Ventilation of Wind-Permeable Clothed Cylinder Subject to Periodic Swinging Motion: Modeling and Experimentation

2008 ◽  
Vol 130 (9) ◽  
Author(s):  
N. Ghaddar ◽  
K. Ghali ◽  
B. Jreije
Keyword(s):  
Cotton Fabric ◽  
Current Model ◽  
Ventilation Rate ◽  
External Pressure ◽  
Motion Modeling ◽  
Tracer Gas ◽  
Wind Speeds ◽  
Air Speed ◽  
Local Thermal Comfort ◽  
Ventilation Rates

Abstract A theoretical and experimental study has been performed to determine the ventilation induced by swinging motion and external wind for a fabric-covered cylinder of finite length representing a limb. The estimated ventilation rates are important in determining local thermal comfort. A model is developed to estimate the external pressure distribution resulting from the relative wind around the swinging clothed cylinder. A mass balance equation of the microclimate air layer is reduced to a pressure equation assuming laminar flow in axial and angular directions and that the air layer is lumped in the radial direction. The ventilation model predicts the total renewal rate during the swinging cycle. A good agreement was found between the predicted ventilation rates at swinging frequencies between 40rpm and 60rpm and measured values from experiments conducted in a controlled environmental chamber (air velocity is less than 0.05m∕s) and in a low speed wind tunnel (for air speed between 2m∕s and 6m∕s) using the tracer gas method to measure the total ventilation rate induced by the swinging motion of a cylinder covered with a cotton fabric for both closed and open aperture cases. A parametric study using the current model is performed on a cotton fabric to study the effect of wind on ventilation rates for a nonmoving clothed limb at wind speeds ranging from 0.5m∕sto8m∕s, the effect of a swinging limb in stagnant air at frequencies up to 80rpm, and the combined effect of wind and swinging motion on the ventilation rate. For a nonmoving limb, ventilation rate increases with external wind. In the absence of wind, the ventilation rate increases with increased swinging frequency.

Ventilation of Wind-Permeable Clothed Cylinder Subject to Periodic Swinging Motion

2007 ◽  
Author(s):  
Nesreen Ghaddar ◽  
Kamel Ghali ◽  
Bassel Jreije
Keyword(s):  
Heat Loss ◽  
Cotton Fabric ◽  
Current Model ◽  
Low Frequency ◽  
Ventilation Rate ◽  
External Pressure ◽  
Combined Effect ◽  
Total Heat Loss ◽  
Wind Speeds ◽  
Ventilation Rates

A theoretical and experimental study has been performed to determine ventilation induced by swinging motion and external wind for a fabric-covered cylinder of finite length representing a limb. The estimated ventilation rates are used in determining the sensible heat loss form a clothed cylinder using a simplified resistance model. A model is developed to estimate the external pressure distribution resulting from the relative wind around the swinging clothed cylinder. A mass balance equation of the microclimate air layer is reduced to a pressure equation assuming laminar flow in axial and angular directions and that the air layer is lumped in the radial direction. The ventilation model predicted the total renewal rate during the swinging cycle. A good agreement was found between the predicted ventilation rates at swing frequencies between 40 and 60 rpm and measured values from experiments conducted in a controlled environmental chamber (air velocity is less than 0.05 m/s) and used the tracer gas method to measure the total ventilation rate induced by the swinging motion of a cylinder covered with cotton fabric for both closed and open aperture cases. A parametric study using the current model is performed on cotton fabric to study the effect of wind on ventilation rates for a non-moving clothed limb at wind speeds ranging from 0.5–8 m/s, the effect of a swinging limb in stagnant air at frequencies up to 80 rpm, and the combined effect of wind and swinging motion on the ventilation rate. For a non-moving limb, ventilation rate increases with external wind. In absence of wind, the ventilation rate increases with increased swinging frequency. The combined effect of wind and swing is not additive of the single effects at high wind speed while at low frequency it can be assumed additive for wind speeds below 2 m/s and frequencies below 40 rpm. The heat transfer by ventilation is more than 50% of total heat loss from a clothed cylinder at f = 80 rpm in abs cense and presence of wind.

