You might well ask: what is the meaning when we have an overlap of the two processes? We haven't looked at this question in any detail. Ik seems to me that we are then talking about kinetics ballistics problems rather than a clear-cut case where we may speak of diffusive or impaction collection. It does seem clear that the collection mechanism, however you chose to name it, is effective, This, then, represents our current thinking on diffusion collection, and its combination with impaction to secure an effective sampling system above 100 kilofeet, implied: Perhaps I should mention again what I have already we are not talking about normal screening action which one expects from a filter. Instead, we are talking about a regime where new phenomena that are not important at atmospheric pressure do become predominant, In facet, looking at our curves, you can see that, at lower altitudes, neither impaction nor diffusion collection would be very effective. Then screening, electrostatic attraction of particles to the filter media, and other such effects become predominant. Because we are talking about somewhat unfamiliar collection mechanisms for conventional filters, we feel that experiment is necessary, both to examine the flow properties of the filters and to check out the effectiveness of these collection mechanisms, Mr, Rigali will talk about the experiments we are planning and the hardware we will use in these experiments. References 1, 2, Cook, T. B., be published, et al., High Altitude Measurements, Operation Hardtack WT-1601, Sandia Corporation, to (See ITR-1601,) Banister, J. R., A Computation of the Sampler Performance for Shots Teak and Orange of Operation Hardtack, SC-4172(TR), Sandia Corporation, December 1958. Ground-Based Testing of Proposed Sampling System (D. J. Rigali) The ground-based testing of the proposed Sandia sampling system will be done in two parts. The first phase will be a filter test setup consisting of a 3-inch-diameter test section and a 50-cubic-foot vacuum system, process, This will be used to determine the best filter materials available by a comparison and elimination Then, an extensive evaluation of the best materials will be continued to determine filter efficiencies and pressure drops at varying values of mass flow, pressure, velocity, and temperature. The equipment for this set-up is partly complete and could be ready for preliminary testing very soon. The second phase of the ground-based testing will be a rotating wing set-up in a presently available 10, 000-cubic-foot spherical vacuum tank. This set-up will be used to check out the full-scale design and operation of the complete rotor assembly at simulated altitudes up to 150,000 feet. With the planned addition of a new vacuum pump, altitudes up to 300, 000 feet can be simulated, The purpose of Phase IJ is to find a filter material or materials with a high efficiency and yet high porosity to give a relatively low pressure drop. The test chamber to be used is shown in detail in Figure 7. It consists ~ oe of a quick-opening valve, replaceable orifice plates to provide any number of constant mass flows, an evaporator wire to provide particle injection, a 3-inch-diameter test chamber with transparent walls, and, finally, the 3-inch-diameter filter, 145