Condensation heat transfer on single horizontal smooth and ﬁnned tubes and tube bundles for R134a and propane Thomas Gebauer a,1 , Alaa R. Al-Badri a,1 , Achim Gotterbarm b,2 , Jean El Hajal b,3 , Alfred Leipertz a,4 , Andreas Paul Fröba a,⇑ a Friedrich-Alexander-Universität Erlangen-Nürnberg, Lehrstuhl für Technische Thermodynamik, Am Weichselgarten 8, D-91058 Erlangen, Germany b Wieland-Werke AG, Tube Division – Heat Transfer Engineering Departement, Graf-Arco-Straße 36, D-89070 Ulm, Germany article info Article history: Received 25 May 2012 Received in revised form 18 September 2012 Accepted 21 September 2012 Available online 27 October 2012 Keywords: Bundle effect CFD Coating Condensation heat transfer Horizontal tubes R134a R290 abstract For the refrigerants 1,1,1,2-tetraﬂuoroethane (R134a) and propane (R290), the condensation heat transfer was investigated on coated and uncoated horizontal smooth, standard ﬁnned and high performance tubes by experiments and computational ﬂuid dynamics (CFD)-simulations. Measurements were carried out at a saturation temperature of 37 °C varying the heat ﬂux between 4 kW m 2 and 102 kW m 2 . In comparison to the Nußelt theory, enhancement factors of 12.8 to 30.2 were experimentally found for sin- gle standard ﬁnned and single high performance tubes. For both refrigerants, the high performance tubes showed a larger bundle effect than the standard ﬁnned tubes, although the latter show a lower heat transfer performance. In general, experimental results for coated tubes show a slightly lower heat trans- fer performance and no improvements of the condensate drainage could be observed for the modiﬁca- tion. CFD-simulations were used to predict the condensation heat transfer on single tubes for the ﬁrst time. Our experimental data and CFD-simulations were compared with analytical models available in the literature. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Shell and tube condensers which are used, e.g., in refrigeration, air conditioning, and petroleum industry, are objects of continuous improvement and optimization. In order to increase their efﬁ- ciency, ﬁnned tubes are used, which can be classiﬁed into standard ﬁnned or high performance tubes. The latter have additional struc- tures on the ﬁn ﬂank leading to a signiﬁcant increase in the con- densation heat transfer coefﬁcient (HTC) on single tube. For the design of tube bundles with standard ﬁnned or high performance tubes, the performance of the single tube and the rate of conden- sate must be taken into account. The drained condensate from upper tubes leads to an additional mass ﬂow rate on the lower tubes in the bundle. Thus, the thermal resistance of the condensate layer increases and the condensation HTC on lower tubes is reduced in comparison to upper ones. This phenomenon, which re- duces the performance and efﬁciency of shell and tube condensers signiﬁcantly, is known as bundle effect. Many efforts can be found in literature, which are focused on the study of the condensation HTC on the outside of horizontal sin- gle tubes and tube bundles with synthetic refrigerants [1–10]. Due to the extensive safety precautions, which must be fulﬁlled in con- nection with ﬂammable natural refrigerants, only few results can be found for their condensation HTC [11]. Within this work, the condensation HTC was studied for propane (R290) and 1,1,1,2- tetraﬂuoroethane (R134a) on smooth, ﬁnned and high perfor- mance tubes. With a new developed apparatus, the condensation HTC on single tubes and tube bundles should be experimentally investigated. Furthermore, for the ﬁrst time to the best of our knowledge, CFD-simulations should be performed to calculate theoretically the condensation HTC outside smooth tubes and low ﬁnned tubes with trapezoidal ﬁns. Here, the validity of the developed CFD-model should be veriﬁed by comparing the theo- retical results with the experimental data. Additionally, the effect of surface modiﬁcations, e.g., in form of ion implantation and plasma polymer coating, on the heat transfer performance should be tested. The individual tasks mentioned above should contrib- ute to a fundamental understanding of the bundle effect. In the following, the apparatus and the data evaluation will be presented as well as the investigated tube characteristics. Subsequently, the basics of the CFD-simulations for modeling the condensation HTC 0017-9310/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2012.09.049 ⇑ Corresponding author. Tel.: +49 9131 852 9789; fax: +49 9131 852 9901. E-mail addresses: thomas.gebauer@ltt.uni-erlangen.de (T. Gebauer), alaa. albadri@ltt.uni-erlangen.de (A.R. Al-Badri), achim.gotterbarm@wieland.de (A. Gotterbarm), jean.elhajal@wieland.de (J.E. Hajal), sek@ltt.uni-erlangen.de (A. Leipertz), apf@ltt.uni-erlangen.de (A.P. Fröba). 1 Tel.: +49 9131 856 5096; fax: +49 9131 852 9901. 2 Tel.: +49 731 944 2489; fax: +49 731 944 42489. 3 Tel.: +49 731 944 2110; fax: +49 731 944 42110. 4 Tel.: +49 9131 852 9900; fax: +49 9131 852 9901. International Journal of Heat and Mass Transfer 56 (2013) 516–524 Contents lists available at SciVerse ScienceDirect International Journal of Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ijhmt