Non-isothermal Moisture Transport calculations with DIM 3.1 / Nicht-isotherme Berechnungen des Feuchtigkeitstransportes mit Hilfe des Porgrammes DIM 3.1

2000 ◽  
Vol 6 (4) ◽  
pp. 367-384
Author(s):  
J. Grunewald ◽  
R. Plagge
Keyword(s):  
Water Vapour ◽  
Liquid Water ◽  
Balance Equation ◽  
Constitutive Equations ◽  
Moisture Transport ◽  
Moisture Transfer ◽  
Transport Model ◽  
Transport Coefficients ◽  
Equation System ◽  
Transport Processes

Abstract The application of a general thermodynamical mass and energy transport model to the coupled heat and moisture transfer in porous materials results in a balance equation system and the related constitutive equations of the considered quantities. The constitutive equations describe moisture transport in a phase-separated manner leading into phase-divided hygric transport coefficients (liquid water permeability, water vapour diffusivity). A conceptual model is presented in the paper in order to circumvent the difficulties resulting from non-isothermal overlaying moisture transport processes. Since phase-divided hygric transport coefficients are not directly measurable, but moisture transport coefficients in distinct hygric ranges, moisture conductivities and a phase dividing function are introduced. The moisture conductivities include liquid water and water vapour transport. For a known phase dividing function, the phase-divided hygric transport coefficients of the balance equation system can be calculated from the measurable moisture conductivities. The influence of a variation of the introduced phase-dividing function on non-isothermal moisture transport processes is investigated by means of computer simulations.

Fiber Hygroscopicity Affects Thermo-Moisture Comfort of Elastic Knitted Fabric

2011 ◽  
Vol 332-334 ◽  
pp. 731-734
Author(s):  
Li Ya Zhou ◽  
Pei Hua Zhang ◽  
Wei Shen ◽  
Mei Di Xie
Keyword(s):  
Water Vapour ◽  
Liquid Water ◽  
Moisture Transfer ◽  
Subjective Evaluation ◽  
Water Transfer ◽  
Knitted Fabric ◽  
Heat And Moisture Transfer ◽  
Water Vapour Absorption ◽  
Heat And Moisture ◽  
Transfer Properties

In the present paper, the influences of fiber hygroscopicity on elastic knitted cotton and cotton blended Modal (50/50) fabric in heat and moisture transfer properties and comfort were studied. The rate of moisture regain, moisture transportation and liquid wicking performance were tested. Besides, wear trials were carried to collect subjective evaluation of thermo-moisture comfort sensation of the wearer. It is found that elastic knitted fabric of cotton-Modal/Spandex has better water vapour absorption and permeability as well as better liquid water transfer and spreading capacity. During wear trial, cotton-Modal/spandex fabric B caused significantly lower wet and sticking perception than cotton/spandex fabric A.

Numerical Simulation of Heat, Air, and Moisture Transfer Through a Wall of Porous Media

2020 ◽  
Author(s):  
Kiflom B. Tesfamariam ◽  
Cheng-Xian (Charlie) Lin ◽  
Fang Liu
Keyword(s):  
Numerical Simulation ◽  
Moisture Transport ◽  
Moisture Transfer ◽  
Simulation Software ◽  
Transport Processes ◽  
Two Dimensional ◽  
Heat And Moisture Transfer ◽  
Porous Walls ◽  
Heat And Moisture ◽  
Benchmark Solutions

Abstract This paper presents the results of two-dimensional (2D) numerical simulation of heat, air, and moisture transfer through porous walls, which have important application background in the built environment and other engineering fields. The air flows, heat and moisture transfer in the walls are studied using a transient heat, air, and moisture (HAM) model. This model treats the non-isothermal airflow through two-dimensional porous geometries in a time-dependent format. The model includes the Brinkman equation describes the flow of air and other mathematical equations that calculate the heat and moisture transfer through the porous region. The equations are solved by a finite element method (FEM) using physics-based modeling, which is implemented in the commercial simulation software, COMSOL Multiphysics. The model prediction is first validated by using published benchmark solutions. Eventually, the numerical results are presented to illustrate the complex effects of material porosity and permeability on the heat and moisture transport, and moisture content variation in space and time through the walls, at different humidity and temperature conditions. Within the investigated parameter ranges, it is demonstrated that the relative humidity and temperature difference are the driving forces for the transient heat, air, and moisture transport processes through the porous area in the porous walls.

scholarly journals ON THE SOLUTION OF ENERGY BALANCE EQUATION SYSTEM TO PREDICT TEMPERATURE DISTRIBUTION IN THE BUILDING ELEMENTS WITH VENTILATED AIR GAP

2014 ◽  
Vol 21 (1) ◽  
pp. 21-30 ◽  
Author(s):  
Edmundas Monstvilas ◽  
Karolis Banionis ◽  
Jurga Poderytė ◽  
Raimondas Bliūdžius ◽  
Arūnas Burlingis
Keyword(s):  
Heat Exchange ◽  
Balance Equation ◽  
Heat Balance ◽  
Internal Surface ◽  
Equation System ◽  
Energy Balance Equation ◽  
Air Gap ◽  
Exchange Processes ◽  
Calculation Results ◽  
Thermal Indicators

The article presents the solution of heat balance equation system, describing heat exchange processes in ventilated envelopes, which was applied to derive formulas for the calculation of temperatures in the ventilated layers of the envelopes. The accurateness of the formulas was assessed by experimental research and analysis of the calculation results. During the process of heat exchange balance equation solution, the equations were simplified by introducing the following restriction into the derived formulas: they may only be applied for the ventilated envelopes with steel or similar coatings as their external layers, i.e. coatings having small heat capacity and minor difference between the external and internal surface temperatures. The derived formulas enable the calculation of the temperatures of the ventilated envelopes in the distance which does not exceed a half of the ventilated air gap length measuring from the air entrance into the gap. However, this restriction does not impede the estimation of the average thermal indicators of the ventilated envelopes.

