Papers by Keyword: Moisture

Abstract: This study investigated moisture diffusion in natural rubber (NR) hybrid composites filled with silica and bentonite clay. Natural bentonite (BNT) was treated with tetradecyldimethylammonium chloride and coco diethanolamide to produce modified bentonite (M-BNT). Varied proportions of silica, M-BNT, and BNT fillers were added to raw NR according to a third-degree simplex lattice mixture design of experiment. The addition of fillers affects the vulcanization characteristics, mechanical properties, and hardness of NR hybrid composites. Moisture diffusion behavior was studied by monitoring the water uptake of NR composites during immersion in deionized water at 80^°C. Data from sorption experiments were fitted on the classical Fickian and Langmuir-type diffusion models. The Fickian model overestimates and underestimates the water uptake of NR composites in the early and later stages of moisture diffusion, respectively. On the other hand, the Langmuir-type model adequately captures the anomalous diffusion behavior of moisture in NR composites. Parameters of the Langmuir model (equilibrium water uptake and diffusion coefficient) vary with the composition of hybrid fillers. Optimum proportions of silica, M-BNT, and BNT in rubber composites were obtained by considering the effect of fillers on mechanical properties and moisture diffusion characteristics of NR.

Abstract: The Glaser method is an assessment procedure for the risk of moisture accumulation in building mono-dimensional structures, that could be used to evaluate mould risk and interstitial condensation risk.It is based on a simplified model that does not represent the real phenomenon and its limitations are well-known qualitatively.This work provides a comparison in terms of moisture content between the Glaser method and WUFI Pro, an advanced heat, air and moisture transfer prediction tool. First the influence of material properties is evaluated on four fictitious materials walls, then six different building envelope typologies for six weather files from Central and Southern Europe are modelled to evaluate the Glaser method results.The effects of the Glaser method simplifications are quantified in terms of moisture content percentage difference.

Abstract: The main trends and prospects of water resources consumption, as well as existing ways of obtaining fresh drinking water, were analyzed. The design of a vortex condenser of atmospheric moisture has been provided. Its operating principle is based on the organization of free-convective flow under the temperature drop effect and air-cooling to a temperature below the dew point. The designed vortex condenser of atmospheric moisture runs on solar energy and do not require using additional energy sources. The results of numerical simulation of the flow structure in a vortex condenser of atmospheric moisture and experimental data, which confirms the formation of air flow inside the condenser and moisture condensation in its lower part, are presented.

Abstract: One of the advanced and unconventional forms of energy, i.e. super high frequency field energy, has been studied. Advantages of super high frequency field application have been demonstrated, in comparison with the other forms of energy. It has been found out, that the sources of super high frequency heating (SHF-heating) allow obtaining the concentrate free of combustion products, as well as reducing pollution of the environment. Drying of Olenegorsk fine grinding masterbatch (Olenegorsk Mining and Processing Plant) proves the value of these advantages and makes it feasible to adopt this process during preparation of the iron-ore pellets for metallurgical treatment. It has been shown that the intensity of drying in the SHF-field is vastly superior to the one achieved in conventional convection units, due to volumetric nature of the heating and more favourable conditions for heat-and mass-exchanging processes in the bed. The obtained results may be used for the development of the design of units for drying fine-grained materials in the SHF-fields.

Abstract: Cotton is a hydrofilic textile fiber and, for this reason, it changes its properties according to the environment changes. Moisture and Temperature are the two most important factors that lead a cotton Spinning sector and influence its quality. Those two properties can change the entire Spinning process. Understanding this, moisture and temperature must be kept under control when used during the Spinning process, once the environment is hot and dry, the cotton yarns absorb moisture and lose the minimal consistency. According to this information, this paper was developed testing four types of cotton yarns, one kind of cotton from Brazil and the others from Egypt. The yarns were exposed to different temperatures and moisture in five different tests and in each test, six samples that were examined through physical and mechanical tests: resistance, strength, tenacity, yarn´s hairness, yarn´s evenness and yarn´s twisting. All the analysis were accomplished at Laboratório de Mecânica dos Fluídos and at COATS Corrente S.A., where, it was possible to use the equipments whose were fundamental to develop this paper, such as the STATIMAT ME that measures strength, tenacity, Zweigler G566, that measure hairiness in the yarn, a skein machine and a twisting machine. The analysis revealed alterations in the yarn´s characteristics in a direct way, for example, as moisture and temperature were increased, the yarn´s strength, tenacity and hairness were increased as well. Having the results of all analysis, it is possible to say that a relatively low temperature and a high humidity, cotton yarns have the best performance.

