1,720,964 research outputs found
Thermo-physiological comfort modelling of fabrics and garments
Full text linkThermo-physiological comfort is a complex feeling affected by clothing, environment and physical activity of a human body. It is very important to understand the influence of the different variables, such as air temperature and humidity, fabric properties and heat and moisture produced from the human body, and their relationships in order to design new textile materials that can satisfy the always more strictly requirements of technical textile in terms of comfort behaviour. While environmental conditions and metabolic heat and moisture production are independent variables that should be analyzed but that cannot be modified because they depends from the physical activity and from the environment where it should be done, garments behaviour can be modified, using different materials, construction parameters, etc..., in order to give the optimal comfort behaviour. In the last decades, always more attention has been paid in the development of comfortable clothing for both technical and common use; for this reason the interaction of garments with both the human body and the environment has been the subject of many studies. This research work aims to analyze the comfort properties that can be measured for fabrics evaluation and to develop, using modelling techniques, a prediction method of comfort behaviour; four fabric properties, namely air permeability, thermal properties, liquid and vapour transport through the fabric has been analyzed. A fabric is a heterogeneous 3D ordered structure made of fibres, yarns and trapped air and for this reason in order to be able to predict its comfort properties it is necessary to predict its geometrical structure using only its basic design parameters; this is the first stage for the development of any prediction method because comfort properties highly depends from fabric structure. In this work, starting from the basic design parameters of yarns and fabrics and using the geometrical fabric model developed by Hearle, all the fabrics geometrical parameters have been defined; later, using TexGen, an open source software developed at the University of Nottingham in 1998, the fabric geometries have been created. The second stage of this research work has been focused on the simulation of the fabrics comfort properties, for different fabrics structures and composition, and their comparison with experimental values. Air permeability, that represent the resistance to the air that flows through the fabric, is one of the most important parameters that influence comfort properties, because it influences both the vapour and moisture transport and thermal properties. Simulations that have been done show that it is possible to predict, with a good approximation, air permeability behaviour of different fabrics. Thermal properties, namely thermal resistance, have been investigated using a simplified geometry of textile fabrics in order to better compare the 3D virtual model with the experimental tests; in this case there is a quite good approximation of the simulated values due to this simplified geometry. For thermal properties modelling not only the comparison with experimental tests has been done but also some simulations that better represents a real case, in which fabric is not pressed between the measuring heads but where its distance from the skin can vary from contact to some millimetres. Also vapour adsorption process have been investigated in order to analyze the behaviour of different fibres and for different temperature and relative humidity conditions. When the human body is under low physical activities the air layer between skin and fabric can reach temperature in the range of 30°C to 40°C and relative humidity in the range of 60% to 90%; in these cases the prediction of the adsorption mechanism, that is an exothemic process, has to be taken into account especially for natural fibres that have high values of differential heat of sorption. Finally a case-study, represented by a 3D model of a back protector, is presented; using the experimental data measured in the climatic chamber at the Advanced Technology Textile Laboratory in Biella, some thermal simulations has been carried out. The research aims to develop a simulation method that starting from the basically constructive parameters of fibres, yarns and fabrics used to create any 3D fabric geometries leads to a fully predictive simulation method that allow to reduce the costs for the development of new high performance fabric
Prediction of Air Permeability Using a Finite Element Method
No full textAir permeability is one of the most important parameters in the study of thermo-physiological comfort of fabrics. The main goal of this work is to develop a virtual process that allows the prediction of air permeability of any fabric without realizing a sample. The Free and Porous Media Flow physics interface was used in COMSOL Multiphysics® software; this allows to use Navier-Stokes equation in the air free volume through yarns and the Brinkman equation inside yarns. This work confirms that air permeability can be predicted with good accuracy, from the basic design parameters of any fabric
Pump and ejector design in wastewater treatment pilot equipment
No full textOzone treatment is an oxidative process used in wastewater treatment plant to demolish complex organic molecule. In the case of textile industry is required to adequately remove residual color, demolishing the chromophoric bonds or groups in the dye molecules. A useful method for adding the ozone gas into water and maximize ozone-water mixing to increase mass transfer, is the use of Venturi ejectors. Forcing water through Venturi body, it creates a differential pressure between the fluid inlet and outlet, which in turn creates a vacuum inside the ejector body. In this part, it is possible introduce ozone. COMSOL Multiphysics® is used to define the design parameter of the ejecto
Modelling of the Wool Textile Finishing Processes
No full textWithin wool textile industries, a very important role is played by the so-called finishing processes, in which the textile substrate undergoes steam treatments to achieve the desired level of stabilisation and appearance. Process parameters, namely temperature and moisture content, are known only at the beginning of the process but not in the textile material being treated, where the actual physicochemical effects takes place. They have been evaluated during time dependent simulations, showing a fast increase of the fibre temperature which reaches values higher than the steam one, due to the heat of moisture sorption, whereas the moisture content increases very slowly, demonstrating that the diffusion coefficient of water molecules into the fibre is the limiting factor of the whole proces
