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Droplet nuclei dispersion patterns in indoor environments are reviewed from a physics view to explore the possibility of airborne transmission of SARS-CoV-2. This review analyzes works on particle dispersion patterns and their concentration in vortical structures in different indoor environments. Numerical simulations and experiments reveal the formation of the buildings’ recirculation zones and vortex flow regions by flow separation, airflow interaction around objects, internal dispersion of airflow, or thermal plume. These vortical structures showed high particle concentration because particles are trapped for long periods. Then a hypothesis is proposed to explain why some medical studies detect the presence of SARS-CoV-2 and others do not detect the virus. The hypothesis proposes that airborne transmission is possible if virus-laden droplet nuclei are trapped in vortical structures associated with recirculation zones. This hypothesis is reinforced by a numerical study in a restaurant that presented possible evidence of airborne transmission by a large recirculating air zone. Furthermore, a medical study in a hospital is discussed from a physical view for identifying the formation of recirculation zones and their relation with positive tests for viruses. The observations show air sampling site located in this vortical structure is positive for the SARS-CoV-2 RNA. Therefore, the formation of vortical structures associated with recirculation zones should be avoided to minimize the possibility of airborne transmission. This work tries to understand the complex phenomenon of airborne transmission as a way in the prevention of transmission of infectious diseases.

Present work focuses on frost accretion in a spine-finned inverted-V tube array evaporator. An experimental evaluation was performed using a standard issue, vertical top-mount, 18 cubic feet, 0.5 m3, refrigerator. Evaporator temperature distribution, inner airflow velocity, and relative humidity were measured to account for convective phenomena influencing frost distribution. Frost formation and accretion on the surface of the evaporator were visualized using thermal and microscopic imagery. The images were processed using a machine vision algorithm to measure frost thickness. Complementarily, frost density and vapor mass transfer were computed using available correlations. An estimation function was derived from the compiled data using a semi empirical approach, i.e., direct measurements and thermophysical substance properties. The resulting mathematical expression estimated the frost accretion rate within an error expectancy, RMSE, of 0.1479 and displayed a goodness-of-fit, R-Squared, of 0.9029. Based on these results, semi empirical estimation, is proposed as a viable approach to construct adequate limits for new predictions, vis-à-vis evaporator performance, ultimately reducing appliance energy consumption via implementing more effective control strategies regarding internal defrosting.

Shallow geothermal energy systems utilize the upper layers of the ground to provide space heating and cooling, with a relatively high efficiency. The research presented aims to assess the potential harnessing of this source and applying it for indoor conditioning of a precision agriculture facility. An experimental phase was conducted to measure the temperature of the ground at 0.75 m, 1.5 m, 2.25 m, and 3.0 m. Field testing was performed employing two probes; one uncovered and a second insulated with a polyethylene sheet, to evaluate the effect soil water content variations exert over the soil temperature. It was found that, given the high permeability and good drainage of the soil material, water content is not statistically significant, ruling out the presence of microconvective phenomena within the interstices of the undisturbed earth. Based on the temperature profile obtained, achievable heat extraction capacity was computed by modelling a buried pipe system. A parametrization was conducted showing that, of all the involved factors, pipe depth, pitch and their interaction, are the ones that contribute the most to the heat output variability. The computed available heat flow was used to simulate the performance of a geothermal heat pumping system for greenhouse heating based on real operation data, provided by the owners. The results show that, shallower layers of the ground, can provide adequate solutions for immediate thermal needs; a 5-pipe, 100m-length ground loop at 0.75 m, could provide 90% of the total thermal demand, whilst an 11-pipe, 200m-length loop, at 1.5 m depth, reaches 84% of the same demand, with a variability reduction in availability of 10% to 20% depending on the severity of surface conditions. However, for deeper layers, i.e., 2.25 m and 3.0 m, respective maximum heat output amounts to 43% and 49% of the total thermal demand. Nonetheless, these configurations yield the most stable and constant heat flow of the lot, making them particularly suitable for preheating/subcooling processes or even long-term thermal storage. Despite not fulfilling the total thermal demand of the greenhouse, these setups are more than capable of providing support to on-site conditioning devices; requiring a lower upkeep and yielding a higher efficiency, which would reduce overall production costs. Furthermore, from the conducted data analysis, it was found that controlling the agronomic values, associated to indoor agriculture, facilitates the physical aspect of greenhouse energy management, paving the way to more optimized thermal solutions, tailored to different sets of operation conditions.

