Heat transfer enhancement using 40 kHz ultrasound and metal foams inside a horizontal mini-channel

The aim of this experimental and numerical study using COMSOL Multiphysics is to analyze the effects of the metal foam and the acoustic streaming generated by ultrasonic waves of 40 kHz on heat transfer in forced convection over a heated plate. The results of the literature show that the metallic foam, and the ultrasonic acoustic streaming, improve heat transfer independently. For this purpose, we carried out a comparative study of different configurations. In the first configuration, aluminum foam occupies the entire surface of the heating body and the cooling fluid passes through it. However, in the second configuration, two aluminum foams of 10 mm thickness, spaced 10 mm apart, arranged in a manner that a quantity of air passes above and the other through its pores. Flow regime is maintained laminar for velocities ranging between 0.2 and 1 m/s. A heat flux of 50 W is kept constant in the bottom of test section. The results revealed that the insertion of aluminum foams improved the heat transfer by a factor of 227% and 125% respectively for a fully and partially porous channel, compared to an empty channel for equal flow velocities. While an enhancement factor of 42% was obtained by the acoustic streaming effect generated by ultrasonic waves of 40 kHz in an empty channel. The coupling of these two intensifying methods showed a slight increase in heat exchange coefficient in a partially porous channel configuration with an enhancement factor of 7% compared to a flow without ultrasound, Otherwise, no ultrasound influence on heat transfer in a fully porous channel configuration, this is explained by the impedance of wave propagation medium which attenuates the acoustic streaming effect.