Simulation Of Moisture Transfer Research Articles

Three-dimensional simulation of heat and moisture transfer in woven fabric structures

Fabric structure parameters have a significant impact on the comfort of heat and moisture transfer in garments. Previous numerical simulations required extensive mathematical calculations and mostly investigated one- or two-dimensional models of fiber assembly without considering the weave structure, which is a key parameter, that significantly influences the porosity of the woven structure and consequently its heat and moisture management. While the finite element method supports the simulation of the optimal shape and material properties with better visibility, previous finite element models focused on heat transfer and neglected water vapor transfer in fabrics. In this article, the finite element simulation of heat and moisture transfer in woven fabrics is established based on the testing principle of thermal resistance and moisture resistance tester using COMSOL Multiphysics software. In this simulation, three-dimensional parametric geometrical models of the fabric are created using curve interpolation methods by acquiring the control point coordinates of different weaves (plain, 2/2 balanced twill, and 4/1 unbalanced twill weaves). Heat and moisture transfer properties of fabric models in the horizontal and vertical directions were analyzed, including the heat flux, moisture resistance, water vapor permeability, and water vapor concentration. The article also deals with the effects of weave structure and fabric cover in a range of 72.1–85.1% on the fabric heat flux and water vapor concentration. Comparison between model and experimental results revealed that the three-dimensional simulation can accurately predict the impact of weave pattern and fabric cover on the fabric heat and moisture transfer performance. In addition, this model can be utilized to study the distribution of heat and water vapor within fabrics, providing a theoretical foundation for optimizing heat and moisture comfort in woven fabrics.

Numerical and experimental estimation of building wall heat flux in presence of moisture transfer

Insulating building envelope is an efficient way to increase building energy efficiency and minimize greenhouse gas emissions related to heating. After building refurbishment, on-site measurements are suitable for verifying the actual thermal transmission properties of plane building components. For instance, the standard ISO 9869-1 describes a HFM method based on the measurement of surface heat flux with heat flow sensor (HFS). This method has been extensively investigated in the literature and successfully applied on vapor tight building walls. Nevertheless, hygroscopic building insulation materials (like biobased materials) are increasingly used, and heat transfer are coupled to moisture transfer within the wall. In this case, the HFS acts as a vapor barrier: it modifies the local moisture transfer and the associated latent heat flux. In this view, this study aims to clarify what it is measured with HFS in presence of moisture transfer. The question is first treated by numerical simulation of heat and moisture transfer within hygroscopic building wall. Then, experiments are carried out on hygroscopic building insulation where the moisture effects are exaggerated.

Extended hygrothermal characterization of unstabilized rammed earth for modern construction

Although hygrothermal properties of rammed earth represent great potential for improving thermal comfort during hot summers, still little knowledge is available about this topic. The literature lacks complete sets of hygrothermal characteristics of rammed earth, although they are fundamental for heat and moisture transfer modeling necessary to predict earthen building performances. The present work reports the results of a large collaboration between four academic laboratories in order to obtain an extended hygrothermal characterization of rammed earth, focusing on the material used in a modern construction in Lyon, France. The aim of the article is to provide for the same kind of soil an extend characterization on a large span of relative humidity to provide complete set of material properties for heat and moisture transfer simulation. The hygrothermal measurements cover adsorption and desorption isotherm, intermediate isotherm loop, specific heat capacity, dry thermal conductivity, moisture-dependent thermal conductivity and water vapor resistance factor for a large span of relative humidity. In addition, the capillary rise test was performed to estimate the liquid transport coefficient for suction and redistribution. The results show that variations in the density of the samples have a low impact on sorption isotherm, while they have a non-negligible impact on thermal conductivity and water vapor permeability. Surprisingly, variations in the grain size distribution do not produce a significant modification in the sorption isotherm, while hysteresis slightly reduces when bigger grains are added to the soil composition. Approximation of empirical model coefficients for the determination of moisture-dependent thermal conductivity is proposed for rammed earth materials.