Modelling of a Wool Hydrolysis Reactor
No full textThe Life+ GreenWoolF project is aimed at demonstrating that green hydrolysis with superheated water is an effective way to convert wool wastes into organic nitrogen fertilizers. The core of the process is represented by the reaction tank (Figure 1) in which the hydrolyses reaction takes place. The temperature of the material during the reaction is one of the most influencing parameter and has to be as much homogeneous as possible, but it is directly connected with the bulk density of the material. From an energy saving point of view, it is advantageous to reach a high bulk density with the lowest water content, but this is in contrast with the propagation of the heat transfer front through the fibrous material
Mapping of ultrasonic fields for dyeing applications
No full textIn the last years textile industries have focused their attention on the development of innovative environmental friendly processes and on the improvement of product quality. The use of ultrasounds (US) waves to improve dyeing processes of natural fibers has been investigated since the begin of fifties; it was shown that US are effective to reduce temperature and operative time of the dyeing. In particular this improvement is very important for natural fibers since reduction of temperature and dyeing time helps in maintaining optimal fiber properties. The tests, carried out in the frame of the Piemonte Regional Project INTEXUSA (INnovation in TEXtile productions by UltraSound Application), were aimed at evaluating the influence of the system geometry on the ultrasound waves propagation in a water-based medium. These runs were performed by monitoring the system with an Ultrasonic Energy Meter (by PPB Megasonics) to evaluate the cavitation energy distribution inside a dyeing prototypal equipment operating with different liquor depths. The main goal of this study was addressed to analyze the influence of the liquid depth on the cavitation phenomena, whose output can be useful to determine an optimal geometric configuration in a novel dyeing equipment provided by US transducers and minimize liquor ratio
Evaluation of actual dyestuff penetration in ultrasonic-assisted wool dyeing
No full textThe application of ultrasounds (US) in dyeing and washing at industrial scale has become an important research topic in the recent years, as this technology appears to have a high potential to reduce the environmental impact of textile productions, as well as to increase the effectiveness of these basic operations. As far as dyeing is concerned, several studies [1, 2] indicate the possibility to operate at a temperature lower than the one typically suggested, yet achieving excellent dye exhaustion, apparently comparable to those obtained in conventional processes. Natural fibres (wool, cotton and silk) seem to be the most suitable materials for USintensified dyeing, since it is not necessary to exceed the glass transition temperature of the constituent polymers, as the dyestuff diffusion within the fibre matrix is a combined effect of hygroscopic pore swelling and US promoted cavitation. Usually, dye-bath exhaustion given by spectrophotometric analysis in the visible range, is one of the promptest parameters to monitor dyeing with time. However in our US-assisted tests, we noticed that this method provided questionable results by varying the operation parameters, namely temperature. In US-assisted dyeing, cavitation phenomena reduce the interphase mass transfer resistance, thus promoting dyestuff adsorption on the fibre surface. In the subsequent rinsing steps, variable amounts of dyestuff leave the textile substrate due to penetration deficiency. For this reason, a new method aimed at determining correctly the dye uptake was based on DMSO (dimethyl sulfoxide) extractions, either after dyeing or rinsing. By comparing the extracted amount, the quantity of adsorbed dyestuff was determined, thus highlighting the mass transfer intensification due to US effec
Mapping of Cavitational Activity in a Pilot Plant Dyeing Equipment
No full textA large number of papers of the literature quote dyeing intensification based on the application of
ultrasound (US) in the dyeing liquor. Mass transfer mechanisms are described and quantified,
nevertheless these experimental results in general refer to small laboratory apparatuses with a
capacity of a few hundred millilitres and extremely high volumetric energy intensity. With the
strategy of overcoming the scale-up inaccuracy consequent to the technological application of
ultrasounds, a dyeing pilot-plant prototype of suitable liquor capacity (about 40 L) and properly
simulating several liquor to textile hydraulic relationships was designed by including US
transducers with different geometries.
Optimal dyeing may be obtained by optimizing the distance between transducer and textile material,
the liquid height being a non-negligible operating parameter. Hence, mapping the cavitation energy
in the machinery is expected to provide basic data on the intensity and distribution of the ultrasonic
field in the aqueous liquor. A flat ultrasonic transducer (absorbed electrical power of 600 W),
equipped with eight devices emitting at 25 kHz, was mounted horizontally at the equipment bottom.
Considering industrial scale dyeing, liquor and textile substrate are reciprocally displaced to achieve
a uniform coloration. In this technology a non uniform US field could affect the dyeing evenness to
a large extent; hence, mapping the cavitation energy distribution in the machinery is expected to
provide fundamental data and define optimal operating conditions. Local values of the cavitation
intensity were recorded by using a carefully calibrated Ultrasonic Energy Meter, which is able to
measure the power per unit surface generated by the cavitation implosion of bubbles. More than 200
measurements were recorded to define the map at each horizontal plane positioned at a different
distance from the US transducer; tap water was heated at the same temperature used for dyeing tests
(60 °C). Different liquid flow rates were tested to investigate the effect of the hydrodynamics
characterizing the equipment.
The mapping of the cavitation intensity in the pilot-plant machinery was performed to achieve with
the following goals: a) to evaluate the influence of turbulence on the cavitation intensity, and b) to
determine the optimal distance from the ultrasound device at which a fabric should be positioned,
this parameter being a compromise between the cavitation intensity (higher next to the transducer)
and the US field uniformity (achieved at some distance from this device).
By carrying out dyeing tests of wool fabrics in the prototype unit, consistent results were confirmed
by comparison with the mapping of cavitation intensity
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