Slip correction measurements for aerosol particles of doublet and triangular triplet aggregates of spheres

• Published in: Journal of aerosol science Vol. 16; no. 1; pp. 57 - 67
• Main Authors: Allen, Michael D., Raabe, Otto G.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 1985; Elsevier Science
• Subjects: Aerosols; Chemistry; Colloidal gels. Colloidal sols; Colloidal state and disperse state; Emulsions. Microemulsions. Foams; Exact sciences and technology; General and physical chemistry; Powders; Aggregation; Slip; Aerosols; Mobility; Non spherical particle; Solid particle; Measurement method; Experimental study; Corrections; Displacement
• ISSN: 0021-8502; 1879-1964
• DOI: 10.1016/0021-8502(85)90020-5

Slip correction measurements were made on six doublets and six triangular triplet aggregates of uniform plastic spheres in an improved Millikan apparatus. The results were compared with theoretical methods for correcting aggregates of uniform spheres for slip. Based on the assumption that the electric field of the Millikan apparatus oriented the aggregates with their long axes parallel to their direction of motion, continuum limit dynamic shape factors of κ 0 = 1.02 for doublets and κ 0 = 1.08 for triplets were used to determine the actual slip correction factor, C( D z ), from the Millikan cell measurements for each aggregate. Each calculated value of C( D z ) was used to solve for the adjusted sphere factor (ψ) in the Knudsen-Weber form of the slip correction equation: C(D 1= 1+ 2λ ψD 1 α+β exp − γψD 1 2λ , where λ is the mean free path of gas molecules, D 1 is the primary particle diameter, D z = ψD 1 is the slip equivalent diameter, and α, β, and γ are the slip correction parameters. For doublets ( n p = 2) of 1.18 μm polystyrene latex spheres in parallel motion, the average value of ψ was computed to be 1.384. For triangular triplets ( n p = 3) in parallel motion, the average value of ψ was computed to be 1.453. Dahneke's (1982) theoretical values of ψ indicate that the value cannot simply be based on the volume equivalent diameter ( ψ = n p 1 3 ) or the surface area equivalent diameter ( ψ = n p 1 2 ) since the value of C( D z ) depends on particle orientation, with respect to the direction of motion relative to the gas; however, our measured value of ψ for doublets in parallel motion ( ψ = 1.384) did not agree well with Dahneke's theoretical value ( ψ = 1.23). Values of ψ that were computed from the reported measurements of other investigators showed fair agreement with our results.