Numerical simulation of heat and moisture transfer in protective clothing under high pressure steam exposure: Effect of fabric properties and steam conditions

Steam disasters often exist during applied thermal engineering. Steam protective clothing plays a crucial role in safeguarding workers in various industries such as navy, petrochemicals, and others, by protecting them from steam hazards and ensuring their health and safety. This study aims to develop a numerical model that accurately simulates the heat and moisture transfer characteristics of thermal protective fabrics when exposed to steam. Subsequently, the integration of skin bio-heat transfer and burn integral models with the steam heat transfer model was performed to provide predictions of skin burns. In addition, the heat transfer mechanism of steam through fabrics to skin and the factors affecting the steam protection of fabrics were also analyzed by parametric studies. The accuracy of model simulation was verified by steam exposure tests with difference of second and third degree burn time less than 0.4s. The findings demonstrated the significant influence of moisture transfer and basic fabric properties on the steam protective performance. Among them, fabric thickness, specific heat and initial moisture content of fabrics have obvious influence. The influence of fabric's moisture regain is slightly smaller, and the impact of thermal conductivity is the least. The steam temperature also shows great effect, but the velocity of steam flow has little effect. This work provides theoretical guidance for the research and development of high performance protective materials and clothing from steam hazards. It is helpful for the virtual design and performance evaluation of steam protective clothing.

Numerical Simulation of Heat and Moisture Transfer in Corrugated Walls Dryer

The primary goal of the current work is to model heat and mass transfer during mango drying in a wavy airflow dryer. By modifying the dryer walls, we were able to produce the undulating airflow (with V-shaped obstacles). With convective boundary conditions applied to all product surfaces, the explicit finite difference approach was used to study heat and mass exchanges in two dimensions during the drying of mango slices. During drying, the transfer coefficients are thought to fluctuate. Using EasyCFD software, the external flow, temperature, velocity, and pressure fields were then analyzed. This provided the profile of the heat transfer coefficient. These profiles were then utilized to calculate the mass transfer coefficient using the Shilton-Colburn analogy. Moreover, the code created to determine the heat and mass transfer coefficients in the product was used to derive the evolution of temperature and moisture content over time. The results allowed for the discovery of a new air flow in dryers called an undular flow and demonstrated how modifying the drying air stream enhanced heat transfer efficiency. By changing the air flow in the dryer, it was possible to achieve heat transfer coefficients ranging from 47.55 W/m²K to 357.38 W/m²K and mass transfer coefficients of 3.21 x 10-5 to 3.21 x 10-4 m²/s. When the outcomes of this investigation were compared to experimental results from the literature (under identical drying circumstances), a reasonable level of adequacy was discovered.

Assessment of frost damage risk in a historic masonry wall due to climate change

Abstract. Historic masonry buildings are an integral part of human cultural heritage, and they need to be preserved for future generations. Brick is susceptible to frost damage which is common in regions with cold and humid climates. The frost damage on the masonry walls is accumulated over the years becoming more and more critical for the integrity of the historic buildings and it is also affected by climate change (CC). In the current research, the focus was placed on a coastal region in southern Norway with a significant number of historic masonry buildings. The frost damage risk of the masonry walls was assessed by using data from a climate reanalysis for the present conditions and from a climate model under past, present, and future conditions. Two climate-based (CB) indices accounting for the air temperature and one material response-based (MRB) index considering the temperature and moisture content inside a simulated masonry wall were used for the frost damage risk assessment. The inputs for the MRB index were calculated by heat, air, and moisture (HAM) transfer simulations. Within the HAM simulations, the indoor climate was in one case representative of an unconditioned building with air leakages and many openings, while in the second case it was representative of a small, conditioned room. The overall impact of CC was a decrease in the frost damage risk of the masonry walls. However, an increased frost damage risk was observed from the present to the future conditions according to the MRB index for the walls of small, conditioned rooms with higher driving rain load and lower solar radiation gains. The (i) number of freeze-thaw events, (ii) periods during which freeze-thaw events occur, and (iii) CC-related trends varied based on the considered index with the most explicit risk assessment being the MRB one. Moreover, the freeze-thaw events experienced by the masonry walls of unconditioned, leaky buildings were 20 times more than the ones for the small, conditioned rooms. Significant differences were observed between the results from the climate model and the climate reanalysis which were mainly linked to the underestimation of the air temperature and the overestimation of the precipitation by the climate model. The outputs of the MRB index were translated into certain damage categories while suggestions on improving the limitations of the current research were made.

