No abstract

The separation of micron-size particles from air by diffusiophoresis in a parallel plate collector was studied theoretically and experimentally. Particle-bearing air flowed under laminar conditions between two plates saturated with water and maintained at different temperatures. Water vapour diffused towards the cooler plate on which the particles deposited due to diffusiophoresis.The collector performance was predicted by assuming that the particles adopt the fluid velocity and this was calculated numerically from the transport equations. These results· (subsequently refined) were the basis for the design of the experimental apparatus.Good agreement between experimental data and theoretical predictions was obtained and diffusiophoresis was found to de pend strongly on the water vapour concentration and concentration gradient. To achieve complete particle removal approximately 1.5 lbs of water vapour per pound of air were required.The effect of the momentum equation on diffusion through a stagnant gas was shown to be negligible under most conditions. ABSTRACTThe removal of micron-size c~garette smoke particles from air by diffusi"ophoresisin a' simple, .parallel plate particle collector was studied theoretically and experimentally.When a vapour diffuses thro~gh a st~gnant. gas which contains small particles, the particles are found to move in the same direction as the vapour and this phenomenon is termed "Diffusiophoresis". The primary cause of diffusiophoresis is that diffusion through a stagnant gas. gives rise to a "bulk" flow in the fluid (Stefan flow). In the present study this effect was utilized by passing particle-bearing air under laminar conditions between two parallel plates (80 11 long, 12" wide) which were saturated with water and maintained at different temperatures. Water vapour thus diffused through the air towards the lower and cooler plate and the particles were deposited on this plate by diffusiophoresis. The performance of the particle collector was predicted theoretically by assuming that the particles move with the local fluid velocity and the design of the experimental apparatus was based on these predictions. It was subsequently found that the experimental data agreed quantitatively with the theoretical results based on the afore-mentioned assumption.The velocity field of the fluid was calculated by solving the fluid transport equations numerically with a minimum number of simplifying assumptions. From this work it was apparent that the diffusiophoretic velocity is a strong function of the vapour concentration and concentration. gradient in the particle collect~r·.