Abstract
We present an experimental investigation of the effect of ultrasound application to increase the heat-transfer coefficient for natural convection of a dielectric fluid. An experimental analysis is carried out to estimate the increase of the convective heat-transfer coefficient between an electronic board and a refrigerant fluid, the Fluorinert Electronic Fluid FC-72. For this purpose, an experimental apparatus composed of an electronic board, its electronic control circuit, and data acquisition systems have been designed and implemented. The data collected appear to confirm in some situations of practical interest the enhancement effect of the convective heat-transfer coefficient in connection with the use of ultrasound. The most favorable condition was observed with the fluid in quite low subcooled conditions.
Highlights
The positive influence that ultrasounds have on the enhancement of the convective heat transfer coefficient has been investigated since the 1930s
The first instance in which the topic was taken into consideration is in an old paper by Martinelli and Boelter [1]. It is in the 1960s–1970s that significant research activity on the subject began, with experimental and theoretical efforts. In such a period, interesting contributions on the topic were provided by Fand et al [2], Kubanskii, [3], Holman and Mott-Smith [4], who studied a gas in the presence of natural convection, and Anantanarayanan and Ramachandran [5], Jackson et al [6], Lemlich and Hwu [7], Fand and Cheng [8], investigated a gas in the presence of forced convection
Larson and London [9], Deaver et al [10], Fand [11], investigated a liquid in the presence of natural convection, while West and Taylor [12], Scanlan [13], Raben [14] and Bergles [15] focused on liquid in the presence of forced convection; in the same period, Isakoff [16], and Nangia et al [17], achieved interesting results with a liquid in pool boiling
Summary
The positive influence that ultrasounds have on the enhancement of the convective heat transfer coefficient has been investigated since the 1930s. One of the authors of the present paper has studied ultrasounds used as promoters of convective heat transfer in the perspective of “Enhancement heat transfer” [25] He investigated the basic physical phenomenon focusing on a stainless steel cylindrical tube with a “sliding” thermocouple insulated from the tube by means of a ceramic electric insulator using distilled water as the coolant fluid. He studied the behavior of water in the form of a subcooled liquid and of completely developed pool boiling [25,26], but without meaningful results: the increase in convective heat-transfer coefficient was lower than the experimental error (14%), in particular, of the order of 7%. An ultrasonic generator with a 500 W output power and a constant ultrasound frequency of 40 kHz is used and a specific fluid is adopted as a coolant, the FC72
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