Characterization and Dispersion of Human Expiratory Droplets – a Review

The paper reviews studies conducted on human expiratory droplets for the purpose of defining the characteristics of expiratory droplets, their maximum dispersion and the forces influencing that in an unventilated environment. The review shows coughing, sneezing and speaking droplets to have comparable size ranges, while breathing droplets have the narrowest size range. Sneezing droplets have the largest average size and highest velocity among expiratory droplets. Compiled data reveal droplet Froude number offers a plausible quantitative measure of the droplet maximum spread. The fate of the airborne droplets is seen to be dictated by an interplay between their inertial force and gravitational force. The higher the Froude number, the greater is the droplet spread. Small droplets with high flow inertia, such as dry sputum droplets, are capable of reaching longer horizontal distances in comparison to large droplets. The review shows the maximum horizontal distance coughing droplets can reach exceeds 2 m, while sneezing droplets can reach distances above 6 m, greater than the 2 m physical distancing currently adopted to avoid virus contamination.publishedVersio

Students Exposure to Sustainable Thermal Energy Storage Technologies at West Texas A&M University

In the mechanical and civil engineering programs at West Texas A&M University, students are exposed to a variety of sustainability-oriented projects through senior design and research courses. The projects are selected to provide an in-depth understanding of the investigated area through analytical and experimental studies. In this particular project, students in thermal design were asked to investigate the feasibility of using paraffin-oil mixture as a phase change material (PCM) in residential walls. A PCM material with a melting point of 23°C (73°F) was designed and mixed. The mass of PCM required for a 1 m2 (10.8 ft2) wall (the size of the test apparatus) was determined to be 5.8 kg (12.8 lb) in a vertical 3.18 cm (1.25 in) thick sheet. A wall containing the PCM and another wall designated as a “control” were placed on 1 meter cubic insulated structures and were monitored through controlled experimentation. The testing was conducted indoors and an interior heating element simulated four complete day cycles. The result of the indoor study proved conclusively that with the correct modifications and optimization, PCM, as a form of insulation, is economically viable over its lifespan of 20 years. The reduced cost to the owner of a 186 m2 (2,000 ft2) home is $129.73/year. The proposed design causes a minuscule 5.76 kg/m2 (1.2 lb/ft2) of additional load to the structure. Because the PCM is in the configuration of a uniform sheet, the majority of the extra load will be supported by the concrete slab of the home.Cockrell School of Engineerin

Numerical heat transfer model for frost protection of citrus fruits by water from a spraying system

A simplified model is developed to simulate the conditions associated with the protection of fruits from frost damage using water from a spraying system. The model simulates the movement of the solidifying water front on a single fruit, and based on that determines the spray frequency needed for a water film to continuously surround the ice-coated fruit to prevent the fruit temperature from dropping below 0ºC. Simulations are presented for the frost protection of sweet oranges (citrus sinensis). The effect of environmental conditions such as air temperature, air velocity, surface radiation and water film evaporation on the development of the ice layer encasing is considered. Simulations show the effect the encasing ice sheet thickness has on the fruit temperature if water from a spraying system is turned off permanently. Experimental tests are also conducted to determine the change in the thermal properties of citrus sinensis for operating temperatures that range from above freezing to sub-freezing. The results of the experimental tests and the numerical simulations shall lead to a better understanding of fruit protection from frost damage by the application of water from a spraying system

Numerical Modeling of the Dynamics and Heat Transfer of Impacting Sprays for a Wide Range of Pressures.

A numerical model is developed to simulate the impingement of liquid sprays on surfaces heated at temperatures ranging from nucleate to film boiling. The droplets are modeled in the Lagrangian frame of reference, and are dispersed stochastically in the continuous gas phase. The model is based on the fundamental basics of single droplet impingements extended to full sprays, where the overall heat transfer process is broken down into its basic components: conduction associated with the droplet contact, bulk air convection, and surface radiation. Droplet dynamics at the wall are modeled based on an empirical correlation relating the droplet incoming to outgoing Weber number. Droplet contact heat transfer is modeled using an effectiveness parameter for the heat transfer that is a function of the droplet Weber number. This attempt of numerically modeling the droplet-wall dynamics with multiple wall collisions and the droplet contact heat transfer has not been addressed before in a numerical model. Simulations are presented for: single-stream droplet impactions, multiple-streams droplet impactions, and conical sprays.The model is tested at atmospheric pressure using experimental data for nozzles that dispense non-uniform droplets. Favorable comparison with the test data is demonstrated. The model capability is then extended to simulate high and sub-atmospheric ambient pressure conditions with a proper accounting of the droplet-wall interaction and air-mist heat transfer mechanism. At high and sub-atmospheric pressures, the model was tested against experiments for single stream impactions at various pressures.Spray simulation conducted for a wide range of pressures reveals the following important issues regarding to the droplet dynamics, heat transfer and vaporization: 1) At higher pressures, the larger the droplet size, the better is the droplet-wall impaction, while for sub-atmospheric pressures, larger droplets have a detrimental effect due to their ballistic impaction. 2) At higher pressures, the Leidenfrost point shifts to a higher temperature that leads to an increase in the droplet wetting capability, and to a higher heat transfer effectiveness. 3) At higher pressures, more vapor is generated from each droplet impaction on the surface, resulting also in an increase in the heat transfer effectiveness

