A surface renewal model for unsteady-state mass transfer using the generalized Danckwerts age distribution function
| Autor: | Siddharth G. Chatterjee, Isabelle R. Horvath |
|---|---|
| Rok vydání: | 2018 |
| Předmět: |
010504 meteorology & atmospheric sciences
surface renewal model 02 engineering and technology 01 natural sciences Wind speed Engineering 020401 chemical engineering Approximation error Danckwerts distribution Mass transfer mass transfer 0204 chemical engineering lcsh:Science Absorption (electromagnetic radiation) 0105 earth and related environmental sciences Physics Multidisciplinary Steady state Turbulence turbulence Mechanics Skewness lcsh:Q Inverse function Research Article |
| Zdroj: | Royal Society Open Science Royal Society Open Science, Vol 5, Iss 5 (2018) |
| ISSN: | 2054-5703 |
| Popis: | The recently derived steady-state generalized Danckwerts age distribution is extended to unsteady-state conditions. For three different wind speeds used by researchers on air–water heat exchange on the Heidelberg Aeolotron, calculations reveal that the distribution has a sharp peak during the initial moments, but flattens out and acquires a bell-shaped character with process time, with the time taken to attain a steady-state profile being a strong and inverse function of wind speed. With increasing wind speed, the age distribution narrows significantly, its skewness decreases and its peak becomes larger. The mean eddy renewal time increases linearly with process time initially but approaches a final steady-state value asymptotically, which decreases dramatically with increased wind speed. Using the distribution to analyse the transient absorption of a gas into a large body of liquid, assuming negligible gas-side mass-transfer resistance, estimates are made of the gas-absorption and dissolved-gas transfer coefficients for oxygen absorption in water at 25°C for the three different wind speeds. Under unsteady-state conditions, these two coefficients show an inverse behaviour, indicating a heightened accumulation of dissolved gas in the surface elements, especially during the initial moments of absorption. However, the two mass-transfer coefficients start merging together as the steady state is approached. Theoretical predictions of the steady-state mass-transfer coefficient or transfer velocity are in fair agreement (average absolute error of prediction = 18.1%) with some experimental measurements of the same for the nitrous oxide–water system at 20°C that were made in the Heidelberg Aeolotron. |
| Databáze: | OpenAIRE |
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