Thermal force on a sphere

Abstract

The thermal force on a sphere of insulating material centered between parallel plates has been measured in the three monatomic gases He, Ne, and Ar and the two diatomic gases N2 and HD over a broad range of mean free paths. These measurements are on a finite system, an apparatus where the sphere radius and the plate spacing are of the same order of magnitude. Behavior near the observed maximum of the thermal force is stressed. The translational heat flux characterizes the dependence of the thermal force on the gas. Comparison with existing theories is made for the three basic Knudsen regimes, and the data are compared to previous measurements of the thermal force on aerosols.

Thermophoresis of a Spherical Particle: Reassessment, Clarification, and New Analysis

“…Takata et al (1993) noted that the solution for arbitrary could be expressed as a linear combination of the solution for → ∞ and that for a spherical particle with a given axisymmetric and sinusoidally varying surface temperature immersed in an infinite expanse of gas at temperature T 0 and pressure p 0 . They obtained Saxton and Ranz (1952), Figure 3 Castor oil in air 9.5 0.05-0.12 Schmitt (1959), Figure 6 Silicone oil in air 7.5 0.11-2.00 Schadt and Cadle (1961), Figure 1b TCP in air 10 0.14-0.76 Schadt and Cadle (1961), Figure 2b NaCl in air 322 0.20-1.49 Schadt and Cadle (1961), Figure 3 Hg in air 581 0.45-3.60 Jacobsen and Brock (1965), Figures 4 and 5 NaCl in Ar 300 0.06-0.67 Tong (1975), Figure 6 Al in He 1519 0.01-0.32 Davis and Adair (1975), Figure 5 Cork in Ar 2.5 0.05-1.80 Li and Davis (1995a), Figure 11 PSL in CO 2 10 0.10-3.50 Li and Davis (1995b), Figure 6 DOP in CO 2 12 0.05-4.20 Li and Davis (1995b), Figure 6 Glass in CO 2 75 0.12-4.00 Li and Davis (1995b), Figure 10 DOP in He 0.8 0.10-1.90…”

“…A. Davis and Adair (1975) measured the thermophoretic force on a cork sphere of radius 6.3 mm suspended in a number of different gases in a vacuum chamber. Their main interest was to investigate the effect of the proximity of the plates producing the temperature gradient and their data is not directly applicable to the present discussion.…”

Effects of gas species on pressure dependence of thermophoretic velocity

“…Fredlund (1938) attempted a systematic experiment to examine the effect of the temperature field upon a disk suspended on a balance. The thermophoretic force and the thermophoretic velocity are measured by several methods: Millikan cell (Rosenblatt & La Mer, 1946;Saxton & Ranz, 1952;Schadt & Cadle, 1961;Jacobsen & Brock, 1965), electrodynamic balance (Li & Davis, 1995a, 1995b, precipitation in a thermoprecipitator (Schadt & Cadle, 1957;Keng & Orr, 1966), jet technique (Kousaka et al, 1976;Prodi et al, 1979;Talbot et al, 1980), and deflection of a particle suspended by a small wire (Davis & Adair, 1975;Tong, 1975).…”

Thermophoresis in Rarefied Gas Flows

“…Davis and Adair (1975) used a microstress gauge to measure the thermophoretic force on a sphere centered between parallel plates as a function of gas pressure. Their measurements were made on a nite system (the sphere radius was approximately 20% of the plate separation), however, so it is not possible to directly compare their results to the previous theoretical analyses, which all assumed R p ¿ L. More recently, Li and Davis (1995a, b) used an electrodynamic balance to study particle thermophoresis in the particle transition regime for a variety of particle/gas combinations.…”