In this study, convective heat transfer and pressure drop in a cross-flow heat exchanger with hexagonal, square and circular (HSC) pin-fin arrays were studied experimentally. The pin-fins were arranged in an in-line manner. For the applied conditions, the optimal spacing of the pin-fin in the span-wise and stream-wise directions has been determined. The variable parameters are the relative longitudinal pitch (S-L/D = 2, 2.8, 3.5), and the relative transverse pitch was kept constant at S-T/D = 2. The performances of all pin-fins were compared with each other. The experimental results showed that the use of hexagonal pin-fins, compared to the square and circular pin-fins, can lead to an advantage in terms of heat transfer enhancement. The optimal inter-fin pitches are provided based on the largest Nusselt number under the same pumping power, while the optimal inter-fin pitches of hexagonal pin-fins are S-T/D = 2 and S-L/D = 2.8. Empirical equations are derived to correlate the mean Nusselt number and friction coefficient as a function of the Reynolds number, pin-fin frontal surface area, total surface area, and total number. Consequently, the general empirical formula is given in the present form.