Inertia Effects on the Modulated Air Layer Heat and Moisture Transport From Clothing With Open Aperture

Volume 1 ◽  
2004 ◽  
Author(s):  
Nesreen Ghaddar ◽  
Kamel Ghali ◽  
Jihad Harathani
Keyword(s):  
Heat Loss ◽  
Flow Model ◽  
Transport Processes ◽  
Parallel Flow ◽  
Open Aperture ◽  
Closed Aperture ◽  
Airflow Rate ◽  
Normal Flow ◽  
Flow Rates ◽  
D Model

A two-dimensional model is developed of the modulated internal airflow in the gap between clothing and skin surface due to walking and in presence of clothing end apertures. The normal airflow renewing the air layer through the fabric is conducted in an oscillatory way during body motion without gross environmental air movement using fabric-three node model [1]. The parallel flow is induced by periodic pressure difference between environment pressure at the aperture of the clothing system and trapped air layer pressure. The parallel flow is assumed locally governed by Womersley solution of time-periodic laminar flow in a plane channel. The three-node fabric ventilation model has been modified to include the diffusion-dominated transport processes in the fabric at low normal flow rates. The low flow rates occurred near the opening and during the periodic ventilation cycle when the airflow rate approaches zero before changing direction in and out of the fabric. The fabric ventilation model and the diffusion model completely overlap at the normal airflow rate of 0.00777 kg/m2·s. The new modified-model has been used in the 1-D steady periodic normal flow model and results have shown good agreement with published experimental data. The 2-D model using Womersley-flow model in the parallel direction has predicted significantly lower flow rates than Poisueille flow model. In addition, the 2-D model predicted the sensible and latent heat loss from the sweating skin in presence of openings in the clothing system. The reported results showed that under walking conditions, a clothing system with an open aperture reduced heat loss from the skin when compared to 1-D normal ventilation model (closed aperture). These results were consistent with previously published empirical data of Lotens [2] and Danielsson [3] on air layer resistance for open and closed aperture of high air permeable fabric.

Modulated Air Layer Heat and Moisture Transport by Ventilation and Diffusion From Clothing With Open Aperture

2005 ◽  
Vol 127 (3) ◽  
pp. 287-297 ◽  
Author(s):  
Nesreen Ghaddar ◽  
Kamel Ghali ◽  
Jihad Harathani
Keyword(s):  
Heat Loss ◽  
Moisture Transport ◽  
Transport Processes ◽  
Parallel Flow ◽  
Open Aperture ◽  
Two Dimensional ◽  
Flow Rates ◽  
Trapped Air ◽  
Heat And Moisture Transport ◽  
Heat And Moisture

A two-dimensional model is developed for the modulated internal airflow, due to walking, in the gap between clothing and skin surface in the presence of clothing apertures. The normal airflow renewing the air layer through the fabric is modeled using the Ghali et al. three-node fabric ventilation model with corrected heat and moisture transport coefficients within the fabric voids to include the diffusion-dominated transport processes in the fabric at low normal flow rates that occur near the open aperture. The parallel flow is induced by a periodic pressure difference between environmental pressure at the aperture of the clothing system and trapped air layer pressure. The parallel flow in the trapped air layer is assumed to be locally governed by the Womersley solution of time-periodic laminar flow in a plane channel. The two-dimensional (2D) model that uses, in the parallel direction, the Womersley flow of the trapped air layer has predicted significantly lower flow rates than a model based on an inertia-free quasi-steady Poisueille flow model (valid only at low ventilation frequencies). In addition, the model predicted lower sensible and latent heat losses from the sweating skin in the presence of open apertures in the clothing system. The percentage drop in total heat loss due to open aperture is 7.52%, and 2.63%, at ventilation frequencies of 25, and 35 revolution per minute, respectively. The reported results showed that under walking conditions, a permeable clothing system with an open aperture reduced heat loss from the skin when compared to a normal ventilation model (closed aperture). These results were consistent with previously published empirical data of Lotens and Danielsson on air layer resistance for open and closed apertures in high air permeable fabrics.

Ignition Forecast Based on Chemical Kinetics and Uncertainty Quantification

2021 ◽  
Author(s):  
Yunan Li ◽  
Timothy I. Anderson ◽  
Anthony R. Kovscek
Keyword(s):  
Activation Energy ◽  
Crude Oil ◽  
Uncertainty Quantification ◽  
Heat Loss ◽  
Chemical Kinetics ◽  
Reactive Transport ◽  
Air Flow ◽  
Heating Rates ◽  
Flow Rates ◽  
Reaction Models

