Radostina A. Angelova

CFD based study of thermal sensation of occupants using thermophysiological model. Part I: Mathematical model, implementation and simulation of the room air flow effect

Purpose – The purpose of the paper is to simulate the effect of clothing insulation and activity on the interaction between the human body and the environment. Design/methodology/approach – A thermo-physiological model, integrated into a Fluent CFD software package is applied. The temperature of the skin surface, clothing surface and heat flux (dry and total heat flux) through layers of clothing with different insulation level are numerically investigated in function of the clothing insulation and the different activities performed indoors. Findings – The increase of the clothing insulation leads to increase of both skin and clothing temperature. Higher temperature difference ΔT between the room temperature and skin temperature provokes more dynamic change of the skin temperature and decreases the thermal comfort of the person. The increase of the metabolic rate, however, leads to more uniform skin temperature, regardless the temperature difference ΔT. With the increase of the clothing insulation for a co...

Computational modeling and experimental validation of the air permeability of woven structures on the basis of simulation of jet systems

The paper presents computational fluid dynamics-based numerical simulation of the through-thickness air permeability of woven structures, applying the theory of jet systems. The flow through the interstices between the warp and weft threads is modeled as an “in-corridor”-ordered jet system, formed by nine jets, issuing from nine pores of the woven structure. Fifteen cases were simulated and three different turbulence models were applied in the simulation: k-ɛ, k-ω and Reynolds stress model. The five simulated woven structures were manufactured and their air permeability was measured experimentally. The performed validation of the numerical results with the experimental values of the air permeability showed very good correlation with the experimental results. The analysis and the verification showed that the method can be applied for further investigation not only of the woven fabrics’ air permeability, but also for investigation of the flow after a textile barrier of a woven type.

Three dimensional simulation of air permeability of single layer woven structures

The paper deals with a CFD based study of the transverse permeability of a textile woven structure. The reported numerical investigation is preconditioned by both previous experimental and CFD study on jet systems. It is also based on detailed experimental investigation of the porous structure of single layer woven fabrics, made of staple fiber yarns. The flow in through-thickness direction of the woven structures is presented as jet systems, issuing from set of orifices. Two different types of jet system (3×3 jets and 5×5 jets) with two types of jet cross sections (square and circular), corresponding to two different woven structures, are simulated. An analysis is made in terms of the structure of the woven fabrics (area and shape of the interstices between the threads), the parameters of the flow passing through the textile (velocity profiles and velocity fields through isosurfaces), the role of the type of the jet systems, representing the flow and the influence of the shape of the interstices between the threads on the flow pattern. It was found that the applied approach could be effectively used for studying of the transverse permeability of the woven fabrics.

CFD based study of thermal sensation of occupants using thermophysiological model. Part II

Purpose – The purpose of the paper is to simulate the effect of clothing insulation and activity on the interaction between the human body and the environment. Design/methodology/approach – A thermo-physiological model, integrated into a Fluent CFD software package is applied. The temperature of the skin surface, clothing surface and heat flux (dry and total heat flux) through layers of clothing with different insulation level are numerically investigated in function of the clothing insulation and the different activities performed indoors. Findings – The increase of the clothing insulation leads to increase of both skin and clothing temperature. Higher temperature difference ΔT between the room temperature and skin temperature provokes more dynamic change of the skin temperature and decreases the thermal comfort of the person. The increase of the metabolic rate, however, leads to more uniform skin temperature, regardless the temperature difference ΔT. With the increase of the clothing insulation for a constant metabolic rate the total heat flux remains constant, but the dry heat flux decreases, while the evaporative heat flux increases. Originality/value – The joint influence of clothing insulation and indoor activities on the thermal interaction between the body and the environment is assesses using a thermo-physiological model, integrated in a CFD software package.

