scholarly journals Experimental Investigation on the Cooling and Inerting Effects of Liquid Nitrogen Injected into a Confined Space

Symmetry ◽  
2019 ◽  
Vol 11 (4) ◽  
pp. 579 ◽  
Author(s):  
Huaijun Ji ◽  
Yunzhuo Li ◽  
Hetao Su ◽  
Wuyi Cheng ◽  
Xiang Wu
Keyword(s):  
Liquid Nitrogen ◽  
Inclination Angle ◽  
Mass Flux ◽  
Environmentally Benign ◽  
Pipe Diameter ◽  
Confined Space ◽  
Confined Spaces ◽  
Friendly Fire ◽  
Fire Extinguishing ◽  
Heat Transfer Capacity

As a highly effective and environmentally benign suppression agent, liquid nitrogen (LN2) has been widely used for fire extinguishing in plants, dwellings, enclosed underground tunnels, and other confined spaces through cooling and inerting. It is of great significance to understand the cooling and inerting effects of LN2 injected into a confined space. A confined-space experimental platform was developed to study the injecting LN2 into the platform with different injection parameters, such as mass flux, pipe diameter, and inclination angle. In addition, a mathematical model of quantitatively assessing cooling and inerting effects was proposed by using heat transfer capacity, inerting coefficient, and cooling rate. Results showed that the inerting effect was gradually enhanced with a mass flux increasing from 0.014 to 0.026 kg/s and then tended to level off; an appropriate pipe diameter of 12 mm was optimal for the cooling and inerting effects in this experiment. In addition, a positively increasing inclination angle could contribute to the cooling and inerting effects. However, there was little effect on the cooling and inerting with an inclination angle less than 0°. This study can provide technical guidances for environmentally friendly fire extinguishing with LN2 in a confined space.

scholarly journals Cockroaches traverse crevices, crawl rapidly in confined spaces, and inspire a soft, legged robot

2016 ◽  
Vol 113 (8) ◽  
pp. E950-E957 ◽  
Author(s):  
Kaushik Jayaram ◽  
Robert J. Full
Keyword(s):  
Body Weight ◽  
High Speed ◽  
Stride Length ◽  
Body Height ◽  
Legged Robot ◽  
Confined Space ◽  
Performance Limits ◽  
Biological Inspiration ◽  
Confined Spaces ◽  
Postural Changes

Jointed exoskeletons permit rapid appendage-driven locomotion but retain the soft-bodied, shape-changing ability to explore confined environments. We challenged cockroaches with horizontal crevices smaller than a quarter of their standing body height. Cockroaches rapidly traversed crevices in 300–800 ms by compressing their body 40–60%. High-speed videography revealed crevice negotiation to be a complex, discontinuous maneuver. After traversing horizontal crevices to enter a vertically confined space, cockroaches crawled at velocities approaching 60 cm⋅s−1, despite body compression and postural changes. Running velocity, stride length, and stride period only decreased at the smallest crevice height (4 mm), whereas slipping and the probability of zigzag paths increased. To explain confined-space running performance limits, we altered ceiling and ground friction. Increased ceiling friction decreased velocity by decreasing stride length and increasing slipping. Increased ground friction resulted in velocity and stride length attaining a maximum at intermediate friction levels. These data support a model of an unexplored mode of locomotion—“body-friction legged crawling” with body drag, friction-dominated leg thrust, but no media flow as in air, water, or sand. To define the limits of body compression in confined spaces, we conducted dynamic compressive cycle tests on living animals. Exoskeletal strength allowed cockroaches to withstand forces 300 times body weight when traversing the smallest crevices and up to nearly 900 times body weight without injury. Cockroach exoskeletons provided biological inspiration for the manufacture of an origami-style, soft, legged robot that can locomote rapidly in both open and confined spaces.

scholarly journals Droplet and Aerosol Suspension Times in Ambient Air in Confined Spaces and Transmission of COVID-19: Influence of Environmental Factors

2021 ◽  
Vol 13 (2) ◽  
pp. 495-506
Author(s):  
M. R. Islam ◽  
S. H. Naqib
Keyword(s):  
Relative Humidity ◽  
Environmental Factors ◽  
Ambient Air ◽  
Confined Space ◽  
Natural Processes ◽  
Confined Spaces ◽  
Potential Source ◽  
Aerosol Droplet ◽  
Exhaled Air ◽  
Mode Of Transmission

The COVID‑19 pandemic, alternatively known as the coronavirus pandemic, is an unfolding pandemic of coronavirus disease 2019 (COVID‑19) across the entire globe in an unprecedented proportion. COVID-19 is caused by severe acute respiratory syndrome coronavirus 2. The mode of transmission of COVID-19 is a subject of intense research. The airborne transmission is one prime possibility. Breathing and talking are natural processes which generate exhaled particles. The exhaled air is an aerosol/droplet composed of naturally produced particulates of varying size. The duration over which the aerosols/droplets are suspended in the air is an important factor. Long suspended aerosols/droplets are potential source of transmission, particularly in confined spaces. We have calculated times of suspension by considering various environmental factors, namely, the ambient temperature and relative humidity in a confined space, in this work. Both temperature and relative humidity affect the suspension time of the exhaled aerosols/droplets with varying degree. The effects of environmental factors are significant for aerosols, particularly for those with small radii. We have discussed the possible implications of our findings in this paper.

