The Mathematics of Blunt Body Sampling by Sarah Jane Dunnett, Derek Binns Ingham (auth.)

By Sarah Jane Dunnett, Derek Binns Ingham (auth.)

Particle samplers are standard in offices in an effort to be sure the focus of airborne debris within the surroundings. they often function by way of drawing air, by way of a pump, via a number of orifices within the sampler physique and housed in the sampler is a filter out wherein the air is in this case drawn. The airborne debris are gathered at the filter out and their focus is decided. a number of samplers were designed for this objective together with "static" samplers, that are situated in a hard and fast place in a operating surroundings and verify the airborne dirt and dust focus averaged over a prescribed time period at that one element, and "personal" samplers that are fixed on a operating individual just about the respiring region. The ORB sampler, a static sampler designed via Ogden and Birkett (1978) to have nearly a similar access potency, for debris with aerodynamical diameter as much as at the very least 25~m, as a human head both uncovered to all wind instructions for wind speeds among zero and a pair of. 75m1s, is proven in Fig. l. l and examples of private samplers are proven in Fig. 1. 2a, b and c and characterize a unmarried 4mm gap sampler, a seven gap sampler and a 25mm open face filter out holder respectively. those 3 samplers are one of the most generic own samplers for sampling the complete airborne concentrations of office dusts in Britain.

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12) Considering the second stagnation point near 6=n, at 6=6 2 say, where 6 2=n+c 2. e. for I{»O. e. 15) 54 as £, and £2 are small this becomes, s - '" a 1. e. 16) '" sin(!! ) 2 )+f2n [ 2kot(!! 5), but when the sampler is orientated at an angle ~ to the flow the distance between the stagnation points is a constant plus a term of 0('1'). In extending the empirical model to include sampling at any orientation Vincent(1987) assumed that s varied with 'I' in the same way as when facing the flow and this is clearly not correct.

1) it can be seen that in Vincents empirical formulae the correction term is positive but from the theoretical model it is negative. 18. In these cases the size of the inlet is significant relative to the diameter of the sampler body and therefore the assumption made in the mathematical model that 5«a is not valid. 1). e. In this case the inlet is 52 small and so the experimental results can be compared with the theoretical model where the inlet is modelled as a line sink. 6), it is seen that the second term in the expansion is not significant relative to the first and therefore s/a=~(~/n), agreeing with Vincents experimental result.

A study of non-spherical particles was also made by Cox (1965, 1970, 1971). Fuchs (1964) described the motion of ellipsoidal particles moving through a viscous fluid under the influence of an external force acting through its centre. In this case, for low particle Reynolds numbers, it has been found that the torque about the particles centre is zero and therefore it will not rotate about its centre. Also, experiments have shown that the resistance offered by a fluid is given by Stokes law, even for particles of non-spherical shape, if the numerical coefficient is adjusted according to the particle shape.

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