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Health care facility ventilation design greatly affects disease transmission by aerosols. The desire to control infection in hospitals and at the same time to reduce their carbon footprint motivates the use of unconventional solutions for building design and associated control measures. This paper considers indoor sources and types of infectious aerosols, and pathogen viability and infectivity behaviors in response to environmental conditions. Aerosol dispersion, heat and mass transfer, deposition in the respiratory tract, and infection mechanisms are discussed, with an emphasis on experimental and modeling approaches. Key building design parameters are described that include types of ventilation systems (mixing, displacement, natural and hybrid), air exchange rate, temperature and relative humidity, air flow distribution structure, occupancy, engineered disinfection of air (filtration and UV radiation), and architectural programming (source and activity management) for health care facilities. The paper describes major findings and suggests future research needs in methods for ventilation design of health care facilities to prevent airborne infection risk

Particulate Matter Emission Characterization From a Natural Gas Fuelled High Pressure Direct Injection Engine

High-Pressure Direct-Injection (HPDI) combustion of Natural Gas can reduce the gaseous and Particulate Matter (PM) emissions compared to a conventional diesel engine. Upcoming EPA and EURO emission limits may restrict particle number as well as particle mass. In preparation for these upcoming limits, the PM mass, size and composition was studied from a heavy-duty Cummins ISX engine converted to HPDI operation. To characterize the PM emissions, tests were based around a mid-speed, high-load operating point. Injection timing, equivalence ratio, gas supply pressure, EGR % and diesel injection mass were isolated and varied. PM emissions were characterized by the mobility size distribution, light scattering and filter loading. In addition a novel thermodenuder was used to determine the PM volatile fraction. It was found that EQR and EGR have the greatest effect on PM mass emissions and the correlations between these parameters are evaluated. The mean particles size and number concentrations are again most effected by EGR and EQR with smaller effects from the GRP and diesel pilot. The size distributions of the parameter variations are similar and there are no nucleation mode ultrafine particles observed. The volatile fraction is fairly constant across the parameter variations and is found to be around 18% of the mass and 11% by number of particles at this high load condition.</jats:p

Phenomenological Simulation of Non-Premixed Gas Jet Flames Including Soot Formation and Oxidation

A phenomenological model (called here “Slice Model”) has been developed to simulate non-premixed gas jet flames including soot formation in the domain. The Slice Model is based on the self-similarity solution of gas jets and forced to satisfy momentum, mass and energy balances in every cross section. The Slice Model can predict the velocity, mass fraction and temperature field of non-reacting and reacting jets over a wide range of changes in the jet parameters. A sub-model for soot formation based on Hiroyasu’ model is applied to predict soot formation in non-premixed flames. Cantera, an open-source chemical kinetics software, is integrated with the Slice Model to predict the temperature distribution (based on equilibrium composition) of reacting jets. The soot formation prediction of the Slice Model is compared with experimental data in the literature. For velocity, soot mass fraction and temperature, agreement with experiment is about as good as it is for the much more computationally intensive RANS CFD simulations. On this basis, the Slice Model is promising as the core of a non-premixed natural gas engine simulation package under development.</jats:p