Dana Kremenakova

Packing Density of Compact Yarns

In this work, fiber distribution through the cross-sections of compact yarns and their packing density values was investigated to provide a better understanding of the internal structures of compact yarns produced by different compact spinning systems, since there is no information available so far regarding their internal structure. The results of packing density analysis indicated that compact yarns had nearly 15—30% higher packing density values compared to that of the conventional ring spun yarns. Also, the packing density values of compact yarns produced by three different compact yarn spinning systems, namely Rieter K44, Suessen Elite and Zinser Air-Com-Tex700, revealed that there were no significant differences among these systems in terms of yarn packing density values.

Study on air permeability and thermal resistance of textiles under heat convection

Convective heat transfer plays a very important role in thermal resistance of textiles due to its porous structure, and the thermal resistance of textiles will be quite different when they are investigated under different testing standards and conditions. Nowadays, however, there is still no commercial instrument for evaluating the thermal resistance of textiles under convective heat transfer. Besides, there is no report about the influence of pore structure (pore size and the ratio of a pore’s cross-sectional area to the total cross-sectional area of fabric) on thermal resistance of textiles. Therefore, in this work, one newly designed device has been developed for evaluating the thermal resistance of textiles with different parameters in terms of porosity, pore size and pore cross-sectional area under heat convection. The results showed that with the increase of the pore size and the ratio of pore area to total area of fabric, the air permeability increases and the thermal resistance of fabric decreases; the pore size and the ratio of pore area have more significant influence compared to the influence of porosity; and the thermal resistance decreases with the increase of air permeability.

Air permeability of polyester nonwoven fabrics

Abstract Air permeability is one of the most important properties of non-woven fabrics in many applications. This paper aims to investigate the effects of thickness, porosity and density on the air permeability of needle-punched non-woven fabrics and compare the experimental values with two models which are based on hydraulic radius theory and drag theory, respectively. The air permeability of the samples was measured by an air permeability tester FX3300. The results showed that the air permeability of non-woven fabrics decreased with the increase in thickness and density of samples, increased with the increase of porosity, and the air permeability was not directly proportional to the pressure gradient. Meanwhile, the prediction model based on hydraulic radius theory had a better agreement with experimental values than the model based on drag theory, but the values were much higher than the experimental results, especially for higher porosity and higher pressure gradient.

An analysis of effective thermal conductivity of heterogeneous materials

Abstract Effective thermal conductivity (ETC) is a very important index for evaluating the thermal property of heterogeneous materials, which include more than two different kinds of materials. Several analytical models were proposed for predicting the ETC of heterogeneous materials, but in some cases, these models cannot provide very accurate predictions. In this work, several analytical models and numerical simulations were studied in order to investigate the differences among them. In addition, some factors which would influence the ETC of heterogeneous materials were investigated by numerical simulation. The results demonstrated that the numerical simulation can provide very accurate prediction, indicated that different analytical models should be selected to predict specific problems based on their assumptions, and suggested that more variables need to be considered in order to improve these analytical models, such as inclusion shape, inclusion size, distribution of inclusions and contact area. Besides, numerical method could be an effective and reliable way to obtain the ETC of heterogeneous materials with any kind of complicated structures.

Modeling of Woven Fabrics Geometry and Properties

There are many ways of making fabrics from textile fibers. The most common and most complex category comprises fabrics made from interlaced yarns. These are the traditional methods of manufacturing textiles. The great scope lies in choosing fibers with particular properties, arranging fibers in the yarn in several ways and organizing in multiple ways, interlaced yarn within the fabric. This gives textile designer great freedom and variation for controlling and modifying the fabric. The most common form of interlacing is weaving, where two sets of threads cross and interweave with one another. The yarns are held in place due to the inter-yarn friction. Another form of interlacing where the thread in one set interlocks with the loops of neighboring thread by looping is called knitting. The interloping of yarns results in positive binding. Knitted fabrics are widely used in apparel, home furnishing and technical textiles. Lace, Crochet and different types of Net are other forms of interlaced yarn structures. Braiding is another way of thread interlacing for fabric formation. Braided fabric is formed by diagonal interlacing of yarns. Braided structures are mainly used for industrial composite materials.

