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72

JOURNAL OF M EASUREMENTS IN E NGINEERING . JUNE 2020, V OLUME 8, ISSUE 2

Investigation of influence of forced ventilation through

3D textile on heat exchange properties of the textile layer

Aušra Gadeikytė

1

, Rimantas Barauskas

2

Department of Applied Informatics, Kaunas University of Technology,

Studentu Str. 50-407, LT-51368, Kaunas, Lithuania

1

Corresponding author

E-mail:

1

ausra.gadeikyte@ktu.lt,

2

rimantas.barauskas@ktu.lt

eceived 4 May 2020; received in revised form 19 June 2020; accepted 26 June 2020

OI htt

s://doi.or

/10.21595/

me.2020.21555

Copyright © 2020 Aušra Gadeikytė , et al. This is an open access article distributed under the Creative Commons Attribution License,

which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract. The intention of this study was to create a computational model in micro-scale that

allows to imitate heat and mass transfer through three-dimensional textile layer with and without

forced ventilation. The four ventilation rates were used 0, 0.2, 0.4 and 0.8 dm

3

min

-1

.

Approximation of a unit cell geometry and heat transfer process were considered. The

time-dependent and steady-state simulations are based on Navier-Stokes/Brinkman partial

differential equations, and energy equation. A finite element modelling package Comsol

Multiphysics was used for numerical simulations. The Laminar flow (.spf) and Heat transfer in

fluids (.ht) modes were coupled with non-isothermal flow (.nitf) multi-physics. The

post-processing analysis was done using Matlab software. The outcomes of simulation are

temperature distributions, surface average temperature and relative humidity through the thickness

of the representative volume. The results enable to create a macro-scale models for efficient

simulation of heat exchange in textile packages.

Keywords: heat transfer, multilayer textile package, finite element modelling, Comsol

Multiphysics 5.3a.

1. Introduction

Thermal protective clothing (e.g. firefighters clothing, winter outdoor clothing, ballistic

protection clothing) usually has a multilayer construction [1, 2]. Each layer has a specific function.

For example, the outer layer protects against environment, the middle thermo-insulating layer

protects the human body from excessive heat loss, the inner layer (usually 3D textile layer) enables

the moisture and air exchange between the body and the surrounding environment [1]. The air gap

between the skin and the inner layer is referred to as the 'microclimate'. It can influence heat and

mass transfer from or to the body (e.g. protective clothing, where microclimate is typically thicker

and therefore the natural convection is more likely to occur) [3]. Investigation and development

of a multi-layer textile package require understanding of the coupled heat and moisture transport

phenomena in order to describe thermal comfort of clothing during wearing. Thermal insulation

properties such as thermal resistance, water-vapor resistance and air permeability are crucially

important comfort-related properties of fabrics [1]. However, theoretical investigations of the

physical behavior of multi-layer textiles are complicated due to complex internal structure,

coupled heat and moisture transfer and other physical processes, which occur in different space

and time scales [2]. Computational Fluid Dynamics (CFD) tools are often used for simulation of

heat and mass transfer processes in different engineering applications [4]. CFD tools and advanced

mathematical models usually based on approximation of the textile due to complex multi-scale

geometry, knowledge of parameters that describe the properties of the textiles. Measurements

often do not provide all necessary data and relationships or require the access to complex and

expensive experimental facilities [2-5].

In recent decades various aspects of heat and mass transport through the fabric have been

investigated. Neves et al. [5] focused on methodologies and experimental procedures that allow

to determine parameters such as fiber fraction, tortuosity as well as mass and heat transfer

INVESTIGATION OF INFLUENCE OF FORCED VENTILATION THROUGH 3D TEXTILE ON HEAT EXCHANGE PROPERTIES OF THE TEXTILE LAYER.

AUŠRA GADEIKYTĖ , RIMANTAS BARAUSKAS

ISSN P RINT 2335-2124, ISSN O NLINE 2424-4635, K AUNAS , L ITHUANIA 73

coefficients that are required as input parameters for numerical studies. In subsequent work [6]

Neves et al. proposed a numerical model for the analysis of heat and mass transfer through

multilayer clothing. It enables to study textiles and fibers characteristics during physical activities

with different intensities (i.e. heat/sweat release). Mayor et al. [7] numerically studied the transport

phenomena across horizontal clothing microclimates with natural convection by using the finite

element method. In this study the effect of different microclimate thicknesses, external air

temperature, external air velocity, and optical properties of the fabric inner surface was analyzed.

