In the present study, thermal optimization of a heat sink with fins branched in the direction normal to fluid flow was conducted using a model based on volume averaging theory (VAT). For a water-cooled system, it was shown that, compared to a rectangular-fin heat sink, the thermal resistance of the optimized branched-fin heat sink decreased by up to 30%. The extent of the reduction increased with an increase in the pumping power and a decrease in the length of the heat sink. (C) 2014 Elsevier Ltd. All rights reserved.