Heat and mass transfer through outerwear clothing for protection from cold: influence of geometrical, structural and mass characteristics of the textile layers

This paper presents a comprehensive experimental study, conducted on a series of woven and non-woven fabric samples from different materials (cotton, polyester, and polyamide) and 14 three-layer systems of textile materials, used for production of outerwear clothing for protection from cold. Heat and mass transfer properties, related to the thermophysiological comfort of the outerwear clothing, namely conductive thermal resistance, water vapor resistance, relative water vapor permeability, air permeability, accumulative one-way transport of liquids, and overall moisture management capacity, were determined for the system of layers and the compound single layers. The transfer properties of the single layers were presented as a function of their thickness, mass per unit area, and areal porosity. The transfer properties of the system of layers were presented as a function of the thickness, mass per unit area, and bulk density of the systems. Regression analysis was applied to derive regression equations. The results obtained allowed assessment of the existence and trend of the influence, as well as evaluation of the strength of the dependences.

Numerical modeling of the air permeability of two-layer woven structure ensembles

This study aims at investigating air permeability in the transversal direction of pairs of woven textiles. Three samples of woven macrostructures with different characteristics are selected for the numerical investigation of 16 two-layer ensembles. Computational fluid dynamics (Reynolds-averaged Navier–Stokes equations) is used for modeling the air permeability, applying the theory of jet-systems: the flow through each of the layers in the ensemble is modeled as an “in-corridor” ordered jet-system. The influence of the order of arrangement of the layers in the ensemble is analyzed, indicating higher air permeability of the ensemble when a tighter structure is placed as a first layer. The effect of the distance between the two woven macrostructures is also analyzed, showing a strong influence on the flow development as well as on the extrema of flow velocities, especially in the drop of the flow velocity in the air gap between the two layers. The analysis made and the results obtained show that the method can be applied for further investigation of ensembles of textile layers.

Determination of the pore size of woven structures through image analysis

The paper presents an experimental procedure developed for determination of the pore size, shape and distribution in a single layer woven fabric, for the construction of a virtual model to be incorporated in a future CFD software package. The procedure is based on non-destructive observation and analysis of woven samples. 14 different samples of gray fabrics of 100 % cotton in plain and twill weaves are investigated. The results obtained allow the creation of reality more realistic virtual model of the woven structure, and theoretical investigation of its porosity and permeability through computer simulation.

Selection of Clothing for a Cold Environment by Predicting Thermophysiological Comfort Limits

Results are presented from a study on the prediction of the insulation abilities of outerwear clothing for cold protection from the point of view of the thermophysiological comfort of the wearer. The Required Clothing Insulation (IREQ) index is used to simulate the abilities of 14 assemblies of layers designed for the production of winter jackets to protect the body in different cold environments. The calculations allow to assess the limits of applicability of the garments in terms of the thermophysiological comfort assured, the activities performed and the weather conditions. Discussions are presented on the correspondence between ISO11079:2007 and the online JavaScript code for calculation of IREQ based on it. The results predicted and their analysis have a practical use, as they allow to estimate the cold protection effectiveness of the textile layers used in an assembly at the design stage, thus giving room for necessary changes depending on the conditions of its use.

The effect of the transfer abilities of single layers on the heat and mass transport through multilayered outerwear clothing for cold protection

This paper deals with performance properties related to human thermo-physiological comfort of three-layer textile systems used for the production of outerwear for cold protection. The transfer of heat and fluids through the compound single layers (woven and non-woven) is investigated and compared to the heat and mass transfer of the systems for clothing. Six characteristics are measured for both single layers and systems of layers: thermal resistance, air permeability, water vapor resistance, relative water vapor permeability, the accumulative one-way transport index and overall moisture management capacity. For each of the characteristics, regression analysis is applied to prove or reject the proposed mathematical dependencies between the transfer abilities of the single layers and the respective systems. The results obtained showed that the fluid transfer abilities of the single layers applied in clothing for cold protection strongly affect the fluid transfer ability of the system of layers, while the heat transfer of the system is dominated by the heat transfer ability of the thermo-insulating layer. The proposed approach for assessment of the transfer processes through a system of layers for the production of outerwear for cold protection could be successfully applied in the design of other textile and clothing items, produced by using systems of different textile layers.

Numerical investigation of the heat transfer through woven textiles by the jet system theory

Abstract 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.