The model coupled the classical set of continuity, momentum (Navier-Stokes) and energy

equations in order to describe transport phenomena that occur in the simulation domain [7].

Siddiqui et al. [8] used the conjugate heat transfer model for investigation of heat transfer from

hotplate to plain weft knitted fabric. Boussinesq approximation was used for the analysis of

buoyancy-driven natural convection. The simulation was carried out using Abaqus software. The

effective thermal conductivity and thermal resistance of the plain weft knitted polyester fabric

were predicted [8]. Santos et al. [3] performed 2D transient simulations of air flow and heat

transfer around a clothed human limb in the horizontal position. It was found that velocity,

temperature and heat fluxes were dependent on the microclimate thickness. Angelova et al. [4]

proposed a numerical model for simulation of the heat transfer through woven textiles by the jet

system theory. A computational model was based on the Reynolds averaged Navier-Stokes partial

differential equations (RANS), and the energy equation that was used together with 𝑘 -𝜀 and RSM

turbulence models. It was found that porosity of the woven macrostructure strongly affects the

heat transfer. Simulations were carried out with Fluent CFD software package [4]. Puszkarz et al.

[9] carried out computer simulation to study the performance of multilayer textile assembly

exposed to heat radiation. The model was built using Solidworks Flow Simulation software that

allowed to couple energy conservation equations and Navier-Stokes equations. The computational

model outcomes were the transmitted heat flux density, the heat transmission factor, and the

radiant heat transfer index that portrayed a good agreement with experimental data [9].

The aim of this study is to develop a computational model that predicts average temperature

and relative humidity values through 3D textile using different ventilation rates, where ventilation

flux is parallel to the layer and is directed through the air gaps of the 3D textile structure. The

model was built using Comsol Multiphysics software.

2. Mathematical model of heat and mass exchange through 3D textile

2.1. Geometry of model

One of challenges using CFD tools is to obtain proper geometry approximation

(homogenization of air and fibers) in order to save computational time simultaneously avoiding

the meshing problems due to complex internal structure of the fabric. For this reason, in our

previous work [10] a single-layer woven fabric was analyzed by numerically simulating air

permeability and water vapor resistance tests. As a result, the model of 3D textile layer was

constructed that consists of two simplified layers coupled with spacer yarn. The results portrayed

a good agreement with experimental [11] and literature data [2].

The single-layer textile geometry was recreated in accordance with actual construction

parameters measured by Zupin et al. [11]. Air permeability test was performed with the Air

Permeability tester FX 3300 Labotester III (Textest Instruments) according to the ISO 9237:1995

(E) standard. The pressure difference was set 200 [Pa] on an area of 20 cm2 [11]. The local

permeability of yarns was calculated by using the Gebart model. More details about local

permeability calculation are presented in [12]. The water vapor resistance test was performed with

The Sweating Guarded Hot Plate M259B according to the LST EN 31902:2002 / International

standard ISO 11092:2014. Our numerical simulations were based on Navier-Stokes and Brinkman

equations together with the continuity equation. Summary of experimental and computational

values of air permeability and water vapor resistance are shown in Table 1. In this work the

INVESTIGATION OF INFLUENCE OF FORCED VENTILATION THROUGH 3D TEXTILE ON HEAT EXCHANGE PROPERTIES OF THE TEXTILE LAYER.

AUŠRA GADEIKYTĖ , RIMANTAS BARAUSKAS

74

JOURNAL OF M EASUREMENTS IN E NGINEERING . JUNE 2020, V OLUME 8, ISSUE 2

geometric model of a unit cell of 3D textile layer is used as created in our previous work [10].

Table 1. Validation of measurement and computational model

No A representative

unit cell

Measured air

permeability

(mm/s) [11]

Numerical

simulation air

permeability

(mm/s) [10]

Measured

Water vapor

resistance coeff.

(s/m) [2]

Numerical

simulation water

vapor resistance

(s/m)

1

One-layer

measured density

(21/15) [11]

2391.67 2387.7 - 4.4675

2 3D textile - 1525.9 6.36 6.0769

Geometry of three-dimensional textile layer is shown in Fig. 1. Model have air domain

1.4 mm×1 mm×4.439 mm in length (𝑥 direction), width (𝑦 direction), height (𝑧 direction), two

textile layers with 0.439 mm thickness, and spacer yarn. Distance between layers is 3.061 mm,

the spacer yarn radius is 0.08 mm.

