Microscale Modeling of Frozen Particle Fluid Systems with a Bonded-Particle Model Method.

An inventive microscale simulation approach is applied to investigate the mechanics of frozen particle fluid systems (PFS). The simulation is based on the discrete element method (DEM) and bonded-particle model (BPM) approach. Discrete particles connected by solid bonds represent frozen agglomerates. Uniaxial compression experiments were performed to gather data for material modeling and further simulation model validation. Different typical mechanical behavior (brittle, ductile, dilatant) were reviewed regarding strain rates, saturation levels, and particle mechanical or surface properties. Among all these factors, strain rate significantly affects the mechanical behavior and properties of the agglomerates. A new solid bond model considering strain-dependent and time-dependent behavior is developed for describing the rheology of the frozen particle fluid systems. Without alternating Young's modulus and Poisson's ratio of the bond material, the developed solid model provides a suitable agreement with the experimental results regarding different strain rates.

Removal and leakage of environmental tobacco smoke from a model smoking room.

Experimental studies on the removal of accumulated environmental tobacco smoke (ETS) and the effectiveness of ETS leakage control were carried out in a model smoking room using carbon monoxide, nicotine, 3-ethenylpyridine, respirable suspended particulates, and ultrafine particles (UFP) as the ETS tracers. The study investigated the effectiveness of the designated smoking room, equipped with a displacement ventilation system under different ventilation rates (10-58 L/sec per person,) in removing the ETS tracers. The extent of ETS leakage through different door operating scenarios under various ventilation rates was intensively studied. In particular, a manikin installed on a motorized rail was used to study the effect of human movement on the leakage of the ETS tracers. A double-door anteroom design was incorporated into the smoking room to study its effectiveness in ETS leakage prevention. It shows that at least 5 Pa of negative pressure, a fresh air supply rate 3-5 times higher than a typical office, direct air exhaust without air recirculation, and keeping the door closed are important for reducing ETS leakage. However, with the smokers moving in and out and the opening of the door, noticeable leakage of ETS can occur. The double-door anteroom design can improve leakage prevention. Among the five tracers, nicotine required the longest purging time to remove, after the smoking activity was stopped in the smoking room, due to its highly sorptive property. At least 4.4-6 hr of purging is needed for minimizing ETS exposure by non-smokers entering the smoking room. The peak size of particulate matter inside the smoking room is about 80-100 nm, suggesting the importance of including UFP as an indicator for monitoring the exposure and leakage of ETS. The impact of manikin movement on contaminant transport was studied, providing useful information on the effects of human activities on indoor air quality multicompartmental modeling.