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Jan Carmeliet - One of the best experts on this subject based on the ideXlab platform.
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influence of uncertainty in heat Moisture Transport properties on convective drying of porous materials by numerical modelling
Chemical Engineering Research & Design, 2013Co-Authors: Twj Thijs Defraeye, Bje Bert Blocken, Jan CarmelietAbstract:The influence of uncertainties in heat-Moisture Transport properties, due to measurement errors and material heterogeneity, on the numerical simulation results of convective drying of two capillary-saturated porous materials is investigated by a Transport-property parameter analysis (TP-PA), based on the Monte Carlo method. Here, the heat-air-Moisture transfer model is evaluated many times, each time using a random set of one or multiple input parameters (i.e. Transport properties), by which a stochastic model output is generated. The propagation of these Transport-property uncertainties to the hygrothermal behaviour of the drying system is evaluated by statistical analysis of the model simulation output. The spread on the hygrothermal response is found to be strongly material dependent and is related to the dominant mode of Moisture Transport in the material, i.e. liquid or vapour Transport. The TP-PA results clearly indicate that uncertainties in the heat-Moisture Transport properties can lead to significant differences in drying behaviour predictions, where differences of the total drying time with respect to its mean value up to 200% are found for the materials considered. Therefore, numerical modelling of heat and Moisture Transport in porous materials should preferably include a quantification of the propagation of these uncertainties, for example by means of the proposed Transport-property parameter analysis. Such analysis however additionally requires detailed (a-priori) experimental material characterisation to determine realistic uncertainty ranges.
Twj Thijs Defraeye - One of the best experts on this subject based on the ideXlab platform.
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convective drying of fruit role and impact of Moisture Transport properties in modelling
Journal of Food Engineering, 2017Co-Authors: Twj Thijs Defraeye, Pieter VerbovenAbstract:Abstract Continuum modelling of fruit dehydration relies on accurate predictions of Moisture permeability or diffusivity. These properties are often taken from literature instead of being explicitly determined for the species, cultivar or drying application of interest. As a large variability on these Moisture Transport properties is reported, this study targets their role and impact on simulations of the fruit drying process. Using a validated hygrothermal model, significant differences in drying rate and internal Moisture content distribution are quantified for a realistic range of tissue permeabilities. Particular differences in drying kinetics are identified between constant permeability and diffusivity formulations, but in general both exhibited roughly similar drying behavior. Previous contradictory findings on the impact of the air speed, thus convective transfer coefficients (CTCs), on the drying process are shown to be most likely related to the magnitude of the tissue permeability. A lower sensitivity of the drying process to the CTCs is found for low permeabilities. A new parameter is introduced to facilitate quantitative comparison of multiple drying processes, namely by characterizing each drying curve with a single characteristic value. This modelling study provides a better quantitative insight in the fruit drying behavior and its link to the Moisture Transport properties of the tissue.
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influence of uncertainty in heat Moisture Transport properties on convective drying of porous materials by numerical modelling
Chemical Engineering Research & Design, 2013Co-Authors: Twj Thijs Defraeye, Bje Bert Blocken, Jan CarmelietAbstract:The influence of uncertainties in heat-Moisture Transport properties, due to measurement errors and material heterogeneity, on the numerical simulation results of convective drying of two capillary-saturated porous materials is investigated by a Transport-property parameter analysis (TP-PA), based on the Monte Carlo method. Here, the heat-air-Moisture transfer model is evaluated many times, each time using a random set of one or multiple input parameters (i.e. Transport properties), by which a stochastic model output is generated. The propagation of these Transport-property uncertainties to the hygrothermal behaviour of the drying system is evaluated by statistical analysis of the model simulation output. The spread on the hygrothermal response is found to be strongly material dependent and is related to the dominant mode of Moisture Transport in the material, i.e. liquid or vapour Transport. The TP-PA results clearly indicate that uncertainties in the heat-Moisture Transport properties can lead to significant differences in drying behaviour predictions, where differences of the total drying time with respect to its mean value up to 200% are found for the materials considered. Therefore, numerical modelling of heat and Moisture Transport in porous materials should preferably include a quantification of the propagation of these uncertainties, for example by means of the proposed Transport-property parameter analysis. Such analysis however additionally requires detailed (a-priori) experimental material characterisation to determine realistic uncertainty ranges.
