In the present work, the effects of tube shapes on the heat transfer and fluid flow characteristics of the shell-and-tube heat exchangers including square, rectangular, circular, elliptical, equilateral- and isosceles-triangular shapes are numerically investigated in detail. Six parameters including (1) rectangular-tube ratios (alpha = tube height/width), (2) triangular-tube ratios (beta= two-side edge/bottom edge), (3) elliptical-tube ratios (gamma = b/a; a: inner semi-major-axis lengths and b: inner semi-minor-axis lengths), (4) the tube lengths from 2 mto 20 m, (5) outer tube diameters from 52 mm to 252 mm, and (6) 500 <= Re <= 8000 are examined variables. For all cases in this study, it is found that at the same boundary conditions, the thermal performance of an elliptical tube is superior to that of a circular tube. A locally thermal optimal triangular tube shape is defined with a maximum effectiveness up to 92.46%. A novel correlation is developed to describe the Nusseltnumbers subject to the examined tube shapes. The proposed correlation is not only in line with the existing round tube correlations but also gives good predictions for other tube geometries with maximum deviation being less than 7.1%. (C) 2018 Elsevier Ltd. All rights reserved.