Evaporative thermal resistance and its influence on microscopic bubble growth
| Autor: | Simon P. Walker, Hyungdae Kim, Satbyoul Jung, Giovanni Giustini |
|---|---|
| Rok vydání: | 2016 |
| Předmět: |
Technology
Materials science Evaporative thermal resistance Thermal resistance Bubble Evaporation Thermodynamics Bubble growth 02 engineering and technology Mechanics 01 natural sciences 09 Engineering 010305 fluids & plasmas Engineering Boiling 0103 physical sciences WATER Mechanical Engineering & Transports Electrical conductor 01 Mathematical Sciences Fluid Flow and Transfer Processes Science & Technology 02 Physical Sciences Mechanical Engineering Allowance (engineering) 021001 nanoscience & nanotechnology Condensed Matter Physics Engineering Mechanical MODEL Boiling point Heat flux Physical Sciences 0210 nano-technology Microlayer |
| Zdroj: | International Journal of Heat and Mass Transfer. 101:733-741 |
| ISSN: | 0017-9310 |
| Popis: | Simulations of the formation of small steam bubbles indicate that the rate of growth of bubbles is very sensitive to the rate of evaporation of the micro-layer of liquid beneath the bubble. Such evaporation is rapid, and is modelled as being driven by the large heat flux through the thin liquid layer caused by the difference in temperature between the solid–liquid interface, and the saturation temperature in the interior of the bubble. However, application of this approach to recent experimental measurements of Jung and Kim generated anomalous results. In this paper we demonstrate that a model of the micro-layer heat flux that includes an allowance for the finite evaporative thermal resistance is able to eliminate these anomalies. This evaporative thermal resistance is a consequence of near-interface molecular dynamics, characterised by a quantity termed ‘evaporation coefficient’. Whilst in most engineering applications evaporative thermal resistance is small compared to conductive resistance, here, with the micro-layer thickness ranging from a few microns down to zero, it becomes of considerable importance. Selection of a molecular ‘evaporation coefficient’ to restore consistency to the anomalous measurements allows a plausible numerical value to be inferred. For the several times and multiple locations studied, a fairly consistent value of between 0.02 and 0.1 is indicated, (for saturated water in laboratory conditions), which itself is consistent with earlier literature values of this rather difficult quantity. It is shown that the evaporative resistance always represents a large fraction of the conductive resistance, and for important phases of the process dominates it. The need for inclusion of this phenomenon in the micro-layer models used in bubble analysis is clear. |
| Databáze: | OpenAIRE |
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