scholarly journals Applying the CO2 concentration decay tracer gas method in long-term monitoring campaigns in occupied homes: identifying appropriate unoccupied periods and decay periods

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Jessica Few ◽  
Clifford A. Elwell
Keyword(s):  
Indoor Air Pollution ◽  
Weather Conditions ◽  
Co2 Concentration ◽  
Ventilation Rate ◽  
Identification Algorithm ◽  
Tracer Gas ◽  
Content Type ◽  
Rate Analysis ◽  
Specific Implementation ◽  
Ventilation Rates

PurposeVentilation is driven by weather conditions, occupant actions and mechanical ventilation, and so can be highly variable. This paper reports on the development of two analysis algorithms designed to facilitate investigation of ventilation in occupied homes over time.Design/methodology/approachThese algorithms facilitate application of the CO2 concentration decay tracer gas technique. The first algorithm identifies occupied periods. The second identifies periods of decaying CO2 concentration which can be assumed to meet the assumptions required for analysis.FindingsThe algorithms were successfully applied in four occupied dwellings, giving over 100 ventilation measurements during a six-month period for three flats. The specific implementation of the decay identification algorithm had important ramifications for the ventilation rates measured, highlighting the importance of interrogating the way that appropriate periods for analysis are identified.Practical implicationsThe analysis algorithms provide robust, reliable and repeatable identification of CO2 decay periods appropriate for ventilation rate analysis. The algorithms were coded in Python, and these have been made available via GitHub. As well as supporting future CO2 tracer gas experiments, the algorithms could be adapted to different purposes, including the use of other tracer gases or exploring occupant exposure to indoor air pollution.Originality/valueEmpirical investigations of ventilation in occupied dwellings rarely aim to investigate the variability of ventilation. This paper reports on analysis methods which can be used to address this gap in the empirical evidence.

Improving local ventilation prediction by accounting for inter-segmental ventilation

2016 ◽  
Vol 87 (5) ◽  
pp. 511-527 ◽  
Author(s):  
Nagham Ismail ◽  
Nesreen Ghaddar ◽  
Kamel Ghali
Keyword(s):  
Wind Velocity ◽  
Ventilation Rate ◽  
Air Permeability ◽  
Statistical Correlation ◽  
Accurate Estimation ◽  
Thermal Manikin ◽  
Tracer Gas ◽  
Local Ventilation ◽  
Wind Velocities ◽  
Ventilation Rates

The inter-segmental ventilation rate at clothing inter-connection of arms and trunk affects the estimation of local ventilation rates of these clothed segments. The accurate estimation of the inter-segmental ventilation rate is based on the integration of a connected clothed cylinders model with a bio-heat model to predict a realistic segmental skin temperature. This integration is validated with experiments on a thermal manikin using the tracer gas method. The results show that accounting for the inter-segmental ventilation rate improves the estimation of the segmental ventilation of the arm and the trunk for different garment apertures at external wind velocities less than 4 m/s. For a wind velocity of 1 m/s, the inter-connection increased the trunk ventilation by up to 12% and heat loss by up to 5.46%. A statistical correlation is established for the inter-segmental ventilation rate in terms of the influencing parameters: air permeability, wind velocity, mean air gap size between skin and clothing, and the upper clothing aperture design. Furthermore, a local ventilation rate correction factor equation is developed as a function of the inter-segmental ventilation rate to correct for local ventilation rates when derived from values of isolated/unconnected clothed segments.

Theoretical and Experimental Estimation of Inter-Segmental Clothing Ventilation and Impact on Human Segmental Heat Losses

2015 ◽  
Author(s):  
Nagham Bilal Ismail ◽  
Nesreen Ghaddar ◽  
Kamel Ghali
Keyword(s):  
Human Body ◽  
Flow Characteristics ◽  
Heat Losses ◽  
The Body ◽  
Thermal Manikin ◽  
Body Parts ◽  
Tracer Gas ◽  
Wind Speeds ◽  
Local Ventilation ◽  
Ventilation Rates

