Stability of the bubble cushion during contactless boiling in micro-evaporators

Huiberts, J. (2015) Stability of the bubble cushion during contactless boiling in micro-evaporators.

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Abstract:When the size of an evaporator is reduced to micro-size, difficulties associated with flow instabilities and regarding the reliability are introduced. Using contactless boiling, the pressure drop can be reduced and fouling is prevented. In this research the micro-size bubbles during contactless boiling are visualized and the shape and behaviour are investigated, in order to predict its stability. The forces working on a single bubble arising from an orifice are investigated. The surface tension and the interface pressure force are found to be dominant, and therefore determine the bubble behaviour. The difference between these forces is the pressure over the water/gas interface of the bubbly cushion. It is made likely that this interface will also be stable for a more vigorous flow. Next to the chamber pressure, also the contact angle, bubble diameter, orifice diameter and surface tension are shown to be relevant for the stability. The bubble size of 20 micrometer predicted by Rops et al. is verified by experiment [?]. The temperature is found not to be signifucant for this application. Furthermore it is seen that the bubble size slightly increases for a larger chamber pressure. However, a clear relation could not be established, due to that the enlargement was still too small. Also, for varying chamber pressure a different behaviour in bubble growth is seen.
Item Type:Internship Report (Master)
Clients:
TNO, the Netherlands
Faculty:ET: Engineering Technology
Subject:52 mechanical engineering
Programme:Mechanical Engineering MSc (60439)
Keywords:Micro evaporator, contactless boiling, stability, fouling
Link to this item:http://purl.utwente.nl/essays/69914
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