JME_V4_N2_RP4 T.V.S.M.R. Bhushan K. Vijaya Kumar Reddy Journal on Mechanical Engineering 2249 - 0744 4 2 33 37 Square Ducts, Natural Convection, Experimental Heat Transfer, IR-Thermometry Experiments have been conducted on square duct to investigate natural convection heat transfer from the outer surface of axially horizontal square ducts. Steady State Heat Transfer characteristics are studied under laminar and transition regions. Constant heat flux heating element is used to heat the duct from the center and 10 equidistant points are located on each side of the duct to measure temperature from all the four sides using IR-Thermometer. Correlations were developed in the form of circumferential averaged Nusselt number, modified Rayleigh number. February - April 2014 Copyright © 2014 i-manager publications. All rights reserved. i-manager Publications http://www.imanagerpublications.com/Article.aspx?ArticleId=2683