Air exchange between a specific garment and the environment could occur 1) through the fabric with the environment, 2) through garment apertures with the environment, and 3) between local body parts’ microclimates. The first mechanism is related to the fabric properties and the flow characteristics around the human body. The second mechanism is induced by buoyancy and pressure alteration due to external wind. The third mechanism named inter-segmental ventilation occurs between different clothing sections caused by position of apertures, relative wind, fabric permeability and microclimate size of connected clothed segments. The objective of this work is to develop a simplified accurate model that solves coupled momentum, mass and heat balances including buoyancy for the connected clothed upper human body to predict inter-segmental ventilation and assess its impact on the air flow characteristics in the microclimate layer and on local ventilation rates. This model is coupled to the bioheat model to predict the effect of the inter-segmental ventilation on the heat losses from the body and on bringing the thermal comfort. The model is validated by performing an improved experimental method on a thermal manikin using the tracer gas method at different wind speeds for permeable clothing.

scholarly journals Proposing Alternative Solutions to Enhance Natural Ventilation Rates in Residential Buildings in the Cfa Climate Zone of Rasht

2021 ◽  
Vol 13 (2) ◽  
pp. 679
Author(s):  
Roya Aeinehvand ◽  
Amiraslan Darvish ◽  
Abdollah Baghaei Daemei ◽  
Shima Barati ◽  
Asma Jamali ◽  
...  
Keyword(s):  
Natural Ventilation ◽  
Residential Buildings ◽  
Residential Building ◽  
Ventilation Rate ◽  
Humid Climate ◽  
The Sustainable Development ◽  
Passive Strategies ◽  
Development Goals ◽  
Ventilation Rates ◽  
Ventilation Systems

Today, renewable resources and the crucial role of passive strategies in energy efficiency in the building sector toward the sustainable development goals are more indispensable than ever. Natural ventilation has traditionally been considered as one of the most fundamental techniques to decrease energy usage by building dwellers and designers. The main purpose of the present study is to enhance the natural ventilation rates in an existing six-story residential building situated in the humid climate of Rasht during the summertime. On this basis, two types of ventilation systems, the Double-Skin Facade Twin Face System (DSF-TFS) and Single-Sided Wind Tower (SSWT), were simulated through DesignBuilder version 4.5. Then, two types of additional ventilation systems were proposed in order to accelerate the airflow, including four-sided as well as multi-opening wind towers. The wind foldable directions were at about 45 degrees (northwest to southeast). The simulation results show that SSWT could have a better performance than the aforementioned systems by about 38%. Therefore, the multi-opening system was able to enhance the ventilation rate by approximately 10% during the summertime.

scholarly journals Local Characteristics of the Nocturnal Boundary Layer in Response to External Pressure Forcing

2017 ◽  
Vol 56 (11) ◽  
pp. 3035-3047 ◽  
Author(s):  
Steven J. A. van der Linden ◽  
Peter Baas ◽  
J. Antoon van Hooft ◽  
Ivo G. S. van Hooijdonk ◽  
Fred C. Bosveld ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Stable Boundary Layer ◽  
Dynamical Behavior ◽  
Geostrophic Wind ◽  
External Pressure ◽  
Near Surface ◽  
Stable Boundary ◽  
Wind Speeds ◽  
Turbulent Characteristics

AbstractGeostrophic wind speed data, derived from pressure observations, are used in combination with tower measurements to investigate the nocturnal stable boundary layer at Cabauw, the Netherlands. Since the geostrophic wind speed is not directly influenced by local nocturnal stability, it may be regarded as an external forcing parameter of the nocturnal stable boundary layer. This is in contrast to local parameters such as in situ wind speed, the Monin–Obukhov stability parameter (z/L), or the local Richardson number. To characterize the stable boundary layer, ensemble averages of clear-sky nights with similar geostrophic wind speeds are formed. In this manner, the mean dynamical behavior of near-surface turbulent characteristics and composite profiles of wind and temperature are systematically investigated. The classification is found to result in a gradual ordering of the diagnosed variables in terms of the geostrophic wind speed. In an ensemble sense the transition from the weakly stable to very stable boundary layer is more gradual than expected. Interestingly, for very weak geostrophic winds, turbulent activity is found to be negligibly small while the resulting boundary cooling stays finite. Realistic numerical simulations for those cases should therefore have a comprehensive description of other thermodynamic processes such as soil heat conduction and radiative transfer.