Temperature changes of plain cotton fabric during liquid absorption process

Purpose – Clothing comfort has been one important and complex area which is the result of a balanced process of heat and moisture/liquid exchange between the human body, the clothing system and the environment. And the clothes will represent different properties when they are in different conditions, which have great influence on human comfort. Therefore, the purpose of this paper is to investigate the hygroscopicity-exothermicity property of plain cotton fabric. Design/methodology/approach – A real-time testing device for monitoring the temperature change of cotton fabrics after adsorbing liquids was constructed, and serveral liuqids such as water, NaCl solution with different concentrations, NaOH solution with different concentrations, and urea solution with different concentrations were used in this work. Findings – It was found out that absorption of liquids by cotton fabric was followed by the liberation of heat, which increased the temperature of cotton fabric as well as the temperature of surroundi...

Surface modification of polymer optical fibers for enhanced side emission behavior

The polymer optical fiber with trade name Flexi was used in this research, because of its flexibility and the range of diameters available in the market. These fibers were dyed using commercial disperse dye under various conditions of dye concentration and dyeing time. Samples were analyzed for side emission of light with the use of an instrument which was specifically designed for the measurement of this nature. The results showed that the dye penetration is dependent on time, if dye concentration and temperature are kept constant. After 40 min of dyeing, the fiber core showed an increase in side emission with lower loss due to attenuation. Excessive time in the hot conditions also degraded the fiber, so that the fiber became very stiff and brittle. Fibers were also subjected to heat, in the form of boiling water bath, for selected periods of time, and it was found that the effect was similar to that of the prior experiments. Surface treatment of Flexi fibers was carried out using ethyl acetate as an etching agent, to possibly accept more disperse dye on the fiber surface. The results after dyeing showed a more significant improvement in both side emission and attenuation of light.

3D Numerical Simulation of Laminar Flow and Conjugate Heat Transfer through Fabric

Abstract The air flow and conjugate heat transfer through the fabric was investigated numerically. The objective of this paper is to study the thermal insulation of fabrics under heat convection or the heat loss of human body under different conditions (fabric structure and contact conditions between the human skin and the fabric). The numerical simulations were performed in laminar flow regime at constant skin temperature (310 K) and constant air flow temperature (273 K) at a speed of 5 m/s. Some important parameters such as heat flux through the fabrics, heat transfer coefficient, and Nusselt number were evaluated. The results showed that the heat loss from human body (the heat transfer coefficient) was smallest or the thermal insulation of fabric was highest when the fabric had no pores and no contact with the human skin, the heat loss from human body (the heat transfer coefficient) was highest when the fabric had pores and the air flow penetrated through the fabric.

Flex Fatigue of Side Emitting Optical Fiber

Side emitting plastic optical fibers can be used in textile structures for some special optical activities due to the light leaking out from their surface. One significant characteristic of plastic optical fibers is their tendency to weaken side emitting capability under mechanical deformation, which can be simulated as repeated bending cycles under prescribed pretension. The principle of evaluation of flex fatigue was based on the repeated bending cycles until break. Q-Q plot and three-parameter Weibull distribution were used for estimation of numbers of bending cycles of plastic optical fibers with different diameters. The relationship between flex fatigue and flexibility were analyzed and compared with logarithmic values.

Simulation of Airflow Motion in Jet Nozzle with Different Geometric Parameters

Jet nozzle with tangentially injected airflow has been applying into spinning technology due to the tangential force produced by swirling airflow. In order to understand the airflow motion trajectory in jet nozzle, modify the nozzle structure and dimension, FLUENT software program is used. Some parameters which are closely related the airflow motion profiles are studied, such as the diameter of nozzle chamber, the diameter and angle of the orifice. The results showed that the intensity of air swirling is more strong in a smaller nozzle chamber; a larger orifice diameter is helpful for producing strong yarn and improving production efficiency, but it requires a larger nozzle chamber, therefore, a reasonable rate of orifice and nozzle chamber diameter is important; as the orifice angle increases, the tangential velocity decreases, which decreases the intensity of airflow swirling, and a small orifice angle will cause a larger reverse jet, which is bad to draw the fibers into the nozzle.