Initial Stage of Natural Convection Over a Hot Aerosol Sphere

[+] Author and Article Information
Elaad Mograbi

Department of Mechanical Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel

Ezra Bar-Ziv

Department of Mechanical Engineering and Institute of Applied Research, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel

J. Fluids Eng 129(6), 695-701 (Oct 20, 2006) (7 pages) doi:10.1115/1.2734195 History: Received January 04, 2006; Revised October 20, 2006

Background: Analytical study is presented on the transient problem of buoyancy-induced motion due to the presence of a hot aerosol sphere in unbounded quiescent fluid. Method of Approach: Because the initial flow field is identically zero, the initial stage of the process is governed by viscous and buoyancy forces alone where the convective inertial terms in the momentum and energy balances are negligible, i.e., the initial development of the field is a linear process. The previous statement is examined by analyzing the scales of the various terms in the Navier-Stokes and energy equations. This scale analysis gives qualitative limitations on the validity of the linear approximation. A formal integral solution is obtained for arbitrary Prandtl number and for transient temperature field. Results: We consider, in detail, the idealized case of vanishing Prandtl number for which the thermal field is developed much faster than momentum. In this case, analytical treatment is feasible and explicit expressions for the field variables and the drag acting on the particle are derived. Detailed quantitative analysis of the spatial and temporal validity of the solution is also presented. Conclusions: The linear solution is valid throughout space for t<10 diffusion times. For t>10, an island in space appears in which inertial effects become dominant. The transient process is characterized by two different time scales: for short times, the development of the field is linear, while for small distances from the sphere and finite times, it is proportional to the square root of time. The resultant drag force acting on the sphere is proportional to the square root of time throughout the process.

Copyright © 2007 by American Society of Mechanical Engineers
Your Session has timed out. Please sign back in to continue.



Grahic Jump Location
Figure 1

Schematic view of the problem

Grahic Jump Location
Figure 2

Temporal behavior of the function χ for three distances from the sphere: ρ=0.01, 0.1 1; based on Eqs. 20, 23, 26

Grahic Jump Location
Figure 3

Behavior of χ with distance based on Eqs. 20, 23, 26 for t=0.1, 1

Grahic Jump Location
Figure 4

Region of validity of the linear solution: based on Eq. 29 (bold line) and based on Eqs. 27,28 (dotted line)

Grahic Jump Location
Figure 5

Streamlines around the sphere for different times: t=0.01, 1, 10, 100

Grahic Jump Location
Figure 6

Streamlines around the sphere for t→0




Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In