Development of a life cycle net zero carbon compact house concept

The paper presents the development process of an innovative, prefabricated compact house, which aims at creating a net zero greenhouse gas emission building design over the whole life cycle. Building Information Modelling helped to quantify the required building materials. Dynamic building simulations were performed in DesignBuilder to calculate the energy demand of the building for the operational period. To evaluate the financial feasibility and the carbon balance of the building, life cycle assessment and life cycle costing were used. A heat and moisture transfer simulation was carried out to provide a more accurate analysis and to identify possible moisture problems.The assessment showed that the ratio of embodied impacts and operational impacts is typically 1:2 for wooden buildings and 1:1.5 for brick buildings. Life cycle carbon neutrality could be achieved in both cases with additional photovoltaic panels installed on the roof. However, a major difference between timber and brick buildings is the time factor: while the initial emissions from the production of brick buildings are gradually offset with excess solar energy, timber buildings act as carbon storage with negative emissions over the study period and the carbon is only released at the eventual end-of-life stage. The necessary size of photovoltaics is largely influenced by the avoided grid impact: if dynamic decarbonization of the electricity mix is considered, the size of photovoltaics required is about 1.5 times larger to offset the environmental load of the construction due to the diminishing benefits.

Estimation of Groundwater Recharge from Rainfall for Arid Coastal Plain of Ninh Thuan Province, Vietnams

Estimation of groundwater recharge from rainfall is a key factor for determining groundwater resources in water development and management for supporting sustainable socio-economic development, especially for arid areas. The paper presents finite element modeling in the simulation of moisture transfer in unsaturated soils through the relationship between soil moisture, soil suction, unsaturated permeability and soil-moisture dispersivity. Those parameters required for soil moisture transfer are derived from the soil-water characteristic curve functions. Element sizes and time steps used in the modelling have been selected based on a detailed analysis of numerical simulation errors. The methodology had been applied to arid coastal plain area of Ninh Thuan province, Vietnam. Five subsurface soil types in the study area have been collected and analyzed, for saturated permeability, porosity, saturated soil water content, field moisture content, etc. Hourly rainfall data of the years 2014–2018 have been analyzed and grouped into different-duration rainfall events (1-hour, 2-hour, 3-hour and so on). The different rainfall durations and depths of rainfall events and temporal infiltration determined by the moisture transfer modelling have allowed determining the groundwater recharge from the rainfall data. The results show that during the rainy months from May to December 2014–2018, the groundwater recharge from the rainfall is very varying through the modeled soil profiles, from 0.280 m (silty clay) to 0.470 m (sandy silt), which is equivalent to 33.3%—55.2% of the rainfall depth during May—December. Lower infiltration in silty clay is due to low permeability and in the sand is due to low suction, and higher infiltration in silt and sandy silt is thanks to their higher moisture dispersivity. On average, in terms of annual rainfall and soil properties, the average infiltration during May—December is 0.380 m which is equivalent to 44.9% of the rainfall depth, which is about 289 106 m3 of rainwater infiltrated into the Quaternary aquifer over 760 km2 of the coastal plain of Ninh Thuan province. The results would be very useful for effective water resources development and management in a given specific hydrogeological condition for such a severe drought area where water is extremely essential.