Fig. 1. Geometry of 3D textile layer with labels of boundary conditions and mesh diagram

Different meshes (normal 502188, coarse 271751, coarser 127480, extra coarse 65740, and

extremely coarse 43311) were adapted for simulation in order to find the grid-independent

solution. It was found that a minimum number of finite elements was 65740. The extra coarse

mesh that was used in simulations is shown in Fig. 1.

2.2. Heat and mass flow simulation

The computational model was created using Comsol Multiphysics 5.3a software. Comsol

Multiphysics is finite element modelling package that has ability to couple different physics

(partial differential equations (PDE)) or multi-physics within a si ngle model domain. PDE can be

specified using physics-based user interfaces or entered symbolically. The COMSOL simulation

environment consists of defining geometry, specifying physics, meshing, solving, and then

postprocessing [13]. The simulation domain Ω consists of union of two subdomains Ω



(air

domain), Ω



(three-dimensional textile layer). The governing equations are based on energy

conservation (heat transfer) equations and Navier-Stokes/Brinkman equations. The assumptions

were made stating that the air flow is incompressible Newtonian si ngle phase flow. Also,

steady-state and time-dependent simulation were conducted considering the laminar flow model.

The fluid flow equations were performed by the classical set of continuity (Eq. (1)),

momentum equation that was considered Navier-Stokes equations (Eq. (2)) in case of free flow,

and Brinkman equations (Eq. (3)) in case of porous media domain. The steady-state governing

INVESTIGATION OF INFLUENCE OF FORCED VENTILATION THROUGH 3D TEXTILE ON HEAT EXCHANGE PROPERTIES OF THE TEXTILE LAYER.

AUŠRA GADEIKYTĖ , RIMANTAS BARAUSKAS

ISSN P RINT 2335-2124, ISSN O NLINE 2424-4635, K AUNAS , L ITHUANIA 75

equations of the fluid flow read as:

𝜌∇⋅ 𝐮  =0, in Ω ,Ω , (1)

𝜌 𝐮⋅∇ 𝐮= 𝛻⋅ −𝑝𝐈 + 𝜇 ∇𝐮 + ∇𝐮 +𝐅 , in Ω , (2)

𝜌

𝜀

𝐮⋅∇ 𝐮

𝜀

=∇⋅−𝑝𝐈+ 𝜇

𝜀  ∇𝐮 +  ∇𝐮    − 2

3𝜇

𝜀  ∇⋅𝐮 𝐈− 𝜇𝑘 𝐮+ 𝐅, in Ω , (3)

where ∇ – the gradient operator, 𝐮 – velocity vector of fluid flow in [m/s], 𝜌 - density of fluid in

[kg/m3 ], 𝑝 – pressure in [Pa], 𝜇 – dynamic viscosity of fluid [Pa·s], 𝐈 – identity tensor and 𝐅

denotes external force (i.e. buoyancy force acting on the fluid elements [N m−3 ]) vector. At micro

level Brinkman equation requires local permeability 𝑘 [m2 ] value and porosity 𝜀 as input of

intra-yarn. The values were taken from literature [12] as 1.64·10-11 [m2 ] and 0.58 respectively.

Thermal energy equation (Eq. (4)) in the fluid region was expressed as:

𝜌𝐶 𝐮⋅∇𝑇+ ∇⋅𝐪= 𝑄, 𝐪= −𝑘 ∇𝑇, in Ω , Ω , (4)

where 𝐶 – specific heat capacity in [J/kg K], 𝑄 – overall heat transfer in [W], 𝑘 – effective

thermal conductivity of the fluid-solid mixture in [W/m·K].

The fluid domain presents the moist air at ambient relative humidity 40 % (𝜑= 0.4). The

relationship between the water-vapor partial pressure 𝑝 and the saturation water-vapor partial

pressure 𝑝 reads as:

𝑝 =𝜑∙𝑝 . (5)

A summary of the boundary conditions applied in this study is presented in Table 2. The labels

of boundary conditions are shown in Fig. 1.

