Generation of high concentration nanoparticles using Glowing Wire Technique
Nanoparticles (size < 100 nm) exhibit strikingly different properties than their bulk counterparts due to higher surface area and quantum effects. Because of their properties, these find application in various fields like medical, industrial and research. The Glowing wire generator (GWG) is one such technique for generation of Nanoparticles, where material is evaporated by the heating of high resistance wire and subsequent quenching by gas stream (Schmidt-Ott et al, 1980). Precise control over contamination and generation of particles in nano size range is the main advantage of this method (Peineke et al. 2009). Another advantage of generating nanoparticles using this method is significantly higher number emission rates which make them suitable to be used for specific purposes such as validation of coagulation based aerosol evolution models etc.
The generation and measurement of nanoparticle aerosols from electrically heated wire (glowing wire) is challenging, considering the control of parameters and characteristics of generated aerosols. The chemical composition of wire, electronic stability, variation in its electrical resistance with increasing temperature and carrier gas flow effects etc. affects the generation and stability of aerosols.
In the present work, we focused on developing a prototype hot wire generator for continuous generation of nanoparticle aerosols. This generator is operated at low power (~30-50 W) and can be used for continuous production of nanoparticle aerosols of concentrations up to the order of 107 cm-3 with mean size of particle agglomerates in the range of ~10-15 nm.
2. Materials & Methods
The prototype aerosol generator was parametrically studied for its response and an optimized set of operating parameters were selected and implemented in the experiments intended for generator performance and usage of generated particles. For parametric studies, GRIMM 5.403 CPC (measuring aerosols having diameter larger than 4.5 nm) was used to measure the integral aerosol number concentration, while GRIMM SMPS+C (11 nm to 1000 nm in 44 size channels) was employed for number size distribution measurements.
2.1 Hot Wire Generator description
The prototype generator (Fig. 1) consists of a metallic coil (1mm Diameter, 20 mm Long, 20 turns) enveloped in a quartz glass providing an interaction volume of 450 cm3 for the generated aerosols. The upper part of the generator was specially fabricated for electrical connection of the metal wire (handling currents in Ampere range) in the generator volume. A variac was used for supplying AC voltage in the range of 5-10 V and circuit current produced was measured to be in the range of 5-10 A. The horizontal sampling ports have been provided to guide the generated aerosols to the aerosol measuring instruments. An excess port has been provided for other parallel measurements and for maintaining the pressure/flow rates within working ranges of measuring instruments. Wire of a specific chemical composition (single or composite) can be used for the generation of nanoparticle aerosols of the material of interest. In present work, commercially available electrical heater wire and nichrome wire were used as aerosol sources. Particle free air was supplied to transport the test aerosols from the generation volume.
Generation of high concentration nanoparticles using glowing wire technique
Charge size distribution of common lab generated aerosols
Global mortality from ambient PM2.5 exposure
Evidence of invigoration of aerosol-limited warm clouds
A new size-composition resolved aerosol model (SCRAM)
Quasi-biennial oscillation of stratospheric aerosol detected
Europe Aerosols Campaign
Cover Image: Attributable premature mortality from ambient PM2.5 exposure for (A) the northern America and (B) Europe and Africa. Dark gray regions indicate areas without attributable mortality due to ambient PM2.5 below theoretical minimum-risk concentration (Courtesy: Apte et al., Environ. Sci. Tech., 2015)