Abstract : A numerical heat transfer study of cross flow heat exchanger, used to supply heat to a cooling fluid, was performed. The computational fluid dynamics (CFD) was used to simulate the cross flow heat exchanger for better understanding the heat transfer capability. Three-dimensional model of the heat exchanger was modeled according to the experiment from the literature. Air to air and water to water cross flow heat exchanger were created and simulated using FLUENT software. The outlet temperature of cold and hot fluid were obtained and compared with experimental results and there were a good agreement in between them