Abstract
Calculation of evaporation requires accurate thermophysical properties of the liquid. Such data are well-known for conventional fossil fuels. In contrast, e.g., thermal conductivity or dynamic viscosity of the fuel vapor are rarely available for modern liquid fuels. To overcome this problem, molecular models can be used. Currently, the measurement-based properties of n-heptane and diesel oil are compared with estimated values, using the state-of-the-art molecular models to derive the temperature-dependent material properties. Then their effect on droplet evaporation was evaluated. The critical parameters were liquid density, latent heat of vaporization, boiling temperature, and vapor thermal conductivity where the estimation affected the evaporation time notably. Besides a general sensitivity analysis, evaporation modeling in a practical burner ended up with similar results. By calculating droplet motion, the evaporation number, the evaporation-to-residence time ratio can be derived. An empirical cumulative distribution function is used for the spray of the analyzed burner to evaluate evaporation in the mixing tube. Evaporation number did not exceed 0.4, meaning a full evaporation prior to reaching the burner lip in all cases. As droplet inertia depends upon its size, the residence time has a minimum value due to the phenomenon of overshooting.
Highlights
Liquid evaporation is involved in numerous processes, including the water cycle, coating processes, dryers, and combustion
The evaporation of the spray is discussed in the case of the same burner, focusing on the evaporation number and the residence time
The results show no significant difference in terms of minimum and maximum deviances in evaporation time between the cases
Summary
Liquid evaporation is involved in numerous processes, including the water cycle, coating processes, dryers, and combustion. This phenomenon is characterized by continuous energy and mass transfer in a wide range of scales [1]. The complexity of evaporation makes its modeling cumbersome in the scale of a practical device, leading to the need for model simplification [2]. After finding a suitable model, the step is finding a reliable thermophysical database for the evaporating liquid, e.g., temperature-dependent properties of mixtures and renewable fuels are rarely available, or their measurement range available in the public literature is rather limited. If there is no opportunity to measure the missing properties, the only way forward is using thermophysical models.
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