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.

Heat and Moisture Transport Through the Microclimate Air Annulus of the Clothing-Skin System Under Periodic Motion

2006 ◽  
Vol 128 (9) ◽  
pp. 908-918 ◽  
Author(s):  
K. Ghali ◽  
N. Ghaddar ◽  
E. Jaroudi
Keyword(s):  
Mass Transfer ◽  
Heat Loss ◽  
Moisture Transport ◽  
Contact Region ◽  
Open Aperture ◽  
Sensible Heat ◽  
Amplitude Factor ◽  
Skin Contact ◽  
Heat And Moisture Transport ◽  
Heat And Moisture

The study is concerned with the heat and moisture transport in a ventilated fabric-skin system composed of a microclimate air annulus that separates an outer cylindrical fabric boundary and an inner oscillating cylinder representing human skin boundary for open and closed aperture settings at the ends of the cylindrical system. The cylinder ventilation model of Ghaddar et al. (2005, Int. J. Heat Mass Transfer, 48(15), pp. 3151–3166) is modified to incorporate the heat and moisture transport from the skin when contact with fabric occurs at repetitive finite intervals during the motion cycle. During fabric skin contact, the heat and moisture transports are modeled based on the fabric dry and evaporative resistances at the localized touch regions at the top and bottom of points of the cylinder. Experiments were conducted to measure the mass transfer coefficient at the skin to the air annulus under periodic ventilation and to measure the sensible heat loss from the inner cylinder for the two cases of fabric-skin contact and no contact. The model predictions of time-averaged steady-periodic sensible heat loss agreed well with the experimentally measured values at different frequencies. The model results showed that the rate of heat loss increased with increased ventilation frequency at fixed (=amplitude/mean annular spacing). At amplitude factor of 1.4, the latent heat loss in the contact region increased by almost 40% compared to the loss at amplitude factor of 0.8 due to the increase in fabric temperature during contact. The sensible heat loss decreased slightly between 3% at f=60rpm and 5% at f=25rpm in the contact region due to higher air temperature and lack of heat loss by radiation when fabric and skin are in touch. The presence of an open aperture has a limited effect on increasing the total heat loss. For an open aperture system at amplitude factor of 1.4, the increase in heat loss over the closed apertures is 4.4%, 2.8%, and 2.2% at f=25, 40, and 60rpm, respectively.

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.

Heat and Moisture Transport Through the Micro-Climate Air Annulus of the Clothing-Skin System Under Periodic Motion

2005 ◽  
Author(s):  
N. Ghaddar ◽  
K. Ghali ◽  
E. Jaroudi
Keyword(s):  
Heat Loss ◽  
Latent Heat ◽  
Moisture Transport ◽  
Contact Region ◽  
Heat Losses ◽  
Sensible Heat ◽  
Skin Contact ◽  
Cylinder Model ◽  
Heat And Moisture Transport ◽  
Heat And Moisture

A dynamic thermal model is developed using the 2D cylinder model of Ghaddar et al [1] of ventilated fabric-skin system where a microclimate air annulus separates an outer cylindrical fabric boundary and an inner human body solid boundary for closed and open apertures. The cylinder model solves for the radial, and angular flow rates in the microclimate air annulus domain where the inner cylinder is oscillating within an outer fixed cylinder of porous fabric boundary. The 2-D cylinder model is further developed in the radial and angular directions to incorporate the heat and moisture transport from the inner cylinder when the fabric touches the skin boundary at repetitive finite intervals during the motion cycle. The touch model is based on a lumped fabric transient approach based on the fabric dry and evaporative resistances at the localized touch regions at the top and bottom of points of the cylinder. The film coefficients at the inner cylinder are needed for the model simulation. Experiments are conducted in an environmental chamber under controlled conditions to measure the mass transfer coefficient at the skin to the air annulus separating the wet skin and the fabric in the cylindrical geometry. In addition, experiments have also been conducted at ventilation frequencies of 30, 40, and 60 rpm to measure the sensible heat loss from the inner cylinder to validate the predictions of sensible and latent heat losses of the 2-D ventilation model for the two cases when fabric is in contact with the skin surface and when no contact is present for close aperture. The model prediction of time-averaged steady-periodic sensible heat loss agreed well with the experimentally measured values. A parametric study is performed to predict sensible and latent heat losses from the system by ventilation at different frequencies, fabric skin contact times during the motion cycle measured by a dimensionless amplitude parameter (ζ = amplitude/mean annular spacing). The rate of heat loss increases with increased ventilation frequency at fixed ζ. The latent heat loss in the contact region increases by almost 40% due to increase in fabric temperature during contact. The sensible heat loss decreases between 3% at f = 60 rpm, and 5% at f = 25 rpm in the contact region due to higher air temperature and lack of heat loss by radiation during the contact between fabric and skin.

