# HW2-6130 - Homework II Single Particle Motion Diffusion...

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Homework II – Single Particle Motion, Diffusion, Thermal Forces (due 02/11/2010) 1. What is the settling velocity of an asbestos fiber in the shape of a cylinder 1 μ m in diameter and 10 μ m long at standard conditions? Assume random orientation and a density of 2.5 g/cm 3 . Neglect slip correction. (10%) 2. (a) Derive an expression for the collection efficiency (as a function of particle size) for a multi-layer settling chamber (see the figure below) with N equispaced sections. Assume a uniform flow, uniform distribution of aerosols at the inlet, and negligible slip correction. Neglect diffusion. (10%) 3. A typical mass size distribution from a diesel-equipped coal mine is bimodal, with one mode for the diesel smoke particles at 0.16 μ m, and the other for coal dust at 7 μ m. The saddle point between the modes is at an aerodynamic diameter of 0.8 μ m. If you are asked to use a single-stage impactor to separate diesel smoke from coal dust in a sample of air from a coal mine, what nozzle diameter will you choose if the total sample flow rate is 2.5 l/min and 8 nozzles are used? (10%)

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HW2-6130 - Homework II Single Particle Motion Diffusion...

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