Heat transfer in the presence of ultrasound has been investigated. Experiments were performed using a specific experimental setup involving a homemade, high-frequency, ultrasonic reactor equipped with a cooling helical coil. The aim of this study was to investigate the effect of ultrasound with different frequencies on heat transfer between water contained within the reactor and cooling water flowing through the coil. It has been shown that the presence of the ultrasonic field results in an increase of the cooling rate due to an enhancement of the overall heat transfer coefficient of the coil by up to 100%, depending on operating parameters.