The boundary 3 represents skin with a constant temperature of 𝑇= 37 ℃ . Three different mass

flow rates (0.2, 0.4, 0.8 dm3 min-1 ) of ventilation layer (boundary 1) were considered. The

covective heat transfer coefficient ℎ= 8.4746 W/(m2 ·K) of three-dimensional textile layer is

based on measurements according LST EN 31902:2002 standard [2].

Table 2. Boundary conditions of simulation

Boundary Fluid flow Boundary Heat transfe

1 Inlet (mass flow): 0.2, 0.4,

0.8 dm3 min-1 4 Convective heat flux: −𝑛 ·𝑞 =ℎ ( 𝑇  −𝑇 ),

ℎ= 8.4746 W/(m2 ·K)

2 Outlet: 𝑝 = 0 Pa 3 Temperature: 𝑇= 37 ℃

Textile

walls No slip: 𝑢=0 default Thermal insulation: −𝑛 · 𝑞=0

default Slip: 𝑢⋅𝑛=0 Note. 𝑢 velocity vector, n normal vector, 𝑞 heat flux

vector, 𝑇  external temperature.

3. Numerical results

The intention of this work was to portray the process of forced heat convection through the

three-dimensional textile layer by the different ventilation rate. Fig. 2 and Fig. 3 summarize the

temperature distribution and average temperature value at different through-thickness positions

along axis 𝑂 with ventilation rate of 0.8 dm3 min-1 and without ventilation rate. The increasing

intensity of ventilation rate reduces the temperature in the microclimate. The microclimate is

represented in the middle of air gap between the skin and bottom of textile layer at the

𝑧= –3.90 mm. In case of ventilation rate of 0.8 dm3 min-1 temperature is 36.19 ℃ and without

ventilation rate is 36.34 ℃ . Fig. 4 and Fig. 5 presents examples of time relationships of average

temperatures in the middle of microclimate gap layer (𝑧= –3.90 mm) and outer surface of the 3D

INVESTIGATION OF INFLUENCE OF FORCED VENTILATION THROUGH 3D TEXTILE ON HEAT EXCHANGE PROPERTIES OF THE TEXTILE LAYER.

AUŠRA GADEIKYTĖ , RIMANTAS BARAUSKAS

76

JOURNAL OF M EASUREMENTS IN E NGINEERING . JUNE 2020, V OLUME 8, ISSUE 2

textile (𝑧= 0.289 mm). There is not significant difference between 0, 0.2, 0.4 dm

3

min

-1

ventilation

rate in the microclimate. However, the tendency and effect of increasing ventilation rate is shown

at ventilation rate 0.8 dm

3

min

-1

. The Fig 6. demonstrates that relative humidity increases with

ventilation rate.

Fig. 2. Simulation results of 3D textile layer. Distribution of the temperature without ventilation rate

Fig. 3. Simulation results of 3D textile layer. Distribution of the temperature

with ventilation rate of 0.8 dm

3

min

-1

INVESTIGATION OF INFLUENCE OF FORCED VENTILATION THROUGH 3D TEXTILE ON HEAT EXCHANGE PROPERTIES OF THE TEXTILE LAYER.

AUŠRA GADEIKYTĖ , RIMANTAS BARAUSKAS

ISSN P RINT 2335-2124, ISSN O NLINE 2424-4635, K AUNAS , L ITHUANIA 77

Fig. 4. Time relationships of average temperatures in the middle of microclimate gap

at four different values of the ventilation rate 0, 0.2, 0.4 and 0.8 dm3 min-1

Fig. 5. Time relationships of average temperatures in the outlet at four different

values of the ventilation rate 0, 0.2, 0.4 and 0.8 dm3 min-1

Fig. 6. Time relationships of average relative humidity in the middle of microclimate gap

(𝑧 position –3.9 mm) at four different values of the ventilation rate 0, 0.2, 0.4 and 0.8 dm3 min-1

4. Conclusions

A computer simulation was conducted on the heat and mass transfer in micro scale using

Comsol Multiphysics software. The numerical simulations were performed as stationary and time

dependent. The first study is dealing with distributions of the air temperature that can be depicted

INVESTIGATION OF INFLUENCE OF FORCED VENTILATION THROUGH 3D TEXTILE ON HEAT EXCHANGE PROPERTIES OF THE TEXTILE LAYER.

