Electrical machines are used in an ever-increasing number of applications, such as transportation systems and energy production, because of their high efficiency. The improvement of their cooling is of interest in order to increase the energy produced per unit volume. To that end, radial channels can be placed inside the stator, allowing the internal fluid to pass through, from the air gap where the mean flow is longitudinal to an external channel. To investigate both the flow between the air gap and the radial channels, and the induced convective heat transfer, an experimental set-up is used. Two fans, whose power can be adjusted, are used to create flows in the two longitudinal channels, which represent the air gap, and the external channel of the real machine. A thin heat foil is used to heat one channel face, and the temperature profiles are measured using an infrared camera. Convective heat transfer coefficients are determined along the radial centerline of each channel face by a conductive 1D model coupled with an inverse method. The inlet Reynolds number is kept constant at approximately 25000, and the mass flow rate ratio between the perpendicular channel and the inlet varies from 0.13 to 0.88. In particular, we will pay special attention to the heat transfers at channel entrances, where PIV measurements are also made. Recirculation areas, whose size are linked to the dynamic conditions, occur and have a direct influence on the local Nusselt numbers.