SCIENCE
Impact of Thermophoresis on Filtration Efficiency An Understanding of Thermophoresis in a Filtration System Requires a Comprehensive Analysis for Effective Filtration By Felix Swamidoss
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hermophoresis is a phenomenon related to particle motion in a fluid due to temperature gradients. In the context of filtration, especially in the field of air filtration, thermophoresis can have an impact on filtration efficiency (may increase or decrease depends on the factors of influence). The effect of thermophoresis on filtration efficiency depends on various factors, including the size of aerosol, characteristics of the particles, the filtration medium, and the operating conditions. Here are some general points to consider:
Particle Size and Composition Thermophoresis tends to be more significant for smaller particles. As particle size decreases, the influence of thermophoresis becomes more pronounced. Variations in filtration efficiency are anticipated with temperature fluctuations. At elevated temperatures, heightened Brownian motion intensifies diffusive deposition of aerosol particles onto the filter. This is due to the increase in viscosity of air as we know the basics. “With increase in temperature, gas molecules
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attain more kinetic energy and the rate of collision is more (Brownian motion). Hence, viscosity of gases increases with an increase in temperature. The increased activity of Brownian motion enhances the chances of particles making contact with and being captured by the filter fibers. Interestingly, a rise in temperature tends to decrease particle penetration, indicating a potential improvement in overall filtration efficiency. This reduction in penetration can be attributed to the combined effects of increased Brownian motion and potentially altered airflow patterns, but this more predominant for smaller particle size which obey only Brownian principle. Also, the factor is considered when rise in viscosity of air with temperature could impact airflow through the filter, potentially leading to higher resistance and changes in pressure drop across the filter medium. While gravitational settling and inertial impaction of particles slows down at higher temperatures due to the increased viscosity of air, this deceleration could result in a decrease in the interception of larger particles by the filter. Larger particles
