Infrared thermography investigation of local heat transfer in a plate fin and two-tube rows assembly D. Bougeard * Ecole des Mines de Douai, De´partement Energe´tique Industrielle, 941 rue Charles Bourseul, B.P. 10838, 59508 Douai Cedex, France Received 3 June 2006; received in revised form 30 January 2007; accepted 31 January 2007 Available online 26 March 2007 Abstract An experimental study is performed using an infrared thermography system. The experimental method uses the temperature transient variation of a thin plate (tested fin) in order to obtain detailed quantitative heat transfer coefficients. The method developed is similar to the lumped capacitance method usually used to measure heat transfer coefficient on heat exchanger fin models. But the method presented here exploits the capabilities of infrared thermography to measure surface temperatures in a transient technique in order to take into account errors effects due to tangential conduction and radiation of the tested fin. The method is validated using a two-dimensional chan- nel experiment and its advantages are highlighted using a plate fin and two-tube rows assembly experiment. Moreover, convection coef- ficient variations with fin pitch and frontal air velocity of an automotive plate fin and two-tube rows assembly are also examined. Ó 2007 Elsevier Inc. All rights reserved. Keywords: Fin and tube heat exchanger; Convection heat transfer; Infrared thermography 1. Introduction Plate finned-tube heat exchangers are intensively used in many industrial processes. The performances of this kind of heat exchanger are directly linked to the air-side thermal resistance. On the air side, the heat transfer surface is usu- ally expanded using continuous fins. Automotive heat exchangers often consist of two rows of round tubes geom- etry with continuous or louvered fins. The fluid flow struc- ture between the fins depends strongly on the geometrical parameters, inline or staggered tube arrangements, tube spacing, tube shape, tube diameter and fin spacing. More- over, alternative enhancement techniques consisting in punching out of the fins some vortex generators that strongly modify the fluid flow structure also exist (see Jacobi and Shah, 1995 for details). Hence in order to deter- mine the best geometrical arrangement one needs to get precise heat transfer coefficient distribution on the fin surface. Several research groups have designed experimental methods to examine local heat transfer rate in tube finned geometries. Kim and Song (2002) use a naphthalene subli- mation technique to investigate local heat transfer in a plate fins/circular tube assembly. The authors show the great importance of the vortex structure developed in front of the tube, called horseshoe vortex (HSV), on the overall heat transfer coefficient. When the Reynolds number is large enough, they also found that a smaller subsidiary vor- tex appears attached to the main one. While the naphtha- lene sublimation technique uses a heat and mass transfer analogy to determine local heat transfer coefficients, other researchers develop experimental thermal methods. Tiggel- beck et al. (1992) use a thermal transient method that exploits time temperature variation of a thin plate suddenly heated by convection using warm air. The convection coefficient is deduced using a time integration of the energy equation using the three following assumptions: conduction and radiation heat fluxes are negligible, and 0142-727X/$ - see front matter Ó 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.ijheatfluidflow.2007.01.008 * Tel.: +33 3 27 71 23 74; fax: +33 3 27 71 29 15. E-mail address: bougeard@ensm-douai.fr www.elsevier.com/locate/ijhff International Journal of Heat and Fluid Flow 28 (2007) 988–1002