AUŠRA GADEIKYTĖ , RIMANTAS BARAUSKAS

78 JOURNAL OF MEASUREMENTS IN ENGINEERING. JUNE 2020, V OLUME 8, ISSUE 2

in whole computational domain. The time dependent study concerns relative humidity effect, the

thermal performance of three-dimensional textile exposed by ventilation rate. This study shown

that relative humidity is dependent from ventilation rate. The input parameters of simulation were

based on experimental and literature data. The findings such as relative humidity, surface average

temperature that is required parameter for determination of thermal resistance can be applied in

macro-scale models for efficient simulation of heat and mass exchange through textile packages.

References

[1] Matusiak M., Kowalczyk S. Thermal-insulation properties of multilayer textile packages. Autex

Research Journal, Vol. 14, Issue 4, 2014, p. 299-307.

[2] Barauskas R., Abraitiene A. A model for numerical simulation of heat and water vapor exchange in

multilayer textile packages with three-dimensional spacer fabric ventilation layer. Textile Research

Journal, Vol. 81, Issue 12, 2011, p. 1195-1215.

[3] Santos M. S., Oliveira D., Campos J. B. L. M., Mayor T. S. Numerical analysis of the flow and heat

transfer in cylindrical clothing microclimates – Influence of the microclimate thickness ratio.

International Journal of Heat and Mass Transfer, Vol. 117, 2018, p. 71-79.

[4] Angelova R. A., Kyosov M., Stankov P. Numerical investigation of the heat transfer through woven

textiles by the jet system theory. Journal of the Textile Institute Vol. 110, Issue 3, 2019, p. 386-395.

[5] Neves S. F., Campos J. B. L. M., Mayor T. S. On the determination of parameters required for

numerical studies of heat and mass transfer through textiles – Methodologies and experimental

procedures. International Journal of Heat and Mass Transfer, Vol. 81, 2015, p. 272-282.

[6] Neves S. F., Campos J. B. L. M., Mayor T. S. Effects of clothing and fibres properties on the heat

and mass transport, for different body heat/sweat releases. Applied Thermal Engineering, Vol. 117,

2017, p. 109-121.

[7] Mayor T. S., Couto S., Psikuta A., Rossi R. M. Advanced modelling of the transport phenomena

across horizontal clothing microclimates with natural convection. International Journal of

Biometeorology, Vol. 59, Issue 12, 2015, p. 1875-1889.

[8] Siddiqui M. O. R., Sun D. Conjugate heat transfer analysis of knitted fabric. Journal of Thermal

Analysis and Calorimetry, Vol. 129, Issue 1, 2017, p. 209-219.

[9] Puszkarz A. K., Machnowski W., Bł asiń ska A. Modeling of thermal performance of multilayer

protective clothing exposed to radiant heat. Heat and Mass Transfer, Vol. 56, 2020, p. 1767-1775.

[10] Gadeikytė A., Barauskas R. Numerical Simulation of Air Permeability Coefficient of 3D Textile

Layer, 2019, https://www.comsol.com/paper/numerical-simulation-of-air-permeability-coefficient-

of-3d-textile-layer-82471.

[11] Zupin Ž., Hladnik A., Dimitrovski K. Prediction of one-layer woven fabrics air permeability using

porosity parameters. Textile Research Journal, Vol. 82, Issue 2, 2012, p. 117-128.

[12] Pezzin A. Thermo-Physiological Comfort Modelling of Fabrics and Garments. Ph.D. thesis., 2015.

[13] Li Q., Ito K., Wu Z., Lowry C. S., Loheide S. P. COMSOL multiphysics: A novel approach to ground

water modeling. Groundwater, Vol. 47, Issue 4, 2009, p. 480-487.

Aušra Gadeikytė received M.Sc. degree in Applied Mathematics from Kaunas University

of Technology (KTU), Kaunas, Lithuania, in 2015, where she is currently pursuing Ph.D.

degree in Informatics. She is currently a Lector with the Department of Applied

Informatics, Faculty of Informatics. Her scientific interests include mathematical

modeling, computer simulation of heat and mass transfer through textile, simulations of

tensile tests.

Rimantas Barauskas, Dr. habil., Professor, graduated the Applied Mathematics studies

from Kaunas University of Technology (KTU) in 1976. Received his Ph.D. (1981) and

habilitation (1992) degrees at KTU. Now is the head of Applied Informatics department at

the Informatics faculty of KTU. He is a true member of Lithuanian Academy of Sciences.

