Question

how might a sonogram tech encounter heat, heat transfer, and/or thermal expansion?

Answer 1

Among the three heat transfer modes, conduction and radiation assisted by ultrasound are the less studied. combination of radiation (artificial or natural) and ultrasound to heat a flowing liquid led to better results than the sum of each process taken separately; besides, metal conduction could be enhanced between 2.25 and 5.55 times. Conversely, during melting of paraffin, when conduction was dominating over convection, little influence of ultrasound was found.

Heat Transfer with Phase Change

a) Melting and Solidification

Power ultrasound is a method to reduce the size of ice crystals on the frozen products and gain in quality. This leads to finest ice crystals and shortens the time between the onset of crystallization and the complete formation of ice, mainly due to acoustic cavitation. Birth of nucleation sites, microstreaming, and some cleaning action of heat exchangers are among the subsequent advantages. Besides, ultrasound is a nonintrusive technique. Comprehensive reviews of the uses of ultrasound in food technology exist with many examples of processing, crystallization, and freezing.

b) Boiling

Boiling heat transfer in the presence of an ultrasonic field is described apart for being a very active research field. Ultrasound allows improvement of boiling heat transfer almost systematically. The first bubbles appearing in the nucleation sites are swept away by the vibrations, and the apparition of film boiling is therefore delayed so that higher heat fluxes are reached.

c) Food Industry/Drying

For being particularly adequate (nonintrusive, nonchemical, etc.), ultrasonic technologies are intensively developing in food industry. Food drying is one of the best examples. If there is a good acoustic match between the transducer and the food material, ultrasonic vibrations can be directly applied to the material to be dried. Power ultrasound mainly affects the external thermal resistance. If the transducer is not in contact with the material and ultrasound is air-borne, it is reported that high air flow rate may introduce modifications in the acoustic field, decreasing also the acoustic energy transmitted to the medium. Power ultrasound increases the effective moisture diffusivities at low air velocities but the improvement becomes negligible at high air velocities

Reference: Enhancement of Heat Transfer by Ultrasound: Review and Recent Advances,

International Journal of Chemical Engineering
Volume 2011, Article ID 670108, 17 pages