Deposition of aerosol particles in contraction fittings

Particle deposition was measured in contraction fittings with half-angles of 12 degrees, 45 degrees, and 90 degrees. It was found that for a given contraction half angle, the losses in a contraction fitting correlate well with the parameter Stk(1-A(o)/A(i)) where: Stk is a Pich-type Stokes number based on inlet velocity and outlet diameter, A, is the outlet area, and A, is the inlet area. A correlation developed from the experimental results allows prediction of the particle losses in contraction fittings as a function of Stokes number, area ratio, and contraction half-angle. Test conditions on which the correlation was based include a range of 0.001 less than or equal to Stk (1-A(o)/ A(i)) less than or equal to 100. Area ratios A(o)/A(i) used in the tests were 0.062, 0.215, and 0.571, and the test conditions encompassed Reynolds numbers based on downstream port diameter of 1120 to 58,500. The aerosol particle deposition in the contraction fitting was also modeled numerically and the numerical results show good agreement with the experimental data. Flow turbulence was taken into account in the numerical work using a standard k-e closure model.