The main topics of research include the methods and applications of computer simulation

of the dynamic behavior of solid structures and coupled systems including vibration,

impact, penetration problems, heat and mass exchange problems.

... Many studies have been undertaken to develop new materials for the manufacturing of protective clothing as well as to create heat transfer models for the prediction of their thermal properties [5][6][7][8][9]. One such model was proposed by Torvi [10] for textiles under high heat fl ux conditions. ...

In this paper the safety and thermal comfort of protective clothing used by firefighters was analyzed. Three dimensional geometry and morphology models of a real multilayer assembles used in thermal protective clothing was mapped by selected Computer Aided Design (CAD) software. In the designed assembles models different scales of resolution were used for the particular layers – a homogenization for nonwoven fabrics model and designing the geometry of the individual yarns in the model of woven fabrics. Then, the finite volume method to simulate heat transfer through the assembles caused by their exposure to flame was applied. Finally, the simulation results with experimental measurements conducted according to the EN ISO 9151 were compared. On the basis of both the experimental and simulation results, parameters describing the tested clothing protective features directly affecting the firefighter's safety were determined. As a result of the experiment and simulations, comparable values of these parameters were determined, which could show that used methods are an efficient tool in studying thermal properties of multilayer protective clothing.

• V S Tynchenko
• Sergei Kurashkin
• A V Murygin
• Ya A Tynchenko

The presented work is devoted to the study of the effect of various values of the electron beam current on the distribution of the energy cross section of the weld when conducting the technological process of electron-beam welding of thin-walled structures. The work is used by the simulation system of COMSOL Multiphysics, in which mathematical models of energy distribution proposed by the authors are implemented with electron beam welding. Imitation modelling was carried out for two materials widely used in the aerospace industry: titan alloy BT14 and AMG aluminum alloy. The values of the parameters for which the simulation was carried out were selected as a result of the predetermined process of optimizing the technological mode of electron beam welding for the construction under study. In the process of the research, a change in the value of the electron beam current is carried out both in less and to the large side. The article presents visualization for the three values of the parameter under study for each material, which makes it possible to judge the effectiveness of the previously formed set of optimal parameter values.

Studies presented in this paper concern wide issue of thermal comfort of protective clothing. The Computer Aided Design (CAD) software tools to analyze thermal insulation of multilayer textile assembly used in thermal protective clothing were applied. First, 3D geometry and morphology of a real textile assembly was modeled. In the designed model different scales of resolution were used for individual layers, ranging from a homogenized nonwoven fabrics model to mapping the geometry of yarns in woven fabrics model. Next, the finite volume method to estimate thermal insulation properties of this assembly, when exposed to heat radiation, was used. Finally, the simulation results were verified experimentally using method described in EN ISO 6942. On the basis of both simulation and experimental results obtained for the multilayer textile assembly, protective clothing parameters directly affecting the ability to protect against heat, were determined. Correlating simulated and experimental values of these parameters were obtained, which may indicate that applied software can be an effective tool in analyzing thermal properties of newly designed multilayer functional clothing.

The paper presents a numerical study on the heat transfer in through-thickness direction of single woven layers, based on the jet system theory. A mathematical model, involving the Reynolds-Averaged Navier-Stokes partial differential equations is used, and two turbulence models (k − ɛ and RSM) are applied to solve the closure problem. Numerical results for the temperature distribution, heat rate, heat flux and thermal resistance of the samples are obtained, analyzed, and validated by experimental data. The presented approach for modeling the heat transfer through woven macrostructures is concluded to be a working numerical tool that has the potential to replace costly design iterations and experiments to produce woven textiles with desired performance. А free copy from a total of 50 copies of the full paper is available at https://www.tandfonline.com/eprint/XVzTt8vu2SBhyAwBDzpr/full

The thermal properties of fabric have significant impact on thermal comfort of the wearers. This research work covers the development of geometrical models of plain weft knitted fabric structures and evaluation of the thermal properties by using the fluid surface interaction technique. The results obtained from the numerical method were compared with the experimental results, and it was found that they were highly correlated. Furthermore, the validated models were utilized to evaluate the velocity and temperature profile of air at out-plane created over the surface of knitted fabric.

