Constant flow can mean:
Area constriction due to face shields leads to higher flow velocity (intake).
Conservation of momentum:
Higher flow velocity -> Higher velocity pressure (either positive if outflow or negative if inflow).
Even without respiration, if a wind flows to the face shield, a negative pressure region will be present beneath.
In airconditioned areas, the temperature differential between the cool air outside the face shield and the warm air beneath the face shield due to the heat radiating from our body will induce flow towards the warm region, most likely, to what's beneath the face shield.
Transport equations determine how a passive scalar (pollution, particulates, energy) is transported with a given velocity field.
Negative pressure regions will be the place where most of the passive scalar (virus) will be deposited, in essence, beneath the face shield.
I remember presenting a journal in the CE 257 class under Doc Jaime about Computational Fluid Dynamics and Transport Equations.
Here I am trying in vain to discuss some basic principles in fluid dynamics, with the given limited materials.
Conservation of Mass
Conservation of Mass (pt.2)
Conservation of Mass (faceshield included).
Clarification: By introducing pressure to the container, I was reducing the volume of the container, resulting to outflow.
Conservation of Momentum
Conservation of Momentum (2)
Transport Equation
In bluff-body aerodynamics, the bluff body often causes flow separation, which are divided into two: strong separation and weak separation.
Strong separation is often found in the windward side. Flow separation causes negative pressure gradient, resulting to reverse flows.
On the other hand, weak separation naturally occurs at the leeward side. Both types of flow separation causes reverse flows, sometimes resulting to flow recirculation.
The advection term (acceleration across space) across the flow recirculation is relatively lower at this point. In the transport equations, since the advection term also amounts to the convection, it also indicates the accumulation of the passive scalar at these regions.
These passive scalars can either be moisture, pollution, heat, energy, and other particulates, including viruses.
Diffusion, on the other hand, is mainly controlled by the fluid's viscosity. The more viscous the fluid is, the higher the diffusion.
Transport equation in a nutshell is:
Change in amount of passive scalar = Transport due to Convection + Diffusion
Face shields encourages flow recirculation beneath it, resulting to higher tendencies for the particulates to retain and accumulate there.
Especially kapag galing sa likod ang direction ng flow ng hangin...
I just did a CFD analysis to prove the point.
The picture shows the pressure field across the domain. The blue cylinder represents the person. The face shield is also present in the model. A negative pressure region will be present beneath the face shield. Flow velocity is 1 m/s
Plotting the streamlines also reveals the existing reverse flows and recirculations beneath the face shield. There are higher tendencies for the passive scalar to accumulate and be deposited in these regions.
Reverse flows and Recirculations also occur from above and below.
Simulation Details:
Finite Volume Size: 0.1 mm^2
Number of Elements: 2.7 million
RAM allocation: 9 gb
Turbulence Model: SST k-omega model (RANS)
Flow velocity: 1 m/s
Maybe, I'll also try to simulate the same in OpenFOAM with the advantage of using the transport equations.
Demonstration of reverse flows
Demonstration: Flow recirculation
Demonstration with aerosols.
I hope na malinaw and nakikita ang pagrecirculate ng aerosol to the region behind ng face shield.
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I advise people to subscribe to vital weather information from weather agencies and reputable scientists with their reputations at hand, since accountability forges trust.
I also would want to you to sit through and read through this thread that gives complementary information🧵
It is also important to anticipate and know where the winds will be coming from due to what's called wind exposure affecting the characteristics of typhoon winds, on how strong and/or consistent they will be depending on your location.
Winds at sea will experience little to no dissipative effects. Therefore the winds will be consistently strong.
The peak gust (bugso) will not be far on how strong the sustained winds will be.
Our study that developed CO2 monitors that informed occupants of the relative risk that they may be subjected to due to airborne diseases transmitted through shared room air transmission has been published. #CovidIsAirborne
Using a multivariate method, the ventilation rates of different indoor spaces are determined and used for the subsequent computations using the Wells–Riley model to derive the respective infection risk, particularly of COVID-19.
"Infection risks are determined to be higher in indoor spaces with low ventilation rates. However, having high ventilation rates does not mean low infection risks as smaller spaces will also have higher infection risks."
High humidity also attributes to high infection rates and deaths due to Covid-19.
Shown below are the trends derived from the correlation between Covid-19 deaths and relative humidity. 60% RH is the Goldilocks Zone: lesser or greater than that results in the increase of the risk
Why 60%?
It has to do with two things: (1) lessening evaporation rates due to inhomogeneous mixing and (2) rate of condensation which attributes to the increase of pore pressure within the mask.royalsocietypublishing.org/doi/10.1098/rs…
Countries above the tropics experience case surges during their winter season when relative humidity is low. The hot and humid respiratory emissions will mix with the cold and dry indoor air resulting in higher evaporation rates,
When used in physical settings, the Cochrane method and RCTs are mere pretentious eminence-based assertions masquerading as empiricism (A thread).
It is important to note that the interventions mentioned are physical in nature, not clinical and medicinal. (1/n)
We have two studies that use the Cochrane method:
The first one is the study headed by Derek Chu (funded by WHO) in 2020, which has determined, using the Newcastle Ottawa Scale & Cochrane method, the effectiveness of face masks in stopping transmission. (2/n)
The second one, headed by John Conly, uses the Cochrane method whose results are being interpreted as "evidence" against face masks.
In fact, the study pointed out the inadequacy of the study design due to the high risk of bias when dealing with physical interventions. (3/n)