Performance Study on Evacuated Tubular Collector Coupled Solar Still in West Texas Climate

Experimental study was performed on a single basin active solar distillation system augmented with a solar collector using evacuated solar tubes. Field tests were conducted over several days under the climatic conditions of West Texas to evaluate the effect evacuated solar tubes have on the daily distillate yield rate. To investigate the feasibility of the solar tubes, active and passive solar stills with and without exterior insulation were examined. The maximum daily production rate for the active distillation system using evacuated solar tubes and the passive distillation system was 3.6 and 1.4 kg/m2day, respectively. The results showed the augmentation of the still with evacuated solar tubes increased its production capacity by a factor of 2.63. It also increased the maximum temperature of the water in the still basin by at least 20 °C. Economic analysis shows that it is feasible to use evacuated tubular collector coupled solar still as an alternative means for reclaiming water in farmlands with a payback period of approximately 6 years

Experimental Heat Transfer Study on Green Roofs in a Semiarid Climate During Summer

An experimental study was conducted on green roofs under the semiarid summer climatic conditions of West Texas to investigate the effect of soil type, moisture content, and the presence of a top soil grass layer on the conductive heat transfer through the roof. Two soil types were investigated: uniform sand and local silt clay. Tests were also conducted on a control roof. A dual-needle heat-pulse sensor was used to conduct thermal property tests on the soils. The tests reveal that unlike sand, the thermal conductivity of silt clay did not increase continuously with soil moisture. Better heat transfer conditions were achieved when the sand and silt clay roofs were watered to a water depth of 10 mm per day rather than double the amount of 20 mm per day. The roof with silt clay soil had the lowest fluctuation in inner temperature between daytime and nighttime. Green roofs with silt clay soil required more than twice the amount of soil moisture than green roofs with sand to achieve similar roof heat transfer rates. The best net heat flux gains for vegetated green roofs were 4.7 W/m2 for the sand roof and 7.8 W/m2 for the silt clay roof

Review of Computer-Aided Numerical Simulation in Wind Energy

Many advances have been made during the last decade in the development and application of computational fluid dynamics (CFD), finite element analysis (FEA), numerical weather modeling, and other numerical methods as applied to the wind energy industry. The current information about this area of study may help researchers gage research efforts. Specifically, micro-siting, wind modeling and prediction, blade optimization and modeling, high resolution turbine flow modeling, support structure analysis, and noise prediction have been the main focuses of recent research. The advances in this area of research are enabling better designs and greater efficiencies than were possible previously. The trends toward system coupling, parallel computing, and replacing experiments are discussed. The shortcomings of recent research and areas of possible future research are also presented

Effect of Nanoparticles Size and Concentration on Thermal and Rheological Properties of AL 2 O 3 -Water Nanofluids

Abstract -An experimental study was conducted to investigate the thermal and rheological properties of various suspensions of AL 2 O 3 in deionized water. Tests were carried out using nanoparticles with average diameters of 5 and 50 nm for suspensions concentration ranging from 0 to 40% by mass. Tests reveal that alumina nanofluids thermal conductivity increases with the increase in operating temperature and in suspensions concentration, but decreases with the increase in nanoparticles diameter. Also, fluids with 5 nm particles exhibit non-Newtonian characteristics of shear thinning fluids. This behaviour intensifies as the suspensions concentration increases. However, fluids with 50 nm particles behave as shear thickening fluids. This behaviour does not seem to be altered by the increase in suspensions concentration. Tests also reveal that alumina nanofluids viscosity increases with the increase in the suspensions concentration. For fluids with 5 nm particles, viscosity is shown to increase with the increase in the operating temperature, but for fluids with 50 nm particles it is shown to decrease with the increase in temperature

Direct correction of haemoglobin E β-thalassaemia using base editors

Haemoglobin E (HbE) β-thalassaemia causes approximately 50% of all severe thalassaemia worldwide; equating to around 30,000 births per year. HbE β-thalassaemia is due to a point mutation in codon 26 of the human HBB gene on one allele (GAG; glutamatic acid → AAG; lysine, E26K), and any mutation causing severe β-thalassaemia on the other. When inherited together in compound heterozygosity these mutations can cause a severe thalassaemic phenotype. However, if only one allele is mutated individuals are carriers for the respective mutation and have an asymptomatic phenotype (β-thalassaemia trait). Here we describe a base editing strategy which corrects the HbE mutation either to wildtype (WT) or a normal variant haemoglobin (E26G) known as Hb Aubenas and thereby recreates the asymptomatic trait phenotype. We have achieved editing efficiencies in excess of 90% in primary human CD34 + cells. We demonstrate editing of long-term repopulating haematopoietic stem cells (LT-HSCs) using serial xenotransplantation in NSG mice. We have profiled the off-target effects using a combination of circularization for in vitro reporting of cleavage effects by sequencing (CIRCLE-seq) and deep targeted capture and have developed machine-learning based methods to predict functional effects of candidate off-target mutations