The ability of clothing to provide protection against external environments is critical for wearer's safety and thermal comfort. It is a function of several factors, such as external environmental conditions, clothing properties and activity level. These factors determine the characteristics of the different microclimates existing inside the clothing which, ultimately, have a key role in the transport processes occurring across clothing. As an effort to understand the effect of transport phenomena in clothing microclimates on the overall heat transport across clothing structures, a numerical approach was used to study the buoyancy-driven heat transfer across horizontal air layers trapped inside air impermeable clothing. The study included both the internal flow occurring inside the microclimate and the external flow occurring outside the clothing layer, in order to analyze the interdependency of these flows in the way heat is transported to/from the body. Two-dimensional simulations were conducted considering different values of microclimate thickness (8, 25 and 52 mm), external air temperature (10, 20 and 30 °C), external air velocity (0.5, 1 and 3 m s(-1)) and emissivity of the clothing inner surface (0.05 and 0.95), which implied Rayleigh numbers in the microclimate spanning 4 orders of magnitude (9 × 10(2)-3 × 10(5)). The convective heat transfer coefficients obtained along the clothing were found to strongly depend on the transport phenomena in the microclimate, in particular when natural convection is the most important transport mechanism. In such scenario, convective coefficients were found to vary in wavy-like manner, depending on the position of the flow vortices in the microclimate. These observations clearly differ from data in the literature for the case of air flow over flat-heated surfaces with constant temperature (which shows monotonic variations of the convective heat transfer coefficients, along the length of the surface). The flow patterns and temperature fields in the microclimates were found to strongly depend on the characteristics of the external boundary layer forming along the clothing and on the distribution of temperature in the clothing. The local heat transfer rates obtained in the microclimate are in marked contrast with those found in the literature for enclosures with constant-temperature active walls. These results stress the importance of coupling the calculation of the internal and the external flows and of the heat transfer convective and radiative components, when analyzing the way heat is transported to/from the body.

• Malgorzata Matusiak
• Sylwia Kowalczyk

Thermal-insulation properties of textile materials play a significant role in material engineering of protective clothing. Thermal-insulation properties are very important from the point of view of thermal comfort of the clothing user as well as the protective efficiency against low or high temperature. Thermal protective clothing usually is a multilayer construction. Its thermal insulation is a resultant of a number of layers and their order, as well as the thermalinsulation properties of a single textile material creating particular layers. The aim of the presented work was to investigate the relationships between the thermal-insulation properties of single materials and multilayer textile packages composed of these materials. Measurement of the thermal-insulation properties of single and multilayer textile materials has been performed with the Alambeta. The following properties have been investigated: thermal conductivity, resistance and absorptivity. Investigated textile packages were composed of two, three and four layers made of woven and knitted fabrics, as well as nonwovens. On the basis of the obtained results an analysis has been carried out in order to assess the dependency of the resultant values of the thermal-insulation properties of multilayer packages on the appropriate values of particular components.

The aim of this study was to develop methodologies and experimental procedures to determine textile parameters required in numerical approaches of heat and mass transfer through textiles. Privileging techniques usually available in textile/clothing laboratories, experimental approaches were defined that allow to estimate all required parameters, while taking into consideration water presence in the fibres and hence the effect of fibres hygroscopic properties. Numerical models usually require values of textile thickness, fibre fraction, and tortuosity, as well as knowledge of the boundary conditions, e.g. convective heat and mass transfer coefficients. To calculate these parameters, thickness, weight, and volume of textile samples were measured, whereas convective and textile evaporative resistances were determined by indirect measurements. Results were obtained for four distinct textile samples (made of wool, cotton, and a mixture of materials), of different hydrophilic nature. When the obtained parameters were incorporated in a numerical model and numerical predictions of temperature and humidity were compared with experimental data obtained during measurements of fabric evaporative resistance, it was shown that the predictions were accurate; this lends support to the developed methods and approaches.