Improved Design Parameters for a Liquid Desiccant Dehumidifier in Confined Spaces

Solar Energy ◽  
2005 ◽  
Author(s):  
D. Dong ◽  
M. Liu
Keyword(s):  
Energy Consumption ◽  
Ventilation System ◽  
Exhaust System ◽  
Design Parameters ◽  
Confined Space ◽  
Confined Spaces ◽  
Exhaust Ventilation ◽  
Moisture Condensation ◽  
Improved Design ◽  
Control Application

Investigations of a desiccant dehumidifier system have been performed for humidity control application in confined spaces. A previous study revealed that the base dehumidifier system can reduce moisture condensation by 22% over a conventional exhaust ventilation system. The current study aims to develop improved design requirements for a desiccant dehumidifier. The energy consumption of an exhaust ventilation system and an improved dehumidifier system was compared. To investigate the improved desiccant dehumidification system, numerical simulations were conducted and an objective function was established. This paper presents simulated results for an existing desiccant dehumidification system and an improved system, in which improved parameters are used. Use of the improved design parameters can reduce moisture condensation by 26.6% over a base dehumidifier system and shorten the dehumidifier performance period by 14%. Energy consumption with the sole use of an exhaust system is compared with that of the improved dehumidifier system under the same conditions. The results show that energy consumption can be substantially reduced, by 63%, in the improved dehumidifier system with the same amount of moisture condensation on surfaces of the confined space.

scholarly journals Characteristic Analysis of Occupational Confined Space Accidents in Taiwan and Its Prevention Strategy

2020 ◽  
Vol 17 (5) ◽  
pp. 1752 ◽  
Author(s):  
Chien-Chen Chiu ◽  
Yi-Ming Chang ◽  
Terng-Jou Wan
Keyword(s):  
Occupational Safety ◽  
Health Administration ◽  
Confined Space ◽  
Characteristic Analysis ◽  
Confined Spaces ◽  
Analysis Technique ◽  
The Us ◽  
Area Of Concern ◽  
Loss Control ◽  
Bureau Of Labor Statistics

According to the US Bureau of Labor Statistics (BLS), 882 people were killed or injured due to confined space accidents in 2011–2017. Occupational accident statistics published in 2008–2018 by the Taiwan Occupational Safety and Health Administration (OSHA, Taiwan) show that 70 people suffered from disasters and 52 were injured in the 64 accident reports involving confined spaces. In the US, on average, 126 people die each year in accidents related to confined spaces, and in Taiwan, an average of 8 people per year are casualties of accidents involving confined spaces, proving that it is an area of concern that cannot be neglected. When misjudgments occur in confined spaces, not only can people be hurt, but they can even lose their lives, and the risks associated with confined spaces can subsequently result in rescue personnel also being killed or injured. This study was conducted via the systematic causal analysis technique (SCAT), which was proposed and developed by the International Loss Control Institute (ILCI), with the intention of identifying the critical basic causes of the confined space accidents that have occurred over the years in the Taiwan area, in order to propose corresponding improvement strategies. After investigating the statistics in Taiwan, it was determined that hydrogen sulfide was involved in 45% of accidental deaths in confined spaces, followed by 11% involving carbon dioxide, 9% involving carbon monoxide, and 7% involving toluene. Additional analysis of non-standard acts identified “failure of operating procedures” as being involved in 27% of accidents, followed by 25% involving “improper personal protective equipment” and 23% involving “incorrect position”. The analysis of non-standard conditions revealed that “dangerous workplace” was involved in 39% of accidents, “improper protective measures” in 30%, and “inadequate ventilation” in 27%. In accordance with our analysis results, it could be suggested that hazard prevention strategies for confined spaces, in addition to encouraging avoidance of non-standard acts by personnel, should also strive to improve these non-standard conditions. Otherwise, if not prevented deliberately and in a fundamental, relevant accidents will remain inevitable.

