chemical Engineering 16 (1976) 359–368.

[24] P. R. H. Blasius; VDI Wärmeatlas; 9th Edition; Springer-Verlag; Ch. Lab.; 2002.

[25] M. M. Shah; Chart correlation for saturated boiling heat transfer: Equations and further study; ASHRAE Transactions 88 (1982) 185–196.

[26] H. Müller-Steinhagen; K. Heck; A simple friction pressure drop correlation for two-phase flow in pipes; Chemical engineering and processing 20 (1986) 297–308. doi: 10.1016/0255-2701(86)80008-3.

[27] L. Wojtan; T. Ursenbacher; J. R. Thome; Investigation of flow boiling in horizontal tubes: Part ii - development of a new heat transfer model for stratified-wavy; dryout and mist flow regimes; International Journal of Heat and Mass Transfer 48 (2005) 2970–2985. doi: 10.1016/0255-2701(86)80008-3.

[28] H. Jiang; Development of a simulation and optimization tool for heat-exchanger design; Ph.D. thesis; University of Maryland at College Park;Department of Mechanical Engineering (2003).

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