Predicting the airborne microbial transmission via human breath particles using a gated recurrent units neural network

Purpose The purpose of this paper is to devise a tool based on computational fluid dynamics (CFD) and machine learning (ML), for the assessment of potential airborne microbial transmission in enclosed spaces. A gated recurrent units neural network (GRU-NN) is presented to learn and predict the behaviour of droplets expelled through breaths via particle tracking data sets. Design/methodology/approach A computational methodology is used for investigating how infectious particles that originated in one location are transported by air and spread throughout a room. High-fidelity prediction of indoor airflow is obtained by means of an in-house parallel CFD solver, which uses a one equation Spalart–Allmaras turbulence model. Several flow scenarios are considered by varying different ventilation conditions and source locations. The CFD model is used for computing the trajectories of the particles emitted by human breath. The numerical results are used for the ML training. Findings In this work, it is shown that the developed ML model, based on the GRU-NN, can accurately predict the airborne particle movement across an indoor environment for different vent operation conditions and source locations. The numerical results in this paper prove that the presented methodology is able to provide accurate predictions of the time evolution of particle distribution at different locations of the enclosed space. Originality/value This study paves the way for the development of efficient and reliable tools for predicting virus airborne movement under different ventilation conditions and different human positions within an indoor environment, potentially leading to the new design. A parametric study is carried out to evaluate the impact of system settings on time variation particles emitted by human breath within the space considered.

Algorithm offers personalized audio in enclosed space

An acoustic algorithm could soon let occupants of a car cabin listen to different audio programmes without the need for headphones.

Semi-transparent Photovoltaic Thermal Greenhouse System Combined with Earth Air Heat Exchanger for Hot Climatic Condition

Semi-transparent photovoltaic thermal (SPVT) greenhouse system combined with an earth air heat exchanger (EAHE) has been developed to make the system sustainable. The system is designed to cultivate plants in a hot climatic condition, where green net is provided which bifurcates the enclosed space of the greenhouse into zone-1 and zone-2, and this green net cuts the solar radiation incident on the plants. The influence of air changes in zone-1, mass flow rate of air flowing through EAHE, and packing factor on PV cell, air of the greenhouse, and the plant temperatures is investigated for a typical harsh summer day by using periodic model of these parameters. Further, for a holistic performance assessment of this SPVT greenhouse, exergy, thermal load leveling, and decrement factor are evaluated. Results indicate that the optimum temperature range for plant growth (30 °C- 37 °C) within the greenhouse can be achieved through a combination of ventilation in zone-1 and integration of EAHE. The temperature of plants reduced by 9 °C for 30 air changes in zone-1, and the temperature reduces further by 24 °C when EAHE having a flow rate of 0.5 kg/s is operated. The SPVT greenhouse system also generates 128 kWh of daily overall exergy that makes the system sustainable.

Modeling the Spread of COVID-19 in Enclosed Spaces

SEIR models are typically conjured for populations in open environments; however, there seems to be a lack of these types of models that deal with infection rates amongst enclosed spaces. We have also seen certain age groups struggle to deal with COVID-19 more than others, and to this end, we have constructed an age-structured SEIR model that incorporates the Gammaitoni–Nucci model, which is used for infective material in an enclosed space with ventilation. We apply some sensitivity analysis to better understand which parameters have the biggest impact on overall infection rates, as well as create a realistic scenario in which we apply our model to see the comparison in sickness rates amongst four different age groups with different ventilation filtration systems (UVGI, HEPA) and differing quanta production rates.

