An experimental and numerical study is conducted to characterize the effects of ultrasound waves on natural convective heat transfer from a spiral heater to distilled water. The test setup is made of two coaxial cylinders where the inner cylinder is filled with water up to a certain height. A spiral heater whose length is 100 times that of its diameter is immersed in water. The power of the heater is varied in a range where heat transfer is limited to the natural convection regime. Five ultrasonic transducers with a frequency of 26 kHz are bonded under bottom of the inner tank. A numerical simulation is also performed to study the effect of ultrasonic waves on fluid flow and heat transfer within the inner tank by a commercially available software, ANSYS Fluent. The effects of several parameters on the heat transfer enhancement are studied. These parameters include: the ultrasonic generator’s power, the heater power and height inside the tank. A comparison is made between the results of experiments with those of the simulations for the heater surface temperature where a good agreement (less than 5% difference) is obtained. A more uniform velocity and temperature distribution within the fluid is observed when ultrasonic waves are applied. Extensive experiments are then performed in various conditions. Finally, two correlations are developed for natural heat transfer from a spiral heater with and without ultrasonic waves. A maximum enhancement of 74% is found in the natural convection heat transfer coefficient due to ultrasonic waves.

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