Study of Distribution and Quantification of Flammable Gas in Confined Space

2014 ◽  
Vol 638-640 ◽  
pp. 2097-2100
Author(s):  
Ales Tulach ◽  
Miroslav Mynarz ◽  
Milada Kozubkova
Keyword(s):  
Natural Gas ◽  
Low Pressure ◽  
Confined Space ◽  
Gaseous Fuels ◽  
Confined Spaces ◽  
Elapsed Time ◽  
Cfd Models ◽  
Flammable Gas ◽  
Broad Overview

The contribution deals with leakage of natural gas from domestic low-pressure piping. Spreading of the leaked natural gas in the confined space is deals with and the areas are defined where local hazardous concentrations are formed. Mathematical CFD models provide broad overview of spreading of natural gas, in dependence on the elapsed time from the start of leakage. The contribution should improve the understanding of spreading and distribution of mixture of gaseous fuels in confined spaces, and thus leads to significant reduction of the risk of occurrence of fire or explosion or to prevention of these hazards.

scholarly journals The Build-Up of Aerosols Carrying the SARS-CoV-2 Coronavirus, in Poorly Ventilated, Confined Spaces

2020 ◽  
Author(s):  
Bjorn Birnir ◽  
Luiza Angheluta
Keyword(s):  
Decay Time ◽  
Air Flow ◽  
Time Frame ◽  
Aerosol Concentration ◽  
Confined Space ◽  
Confined Spaces ◽  
Turbulent Air Flow ◽  
Short Time ◽  
Respiratory Droplets ◽  
Standard Ventilation

Abstract A model of the distribution of respiratory droplets and aerosols by Lagrangian turbulent air-flow is developed and used to show how the SARS-CoV-2 Coronavirus can be dispersed by the breathing of an infected person. It is shown that the concentration of viruses in the exhaled cloud can increase to infectious levels with time (grow linearly), in a confined space where the air re-circulates. The model is used to analyze the air-flow and SARS-CoV-2 Coronavirus build-up in a restaurant in Guangzhou, China [23, 21]. It is concluded that the outbreak of Covid-19 pandemic in the restaurant in January 2020, is due to the build-up of the airborne droplets and aerosols carrying the SARS-CoV-2 Coronavirus and would not have been pre- vented by standard ventilation. A comparison with standard models for aerosol concentration shows that, in the absence of ventilation, the decay of the aerosol concentration is also con- trolled by the decay time of the virions in aerosols. This decay time is very long and a steady state is not achieved in the time-frame of the contagion. Instead the concentration exhibits a polynomial increase and reaches infectious levels in a relatively short time, explaining the outbreak in the restaurant in Guangzhou.

scholarly journals Upper-room ultraviolet air disinfection might help to reduce COVID-19 transmission in buildings

2020 ◽  
Author(s):  
Clive B. Beggs ◽  
Eldad J. Avital
Keyword(s):  
Feasibility Study ◽  
Published Data ◽  
Confined Space ◽  
Uv Damage ◽  
Worst Case ◽  
Confined Spaces ◽  
The World ◽  
Air Disinfection ◽  
Uv C ◽  
Upper Room

AbstractAs the world economies get out of the lockdown imposed by the COVID-19 pandemic, there is an urgent need to assess the suitability of known technologies to mitigate COVID-19 transmission in confined spaces such as buildings. This feasibility study looks at the method of upper-room ultraviolet (UV) air disinfection that has already proven its efficacy in preventing the transmission of airborne diseases such as measles and tuberculosis.Using published data from various sources it is shown that the SARS-CoV-2 virus, which causes COVID-19, is highly likely to be susceptible to UV damage while suspended in air irradiated by UV-C at levels that are acceptable and safe for upper-room applications. This is while humans are present in the room. Both the expected and worst-case scenarios are investigated to show the efficacy of the upper-room UV-C approach to reduce COVID-19 air transmission in a confined space with moderate but sufficient height. Discussion is given on the methods of analysis and the differences between virus susceptibility to UV-C when aerosolised or in liquid or on a surface.

Experimental Study on Condensation in the Outer Annular Region Outside Horizontal Enhanced Tubes

2020 ◽  
Author(s):  
Zeguan Dong ◽  
Jianghui Zhang ◽  
Zhen Li ◽  
Yan He ◽  
David J. Kukulka ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Surface Structures ◽  
Annular Region ◽  
Diagram Method ◽  
Enhanced Tubes ◽  
Heat Transfer Capacity

Abstract Single-phase and flow condensation experiments were performed using refrigerant R410A in the outer annular region of horizontal enhanced tube with different enhanced surfaces at a saturation temperature of 45°C in the range of mass flux 44.43–102.23kg/(m2s). The vapor quality ranges from 0.8 to 0.2. The outer diameters of the tubes are all 19.05mm, but the inner diameters are slightly different due to different surface structures. The surface structures of the three enhanced tubes are fins(EHT1 tube), toothed structures (EHT2 tube) and fine cavities(EHT3 tube) of different sizes and densities. Among them, the EHT3 tube has internal threads. Wilson diagram method was used to determine the enhancement ratio of the water side heat transfer coefficient of EHT3 tube. It was found that the pressure drop increased with the increase of mass flux, while the heat transfer coefficient showed different trends, and the smooth tube was always the lowest of the four tubes. A comprehensive evaluation factor α combining heat transfer enhancement factor (EF) and pressure drop penalty factor (PF) was defined, in which EHT2 tube (1.38–1.75) was the largest, with strong heat transfer capacity and small pressure drop, so the condensing heat transfer capacity of EHT2 tube was the best.

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