Federica Baffigi

Effects of Ultrasounds on the Heat Transfer Enhancement From a Circular Cylinder to Distilled Water in Subcooled Boiling

The main aim of this work is to investigate experimentally the influence of ultrasonic waves, on the heat transfer enhancement, from a stainless steel circular cylinder to distilled water, in subcooled boiling conditions. This study has carried on for a few years at the Department of Energetics L.Poggi. The effect was observed since the 1960s: Different authors had investigated the cooling effect due to the ultrasonic waves at different heat transfer regimes, especially from a thin platinum wire to water. They had found out that the highest heat transfer coefficient enhancement was in subcooled boiling conditions. So this paper has the purpose to clarify the physical phenomenon and optimize a large range of variables involved in the mechanism. It reports the experimental results obtained with ultrasound at the frequency of 38 kHz, at two different subcooling degrees, ΔT sub = 25°C and 35°C. The heat fluxes applied on the cylinder, the ultrasonic generator power Pg en , and also the placement of the heater inside the ultrasonic generator tank were varied. The ultrasonic waves seem to be very useful for a practical application in the last generation electronic components cooling: They need dissipating huge heat fluxes and avoiding high temperatures (≈150°C), after that they could damage themselves.

Heat Transfer Enhancement by Ultrasound Pressure Waves in Liquid Water: A Cooling Method for New Electronic Components

The objective of this work is to study the increase of the convective heat transfer coefficient in the presence of ultrasound waves and, in particular, to find a relationship between the ultrasonic power and the effective pressure of water. The tests have focused on the heat exchange by natural convection, in single-phase conditions, at atmospheric pressure, between a cylinder, heated by means of the Joule effect, and distilled water, with and without the action of ultrasonic waves. The variables involved in the heat exchange have been varied within the range allowed by the experimental apparatus and the convective heat transfer coefficient has been maximized. The specific thermal flow has been chosen in a range compatible with applications in the field of electronics. For the first time the pressure of water at various ultrasonic power levels has been measured, in the vicinity of the cylindrical surface, thanks to the collaboration with the Naval Experimentation and Support Center (CSSN) of the Italian Navy in La Spezia, Italy.

Heat Transfer Enhancement From a Circular Cylinder to Distilled Water by Ultrasonic Waves at Different Subcooling Degrees

The main aim of this work is to investigate experimentally the influence of ultrasonic waves, on the heat transfer enhancement, from a stainless steel circular cylinder to distilled water, in subcooled boiling conditions. This study has carried on for a few years at the Department of Energetics “L.Poggi”. The effect was observed since ’60s: different authors had investigated the cooling effect due to the ultrasonic waves at different heat transfer regimes, especially from a thin platinum wire to water. They had found out that the highest heat transfer coefficient enhancement was been in subcooled boiling conditions. So this paper has the purpose to clarify the physical phenomenon and optimize a large range of variables involved in the mechanism. It reports the experimental results obtained with ultrasound at the frequency of 38 kHz, at two different subcooling degrees, ΔTSUB = 25 and 35°C. The heat fluxes applied on the cylinder, the ultrasonic generator power, Pgen and also the placement of the heater inside the ultrasonic generator tank, are been varied. The ultrasonic waves seem to be very useful for a practical application in the last generation electronic components cooling: they need dissipating huge heat fluxes and avoiding high temperatures (≈150°C), after that they could damage themselves.© 2010 ASME

“Forced convection between a wire and an upward flow slot submerged jet: preliminary results”

Heat transfer from a platinum wire 0.2 mm. in dia., heated by Joule effect, to an impinging upward flow submerged slot jet of distilled water is studied in two–phase conditions. A new experimental apparatus is built for this experimental activity. Different geometrical configurations were investigated in order to find out which of them could maximize the heat transfer coefficient. Its dependence on some parameters as jet velocity, heat flux and distance between exit jet and wire is also examined. In the future the results of this paper will be compared with the previous ones presented in literature, referred to cylinders of one size order bigger than the platinum wire and the same slot, all parameters being equal.Copyright