Fuel and Combustion

Fuel and Combustion

Evaluation of Unity Lewis Number Assumption in Modeling of Water and Fuel Droplets Evaporation

Authors
Amir Omidvar
Reza Mehryar
Amir Hossein Mahdavi
Faculty of Mechanical Engineering, Shiraz University of Technology, Shiraz, Iran
Abstract
Over the recent decades, spray systems have been widely utilized in a variety of applications within the areas of engineering. In this regard, studying the evaporative behavior of droplets in spray can give us a good view point. One of the most common assumptions in dropletsandrsquo; evaporation is to consider the Lewis number to be unity. In this paper the correctness of this assumption has been evaluated for water and n-Heptane single droplets. The results for dropletsandrsquo; evaporation trend have been compared with some relevant experimental and numerical data. Evaporation time and dropletsandrsquo; temperature have been investigated in both conditions. According to obtained results, although the unit Lewis number is not a good assumption for studying n-Heptane droplet evaporation, this assumption gives acceptable results for predicting the water droplets evaporation. Moreover, by assuming the unity Lewis number for water droplet, the calculated temperature of the droplet is close to wet bulb temperature of air.
Keywords
Droplet
evaporation
Lewis number
1.     C. Baumgurten, Mixture Formation in Internal Combustion Engines, Springer, Berlin, Germany,  2005.
2.     H. Nomura, Y. Ujiie, H. J. Rath, J. Sato and M. Kono, “Experimental Study on High-Pressure Droplet Evaporation using Microgravity Conditions,” 26th Symposium (International) on Combustion/ The Combustion Institute, 1996, pp. 1267-1273.
3.     C. Gokalp, J. Chauveau, R. Richard, M. Kramer and W. Leuckel, “Observation on the Low Twmperature Vaporization and Envelope or Wake Flame Burning of n-Heptane Droplets at Reduced Gravity during Parabolic Flight,” 22th Symposium (International) on Combustion/The Combustion Institute, 1988, pp. 2027-2035.
4.     S. S. Sazhin, W. A. Abdelghaffar, E. M. Sazhina and M. R. Heikal, “Models for Droplet Transient Heating: Effects on Droplet Evaporation, Ignition, and Break-up,” International Journal of Thermal Science, 44, 2005, pp. 610-622.
5.     B. Abramzon and W. A. Sirignano, “Droplet Vaporization Model for Spray Combustion Calculations,” International Journal of Heat and Mass Transfer, 32, 1989, pp. 1605-1618.
6.     G. F. Yao, S. I. Adel-Khalif and S. M. Ghiaasiaan, “An Investigation of Simle Evaporation Models used in Spray Simulation,” ASME, Journal of Heat Transfer, 125, 2003, pp. 179-182.
7.     A. Collin, P. Boulet, G. Parent, M. R. Vetrano and J. M. Buchlin, “Dynamic and Thermal Behaviour of Water Sprays,” International Journal of Thermal Sciences, 47, 2008, pp. 399-407.
8.     S. C. kim and H. S. Ryou, “An Experimental and Numerical Study on Fire Suppression using a Water Mist in an Enclosure,” Buildng and Environment, 38, 2003, pp. 1309-1316.
9.     T. Yoshida and T. Hyodo, “Evaporation of Water in Air, Humid Air and Superheated Steam,” Industrial and Engineering Chemistry Process Design and Development, 9, No. 2, 1970, pp. 207-214.
10.  K. Shirai, S. Matsui and A. Shinjo, “On the Temperature Change of Sprayed Water Drops Ι: Theoretical Study,” Transaction of the Japanese Society of Irregation, Drainage and Reclammation  Engineering, 35, 1971, pp. 24-29.
11.  K. Shirai, S. Matsui and A. Shinjo, “On the Temperature Change of Sprayed Water Drops ΙΙ: Experimental Study,” Transaction of the Japanese Society of Irregation, Drainage and Reclammation  Engineering, 35, 1971, pp. 30-35.
12.  Y. F. Li and W. K. Chow, “Study of Water Droplet Behavior in Hot Air Layer in Fire Extinguishment, Fire Technology,” Fire Technology, 44, 2008, pp. 351-381.
13.  L. Di-pin and C. Zu-ming, “Numerical Simulation of Water Mist Fire Suppression Technology,” Procedia Engineering, 11, 2011, pp. 205-209.
14.  L. Zheng and W. Quan, “Experimental Study of Explosive Water Mist Extinguishing Fire,” Procedia Engineering, 11, 2011, pp. 258-267.
15.  R. B. Montgomery, “Viscosity and Thermal Conductivity of Air and diffusivity of Water Vapor in Air,” Journal of Meteorology, 4, 1947, pp. 193-197.
16.  A. C. S. Baptista da Silvia, J. A. Bellini da Cunha Neto, and R. Lamberts, “Computer Simulation of Evaporative Cooling of Buildings by Water Spray Vaporization,” Ninth International IBPSA Conference, Montreal, Canada, 2005.
17.  E. K. Shashank, and H. Pitsch, “Spray Evaporation Model Sensetivities,” Center for Turbulence Research, Annual Research Briefes, Stanford University, USA, No. 20, 2011, pp. 2013-2024.