Abstract The description of chemical kinetics is very import to the simulation of reactive transport for enhanced oil recovery (EOR). Characterizing petroleum ignition is especially important for simulation and prediction of In-Situ Combustion (ISC). In order to model crude oil oxidation reactions accurately, an experimental workflow is introduced to obtain kinetic parameters for ISC chemical reaction models. An optimization algorithm assists to match the reaction model parameters to the experimental results, and this validated model is used to predict ignition of crude oil in porous media. Apparent activation energy is estimated from ramped temperature oxidation experiments under several heating rates, including 1.5, 2.0, 2.5, 3.0, 5, 10, 15, and 20 °C/min. These experiments are separated into a small heating rates group (1.5, 2.0, 2.5, 3.0 °/min) and large heating rates (5, 10, 15, 20 °/min). The results show that experiments with small heating rates capture the details of reaction kinetics such that the estimated activation energy is more accurate, with the validated simulation model able to make accurate predictions for this particular crude oil. After matching the kinetics parameters, we predict the ignition conditions as a function of the air flow rates and the heat loss rates. The ignition envelope indicates that the window for air flow rates to ignite the oil decreases if the heat loss rate is high. Greater heat losses require more thermal energy to be released from the reaction to overcome losses and for ignition to occur. This leads to a narrower range of ignition air flow rates due to convective heat transfer. The uncertainty quantification results provide a confidence region for the ignition envelope impacted by the threshold temperature of the ignition criterion. The novelty of this work is the description of optimized combustion reaction models with rigorous experimental verification and uncertainty quantification for reactive transport simulations.

Stimulation of oxygen uptake by glucagon is oxygen dependent in perfused rat liver

1989 ◽  
Vol 256 (2) ◽  
pp. G369-G376
Author(s):  
Z. Kizaki ◽  
R. G. Thurman
Keyword(s):  
Intracellular Calcium ◽  
High Flow ◽  
Perfused Liver ◽  
Normal Flow ◽  
Sprague Dawley ◽  
O2 Uptake ◽  
Intact Cells ◽  
Flow Rates ◽  
Isolated Mitochondria ◽  
Stimulation Of

Livers from well-fed female Sprague-Dawley rats (100-150 g) were perfused at flow rates of 4 or 8 ml.g liver-1.min-1 to deliver O2 to the organ at various rates. During perfusion at normal flow rates (4 ml.g-1.min-1), glucagon (10 nM) increased O2 uptake in perfused liver by approximately 40 mumol.g-1.h-1. In contrast, glucagon increased O2 uptake by nearly 100 mumol.g-1.h-1 when livers were perfused at high flow rates. Increase in O2 uptake was directly proportional to flow rate and was blocked partially by infusion of phorbol myristate acetate (100 nM) before glucagon. Increase in O2 uptake due to elevated flow was not due to enhanced glucagon delivery, since infusion of 120 nM glucagon at normal flow rates only increased O2 uptake by approximately 40 mumol.g-1.h-1. On the other hand, when O2 tension in the perfusate was manipulated at normal flow rates, the stimulation of O2 uptake by glucagon increased proportional to the average O2 tension in the liver. Infusion of 8-bromo-adenosine 3',5'-cyclic monophosphate (BrcAMP; 25 microM) also increased O2 uptake more than twice as much at high compared with normal flow rates. In the presence of angiotensin II (5 nM), a hormone that increases intracellular calcium, glucagon increased O2 uptake by nearly 100 mumol.g-1.h-1 at normal flow rates. Infusion of glucagon or BrcAMP into livers perfused at normal flow rates increased state 3 rates of O2 uptake of subsequently isolated mitochondria significantly by approximately 25%. In contrast, perfusion with glucagon or BrcAMP at high flow rates increased mitochondrial respiration by 50-60%. Glucagon addition acutely to suspensions of mitochondria, however, had no effect on O2 uptake. These data are consistent with reports that glucagon administration in vivo or treatment of intact cells with glucagon increases O2 uptake of subsequently isolated mitochondria, a phenomenon that can account for the observed increase in O2 uptake in livers perfused at high flow rates with glucagon. Furthermore, these results are consistent with the hypothesis that the effect of glucagon on mitochondria is O2 dependent in the perfused liver. This is most likely due to an effect of intracellular calcium on a mechanism mediated via cAMP.(ABSTRACT TRUNCATED AT 250 WORDS)

Transient heat loss analysis of fabrics using a dynamic sweating guarded hot plate protocol

2019 ◽  
Vol 90 (9-10) ◽  
pp. 1130-1140
Author(s):  
Courtney Oswald ◽  
Emiel DenHartog
Keyword(s):  
Water Absorption ◽  
Heat Loss ◽  
Fiber Type ◽  
Transport Processes ◽  
Cooling Power ◽  
Wool Fabric ◽  
Hot Plate ◽  
Guarded Hot Plate ◽  
Moisture Management ◽  
Sweat Production

