Experimental studies on the air side heat transfer and pressure drop characteristics for 20 types of multi-louvered fin and flat tube heat exchangers were performed. A series of tests were conducted for air Reynolds numbers of 200-2500 based on the louver pitch with different fin pitch, fin height, fin thickness, fin louver angle and flow length at a constant tube side flow rate of 2.8 m(3)/h.The air side thermal performance data were analyzed using the effectiveness-NTU method. Characteristics of the heat transfer and pressure drop for the different geometry parameters were reported in terms of Colburn j-factor and Fanning friction f-factor as a function of Re-Lp. The general correlations for the j and f factors were derived by regression analysis and F test of significance. The correlations of the j and f factors predict the test data within a rms error of +/- 10% and +/-12%, and the mean deviations are 4.1% and 5.6%, respectively. In addition, two comparison methods were adopted to evaluate the air side thermal hydraulic performance of the multi-louvered fins. (C) 2006 Elsevier Ltd. All rights reserved.