No abstract

Most of the developed models for the air-gap membrane distillation (AGMD) process are one-dimensional and rely on experimentally determined parameters. Herein, inspired by the effectiveness-number of transfer units method for the design of heat exchangers, a new approach of theoretical model is developed based on mass and heat transfer mechanisms in the AGMD process by considering the temperature variation in two dimensions. The results of our self-sustained model match well with the AGMD experimental results, with less than 4% deviation. Using the developed model, the AGMD performance is systematically investigated in terms of permeate flux, energy efficiency, and temperature and concentration polarization effects, and the results are compared with direct contact membrane distillation (DCMD). The results showed that the feed temperature had the most significant impact on the permeate flux and energy efficiency. The thickness of the air-gap and the flow rate were found to be the second most effective parameters. In contrast, the membrane thermal conductivity and porosity did not play a determining role. A 60% increase in the feed temperature increased the permeate flux and energy efficiency by 200 and 2%, respectively. By increasing the flow rate from 0.2 to 8 liters per minute, the permeate flux was enhanced by 67.19%. The air-gap thickness increment from 0.6 to 5.6 mm caused a 36.8% reduction in the permeate flux. In our comparative study, the permeate flux and the gained output ratio for DCMD were 56.6 and 27.3% higher as compared to AGMD at the same conditions. However, the thermal efficiency of the AGMD process was 24.7% larger than that of the DCMD process. The developed model provides solutions to minimize the undesirable effects of temperature and concentration polarization and proposes an optimum design map to achieve higher energy efficiency and permeate flux.

No abstract

Electrostatic charge on inhaled aerosol particles has only a minor effect on deposition for large particles at higher flow rates, because in this case inertial impaction dominates deposition. However, for particles with low inertia, for example, small particles or low flow rates, large values of electrostatic charge strongly increase nasal deposition in the present infant extrathoracic airway.

An in vitro study was conducted in the Alberta idealized child mouth-throat, which mimics average deposition in a set of nine 6-14-year-old subjects, to examine the enhancement of deposition of monodisperse uniformly charged particles as a result of induced electrostatic forces. A purpose-based atomizer was designed and built for generating monodisperse, uniformly charged particles. The atomizer generates droplets by jet break up under the action of capillary waves and charges them via electrostatic induction. The experiments cover different particle aerodynamic diameters (d a = 3.6, 4.4, and 5.9 µm), at two flow rates (Q = 10 and 20 L/min), over a wide range of elementary charges per particle (0-10,000 e). The results show substantial increases in particle deposition in the present idealized pediatric mouth throat compared to neutral aerosols. Two empirical equations, as a function of Reynolds number, Stokes number, and induced charge number are introduced for the prediction of mouth-throat deposition in children, based on two different characteristic diameters of the airway.