We interview Joaquim Rigola, professor in the UPC Department of Heat Engines (MMT) and promoter of the CTTC UPC research group

“Since the COVID 19 crisis, CTTC research on fluid dynamics in enclosed spaces has been arousing interest”

“Humidity could play an important role in the risk of airborne contamination with SARS COVID 2”

“At technological and industrial level, we will overcome new challenges by investigating COVID 19”

Joaquim Rigola

Joaquim Rigola is professor at the Universitat Politècnica de Catalunya (UPC), and researcher and promoter of the research group on heat transfer (CTTC UPC). He is an expert in mathematical formulation, numerical resolution and experimental validation of heat and mass transfer phenomena applied to heat systems and equipment in general, and to the field of Heating, Ventilation and Air-Conditioning and Refrigeration (HVAC&R) in particular. This summer, he has taken part in two international webinars in which he contributed his knowledge and proposals to the study of airborne transmission of SARS COVID 2, specifically in public transport.

Your research group is an expert in fluid dynamics. What impact does the presence of the SARS COVID 2 virus have in the air?

A lot. Since the start of the crisis, we have made available to companies and organisations our knowledge in the area of fluid physics, to study the transmissibility of the virus through the droplets that people exhale when they speak, cough, sneeze or simply breath heavily. This is important to the treatment of air in enclosed spaces and in sectors such as that of transport.

Do you usually collaborate with researchers in the biomedical field?

Yes, we have done for some time. For example, we collaborated through a European project on a study of the aerosol transport and degree of deposition in the respiratory system of drugs administered orally or via inhalers. We used computational fluid and particle dynamics (CFPD) simulations for this study. In the industrial area, we are working on a European project in which we simulate, design and optimise using the same CFPD tools the new particle separators in air conditioning systems for equipment on European commercial aircraft.

Are you applying this knowledge to the airborne spread of the virus?

Yes, that is the idea. There are three ways the virus spreads from an ill person to the air: through droplets that they exhale with enough force that they directly reach sensitive surfaces and the face of another person; through direct contact, when heavier droplets adhere to surfaces and are touched by another person; and thirdly through airborne transport, when aerosolized particles remain in suspension and can come into contact with others. Hence the three main rules that contribute to avoiding infection: use of a mask, hand hygiene and social distancing.

Images of simulation of air flow and entry of particles on inhalation in the human respiratory system

Your work has a theoretical part that is based on mathematical models. Can physical models also be used to verify the hypotheses?

Computational fluid and particle dynamics determine the position of the particles as well as the pressure, speed and temperature of any fluid. To solve these equations with numerical methods using direct simulation of turbulence requires an immense volume of calculation. What we do is implement and develop turbulence models and parallelization strategies that can be used to reduce the calculation time as much as possible. However, models cannot always be adapted to different cases, which is why experimental validation is important.

In what cases could this type of research be applied?

One application that has caused a lot of interest is the ventilation and renewal of air in interiors. This is something that already happens on public transport, trains, buses and the metro. To date, studies have focused on the energy optimization of these processes, but now we should also consider airborne transport of particles that could contain the virus. Therefore, since the COVID 19 crisis, the research that we do at the CTTC on fluid dynamics in enclosed spaces is arousing interest.

What type of devices are required to carry out these processes of air disinfection?

Research is being carried out on filters that, when they are applied to air recirculation systems, can retain these droplets and microdroplets that could contain a viral load.

Who is interested in this type of research?

Mainly private or semi-private companies.

What percentage of infections occur in means of transport?

Some statistical studies indicate that transmission does not occur during the transport, but that the risk increases before and after the journey. However, this is not known with any certainty. We have all heard during the lockdown of possible cases of transmission in restaurants, offices or buses in China. We will have to wait for scientific publications to provide rigorous information on this topic.

Does constant use of masks completely eliminate the risk of airborne infection?

What has been published in the scientific field is that the use of masks dramatically reduces the possibilities of infection. However, this depends, among other issues, on quality, good use, etc.

What is the role of humidity in the conditions of airborne transmission of this disease?

Humidity could be an important factor in the form of transmission. In an area with relatively low humidity, part of the water in the droplets and microdroplets that we exhale becomes vapour, and as the size of the droplet is reduced it is easier for it to be transported in the air and to remain suspended in the air for longer. In contrast, in a place where there is more humidity this does not happen, and the droplets and microdroplets tend to be deposited more on surfaces and come into greater contact with people.

Public transport is a sensitive element in a situation such as that we are experiencing. What measures must government bodies and companies that manage public transport take with respect to the risk of airborne infection with the virus?

The level of ventilation and renewal of air in public transport was already considerable before Coronavirus for health reasons. In this respect, it would be useful to reinforce the study of the percentage of risk of airborne infection that exists, even if it is small. Researchers must provide data so that society is informed, and work on filtration and purification systems, etc. The more information we have, the better decisions we will be able to take.

Images of jet simulation under various flow conditions and a comparison with maps of structures of free surfaces, droplets and sprays

Could the situation that we are experiencing give rise in the mid-term to changes in the design and construction of buses, trains and airplanes?

This is already happening. The installation of screens, taking temperatures and disinfection processes are innovations that are already being introduced. I suppose that in terms of design, progress will be made to introduce additional filtration and purification elements, which would cause the least possible distortion and improve air redistribution processes.

What should people do to avoid infection with Coronavirus through the air?

As citizens, we must ask for information to learn as much as possible about what is happening at all levels. Raising awareness continues to be very important. Things change depending on what we find out over time. We have gone from not recommending masks to making them compulsory. On the topic of aerosolized transport of the virus, first it was said that there was little incidence, and now we are seeing that there is. Researchers must do our job and provide information. I am sure that in the technological and industrial area, we will overcome new challenges due to the fact that we are researching COVID 19, but in the social area results will also depend on raising awareness.

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