Numerical Simulation of Heat, Air, and Moisture Transfer Through a Wall of Porous Media

2020 ◽  
Author(s):  
Kiflom B. Tesfamariam ◽  
Cheng-Xian (Charlie) Lin ◽  
Fang Liu
Keyword(s):  
Numerical Simulation ◽  
Moisture Transport ◽  
Moisture Transfer ◽  
Simulation Software ◽  
Transport Processes ◽  
Two Dimensional ◽  
Heat And Moisture Transfer ◽  
Porous Walls ◽  
Heat And Moisture ◽  
Benchmark Solutions

Abstract This paper presents the results of two-dimensional (2D) numerical simulation of heat, air, and moisture transfer through porous walls, which have important application background in the built environment and other engineering fields. The air flows, heat and moisture transfer in the walls are studied using a transient heat, air, and moisture (HAM) model. This model treats the non-isothermal airflow through two-dimensional porous geometries in a time-dependent format. The model includes the Brinkman equation describes the flow of air and other mathematical equations that calculate the heat and moisture transfer through the porous region. The equations are solved by a finite element method (FEM) using physics-based modeling, which is implemented in the commercial simulation software, COMSOL Multiphysics. The model prediction is first validated by using published benchmark solutions. Eventually, the numerical results are presented to illustrate the complex effects of material porosity and permeability on the heat and moisture transport, and moisture content variation in space and time through the walls, at different humidity and temperature conditions. Within the investigated parameter ranges, it is demonstrated that the relative humidity and temperature difference are the driving forces for the transient heat, air, and moisture transport processes through the porous area in the porous walls.

scholarly journals Heat and Moisture Transport in Multi-Layer Walls: Interaction and Heat Loss at Varying Outdoor Temperatures / Siltuma Un Mitruma Pārnese Caur Daudzslāņainām Būvkonstrukcijām: Āra Temperatūras Izmaiņu Ietekme Uz Siltuma Zudumiem Iekštelpā

2012 ◽  
Vol 49 (6-I) ◽  
pp. 32-43 ◽  
Author(s):  
A. Ozolinsh ◽  
A. Jakovich
Keyword(s):  
Mathematical Model ◽  
Energy Efficiency ◽  
Moisture Transport ◽  
Heat Losses ◽  
Condensate Formation ◽  
Heat And Moisture Transport ◽  
U Value ◽  
Technical Solutions ◽  
Heat And Moisture ◽  
Humidity Profiles

Abstract The heat and moisture transport in multi-layer walls is analysed for five building units. Using the developed program, a typical of Latvian conditions temperature and relative humidity profiles in multi-layered constructions has been obtained and the indoor heat losses estimated. Consideration is also given to the risk of condensate formation and to the influence of moisture on the U-value. The created mathematical model allows forecasting the energy efficiency and sustainability of different technical solutions as refer to the heat and moisture transport in buildings.

scholarly journals Selected Topics in Homogenization of Transport Processes in Historical Masonry Structures

2012 ◽  
Vol 6 (1) ◽  
pp. 148-159
Author(s):  
Jan Sykora ◽  
Jan Zeman ◽  
Michal Ŝejnoha
Keyword(s):  
Initial Conditions ◽  
Heat Conduction Problem ◽  
Transport Processes ◽  
Random Pattern ◽  
Binary Sample ◽  
Homogenization Approach ◽  
Heat And Moisture Transport ◽  
Historical Masonry ◽  
Steady State Heat ◽  
Heat And Moisture

The paper reviews several topics associated with the homogenization of transport processed in historical ma-sonry structures. Since these often experience an irregular or random pattern, we open the subject by summarizing essen-tial steps in the formulation of a suitable computational model in the form of Statistically Equivalent Periodic Unit Cell (SEPUC). Accepting SEPUC as a reliable representative volume element is supported by application of the Fast Fourier Transform to both the SEPUC and large binary sample of real masonry in search for effective thermal conductivities lim-ited here to a steady state heat conduction problem. Fully coupled non-stationary heat and moisture transport is addressed next in the framework of two-scale first-order homogenization approach with emphases on the application of boundary and initial conditions on the meso-scale.

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