Comment on Cabrera et al. A User-Friendly Tool to Characterize the Moisture Transfer in Porous Building Materials: FLoW1D. Appl. Sci. 2020, 10, 5090

In July 2020, this journal published “A User-Friendly Tool to Characterize the Moisture Transfer in Porous Building Materials: FLoW1D”. That article presents and applies a forward-Euler-based tool, implemented in Visual Basic for Applications in Excel, for simulating moisture transfer in building materials. In that tool, the building materials’ hygric properties are described via the unimodal van Genuchten and Mualem equations. All parameters needed therein are inversely identified from only a capillary absorption experiment. These are three feats that, if valid, would strongly progress the state-of-the-art on moisture transfer simulation, hygric property description, and hygric property characterisation. This critique voices severe doubts, however, about the applicability of FLoW1D, the adequacy of the van Genuchten-Mualem equations, and (most fundamentally) the uniqueness of the inverse characterisation.

Damage risk assessment of building materials with moisture hysteresis

Heat and Moisture Transfer (HMT) simulations are used to evaluate moisture related damage risks in building envelopes. HMT simulations are commonly performed accepting the hypothesis of not considering the moisture hysteresis of materials. The results of HMT simulation of a timber wall with hysteresis are presented, and compared to the results of three simplified models, showing the effects of hysteresis on the simulation results and on the assessment of the risk of decay. Moisture content is the most influenced variable, while temperature and relative humidity are slightly affected. The wood decay risk analysis is performed using the simplified 20% moisture content rule. Similar temperature values and relative humidity values are calculated as simplified models, while the moisture content annual average values have differences up to 2.3%. The wood decay risk obtained with the simplified models could be overestimated if the simulation is performed using the desorption curve, while it could be underestimated with the adsorption curve. The best approximation is obtained with the mean sorption curve, while the desorption curve and the adsorption curve could be used to calculate the upper and lower boundary of the moisture contents respectively.

Multiyear hygrothermal performance simulation of historic building envelopes

The objective of this work is to quantify the effects of the short-term climate change with a multiyear (MY) approach on the results of the heat and moisture transfer simulations of an historic building located in Udine (Italy) and to evaluate if a single year simulation could be representative of the results obtained with the MY. The hygrothermal performance and the moisture related risk are evaluated for a brick wall with and without insulation, with a MY of 25 years and with three single years selected form the MY. The software DELPHIN is used for the simulations and the damage indicators are calculated using simplified methods (number of days with unfavourable conditions). Depending on the damage considered, the years have different effects on the studied wall. The simulations that use the MY weather file allow to obtain more accurate results than using one-year simulations, but the effort and time required for the interpretation of the simulation results could be not acceptable. It is then shown that the choice of a representative weather file is crucial to the results of the risk analysis and that considering more than one weather file is necessary to obtain representative results for different damages mechanisms.

Evaluating the Impact of Indoor Insulation on Historic Buildings: A Multilevel Approach Involving Heat and Moisture Simulations

The energy refurbishment of historic buildings is a complex task for building envelope designers who need to carefully consider building conservation guidelines and principles. In most cases, external wall insulation techniques can determine an unacceptable alteration of the historical value of a building. For this reason, internal wall insulation techniques have been used widely in the last few decades. Nevertheless, dealing with internal wall insulation requires a complex design to avoid the risk of condensation and moisture-related pathologies. Moreover, an internal wall insulation may have a relevant impact on indoor comfort conditions. In this paper, the Monastery of Santa Maria de Monfero in Galicia (Spain) has been adopted as a building case study to compare different technological solutions based on: (i) an insulating plaster layer, (ii) dry counter wall systems. In the first step, heat and moisture transfer simulations of the wall components were performed to analyze the hygrothermal behavior of the different alternatives considering two different climate conditions. In a second step, a simulation of the whole building was performed to analyze the impact of the retrofitting strategies on the indoor climate and on the building heating and cooling demand. The obtained results show that the counter wall solution leads to higher energy savings during the heating season in the colder winter climate. However, the use of insulating thermal plaster could also be a viable solution since they lead to several advantages in summer because of their higher thermal inertia. Therefore, the selection of the most appropriate insulation technique has to be evaluated carefully considering the outdoor/indoor climate and using a case-by-case approach.

