Y.C. Chang

Experimental measurements of thermophoretic deposition of glass spheres in an annulus

Abstract An apparatus was developed for the measurement of thermophoretic deposition under a fixed thermal gradient. The experiments strongly suggest that measurements of the nuclei alone do not provide the discrimination that is available for particles in the micron size range. The instrument proved sufficiently reliable to discriminate between relatively small differences in the thermal gradient. It was found that thermophoretic deposition was approximately 20–24%. No evidence of thermal instability within thermal cell was observed. Moreover, simulations indicated that the critical Rayleigh number (based on zero velocity) was not exceeded at the thermal gradient employed.

Experimental determination of size dependence forthermophoretic deposition between concentric cylinders

Abstract An experimental assembly was designed to measure the thermophoretic deposition of aerosols between concentric cylinders of a fixed temperature gradient. The deposition was measured for glass aerosols between 0.25 to 0.65 μm

The use of fibonacci sequences to model ternary breakages

Abstract An algorithm based on Fibonacci sequences was developed for use in describing ternary breakageof droplets or particles. The simulations using 3 and 6 interlaced sequences indicated that the Sauter mean diameter was almost invariant to the breakage rule and that the the logarithmic variance was strongly dependent on the rule. It was found that an algorithm based on the method could determine single pass breakage frequencies.

The potential use of sequences of fibonacci series to simulate breakage and agglomeration

Abstract Simulations were conducted to investigate the use of discrete size classes defined by sequences of interlaced Fibonacci series to describe particle breakage and agglomeration. The method was used to examine the evolution of various mean diameters for repeated ternary breakage events that yielded two equal-sized daughters and a smaller satellite. An inverse algorithm was also developed to extract size-dependent breakage frequencies from sequential size distribution measurements. Simulated mean diameters were found to depend weakly upon the assumed progeny distribution. Similarly, retrieved breakage frequencies were found to be insensitive to the assumed breakage rule. When agglomeration is considered, it is not possible to limit the resulting products to the discrete sizes which define each of the size classes. It was therefore necessary to develop an algorithm for adjusting particle numbers between bins so that mass was conserved. Simulations were carried out for constant and Brownian kernels and the results were compared with exact solutions of the Smoluchowski equation for constant kernels.

Algorithm for calculating the collection efficiency of nuclepore filters for fibers

Abstract An algorithm for obtaining the size dependent collection efficiency (or penetration) of ultrathin chrysotile fibers through nuclepore filters as a function of fiber diameter and aspect ratio is presented. Numerical simulations are used to provide estimates of the uncertainty in the calculated efficiencies. The algorithm is used to determine the variation of the efficiency (or penetration) for measurements with NPF filters of four different pore sizes.