Moisture management is important for the human comfort of clothing, especially while perspiring. Ideally, the fabric chosen for a garment enables moisture to migrate away from the skin surface, facilitating the liquid to be evaporated into the surrounding environment, which causes a cooling sensation for the wearer. This process is influenced by factors such as fiber type, fabric construction, and fabric treatments, all of which impact the resulting wicking and moisture management properties of the fabric. This research explored the heat loss associated with combined water absorption, wicking, and evaporative cooling during wetting of fabrics. A dynamic sweating guarded hot plate was used to measure transitional heat loss as water was introduced at a steady rate over a 65-minute testing period. The results on a cotton and polyester blend fabric as well as a wool fabric indicated that the liquid water absorption and transport processes significantly influence heat loss properties during this transition. However, the results also show novel aspects in the efficiency of cooling associated with the wicking of sweat and different stages of wetting of fabrics leading to different cooling power. Furthermore, this method raises questions as to whether current sweating guarded hot plate technologies are an appropriate representation of human sweat production or that the scalability of sweat production per unit area is limited. This developed testing method can be successful in quantifying the differences in transitional heat loss and will enable testing of fabrics for comfort in changing conditions.

scholarly journals Performance and applicability of a 2.5-D ice-flow model in the vicinity of a dome

2016 ◽  
Vol 9 (7) ◽  
pp. 2301-2313 ◽  
Author(s):  
Olivier Passalacqua ◽  
Olivier Gagliardini ◽  
Frédéric Parrenin ◽  
Joe Todd ◽  
Fabien Gillet-Chaulet ◽  
...  
Keyword(s):  
Flow Model ◽  
Three Dimensional ◽  
Thermal Conditions ◽  
Observation Data ◽  
Flow Tube ◽  
Ice Flow ◽  
Linear Temperature ◽  
Ice Surface ◽  
Scanning Window ◽  
D Model

Abstract. Three-dimensional ice flow modelling requires a large number of computing resources and observation data, such that 2-D simulations are often preferable. However, when there is significant lateral divergence, this must be accounted for (2.5-D models), and a flow tube is considered (volume between two horizontal flowlines). In the absence of velocity observations, this flow tube can be derived assuming that the flowlines follow the steepest slope of the surface, under a few flow assumptions. This method typically consists of scanning a digital elevation model (DEM) with a moving window and computing the curvature at the centre of this window. The ability of the 2.5-D models to account properly for a 3-D state of strain and stress has not clearly been established, nor their sensitivity to the size of the scanning window and to the geometry of the ice surface, for example in the cases of sharp ridges. Here, we study the applicability of a 2.5-D ice flow model around a dome, typical of the East Antarctic plateau conditions. A twin experiment is carried out, comparing 3-D and 2.5-D computed velocities, on three dome geometries, for several scanning windows and thermal conditions. The chosen scanning window used to evaluate the ice surface curvature should be comparable to the typical radius of this curvature. For isothermal ice, the error made by the 2.5-D model is in the range 0–10 % for weakly diverging flows, but is 2 or 3 times higher for highly diverging flows and could lead to a non-physical ice surface at the dome. For non-isothermal ice, assuming a linear temperature profile, the presence of a sharp ridge makes the 2.5-D velocity field unrealistic. In such cases, the basal ice is warmer and more easily laterally strained than the upper one, the walls of the flow tube are not vertical, and the assumptions of the 2.5-D model are no longer valid.

The numerical methods for analyzing the Z-scan data

2014 ◽  
Vol 23 (02) ◽  
pp. 1450020 ◽  
Author(s):  
Lam Thanh Nguyen ◽  
Nghia Tran Hong ◽  
Cam Tu Bui Thi ◽  
Anh Quynh Le
Keyword(s):  
Refractive Index ◽  
Open Aperture ◽  
Closed Aperture ◽  
Initial Estimate ◽  
Reasonable Accuracy ◽  
Nonlinear Parameters ◽  
Fitting Method ◽  
Scan Data ◽  
Curve Fitting Method ◽  
Two Parameter

In this paper, we are dedicated to exemplifying a two parameter curve fitting method and developing a Matlab-based simulation program to extract the nonlinear refractive index and nonlinear absorption coefficient from closed-aperture Z-scan or R(z) data without the need for performing open-aperture Z-scan measurement. It should be noted, however, that both approaches can only be applicable to a case for which the on-axis phase shift at the focus is small. In this way, we not only determine the nonlinear parameters quickly with reasonable accuracy, as well as save time, efforts and equipment in the process of Z-scan implementation, but also obtain an initial estimate in order to compare with the results of the open-aperture Z-scan measurement when needed.

scholarly journals Thermal Performance of Solar Collectors with EPDM Absorber Plates

1988 ◽  
Vol 41 (4) ◽  
pp. 623
Author(s):  
MJ O'Keefe ◽  
JLA Francey
Keyword(s):  
Experimental Study ◽  
Thermal Resistance ◽  
Flat Plate ◽  
Heat Loss ◽  
Thermal Performance ◽  
Critical Value ◽  
Solar Collectors ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
High Thermal Resistance