Luis Gimeno - One of the best experts on this subject based on the ideXlab platform.
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recent progress on the sources of continental precipitation as revealed by Moisture Transport analysis
Earth-Science Reviews, 2020Co-Authors: Luis Gimeno, Marta Vazquez, Jorge Eirasbarca, Rogert Sori, Milica StojanovicAbstract:Abstract The assessment of sources of Moisture is key to the understanding of the hydrological cycle at different time scales, because it enables the establishment of source-sink relationships and the identification of the main Moisture Transport conveyors and associated processes, the result of which is precipitation. Gimeno et al. (2012) provided a comprehensive review of the state-of-the-art in the assessment of Moisture source-sinks and how different approaches can contribute to improving our knowledge of this component of the Earth’s Climate System. Since then, a variety of studies have focused on more specific aspects of the Moisture budget and the source-sink distribution across the globe by integrating observations, satellite-derived products, physical tracers and numerical modelling. Here, we summarise the main advances in the field related to the impact of the Moisture source-sink relationship on rainfall distribution, and add to the scientific debate on the question of the residence time of water vapour. We also revisit some of the recent advances in the role of the major mechanisms of Moisture Transport at a global scale, mainly Atmospheric Rivers and Low-Level Jet systems ( Gimeno et al., 2016 ), in terms of their effects on precipitation extremes. Finally, we set out some of the main challenges for future research.
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major mechanisms of atmospheric Moisture Transport and their role in extreme precipitation events
Annual Review of Environment and Resources, 2016Co-Authors: Luis Gimeno, Francina Dominguez, Raquel Nieto, Ricardo M Trigo, Anita Drumond, C J C Reason, Andrea S Taschetto, Alexandre M Ramos, Ramesh KumarAbstract:We review the major conceptual models of atmospheric Moisture Transport, which describe the link between evaporation from the ocean and precipitation over the continents. We begin by summarizing some of the basic aspects of the structure and geographical distribution of the two major mechanisms of atmospheric Moisture Transport, namely low-level jets (LLJs) and atmospheric rivers (ARs). We then focus on a regional analysis of the role of these mechanisms in extreme precipitation events with particular attention to the intensification (or reduction) of Moisture Transport and the outcome, in terms of precipitation anomalies and subsequent flooding (drought), and consider changes in the position and occurrence of LLJs and ARs with respect to any associated flooding or drought. We then conclude with a graphical summary of the impacts of precipitation extremes, highlighting the usefulness of this information to hydrologists and policymakers, and describe some future research challenges including the effects of...
Zhidong Zhang - One of the best experts on this subject based on the ideXlab platform.
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A Dual-Permeability Approach to Study Anomalous Moisture Transport Properties of Cement-Based Materials
Transport in Porous Media, 2020Co-Authors: Zhidong Zhang, Ueli AngstAbstract:Anomalous Moisture Transport in cement-based materials is often reported in the literature, but the conventional single-porosity Moisture Transport models generally fail to provide accurate simulation results. Previous studies suggested that the anomalous Moisture Transport could be caused by different Moisture Transport velocity in large and small pores. Based on this concept, the present study proposes a continuous dual-permeability model for cement-based material. The proposed model includes the Transport contribution of both liquid water and water vapor, which are governed by liquid advection and vapor diffusion, respectively. We explicitly consider that Moisture Transport in the large pore region is faster than the small pore region. The volumetric fraction of each region is determined when fitting the measured sorption isotherms by using a bimodal equation. The validation with experimental data shows that the dual-permeability model can well simulate both the “normal” and the anomalous Moisture Transport. The applicability of the proposed model implies that the “dual-porosity property” could be one of reasons that cause anomalous Moisture Transport in cementitious materials. In addition, results show that vapor diffusion can be neglected for Moisture Transport in both porosities at high relative humidity (RH), while at low RH, vapor diffusion must be considered.
