**1. Introduction**

The COVID-19 disease caused by the novel SARS-CoV-2 coronavirus has resulted in infections worldwide and has been classified as a pandemic. Coronavirus is a large family of viruses known to cause respiratory infections in humans and animals. These can range from mild common colds to more severe diseases. COVID-19 first appeared in December 2019 and due to person-to-person transmission, has spread worldwide [1]. According to John Hopkins Coronavirus Resource Center [2], there have been over 645 million known COVID-19 cases as of November 2022. Symptoms of COVID-19 include fever or chills, cough, nasal congestion, shortness of breath, headaches and body aches.

The spread of SARS-CoV-2 is reported to be mainly due to respiratory droplets, air-borne particles and close contact. Respiratory droplets are released due to activities like coughing, sneezing, talking and even breathing. Use of face masks, face shields and maintaining a distance of 6 ft or more from each other are recommended by the Center for Disease Control (CDC) guidelines to limit the spread of this disease. Other methods include washing hands with soap and water and use of alcohol-based hand sanitizers [3].

Since first recognizing COVID-19 as a novel, rapidly spreading virus, significant research has been pursued to study the possible ways of infection and methods of prevention. Karia et al. [4] detail the different modes of COVID-19 transmission. It has been determined that COVID-19 can spread via methods like secretions of body fluids, airborne transmission and fomites (contaminated surfaces). However, the highest risk of transmission is through airborne respiratory particles like aerosols and droplets. Liu et al. [5] studied aerosol transmission, measuring the concentration of SARS-CoV-2 RNA amongst the aerosols sampled from the air in COVID-19 patient wards and other areas frequented by patients and medical staff in two hospitals in Wuhan, China. The study showed that concentration of virus RNA was lower in ventilated patient wards but higher in bathrooms and other crowded areas.

As there are plenty of diseases that spread via airborne droplets, such as influenza and common cold, various studies were conducted to measure the quantity and size distribution of saliva droplets released during human respiratory activities. In one of the earliest experiments, Duguid et al. [6] measured droplets released during coughing, talking and sneezing using direct micrometry from droplet nuclei settled on oiled slides. More recently, a similar experiment was conducted by Xie et al. [7] using glass slides and a microscope to measure the size and number of droplets released due to respiratory activities. They also measured the total mass of droplets released with the help of surgical masks and plastic bags. The study gave the diameter distribution for droplets released during coughing and talking by averaging results for five people coughing 20 times and talking. Wilson et al. [8] measured the total number and volume of aerosols exhaled during breathing, talking, shouting and coughing and therapies such as high-flow nasal oxygen. The study showed that respiratory activities that mimic respiratory patterns during illness generate substantially more aerosols than non-invasive respiratory therapies, which conversely can reduce total emissions. In another study by Leonard et al. [9], the authors demonstrated the efficacy of surgical masks in reducing particulate transmission.

Apart from experiments, studies using numerical methods and computational fluid dynamics (CFD) to model particles released during respiratory activities have been conducted to analyze the spread of COVID-19. Wei and Li [10] studied the effect of turbulence and evaporation on dispersion of droplets in a cough jet using a discrete random walk model. In presence of velocity fluctuations, small droplets were dispersed in the whole jet region, of which 1% of large droplets (100 mm) were transported over 2 m. Small droplets (30 mm) were not sensitive to relative humidity (RH) and became droplet nuclei soon after being expired, and then behaved similarly as small particles. Medium droplets were very sensitive to humid conditions (RH above 80%), as they settled but deposited slowly, and therefore were carried forward in the jet-induced velocity field. Zhu et al. [11] used CFD to study transport characteristics of saliva droplets in an indoor space. They showed that for smaller droplets (30 *μ*m), inertia and gravity do not play a significant role and droplets were carried along with the airflow. For droplets 50 *μ*m–200 *μ*m, gravity was significant and they fell as the airflow weakened, whereas, larger droplets (300 *μ*m), traveled farther due

#### *Assessing Ventilation Strategies to Reduce the Spread of Pathogens in Restaurants DOI: http://dx.doi.org/10.5772/intechopen.109634*

to inertia. Yan et al. [12] studied the thermal effect of the human body on evaporation and dispersion of cough droplets. An Eulerian-Lagrangian coupling approach was used to model the cough droplets released from a body with and without heat transfer. It was found that the thermal effect did not cause a significant change in the evaporation rate of droplets. But it affected the deposition time of smaller droplets (0.35 *μ*m– 20 *μ*m) that were trapped in the ascending thermal flow and stayed in air longer.

Zhang et al. [13] conducted experimental and CFD analyses of virus transmission in a university campus bus. The study showed 2 m distance was not enough to prevent virus transmission due to turbulent airflow caused by the HVAC system. On the other hand, the turbulence mixed the aerosols with the ambient air thereby reducing concentration. Opening the doors and windows reduced the aerosol concentration by half. The use of transparent barriers to mitigate the spread of aerosols was investigated by Abuhegazy et al. [14] for a classroom and Joshi and Battaglia [15] to assess infection risk of musicians in an orchestra. Liu et al. [16] recreated a scenario of a restaurant in China where an asymptomatic COVID-19 patient led to the infection of eight people seated at the same and adjacent tables. This simulation used an in-house large eddy simulation (LES) solver with Eulerian-Lagrangian coupling. The regions of aerosol exposure in the simulation corresponded to the reported pattern of infection in the restaurant.

Most indoor restaurants have a ventilation system to maintain thermal comfort and air quality for patrons and employees. Clean air is introduced in the room through the supply vents while room air is exhausted through the return vents and sent to the air conditioning system. Ventilation strategies for maintaining thermal comfort were studied by Joshi et al. [17]. The rate of change of air in the room is important for maintaining acceptable air quality. ASHRAE standard 62.1 [18] recommends an air flow rate of 7.5 cfm per person or 0.18 cfm/ft.<sup>2</sup> for restaurant dining rooms.

Eating at restaurants is an important part of our social lives. Many restaurants have reduced capacity and increased distance between tables to maintain social distancing during the pandemic. However, patrons remove masks while eating and this may not guarantee the prevention of COVID-19 transmission. Respiratory droplets from infected carriers may be inhaled by other people or deposit on food at other tables, potentially spreading infection. These respiratory droplets can be entrained in the moving air. In closed-space air-conditioned restaurants, the position of air vents and direction of air flow plays an important role in risk of infection for the patrons as evident by the study conducted by Liu et al. [16] on COVID-19 transmission in a restaurant in Guangzhou, China.

While there are plenty of studies that use CFD to analyze COVID-19 transmission, few are focused specifically on restaurants, despite having a large influence on the spread of the virus. This study aims to incorporate CFD to model saliva droplets released through various respiratory activities in a restaurant scenario. Ventilation strategies, including vent locations and air flow rates, will be examined to determine ways to reduce infection risk. Respiratory activities like sneezing and talking will be studied in order to determine if a distance of 2 m between restaurant tables is sufficient to reduce virus transmission.