Moisture Transport in Wood-Based Structural Panels under Transient Hygroscopic Conditions

2020 ◽  
Vol 70 (3) ◽  
pp. 283-292
Author(s):  
Daniel Way ◽  
Frederick A. Kamke ◽  
Arijit Sinha
Keyword(s):  
Moisture Transport ◽  
Transport Model ◽  
Oriented Strand Board ◽  
Primary Objective ◽  
Accelerated Weathering ◽  
Wood Composite ◽  
Transport Parameters ◽  
Moisture Profile ◽  
Cyclic Changes ◽  
Wood Based Composite

Abstract Development of moisture gradients within wood and wood-based composites can result in irreversible moisture-induced damage. Accelerated weathering (AW), generally employing harsh environmental conditions, is a common tool for assessing moisture durability of wood composite products. Use of milder AW conditions, such as cyclic changes in relative humidity (RH), may be of interest to the wood-based composites industry in assessing moisture durability under more realistic conditions. The primary objective of this study was to determine whether moisture profile development in oriented strand board and plywood during cyclic RH changes could be reasonably predicted with a simple moisture transport model, which may be practical for wood-based composite industry members seeking to develop new AW protocols. The diffusion model based on Fick's second law with empirically determined moisture transport parameters fits the experimental data reasonably well for the purpose of screening RH parameters.

A Simplified Thermodynamic Analysis of a LiBr-H2O Vertical Tube Absorber

2002 ◽  
Author(s):  
E. D. Rogdakis ◽  
V. D. Papaefthimiou
Keyword(s):  
Mass Transfer ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Water Vapour ◽  
Liquid Water ◽  
Mass Fraction ◽  
Superheated Steam ◽  
Vertical Tube ◽  
Solution Temperature ◽  
Absorption Process

One of the most important components of an absorption air-conditioning/heat pump system is the absorber, where the refrigerant water vapour is absorbed into the liquid solution. While absorption systems have been in use for several years, the complex transport phenomena occurring in the absorber are not fully elucidated yet. Thus, an attempt is made to model the absorption process of water vapour in aqueous solutions of lithium bromide considering a falling-film, vertical-tube absorber. The proposed analysis is based on the formulation of four differential equations describing the spatial variation (parallel to the tube-axis) of solution mass, temperature, mass fraction and coolant temperature. The system of ordinary differential equations is numerically solved using a non-stiff numerical method. Thermophysical properties and especially, heat and mass transfer coefficients are calculated using widely-accepted and reliable relationships, which are extracted from the literature using recently published information on wavy-laminar flows. In the present study, the questionable assumption of treating the water vapour as an ideal gas is heavily modified utilizing. Consequently, the hypothesis of saturated water vapour at the steam-solution interaction surface is revised by introducing an energy difference between the superheated steam and the liquid water within the binary solution. The last correction encouraged us to compare theoretical results for solution temperature, mass fraction and mass flow rate, which were obtained using both assumptions. It was proved that the initial treatment causes an underestimation of the absorbed steam mass and correspondingly, an underestimation of solution temperature and mass fraction at the mass exchange interface. An attempt is made also to identify the effect of mass transfer coefficient on the effectiveness of the absorption process and on the energy differences between the superheated steam and the liquid water either as pure substance or as component of the binary mixture. It was shown that the increase of mass transfer coefficient leads to an increase of steam mass transfer rate and to a corresponding decrease of solution temperature slope at the entrance of a tube. Correspondingly, the increase of mass transfer coefficient results in an increase of heat of absorption and heat of dilution at the same variation range of the solution mass fraction.

scholarly journals Liquid water infiltration into a layered snowpack: evaluation of a 3-D water transport model with laboratory experiments

2017 ◽  
Vol 21 (11) ◽  
pp. 5503-5515 ◽  
Author(s):  
Hiroyuki Hirashima ◽  
Francesco Avanzi ◽  
Satoru Yamaguchi
Keyword(s):  
Liquid Water ◽  
Laboratory Experiments ◽  
Preferential Flow ◽  
Transport Model ◽  
Three Dimensional ◽  
Water Infiltration ◽  
Flow Paths ◽  
Preferential Flow Paths ◽  
Capillary Barriers ◽  
Wet Snow

Abstract. The heterogeneous movement of liquid water through the snowpack during precipitation and snowmelt leads to complex liquid water distributions that are important for avalanche and runoff forecasting. We reproduced the formation of capillary barriers and the development of preferential flow through snow using a three-dimensional water transport model, which was then validated using laboratory experiments of liquid water infiltration into layered, initially dry snow. Three-dimensional simulations assumed the same column shape and size, grain size, snow density, and water input rate as the laboratory experiments. Model evaluation focused on the timing of water movement, thickness of the upper layer affected by ponding, water content profiles and wet snow fraction. Simulation results showed that the model reconstructs relevant features of capillary barriers, including ponding in the upper layer, preferential infiltration far from the interface, and the timing of liquid water arrival at the snow base. In contrast, the area of preferential flow paths was usually underestimated and consequently the averaged water content in areas characterized by preferential flow paths was also underestimated. Improving the representation of preferential infiltration into initially dry snow is necessary to reproduce the transition from a dry-snow-dominant condition to a wet-snow-dominant one, especially in long-period simulations.

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