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modeling anomalous Moisture Transport in cement based materials with kinetic permeability
International Journal of Molecular Sciences, 2020Co-Authors: Zhidong Zhang, Ueli AngstAbstract:The durability of reinforced concrete structures is closely related to Moisture state in cement-based materials. Therefore, it is crucial to develop Moisture models that can accurately predict Moisture state in the materials. However, many studies reported anomalous Moisture Transport in cement-based materials that cannot be well simulated by the conventional models. Several reasons have been investigated in the literature, such as the complex pore structure, chemical reactions with water, dimensional changes of the tested specimen, etc. Nevertheless, only a few models are able to capture the anomaly of Moisture Transport. This study viewed the main Moisture Transport coefficient-permeability-as a kinetic variable that depends on both the degree of Moisture saturation and the contact time. The time-dependence was formulated by the decay (for drying) or growth (for wetting) functions. The saturation-dependence was calculated by the van Genuchten-Mualem (VGM) model. These functions were then implemented into a Moisture Transport model that was developed in previous studies. The proposed model was validated by experimental data and showed a good agreement for cement pastes that were dried or wetted in the hygroscopic range. Numerical simulation results were also compared with the simplified solutions to a fractional derivative model (FDM) of anomalous diffusion and the empirical Weibull function. We found that the solutions to the FDM cannot provide appropriate results. Weibull function performs as well as the proposed model, but the empirical function lacks physical meanings.
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determination of water permeability for a Moisture Transport model with minimized batch effect
Construction and Building Materials, 2018Co-Authors: Zhidong Zhang, George W SchererAbstract:Abstract Values of water permeability for cementitious materials reported in the literature show a large scatter. This is partially attributed to the fact that materials used in these studies are different. To eliminate the effects of cements, specimen preparation, curing conditions and other batch effects, this study employs a single cement paste to prepare all specimens for a variety of permeability determination methods, such as beam-bending, sorptivity, Katz–Thompson and Kozeny-Carman equations. Permeabilities determined by these methods are then used in a Moisture Transport model. Compared with the measured mass loss curves, we found that permeability determined by the beam-bending method is more suitable for the Moisture Transport model than the other methods. The difference results from the use of a saturated specimen in the beam-bending method, while specimens in the other methods are dried (or rewetted). As already shown in the literature, the microstructure of the dried or rewetted specimens is altered and different to the original microstructure of the water saturated specimens. In addition, we found that drying tests for the inverse analysis method must be done at high RHs (63% in this study) to reduce the effect of vapor diffusion on the determination of water permeability.
Marie C Mcgraw - One of the best experts on this subject based on the ideXlab platform.
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changes in arctic Moisture Transport over the north pacific associated with sea ice loss
Climate Dynamics, 2020Co-Authors: Marie C Mcgraw, Cory Baggett, Chengji Liu, Bryan D MundhenkAbstract:Recent work has emphasized the important role of midlatitude Moisture fluxes in enhancing Arctic warming and sea ice loss. Conversely, less attention has been paid to the impact of Arctic warming and sea ice loss on midlatitude Moisture fluxes. Analysis of an atmosphere-only general circulation model indicates that sea ice loss promotes changes in the large-scale midlatitude atmospheric circulation that have a substantial impact on Moisture Transport into and out of the Arctic. While poleward Moisture Transport into the Arctic does increase in a reduced sea ice climate, the increase in equatorward Moisture Transport out of the Arctic is larger, particularly in boreal winter over the North Pacific. A decomposition of the meridional Moisture Transport reveals that this increase in equatorward Moisture Transport is driven, at least in part, by changes in the background circulation. Specifically, sea ice loss drives a series of large-scale tropospheric circulation changes, including an increase in cyclonic Rossby wave breaking over the North Pacific that results in a preferential enhancement of equatorward Moisture Transport out of the Arctic in the days following the peak of the Rossby wave breaking event.