Heat and moisture transfer and shrinkage simulation of beetroot (Beta vulgaris) drying

Heat and moisture transfer and shrinkage simulation of beetroot (Beta vulgaris) drying

Study on groundwater recharge assessment by rainfall in coastal district Thai Thuy, Thai Binh province

Groundwater always plays a vital role in socio-economic development. One of the components of groundwater resource potential is the recharge from rainfall and surface water. The paper presents finite element modeling in the moisture transfer simulation in unsaturated soils through the relationship between soil moisture, soil suction, unsaturated permeability, and moisture dispersion coefficient. Parameters required for moisture transfer in four subsurface soil types have been collected and analyzed: Saturated permeability, porosity and field moisture content. Hourly rainfall data of 2015 have been studied and grouped into different rainfall duration (1-hour, 2-hour,... 36-hour continuous rainfall). The different duration rainfall and temporal infiltration determined by the moisture transfer modeling allow calculating the groundwater recharge from the downpour. We had applied the methodology to coastal district Thai Thuy, Thai Binh province. The results show that during the rainy months from June to October 2015, the groundwater recharge from the rainfall is: Through silty clay 0.233 m, through silt 0.338 m, through sandy silt 0.374 and through silty sands 0.561 m. The rainfall recharge to groundwater through those four soil types in terms of percentage of total 2015 rainfall respectively is 12.85%, 18.65%, 20.63% and 30.95%. The methodology may be applied to other areas with an advantage in the minimal expense of budget and time and relatively high reliable results.

Computer simulation of moisture transfer in walls: impacts on the thermal performance of buildings

ABSTRACT In order to reduce electricity consumption in buildings, it is imperative to improve their thermal performance. Due to the many variables involved in thermal processes computer simulation is a consolidated method for thermal analysis. However, in many energy efficiency analyses calculus of heat conduction through the dwelling envelope does not consider moisture transportation and storage. The objective of this work was to evaluate the impacts of moisture transfer in walls on the thermal performance of naturally ventilated and artificially conditioned buildings using EnergyPlus computer simulation. This research contributed to the literature by showing the difference in thermal zone air humidity, temperature and annual energy demand (i.e. electricity consumption) when moisture effects are considered in walls. Buildings were composed of masonry and solid concrete envelopes and three numerical models were simulated: Conduction Transfer Function Model (CTF), Effective Moisture Penetration Depth Model (EMPD) and Combined Heat and Moisture Transfer Model (HAMT). The CTF model does not consider moisture effects. Results found a higher relative air humidity for the studied thermal zone by applying the HAMT model in the numerical simulation, and the envelope porosity was proven to affect HAMT humidity results. Comparing the HAMT and EMPD models with the CTF model, the annual energy demanded for cooling presented a 21% reduction for the EMPD model in the masonry and 9% increase for the HAMT model in the solid concrete. This article shows the importance of an accurate EnergyPlus heat transfer model for simulating a whole building to check edification attendance of minimum comfort parameters and select envelope materials aiming the reduction of electricity consumption.

