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Abstract

In order that the effect of heat transfer between a heated gas bubble being formed at an orifice submerged in a cooler liquid could be determined both an experimental and theoretical investigation was undertaken.

It was considered necessary to investigate also the situation of no heat transfer between the gas bubble and the liquid in which the bubble is forming so as to quantify the effects of heat transfer.

Experiments were carried out by bubbling dried air, supplied from a gas ante-chamber, through a single orifice into distilled water. Orifice sizes of 0.0793, 0.1013, 0.1255 and 0.1517 cms were employed. The volume of the gas ante-chamber was 1192 cc's and the range of air flow rates supplying the ante-chamber varied from 0.5 x 10~°ko/s to 29.2 x 10-6 kg/s. By pre-heating the gas prior to entry to the orifice overall temperature differences between the injected gas and the liquid of 30°c and 47°C were employed.

Since the temperature of the bubble could not be measured directly, the effect of heat transfer was quantified by determining the volumetric growth rate of the bubble during its formation period by means of high speed photography.

It was found that the effect of heat transfer had only a small effect on the bubble formation process, although the range of the mass flow rates of the air where regular, stable bubble formation could be maintained was found to reduce as the temperature difference between the injected gas and the cooler liquid was increased.

Several theoretical formulations for the rate of heat transfer from the bubble to the liquid where investigated in a theoretical model of the bubble formation process. This model gave results in very good agreement with the experimental study undertaken for bubble formation both with and without heat transfer.

As a consequence of the theoretical studies, it was concluded that the vast majority of heat transfer took place in the first few instants of bubble formation. Using the theoretical results, values for the convective surface heat transfer coefficient were obtained and discussed.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > T Technology (General) T Technology > TA Engineering (General). Civil engineering (General) T Technology > TJ Mechanical engineering and machinery
Departments:	School of Science & Technology > Department of Engineering School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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