Simulation of Possible Fire and Explosion Hazards of Clean Fuel Vehicles in Garages

Clean fuel is advocated to be used for sustainability. The number of liquefied petroleum gas (LPG) and hydrogen vehicles is increasing globally. Explosion hazard is a threat. On the other hand, the use of hydrogen is under consideration in Hong Kong. Explosion hazards of these clean fuel (LPG and hydrogen) vehicles were studied and are compared in this paper. The computational fluid dynamics (CFD) software Flame Acceleration Simulator (FLACS) was used. A car garage with a rolling shutter as its entrance was selected for study. Dispersion of LPG from the leakage source with ignition at a higher position was studied. The same garage was used with a typical hydrogen vehicle leaking 3.4 pounds (1.5 kg) of hydrogen in 100 s, the mass flow rate being equal to 0.015 kgs−1. The hydrogen vehicle used in the simulation has two hydrogen tanks with a combined capacity of 5 kg. The entire tank would be completely vented out in about 333 s. Two scenarios of CFD simulation were carried out. In the first scenario, the rolling shutter was completely closed and the leaked LPG or hydrogen was ignited at 300 s after leakage. The second scenario was conducted with a gap height of 0.3 m under the rolling shutter. Predicted results of explosion pressure and temperature show that appropriate active fire engineering systems are required when servicing these clean fuel vehicles in garages. An appropriate vent in an enclosed space such as the garage is important in reducing explosion hazards.

A simplified model to estimate COVID19 transport in enclosed spaces

Airborne pathogen respiratory droplets are the primary route of COVID19 transmission, which are released from infected people. The strength and amplitude of a release mechanism strongly depend on the source mode, including respiration, speech, sneeze, and cough. This study aims to develop a simplified model for evaluation of spreading range (length) in sneeze and cough modes using the results of Eulerian-Lagrangian CFD model. The Eulerian computational framework is first validated with experimental data, and then a high-fidelity Lagrangian CFD model is employed to monitor various scale particles’ trajectory, evaporation, and lingering persistency. A series of Eulerian-Lagrangian CFD simulations is conducted to generate a database of bioaerosol release spectrum for the release modes in various thermal conditions of an enclosed space. Eventually, a correlation fitted over the data to offer a simplified airborne pathogen spread model. The simplified model can be applied as a source model for design and decision-making about ventilation systems, occupancy thresholds, and disease transmission risks in enclosed spaces.

On the Low Frequency Impact Noise Measurement in Residential Buildings

We commonly encounter cases that, despite the fact that buildings meet normative requirements, people are disturbed by unwanted noise generated by walking and other sources of impact noise. It is not unusual that in practice the designer often moves on the edge of the required criteria in order to reduce the cost of constructions and its parts. In this article, we selected 4 blindly chosen cases of flats where complaints from residents about high levels of impact noise were recorded although the construction meets the requirements set out in the standard. Based on the obtained documentation of in-situ performed measurements by different consulting companies, BEM and FEM models were created, and the distribution of acoustic pressure in an enclosed space and compared different methods of spatial averaging of the resulting acoustic pressure were simulated. The aim of this analysis is to point some of the reasons for possible user complaints about the impact noise despite normative requirements. The usual problems are benevolent national requirements and the issue of measuring noise in the low frequency range and underestimating its significance. The article also discusses the currently set requirements for the evaluation of floor structures in selected countries.

Experimental Correlations Nu vs Gr.Pr at Varying Widths for Convective Heat Flow Through a Large Aperture in a Full Scale Enclosed Space

Convective heat transfer through a large aperture has been studied theoretically and experimentally using reduced scale models for many years. This paper describes the effect of the width of a large opening on the convective heat flow in an enclosure for 5.6×108< Rayleigh number (Ra)<2.8×1010. In our case a full scale realistic calorimetric chamber (5.5m x 2.5m x 2.5m) was used in this study. This chamber contains two zones connected by a large aperture of height H. A hot and cold wall on each side of the aperture will create a temperature difference between the two zones. Empirical equations are expressed in terms of varying door aspect ratio ADS, i.e.: NuPr=(α+βWH)∗Grb, at various temperature differences between the two zones. It was clearly found that as the width decreases the convective flux increases substantially. The instability of the air flow due to the apparition of a small turbulence increased when the opening width gets larger. It was also noticed that the neutral axis (air velocity = 0) goes up when the width of the opening decreases resulting in an acceleration of the air flow above the neutral axis. The liability of these experimental results could be useful for the validation of simulation models.