GenRH-A used in an electrodynamic balance experiment by University of Bristol

Recently James Davies in the Aerosol Dynamics Research Group at the University of Bristol completed a study using the GenRH-A to control the humidity conditions in his electrodynamic balance. The GenRH-A’s ability to set an RH and have it maintained at a constant value allowed experiments to be done over a short period of time with no drift in the conditions.

The concentric-cylinder electrodynamic balance used in the study was introduced by Heinisch et al. 2009 and lends itself well to conducting kinetic measurements on droplets in conditions far from equilibrium – such as evaporation of droplets into sub-saturated conditions (0 – <100% RH).

Figure 1

A single charged droplet is generated on the fringes of the trapping cell and travels horizontally into the trapping region where it is caught within the electric fields and confined within a laser beam for imaging. The experiment has utilized the GenRH-A device to study water evaporation into humid conditions (work to be published soon by J.F. Davies, A.E. Haddrell, J.B. Wills and J.P. Reid).

Over the years there have been many EDB designs (Davis 1997), and it has become one of the most well established single particle techniques available. The cylindrical EDB provides excellent optical access for measuring droplet properties and, due to the electrode design, can confine droplets much more tightly in a central electric potential minima than in previous implementations. The design incorporates an air flow which enters the trapping cell from beneath (Figure 1) and passes as a jet over the droplet (Figure 2), isolating it from the ambient conditions. The humidity in this airflow can be set prior to the cell allowing humid conditions to be utilized in experiments.

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