scholarly journals A comparison between tracer gas and tracer particle techniques in evaluating the efficiency of ventilation in operating theatres

1983 ◽  
Vol 91 (3) ◽  
pp. 509-519 ◽  
Author(s):  
Per-Arne Andersson ◽  
Anna Hambraeus ◽  
Ulla Zettersten ◽  
Bengt Ljungqvist ◽  
Kenneth Neikter ◽  
...  
Keyword(s):  
Tracer Particle ◽  
Ventilation System ◽  
Airborne Bacteria ◽  
Tracer Gas ◽  
Operating Theatres ◽  
Ventilation Rates ◽  
Operation Wound

Operating theatres are ventilated for a number of reasons, one of them being to keep numbers of airborne bacteria low at the operation wound. No matter how air is brought into the room, bacteria are removed by dilution rather than by air currents, because of turbulence caused by heat liberated by people and equipment and by movement in the room (Lidwell & Williams, 1960). With ventilation rates up to 20 air changes/hour, the dilution may differ at different sites in the room depending on the design of its ventilation system.

Abstract 264: Automatic Detection of Ventilations Using the Thoracic Impedance Signal During Lucas Chest Compressions

Circulation ◽  
2019 ◽  
Vol 140 (Suppl_2) ◽  
Author(s):  
Xabier Jaureguibeitia ◽  
Unai Irusta ◽  
Elisabete Aramendi ◽  
Pamela Owens ◽  
Henry E Wang ◽  
...  
Keyword(s):  
Cardiac Arrest ◽  
Minute Ventilation ◽  
Lung Ventilation ◽  
Detection Algorithm ◽  
Ventilation Rate ◽  
Thoracic Impedance ◽  
Chest Compressions ◽  
Signal Processing Algorithm ◽  
Ventilation Rates ◽  
Mechanical Cpr

Introduction: Resuscitation from out-of-cardiac arrest (OHCA) requires control of both chest compressions and lung ventilation. There are few effective methods for detecting ventilations during cardiopulmonary resuscitation. Thoracic impedance (TI) is sensitive to changes in lung air volumes and may allow detection of ventilations but has not been tested with concurrent mechanical chest compressions. Hypothesis: It is possible to automatically detect and characterize ventilations from TI changes during mechanical chest compressions. Methods: A cohort of 420 OHCA cases (27 survivors to hospital discharge) were enrolled in the Dallas-Fort Worth Center for Resuscitation Research cardiac arrest registry. These patients were treated with the LUCAS-2 CPR device and had concurrent TI and capnogram recordings from MRx (Philips, Andover, MA) monitor-defibrillators. We developed a signal processing algorithm to suppress chest compression artifacts from the TI signal, allowing identification of ventilations. We used the capnogram as gold standard for delivered ventilations. We determined the accuracy of the algorithm for detecting capnogram-indicated ventilations, calculating sensitivity, the proportion of true ventilations detected in the TI, and positive predictive value (PPV), the proportion of true ventilations within the detections. We calculated per minute ventilation rate and mean TI amplitude, as surrogate for tidal volume. Statistical differences between survivors and non-survivors were assessed using the Mann-Whitney test. Results: We studied 4331 minutes of TI during CPR. There were a median of 10 (IQR 6-14) ventilations per min and 52 (30-81) ventilations per patient. Sensitivity of TI was 95.9% (95% CI, 74.5-100), and PPV was 95.8% (95% CI, 80.0-100). The median ventilation rates for survivors and non-survivors were 7.75 (5.37-9.91) min -1 and 5.64 (4.46-7.15) min -1 (p<10 -3 ), and the median TI amplitudes were 1.33 (1.03-1.75) Ω and 1.14 (0.77-1.66) Ω (p=0.095). Conclusions: An accurate automatic TI ventilation detection algorithm was demonstrated during mechanical CPR. The relation between ventilation rate during mechanical CPR and survival was significant, but it was not for impedance amplitude.

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