An experimental study of flat-plate solar collectors using ethylene, propylenediene monomer (EPDM) absorber plates is descn"bed. In spite of the high thermal resistance of this material the performance is found to compare well with metal absorbers and to be in agreement with the Hottel-Whillier-Bliss equation. There is, however, an observed increase in the heat loss coefficient for mass flow rates below a critical value.

scholarly journals Overtopping breaching of river levees constructed with cohesive sediments

2016 ◽  
Vol 16 (7) ◽  
pp. 1541-1551 ◽  
Author(s):  
Hongyan Wei ◽  
Minghui Yu ◽  
Dangwei Wang ◽  
Yitian Li
Keyword(s):  
Soil Properties ◽  
Discharge Coefficient ◽  
Flow Model ◽  
Impinging Jet ◽  
Cohesive Sediments ◽  
Flow Shear ◽  
Flow Rates ◽  
Side Slope ◽  
Weir Flow ◽  
Headcut Retreat

Abstract. Experiments were conducted in a bend flume to study the overtopping breaching process and the corresponding overflow rates of river levees constructed with cohesive sediments. The river and land regions were separated by the constructed levee in the bend flume. Results showed that the levee breaching process can be subdivided into a slope erosion stage, a headcut retreat stage and a breach widening stage. Mechanisms such as flow shear erosion, impinging jet erosion, side slope erosion and cantilever collapse were discovered in the breaching process. The erosion characteristics were determined by both flow and soil properties. Finally, a depth-averaged 2-D flow model was used to simulate the levee breaching flow rates, which is well expressed by the broad-crested weir flow formula. The deduced discharge coefficient was smaller than that of common broad-crested rectangular weirs because of the shape and roughness of the breach.

Nasal airflow in inspiration and expiration

1990 ◽  
Vol 104 (6) ◽  
pp. 473-476 ◽  
Author(s):  
Laura Viani ◽  
Andrew S. Jones ◽  
Ray Clarke
Keyword(s):  
Flow Rate ◽  
Peak Flow ◽  
Phase Relationship ◽  
Low Flow ◽  
Airflow Rate ◽  
Nasal Resistance ◽  
Nasal Airflow ◽  
Flow Rates ◽  
Induced Changes ◽  
Peak Inspiratory Flow Rate

AbstractInspiratory and expiratory airflow rates were measured in 30 subjects during quiet respiration (at a pressure gradient of 150 Pa) and at peak flow rates.For low flow rates airflow rate was greater for inspiration than for expiration. Conversely at peak flow rates flow was greatest during expiration. Thus there was a reversal in the phase relationship between inspiration and expiration as flow rate increased.It was also found that peak inspiratory flow rate correlated better with values for nasal resistance than did peak expiratory flow rate. Flow rate measured by rhinomanometry during quiet respiration was more sensitive to physiologically induced changes in nasal resistance than was peak flow rate.The findings are discussed with reference to previous work on the physiology of nasal airflow.

Simulation of Spray Transfer Processes in Electrostatic Rotary Bell Sprayer

2004 ◽  
Vol 126 (3) ◽  
pp. 449-456 ◽  
Author(s):  
Kyoung-Su Im ◽  
Ming-Chia Lai ◽  
Sheng-Tao John Yu ◽  
Robert R. Matheson,
Keyword(s):  
Numerical Study ◽  
Operating Parameter ◽  
Transport Processes ◽  
Operating Conditions ◽  
Transfer Efficiency ◽  
Airflow Rate ◽  
Flow Solver ◽  
Voltage Range ◽  
Spray Transfer ◽  
Transfer Processes

A numerical study of the spray transfer processes in an electrostatic rotary bell applicator (ESRB) has been conducted utilizing code for a newly developed simulation code. This code consists of three modularized solvers: a fluid flow solver, a spray dynamics solver, and an electrostatic solver. The development of the code consisted of the following steps. First, the flow solver designed for an unsteady three-dimensional Navier-Stokes equation was developed to simulate the shaping airflow with the initial condition and the boundary condition supported by experimental data. Second, the particle trajectory solver, which interacts with the airflow by momentum coupling, was developed to apply the spray transport processes. Finally, the electrostatic solver was developed to calculate the electrostatic field within the two phase flow field. The integrated code created by combining those three solvers was then applied to simulate the paint spray transport processes according to the operating conditions of interest. The numerical results show that the spray shape is very sensitive to changes in the charge to mass ratio. The voltage setting is a dominant operating parameter affecting the numerical transfer efficiency. The voltage range studied was 0 kV to 90 kV. In addition, the transfer efficiency decreases as the shaping airflow rate increases. However, a high shaping airflow rate produces a more uniform distribution of spray mass on the target plane.

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