Air permeability is one of the fundamental textile properties influencing the design of comfortable clothes. In particular, it is very important in the field of technical textiles. Air permeability depends mainly on the fabric structure, which can be described by yarn linear density, type of yarn, warp/weft density and weave. The purpose of our study was to identify a small number of parameters that have the strongest influence on air permeability of cotton fabrics and enable its good prediction. Rather than focusing on the constructional parameters, we decided to include a composite parameter known from the theory of fluids, hydraulic diameter of pores, which treats rectangular-shaped pores as circular ones. In addition to the hydraulic diameter of pores, two other parameters were used for the prediction of air permeability: the number of macro pores and the total porosity of woven fabrics. 36 woven fabric samples were produced using nine frequently implemented weave types together with two warp densities (29.3 and 22 ends/cm) and two weft densities (15 and 20 picks/cm), resulting in four different densities of woven fabrics. The yarns had the same linear density and material in warp and weft directions. Air permeability measurements were performed with the Air Permeability tester FX 3300 Labotester III (Textest Instruments) according to the ISO 9237:1995 (E) standard. Principal components analysis revealed that the four investigated plain weave specimens behave differently than the other samples, which might be explained by weave structure. This multivariate statistical method also confirmed the appropriateness of the three selected parameters for air permeability prediction which was done using multiple linear regression. The high adjusted coefficient of determination (R ² ) value of 0.94 indicates that the model explains variability in the air permeability to a large extent.

Clothing microclimates, i.e. the space between the skin and the clothing, can play a central role in the heat and mass exchanges from or to the body. This is especially true for protective clothing, where microclimates are generally thicker and natural convection is more likely to occur. We used a computational fluid dynamics approach to perform numerical studies of fluid flow and heat transfer across cylindrical clothing microclimates for Reynolds number of 3900. Transient simulations were performed for three different values of microclimate thickness to diameter ratio (0.05, 0.10 and 0.25), considering a two-dimensional cross-section of a human limb surrounded by a porous fabric and exposed to cool external air (10°C). The obtained local heat transfer along the skin shows that increasing the microclimate thickness ratio from 0.05 to 0.25 decreases the convective heat fluxes by up to 100% in the upstream regions of the microclimate, and increases them up to 190% in the downstream regions. This asymmetry, which indicates an increasingly important role of natural convection as the microclimate thickness ratio is increased, is often overlooked in space-averaged approaches due to the opposite changes in the different regions of the microclimate. Local variations in temperature along the outer fabric and in convective fluxes along the skin were significant, reaching up to 14K and 90%, respectively. The critical thickness ratio above which natural convection should not be ignored was found to be 0.1 (e.g. corresponding to a microclimate thicknesses of 11 mm or 8 mm, around an upper arm or forearm, respectively).

Clothing plays a key role in the capacity of the body to adapt to the surrounding thermal environments. Thus, it is critically important to have a solid understanding of the effects of clothing and fibres properties on the body exchange rates. To this end, a detailed transfer model was implemented to analyse the effect of several textiles characteristics (outer surface emissivity, tortuosity, and fraction of fibre) and fibre properties (affinity with water, coefficient of water diffusion in the fibres, thermal conductivity, density, and specific heat), on the heat and mass transfer through multilayer clothing, for different intensities of heat/sweat release. The temperature and humidity predictions were validated with experimental data obtained during measurements of textile evaporative resistance. The results obtained for the multilayer clothing during an energy-demanding activity (i.e. metabolic heat production of 300 W m−2 and sweating of 240 g m−3 h−1) show that a decrease in the emissivity of the outer surface (0.9 – 0.1), and an increase in the coefficient of water diffusion in the fibres of the inner layer (4 × 10−16 – 4 × 10−11), induce an increase in the maximum skin temperature (of 4.5 °C and 6.8 °C, respectively). Moreover, the water trapped inside clothing is significantly increased by augmenting the fraction of fibre (0.07 – 0.4), the density of the fibre (910 – 7850 kg m3), the fibre affinity with water (i.e. regains of 0.07 – 0.3), and the coefficient of water diffusion in the fibres (4 × 10−16 – 4 × 10−11). During the post-exercise phase (with metabolic heat production of 65 W m−2 and perspiration of 9 g m−3 h−1), the parameters affecting significantly the water content of the inner layer are the fraction of fibre, its density, and its affinity with water. The proposed numerical approach allows the study of strategies to optimise heat/mass transport rates through materials surrounding the body (e.g. in clothing applications, automotive environments or workplace microclimates) in order to minimise thermal discomfort and/or problems of high water content (e.g. friction burns and/or growth of fungi and bacteria).

Source: https://www.researchgate.net/publication/342576432_Investigation_of_influence_of_forced_ventilation_through_3D_textile_on_heat_exchange_properties_of_the_textile_layer

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