Differential diffusion analyzer

Figures & data

Figure 1. The solution of a one-dimensional diffusion equation for x = 1 cm and t = 10 s. On the vertical axis is the concentration according to Equation (2[2] ) and on the horizontal axis is the diffusion coefficient.

Figure 2. A schematic presentation of the DDA.

Figure 3. Illustration of the numerical model and its boundary conditions presented in Equations (4[4] )–(7).

Figure 4. (a) Theoretical DDA transmission functions for different sample to sheath flow ratios (solid lines), the charge fraction of singly charged particles in equilibrium (dashed line, Wiedensohler 1998), and the collected particle fraction for the second stage of a two-stage screen diffusion battery (gray line, Dubtsov et al. 2017). Numbers adjacent to curves represent the ratio of the sample to sheath flow. (b) Theoretical transmission functions for different flow ratios as a function of the diffusion coefficient for the DDA and a DMA. The DMA dimensions correspond to the TSI's Nano DMA, and the DDA parameters used in the model were the same as in Figure (a). The DMA transmission efficiency was calculated according to the theory presented by Stolzenburg (1988).

Figure 5. Concentration profiles in the half-cross section of the DDA for 2 nm (a), 5 nm (b), and 25 nm (c) particles. The sample flow rate is 0.32 lpm and sheath flow rate is 0.96 lpm. The concentration is normalized to the unity at the inlet.

Figure 6. A schematic of the generation and measurement setup used to calibrate the DDA with monodisperse Ag particles.

Figure 7. Measured and CFD simulated transmission efficiency of the DDA for the sheath flow of 0.48 lpm and sample flow of 0.16 lpm.

Figure 8. (a) Geometric mean diameter (GMD) of the output particle size distribution from the DDA as a function of the total flow rate (for Q_sample/Q_sheat = 0.33). (b) Geometric standard deviation (GSD) of the output particle size distribution as a function of the aerosol to sheath flow ratio. (c) Transmission efficiency as a function of the sample to sheath flow ratio. Different symbols represent the charge state of particles and the solid and the dashed lines represent the CFD and analytical model results, respectively. The analytical model was calculated based on Equation (3).

Wiedensohler, A. (1998). An Approximation of the Bipolar Charge Distribution for Particles in the Submicron Size Range. J. Aerosol Sci., 19:387–389.

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Dubtsov, S., Ovchinnikova, T., Valiulin, S., Chen, X., Manninen, H. E., Aalto, P. P., and Petäjä, T. (2017). Laboratory Verification of Aerosol Diffusion Spectrometer and the Application to Ambient Measurements of New Particle Formation. J. Aerosol Sci., 105:10–23.

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Stolzenburg, M. R. (1988). An Ultrafine Aerosol Size Distribution Measuring System. Ph.D. dissertation, Department of Mechanical Engineering, University of Minesota.

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