Mathematical modelling of renewable construction materials for green energy-efficient buildings at permafrost regions of Russia

The main goal of this work is to assess the influence of moisture transfer processes on the operational properties of complex structures with wooden elements. A physical-mathematical model of the combined heat and moisture transfer in the walls of insulated timber with connectors has been presented in the paper. The model is intended for use in the climatic conditions of the northern territories. The model has been confirmed by experimental data on moisture sorption isotherms in wood, as well as the dependence of moisture conductivity and thermal conductivity coefficients on the temperature and humidity. Based on numerical simulation of nonstationary heat and moisture transfer in external building envelopes made of thermal insulating profiled timber with connectors, heat and mass fluxes in the selected inhomogeneous fragments have been calculated, and their thermal properties have been evaluated. It is shown that moisture transfer processes result in a decrease in thermal properties of walls made of insulated timber with connectors by 6-8%. The presence of connectors does not lead to the formation of any local zones with a significant accumulation of moisture. The studied properties and characteristics of green building materials enabled to development of the methodology of energy-efficient buildings and provide the background for the calculation of energy systems. The results of this work may be combined with other research on renewable or low-carbon energy technology to create a new strategy of sustainable construction in Russian permafrost regions.

Effects of considering moisture hysteresis on wood decay risk simulations of building envelopes

Wood decay risk assessment of building envelopes is commonly performed by engineers, architects and practitioners using results of Heat and Moisture Transfer (HMT) simulations and damage models. The commonly accepted HMT models use bijective sorption functions, accepting that materials reach hygrothermal equilibrium with the humidity contained in the air of the material’s pores and of the environment at a single MC. On the other hand, due to moisture hysteresis, equilibrium can be reached at different MCs for the same air condition, depending on previous equilibrium states. The aim of this work is to quantify the effect of considering hysteresis in HMT simulations and to evaluate its propagation in the risk assessment procedure for the case of wood decay. The software MATCH is used, implementation of an HMT model with hysteresis. Three timber walls are simulated in seven locations (Bolzano, Copenhagen, Hong Kong, Ottawa, Shanghai, Udine, and Vienna), first with hysteresis and then with simplified bijective sorption functions (adsorption, desorption, and mean sorption curve). MC and temperature time series are used to perform wood decay risk assessment with two damage models. The results show that the influence of hysteresis can be relevant, and that the choice of the sorption curve used in the simulations should be discussed. For the case of a CLT wall in Shanghai, simulated using the adsorption curve, a mean difference of 1.6% MC is found from the hysteresis case. This resulted in a difference of 0.7 decay rating in 10 years and 6% mass loss in 30 years.

Simulation of conjugate heat and moisture transfer in multilayer porous materials with ventilated channels

A physical and mathematical model for calculating the thermal and moisture state of the facade of a building with ventilated channels has been developed. The model is based on the joint solution of a system of non-stationary differential equations of heat and moisture transfer in multilayer porous materials. In addition, equations describing heat and mass transfer in ventilated air channels are included in the model. The calculations of the thermal and moisture state of the brick wall of the building, insulated from the outside with heat-insulating panels with ventilated channels, have shown that the selected geometry of the ventilated channels provides a low level of moisture content in the facade materials.

POD–DEIM model order reduction for nonlinear heat and moisture transfer in building materials

In this paper, the proper orthogonal decomposition (POD) method and the discrete empirical interpolation method (DEIM) are combined to construct a reduced-order model for a cost-optimal simulation of heat and moisture transfer in building materials. The POD-DEIM performance is assessed via two applications: a relatively simple case study on nonlinear heat conduction and a more complex case study on nonlinear moisture redistribution. In both, the results of the POD-DEIM model are compared to results from POD and finite volume methods simulations, to evaluate the accuracy of the POD-DEIM as a function of the numbers of construction modes and interpolation points. Also, as the number of POD construction modes and DEIM interpolation points does not entirely represent the computational cost of different models, the accuracies of the different models are compared as a function of the respective calculation times, to provide a fair comparison of their computational performances. Further, the use of POD-DEIM to simulate a problem different from the POD training snapshot simulation is investigated. The outcomes show that when a rather highly accurate result is desired, POD-DEIM model is capable of reducing the computational cost relative to POD and FVM.

Modelling and Simulation of Heat and Moisture Transfer in Human-chemical Protective Clothing-environment System

Modelling and Simulation of Heat and Moisture Transfer in Human-chemical Protective Clothing-environment System