Experimental study on the convective heat transfer enhancement in single-phase steam flow by a support grid

•The convective heat transfer enhancement by support grids is investigated.•Experiments were performed in a square array 2×2 rod bundle.•The enhancement was affected not only by the blockage ratio also by the Reynolds number.•For low Reynolds numbers, the enhancement depends on the Reynolds number (Re).•For high Reynolds numbers, the enhancement is nearly independent of Re.