In this work the numerical results of natural convection and surface thermal radiation in an open cavity receiver considering large temperature differences and variable fluid properties are presented. Numerical calculations were conducted for Rayleigh number (Ra) values in the range of 10(4)-10(6). The temperature difference between the hot wall and the bulk fluid (Delta T) was varied between 100 and 400 K, and was represented as a dimensionless temperature difference (phi) for the purpose of generalization of the trends observed. Noticeable differences are observed between the streamlines and temperature fields obtained for phi = 1.333 (Delta T = 400 K) and phi = 0.333 (Delta T = 100 K). The total average Nusselt number in the cavity increased by 79.8% (Ra = 10(6)) and 88.0% (Ra = 10(4)) as phi was varied from 0.333 to 1.333. Furthermore the results indicate that for large temperature differences (0.667 <= phi <= 1.333) the radiative heat transfer is more important that convective heat transfer. (C) 2012 Elsevier Ltd. All rights reserved.