The work aims to numerically evaluate different injection configurations for the analysis of a two-phase flow behavior and evolution through a staggered Y-junction pipeline. To minimize agglomeration between inlets, the injection zones have a separation distance, avoiding areas with eddies or swirls owing to strong turbulence. Six input scenarios were examined accordingly with injection system experimental data. Results show significant variations because the main fluid develops a swirl over the pipe center. This is generated immediately after the phases’ supply zone due to the oil-phase because it presents a partial pipe flooding, even in the water injection zone. Moreover, the supply configuration has significant relevance to the main flow development. Accordingly, many flow patterns can be achieved depending on the phases’ confluence coming from the supply system. The interface velocities confirm the transition process and flow pattern development, which are driven by the phases’ velocities describing the early stages of three flow patterns formed during the fluids’ confluence. Finally, a substantial extent of the conjunction process points out that caution must be exercised during the injection supply system selection for this type of junction pipeline to achieve a better, and smooth blend, with either narrow, medium, or wide emulsions.

This work aims to analyse different injection configurations for the analysis of the emulsification process in a Y-junction staggered horizontal pipeline. The case study comprises a multiphase analysis between two liquids, one with high and the other with low viscosity. Through numerical simulations, it is intended to explain the behaviour and describe the mechanism that produces the water–glycerol emulsification process with three supply zones for both fluids. According to the phase injection scheme, six input scenarios or combinations were analysed. Through strain rate and shear velocity analyses, it was possible to describe the early stages of the emulsification process before a flow pattern is constituted. The results show significant variations concerning the high viscosity fluid, mainly because it presents a partial pipe flooding, even in the injection zone of the low viscosity fluid. The fluid ratio varies according to the input position of the phases. Additionally, a smooth blending process was observed in some scenarios, due to the fact that the continuous phase gradually directs the main fluid to the pipeline centre. The analysis revealed that supply configuration has a significant relevance on the development of the main fluid flow and a substantial extent on the emulsification process.

The flow of water through a horizontal small-scale Venturi tube of rectangular cross-section is simulated using a modified version of the open-source code DualSPHysics, which is based on Smoothed Particle Hydrodynamics (SPH) methods. Water is simulated using the Murnaghan-Tait equation of state so that weak compressibility is allowed. The hydrodynamics is coupled to a Large-Eddy Simulation (LES) turbulence model. The convergence properties of SPH are improved by adopting a C[Formula: see text] Wendland function as the interpolation kernel, increased number of neighboring particles and non-reflective open boundary conditions at the outlet of the Venturi tube. The flow structure and differential pressure as well as the mainstream velocity profiles at different stations are compared with calibrated experimental data. A resolution independence test shows that good convergence to the experimental measurements is achieved using four million particles. At this resolution the simulations predict the experimental centerline velocity profile along the Venturi meter for a volumetric flow rate of ten liters per minutes (lpm) with a root-mean-square error of 4.3%. This error grows to 7.1% when the volumetric flow rate increases to 25 lpm. The predicted differential pressure matches the experimental data with errors varying from 1.4% (for 10 lpm) to 6.8% (for 25 lpm). Cross-sectional velocity profiles within the throat and divergent sections differ from the experimental measurements in less than 5.5%. In general, it is shown that the SPH model can provide an efficient and accurate method for recalibrating flow meters at moderately high Reynolds numbers instead of using costly experimental tests., (© 2023. The Author(s).)

Droplet nuclei dispersion patterns in indoor environments are reviewed from a physics view to explore the possibility of airborne transmission of SARS-CoV-2. This review analyzes works on particle dispersion patterns and their concentration in vortical structures in different indoor environments. Numerical simulations and experiments reveal the formation of the buildings' recirculation zones and vortex flow regions by flow separation, airflow interaction around objects, internal dispersion of airflow, or thermal plume. These vortical structures showed high particle concentration because particles are trapped for long periods. Then a hypothesis is proposed to explain why some medical studies detect the presence of SARS-CoV-2 and others do not detect the virus. The hypothesis proposes that airborne transmission is possible if virus-laden droplet nuclei are trapped in vortical structures associated with recirculation zones. This hypothesis is reinforced by a numerical study in a restaurant that presented possible evidence of airborne transmission by a large recirculating air zone. Furthermore, a medical study in a hospital is discussed from a physical view for identifying the formation of recirculation zones and their relation with positive tests for viruses. The observations show air sampling site located in this vortical structure is positive for the SARS-CoV-2 RNA. Therefore, the formation of vortical structures associated with recirculation zones should be avoided to minimize the possibility of airborne transmission. This work tries to understand the complex phenomenon of airborne transmission as a way in the prevention of transmission of infectious diseases., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2023 The Author(s).)