Papers by Keyword: Moisture Transport

Abstract: This paper concerns the evaluation and the validation of a heat and moisture transfer models in stone walls using in situ measurements on an instrumented wall. Firstly, a pure thermal (respectively moisture) diffusion problems are considerate, then this problem was combined with convection on the external edge of model. It is found that, despite of an uncoupled approach, the nonlinear thermal diffusive model performs quite well and reproduces perfectly the measured temperatures. It is the same for the convective-diffusive thermal problem, where the temperature on the surface wall is also reproduced quite well. An improvement of this second type problem results could be expected by taking into account the radiation. Otherwise, the both cases of moisture transfer problem (purely diffusive or diffusive-convective problem) are ill-simulated by the Kunzel’s model.

Abstract: The development of lightweight thermal insulation plasters containing alternative binders as a partial cement substitute opens the possibilities of using new, eco-friendly materials in civil engineering. The substitution of cement significantly reduces the energy consumption these materials’ manufacturing. In addition, they contribute to the overall energy performance of buildings, which represents another environmental benefit. Concerning the negative effect moisture has on the thermal insulation properties of plasters, the investigation focused on the influence of various hydrophobic agents on the hygrothermal behaviour of the newly developed porous materials. The goal of the research was to develop eco-friendly thermal insulation and rehabilitation silicate materials and to analyse their moisture transport.

Abstract: Concrete was considered as a three-component composite material consisting of mortar matrix, coarse aggregates and interfacial transition zones (ITZ) at the mesoscale level. Based on the random accumulation model of spherical aggregates, a mesoscale geometric model was developed after discretizing the mortar matrix and ITZ into mesh elements using Voronoi diagram method. Combined with the third boundary condition, a mesoscale three-dimensional model to simulate the moisture transport process in concrete exposed to atmosphere environment was then developed using finite difference numerical method, where the transport of liquid water and water vapor were considered as permeation and diffusion respectively. Moreover, the model was verified and then applied to investigate the influence of ITZ on the distribution of relative humidity in concrete. The results indicated that the moisture transport process was overall accelerated since blocking effect of coarse aggregates was partially counteracted by the existence of ITZ.

Abstract: The temperature field in concrete has a significant influence on durability of concrete structures. Meanwhile, there is always damage caused by loads in concrete of a real structure, which affects heat transfer and temperature field. In this paper, the tests on temperature response to heating and cooling as well as moisture transport in concrete with different damage levels were carried out. Five concrete specimens were compressed under uniaxial load to 25%, 40%, 55%, 70% or 85% of the compressive strength, corresponding to different damage levels. One concrete specimen was not subjected to any load, as a comparison specimen. The internal temperature in concrete specimens during heating or cooling process was measured by an embedded humidity and temperature sensor. Thermal conductivity of concrete is the key parameter in denoting the ability of concrete to transfer heat and decreases with the increasing damage level. When the temperature gradient exists in both sides of concrete, the moisture transport will occur in the heat transfer direction. Regardless of heating or cooling process, there is always a hysteresis effect and the temperature response rate changes quickly in the initial stage and decreases gradually with time in damaged concrete. The greater the initial temperature difference is, the greater the initial temperature response rate is. In the same initial temperature difference, the temperature response rate decreases slightly with the increasing damage level, while the moisture transport mass increases evidently.

Abstract: Building construction drying using high-frequency electromagnetic radiation (EMW), or microwave technology (MW), is gaining more usage in practise. It is the quickest way of eliminating water content in construction (wall, ceiling, etc.). Microwave is a term for a part of the electromagnetic radiation of 300 MHz to 300 GHz frequency with a wavelength from 1 mm to 1 m. The frequency of 2,45 GHz and 122 mm wavelength is used for technical practice. Due to the effect of MW radiation a different homogeneity of temperature field can be observed.This article discusses the spreading of the temperature field depending on the water volume and thereby the amount of mass moisture of the material (silica fume). Temperature fields will be shown by the thermo camera at certain time cycles of heating.

Abstract: Moisture transport in high strength concrete is investigated in this paper. The experiment that involves the water suction is carried out in a long-term. The moisture profiles are measured by non-destructive capacitance method, the last profile is determined gravimetrically. The suction experiment is carried out in isothermal condition at the temperature of 22±1 °C and 25-30% relative humidity.

Abstract: The article deals with testing materials for using in enthalpy exchangers. The purpose of the enthalpy heat exchangers is to transport the heat and moisture together. Such heat exchangers are used in heat and ventilation air conditioning units. There are several methods how to test transport of moisture through material used in textile industry. However, these methods are not suitable for testing of materials, which are considered to be in heat exchangers. Methods for testing of moisture transport are usually based on free convection around membrane, which separates spaces with air of low humidity and air saturated with water. The free convection does not occur in heat exchangers and moisture varies in wide range. Therefore we developed and tested a devise to simulate moisture transport in enthalpy heat exchangers with plates, where co-current and countercurrent occur. With the help of this device, we could compare materials and evaluate the influence of the surface structure, which affect the boundary layers and heat and mass transport, when the flow is tangential to the material surface. We could also investigate the effect of flow velocity and humidity. The methods of evaluation are discussed and some results are presented.

Abstract: Abstract: The moisture flow and drying of porous media, such as concrete, is tackled through the Navier-Stokes equation, where the Navier-Stokes equation is considered as the link between the theory of fluid flow, Acoustic Emission (AE) experiments on cracking (sound propagation based on the wave equation) and Lattice Gas Automata, (LGA) being a numerical simulation of the Navier-Stokes equation. Early age cracking in the ITZ is induced by using the moisture flow as the only “load” that causes cracking due to drying shrinkage volume changes in Environmental Scanning Electron Microscopy (ESEM) tests. An attempt is made to link and compare experimental results conducted by means of AE and ESEM to the results of 2-D LGA numerical simulation. Lattice Gas Automata (FHP model) is used as a basis to generate a new model for drying of porous medium. Special emphasis in a model creation is given to the Interface Transition Zone (ITZ), between aggregate and cement paste, because of the early crack initiation in this highly porous and strength-weak zone.

Abstract: Lime plaster modified with pozzolana based on calcined kaoline mixed with mudstone and reference lime plaster are studied in the paper. For the studied materials, determination of bulk density, matrix density and total open porosity is done first. Then, specific attention is paid to the assessment of moisture diffusivity and chloride diffusion coefficient that are considered as decisive parameters for the materials’ durability. The measured data are used as input parameters for computational modeling of studied materials’ performance using computer code TRANSMAT 6.2 based on finite element computer simulation tool. On the basis of measured and calculated results, the applicability of newly developed plaster for renewal of historical buildings is discussed.

Abstract: A series of experiments was performed on studying the dynamic heat and moisture transferring procedure and evaluating heat-moisture comfort properties of functional moisture transported and dry-fast fiber in wearing conditions that produce continued sweat. Experiments were performed in two different environmental conditions, which were the most comfortable condition and an extremely uncomfortable condition for humans. The real time changes of temperature and relative humidity in inner and outer surfaces of different fiber fabrics were measured using self-made textile-microclimate measuring instrument. Then, fabric’s comprehensive heat-moisture comfort properties were obtained. Results show that fine denier polypropylene fiber as a newly moisture transported and dry-fast functional fiber has better heat-moisture comfort properties than other conventional fibers, and it is more suitable for sportswear fabric.