The combined effects of the included angle and the heat flux of the lower tube on heat transfer enhancement of V-shape tubes were investigated. For the test, two heated stainless steel tubes of 19 mm diameter and the water at atmospheric pressure were used. The increase in the angle eventually increases the bundle effect. When the angle changes from 2 to 18 the value of the bundle effect increases about 20.3% when the heat flux of the upper tube is 10 kW/m(2). The enhancement is clearly observed at the low heat fluxes where the convective effect is dominant. The results of the present study were compared with the results of the parallel tubes and two cases show similar tendencies. However, the values of the bundle effect for the present study are slightly higher than the parallel tubes. (C) 2016 Elsevier Ltd. All rights reserved.