This work introduces a three-dimensional analysis of an inline module composed of two thermal sources using ANSYS-FLUENT Computational Fluid Dynamics (CFD) package. The effect of package spacing ratio (1 ≤ S ≤ 3) on the heat transfer coefficient of the upstream (UTS) and downstream (DTS) thermal sources within Reynolds number range of 2464⩽ReL⩽16,430 are considered. The predictions are compared with the experiments performed on air wind tunnel with two thermal sources mounted on its horizontal surface within Reynolds number range of 4848⩽ReL⩽13,635. The numerical results are compared and validated with the experimental results and a good agreement is obtained. Compared to a single thermal source (STS), it is observed that the reduction in the average Nusselt number of the UTS and DTS is 26.3% and 35.6%, respectively, at S = 1. This reduction decreases to 4.9% and 12.6%, respectively, at S = 3. Finally, the present study aims to extend the printed circuit boards designers with average Nusselt number correlations for the UTS and DTS as a function of Reynolds number and package spacing within 2464⩽ReL⩽16,430 and (1 ≤ S ≤ 3).