Abstract: Building structures have been designed such that they are able to withstand the adverse effects of the environment for a certain time. The terms "for a certain time" and "the surrounding environment" are used for a purpose here, and that is because the phenomenon of ageing buildings is currently an increasingly discussed problem that is faced by every larger city. The materials used in the buildings, such as façade cladding, age just as the buildings themselves do. An immense pressure has been currently put on designers to use environmentally friendly materials not only for new buildings but also for the retrofitting of existing ones. The aim of this paper is to demonstrate that wood or wood composite materials are convenient solution for restoration of façades of administrative or commercial buildings, however, since the new cladding have to be connected with an old load-bearing structure, the designers have to overcome many limitations. One of the main difficulties is high thermal and moisture expansion of these materials which has a direct impact on the appearance of the façade. The obtained results showed that expansion properties should be studied closely when using wooden elements in the design and that a neglection can lead to a premature failure of the system.

Abstract: Fibre reinforced composite materials are demanded by the industry especially for the applications where weight reduction is critical because of their high specific strength, ability to resist corrosion. The present work aims on evaluation of various mechanical properties of glass fiber reinforced polymer composites (GFRP) with inclusion of single walled carbon nanotube (SWCNT) in different weight fractions. Before performing the tests, the specimens were allowed to immerse in fresh water and sea water simultaneously for a period of 11 days (110 Hours) under hydrostatic pressure and further observing the amount of moisture content that has been accumulated in the specimens if any. This type of material can be used in marine industries as an alternative material for fabrication of hull of a ship and also used to design and fabricate various components of a ship.

Abstract: Sorption and desorption of moisture in epoxy composites reinforced with triangular and V-shaped bar fillers were studied. Epoxy was reinforced with vinyl ester bar assemblies fabricated according to 4 varied factors: bar orientation relative to diffusion direction (pointed or base side), bar alignment (parallel or staggered), spacing between bars (1 or 5 mm), and bar cross-sectional shape (triangular or V-shaped). Unlike previous studies, the bar fillers were initially coated with small amount of epoxy resin to improve wetting during fabrication of composites. Moisture uptake and loss of composites during one-side exposure to water vapor (50% relative humidity at 60°C) and hot air (60°C), respectively, were monitored with time. Experimental results show weight change of composites during moisture sorption and desorption varies linearly with square root of exposure time. Diffusion coefficients of composites were determined by assuming the material to be semi-infinite and fitting a mathematical solution to Fick’s second law of diffusion to weight change data. Results show diffusion coefficient of composites during moisture sorption is increased when bars are oriented pointed relative to diffusion direction, aligned parallel, spaced at 1 mm, and has triangular cross-sectional shape. However, during desorption, the diffusion coefficient is increased when base side of bars are exposed and when the bars are aligned staggered. The observed effects of factors on moisture diffusion coefficients of epoxy composites during sorption and desorption are discussed in relation to path length, available diffusion area, and status of epoxy/vinyl ester interphase before and after moisture sorption in composites.

Abstract: A moisture measuring device based on non-destructive method of gamma rays attenuation, allows measures to deepen concepts in building physics related to the moisture transfer; study the influence of the interface between layers in moisture transfer; analyse the influence of gravity on absorption and drying of different building materials; study the kinetics of absorption and drying of walls of one or more layers; analyse the importance of the temperature gradient in the movement of moisture; calculate the coefficient of water diffusivity of some building materials. In this work the proposed non-destructive method of gamma ray’s attenuation was used to analyse the transport of liquid water along a constructive element. For that propose gamma ray hydric profiles with red brick samples, 2 types: “A” and “B”, were obtained. Gamma ray hydric profiles are very interesting and original considering that the equipment exists in just a scarce laboratory. It is also intended to show how the equipment works and the way that those profiles can be taken. The water content profiles experimentally measure are very interesting, and the preliminary results obtained, for red brick samples with different densities and sectional area, will be shown and discussed.

Abstract: This study investigated the effects of clay filler treatments on moisture diffusion in natural rubber (NR)/bentonite nanocomposites. Four types of clay filler treatments were considered: sodium activation using sodium chloride (NaCl), ion exchange using hexadecyldimethylamine (HDA) chloride salt, modification using coco diethanolamide (CDEA), and wet grinding using ethanol as medium. A 2⁴ full factorial design of experiment (DOE) was utilized during clay filler treatments. The measured vulcanization characteristics of rubber specimens show the NR nanocomposites to be stiffer than unfilled NR, with very small differences in scorch and curing times. The moisture uptake of rubber specimens at 80°C is linear with square root of immersion time showing Fickian behavior. The rate of moisture uptake (slope of moisture uptake versus square root time) was measured. Determination of factor effects and analysis of variance show all clay filler treatments except for wet grinding significantly increase the rate of moisture uptake of NR nanocomposites. When compared to unfilled NR, only wet grinding of clay is found effective in lowering moisture diffusion.