Combined thermocapillary and buoyancy-driven convection within short-duration pulse-heated liquid droplets

Journal Article · Wed Dec 01 04:00:00 EST 1999 · Numerical Heat Transfer. Part A, Applications

OSTI ID:20005617

Shen, F; Khodadadi, J M

Containerless processing of advanced materials and thermophysical property determination techniques for high-temperature materials almost exclusively manipulate spherical droplets. Spherical droplets are also observed in other industrial applications and naturally occurring phenomena, such as spray forming, fuel droplet vaporization, thermal storage technology, powder metallurgy, and environmental transport. In addition to the heat diffusion mode of thermal transport, the possible mechanisms of convection that may be encountered within droplets are surface-tension-driven and buoyancy-driven convection. Here, buoyancy-driven convection and its interaction with thermocapillary flow within short-duration-heated liquid droplets was studied computationally. A parametric study was conducted to investigate the effect of the Grashof number Gr and the surface-tension Reynolds number Re for fluids with different Prandtl numbers Pr having both negative and positive surface-tension temperature coefficients ({partial{underscore}derivative}{sigma}/{partial{underscore}derivative}T). Both the additive and impeding effects of buoyancy-driven convection on the thermocapillary flow was observed. The numerical analysis indicated that the buoyancy-driven convection has a weak effect on low-Pr fluids during the short-pulse-heating condition. For mid-Pr fluids the buoyancy effect is more prominent. In monitoring the history of the surface temperature rise, it was found that the buoyancy-driven convection has a weak effect for low-Pr fluids at the side and bottom observation points, whereas buoyancy-driven convection has substantial influence at the bottom observation point for mid-Pr fluids with a positive surface-tension temperature coefficient. It was concluded that the presence of additive or impeding modes depends not only on the sign of the surface-tension temperature coefficient of fluids as proposed by other researchers, but also on Pr, geometry, and boundary conditions. The finite-time-pulse duration effect was also simulated, and it was concluded that the finite-time pulse enhances both modes of convection.

• Research Organization: Auburn Univ., AL (US)
• OSTI ID: 20005617
• Journal Information: Numerical Heat Transfer. Part A, Applications, Journal Name: Numerical Heat Transfer. Part A, Applications Journal Issue: 8 Vol. 36; ISSN 1040-7782; ISSN NHAAES
• Country of Publication: United States
• Language: English

Related Subjects

42 ENGINEERING
CAPILLARY FLOW
DROPLETS
FLUIDS
GRASHOF NUMBER
NATURAL CONVECTION
NUMERICAL ANALYSIS
PARAMETRIC ANALYSIS
PRANDTL NUMBER
SURFACE TENSION