Steady laminar two-dimensional incompressible flow over in-line flat-tube bundles used in heat exchanger applications is considered in this work. The effect of Reynolds number (Re = 50, 100, 200, and 400) and (height/length) aspect ratio (H/D / L/D = 2/4, 2/5, 2/6, and 4/4) on the pressure drop and heat transfer were studied. A finite-volume-based FORTRAN code was developed to solve the governing equations. A computational fluid dynamic (Flunet 6.2.16) is used to predict the heat transfer and fluid flow over in-line flat-tube bank. A small change in the heat transfer rate can be predicted since the fluid has almost the same behavior when the (height/length) ratio is increased. The (height/length) ratio was found to have very little effect on pressure. The comparison is made between the present computational fluid dynamic results and Bahaidarah (2004) for normalized pressure difference versus Re number, across a single in-line configuration module. A reasonable agreement is observed. Also, the comparison between the present predictions, the empirical and experimental works of in-line tube bank for the variation of Nu with Re at (H/D / L/D = 4/4) is done and a fair agreement is found. The results show that, as the Reynolds number increases, the maximum velocity in the passage between the upper and lower tubes increases.