Condensation heat transfer of R-134a inside a microfin tube with different tube inclinations M.A. Akhavan-Behabadi, Ravi Kumar * , S.G. Mohseni Department of Mechanical Engineering, Faculty of Engineering, University of Tehran, Iran Received 2 February 2006; received in revised form 13 February 2007 Available online 2 May 2007 Abstract Experimental heat transfer studies during condensation of pure R-134a vapor inside a single microfin tube have been carried out. The microfin tube has been provided with different tube inclination angles of the direction of fluid flow from horizontal, a. The data are acquired for seven different tube inclinations, a, in a range of 90 to +90° and three mass velocities of 54, 81, and 107 kg/m 2 -s for each inclination angle during condensation of R-134a vapor. The experimental results indicate that the tube inclination angle of, a, affects the condensation heat transfer coefficient in a significant manner. The highest heat transfer coefficient is attained at inclination angle of a = +30°. The effect of inclination angle, a, on heat transfer coefficient, h, is more prominent at low vapor quality and mass velocity. A correlation has also been developed to predict the condensing side heat transfer coefficient for different vapor qualities and mass velocities. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Microfin tube; Condensation; Heat transfer; Inclination; Two-phase flow 1. Introduction The condensers have a very important role to play in dif- ferent industries such as in refrigeration, air-conditioning, power plants and chemical industries. As the energy sources are limited and for their conservation, appropriate design and optimization of condensers is very important. There- fore, different methods have been used by different investi- gators to increase heat transfer rate in these condensers [1]. In refrigeration and air-conditioning industries, due to the high wettability of the refrigerants, only film-wise con- densation is observed and since the thermal conductivity of refrigerants is low, it is desired to augment the heat transfer coefficient in refrigerant side of condensers. There are number of techniques to enhance the heat transfer coef- ficient [2,3]. One of the passive techniques to enhance heat transfer coefficient is the use of microfin tubes. Numerous researchers have carried out experiments to study the effect of fin geometry [4], presence of lubricating oil in refrigerant [5] and, different refrigerants flows [6] on the performance of microfin tubes. A review of the existing literature reveals that, although vast studies have been done on heat transfer enhancement in these tubes, yet the focus of almost all of the studies is to study the condensa- tion during refrigerant flow in a horizontal tube. In fact, the mechanism of heat transfer augmentation in microfin tubes is dependent on the flow regime of two-phase flow. The flow regime is also influenced by interfacial shear stress, surface tension and gravitational force. Thus, there is a great necessity to consider and study the effect of grav- itational force on heat transfer rate during condensation of refrigerants inside a tube. Therefore, an experimental inves- tigation has been carried out to study the condensation of R-134a vapor inside a microfin tube with different inclina- tions of the tube. 0017-9310/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijheatmasstransfer.2007.02.030 * Corresponding author. Address: Department of Mechanical and Industrial Engineering, Indian Institute of Technology, Roorkee-247667, India. Tel.: +91 1332 285740; fax: +91 1332 285665. E-mail address: ravikfme@iitr.ernet.in (R. Kumar). www.elsevier.com/locate/ijhmt International Journal of Heat and Mass Transfer 50 (2007) 4864–4871