Development of a Low-Cost, Open Source Condensation Particle Counter (CPC)
AARON COLLINS,
OpenAeros LLC Abstract Number: 105
Working Group: Instrumentation and Methods
AbstractFor 100 years, condensation particle counters (CPCs) have used supersaturated vapor to grow particles to optically detectable sizes. The most ubiquitous style is the continuous, laminar-flow forced convection design. Many improvements have been made, including reducing the minimum detectable particle size, response time, and simpler working fluids such as water. However, little effort has been focused on reducing cost and thus increasing accessibility. In this work, the design of a low-cost, open source condensation particle counter (“OpenCPC”) is presented. Inventive elements that both improve on the existing technology and cost-saving measures are employed, enabling manufacture of the OpenCPC for approximately an order of magnitude less than other commercially available CPCs, based on bill-of-material costs. These features include a low-cost optical design, featuring a lens-less scattered light collection system, a tightly focused laser module, and an off-the-shelf nozzle. Additionally, a low-cost flow control system leverages the optical pulse width of particles as they traverse the beam providing a measurement of gas velocity at the nozzle, and thus flow rate. One challenge with CPC optical detectors is the flow entering the detector is saturated with vapor which can result in condensation on the optics if the temperature is below the vapor dew-point. Traditionally, this is avoided by heating the optical detector above the dew-point, but it is not possible to heat the thermally insulating plastic used in this low-cost optics design. To overcome this obstacle, a bifurcated flow concept is used wherein a portion of the inlet flow bypasses the saturator and condenser sections and is reintroduced in the optics as a sheathing flow to prevent the primary vapor laden flow from condensing within the optical detector.
This work was supported by a gift from the Balvi Philanthropic Fund and by contributions from M. Pang, R. Andreasen, C. Libby, and L. Goessling.