Modeling Tortuosity in Thin Fibrous Porous Media Using Computational Fluid Dynamics

Vallabh, Rahul

doi:10.1615/jpormedia.v14.i9.40

Cited by 17 publications

(12 citation statements)

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“…For that reason, the properties of sample IV (q ef , e ds , and s) were defined based on a weighted average of the properties of the materials in higher proportion (wool and cotton; Table 3). The several textiles parameters shown in Table 2 are in good agreement with the results reported by other authors [1,9,12,[26][27][28].…”

Section: Resultssupporting

confidence: 90%

“…Furthermore, since the transport of water through the porous network of a textile is dependent on its complexity, an increasing sinuousness or tortuosity implies slower transport. Expressions relating textile tortuosity and porosity are reported in the literature [11,12], however, they refer to specific textiles and were developed neglecting the presence of water accumulated in the fibres. Given the mentioned effect of water retention on textile structure (and hence on its transport properties), there is a clear need for a new method to determine textile tortuosity taking into account the water retained in fibres.…”

Section: Introductionmentioning

confidence: 99%

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On the determination of parameters required for numerical studies of heat and mass transfer through textiles – Methodologies and experimental procedures

Neves

Campos

Mayor

2015

International Journal of Heat and Mass Transfer

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a b s t r a c tThe aim of this study was to develop methodologies and experimental procedures to determine textile parameters required in numerical approaches of heat and mass transfer through textiles. Privileging techniques usually available in textile/clothing laboratories, experimental approaches were defined that allow to estimate all required parameters, while taking into consideration water presence in the fibres and hence the effect of fibres hygroscopic properties. Numerical models usually require values of textile thickness, fibre fraction, and tortuosity, as well as knowledge of the boundary conditions, e.g. convective heat and mass transfer coefficients. To calculate these parameters, thickness, weight, and volume of textile samples were measured, whereas convective and textile evaporative resistances were determined by indirect measurements. Results were obtained for four distinct textile samples (made of wool, cotton, and a mixture of materials), of different hydrophilic nature. When the obtained parameters were incorporated in a numerical model and numerical predictions of temperature and humidity were compared with experimental data obtained during measurements of fabric evaporative resistance, it was shown that the predictions were accurate; this lends support to the developed methods and approaches.Since an uncertainty in the measured parameters can compromise the accuracy of numerical predictions, a sensitivity analysis was conducted to study the influence of deviations in the model input parameters and of assumptions regarding water presence in the fibres, on the predictions of heat and mass transfer rates. The results show that a deviation in textile weight and thickness as well as the assumption of no water retained in fibres during their characterisation, have a significant effect on the predicted heat transfer and water distribution over time. Moreover, a deviation in the total evaporative resistance, convective evaporative resistance, and sorption rate factor has great influence on the heat flux obtained in the initial period of testing.

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Section: Resultssupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

On the determination of parameters required for numerical studies of heat and mass transfer through textiles – Methodologies and experimental procedures

Neves

Campos

Mayor

2015

International Journal of Heat and Mass Transfer

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“…The high resistance to xylem embolism observed in both seedling and adult laurels is consistent with the fact that this species, like other Mediterranean species, displays thicker intervessel pit membranes compared to species from mesic temperate forests (Jansen et al 2009). Thick intervessel pit membranes are indeed a critical determinant of embolism resistance in the xylem of angiosperms (Li et al 2016), probably thanks to their longer pore pathways for air-seeding, while pit membrane thickness will also increase tortuosity (defined as the ratio of the length of a flow path through pit membrane to the width of the pit membrane; Vallabh et al 2011). Our findings may explain why laurel, contrary to other Tethyan Fig.…”

Section: Discussionmentioning

confidence: 92%

An inconvenient truth about xylem resistance to embolism in the model species for refilling Laurus nobilis L.

Lamarque

Corso

Torres‐Ruiz

et al. 2018

Annals of Forest Science

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& Key message Direct, non-invasive X-ray microtomography and optical technique observations applied in stems and leaves of intact seedlings revealed that laurel is highly resistant to drought-induced xylem embolism. Contrary to what has been brought forward, daily cycles of embolism formation and refilling are unlikely to occur in this species and to explain how it copes with drought. & Context There has been considerable controversy regarding xylem embolism resistance for long-vesselled angiosperm species and particularly for the model species for refilling (Laurus nobilis L.). & Aims The purpose of this study was to resolve the hydraulic properties of this species by documenting vulnerability curves of different organs in intact plants. & Methods Here, we applied a direct, non-invasive method to visualize xylem embolism in stems and leaves of intact laurel seedlings up to 2-m tall using X-ray microtomography (microCT) observations and the optical vulnerability technique. These approaches were coupled with complementary centrifugation measurements performed on 1-m long branches sampled from adult trees and compared with additional microCT analyses carried out on 80-cm cut branches. & Results Direct observations of embolism spread during desiccation of intact laurels revealed that 50% loss of xylem conductivity (Ψ 50) was reached at − 7.9 ± 0.5 and − 8.4 ± 0.3 MPa in stems and leaves, respectively, while the minimum xylem water potentials measured in the field were − 4.2 MPa during a moderate drought season. Those findings reveal that embolism formation is not routine in Laurus nobilis contrary to what has been previously reported. These Ψ 50 values were close to those based on the flow-centrifuge technique (− 9.2 ± 0.2 MPa), but at odds with microCT observations of cut branches (− 4.0 ± 0.5 MPa).

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“…Since high porosity values between 80% and 95% are characteristic of non-woven porous media composed of fibrils (Shou et al, 2011;Vallabh, Banks-Lee, & Seyam, 2010;Vallabh, Ducoste, Seyam, & Banks-Lee, 2011), it is not surprising that pit membranes possess a considerably high porosity, with a mean porosity of 81% for fresh pit membranes based on our shrinkage model. This means that pore spaces represent a very high proportion of the pit membrane volume.…”

Section: The Functional Significance Of Pit Membrane Porosity Geodmentioning

confidence: 88%

High porosity with tiny pore constrictions and unbending pathways characterize the 3D structure of intervessel pit membranes in angiosperm xylem

Zhang

Carmesin

Kaack

et al. 2019

Plant Cell & Environment

108

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Pit membranes between xylem vessels play a major role in angiosperm water transport. Yet, their three‐dimensional (3D) structure as fibrous porous media remains unknown, largely due to technical challenges and sample preparation artefacts. Here, we applied a modelling approach based on thickness measurements of fresh and fully shrunken pit membranes of seven species. Pore constrictions were also investigated visually by perfusing fresh material with colloidal gold particles of known sizes. Based on a shrinkage model, fresh pit membranes showed tiny pore constrictions of ca. 20 nm, but a very high porosity (i.e. pore volume fraction) of on average 0.81. Perfusion experiments showed similar pore constrictions in fresh samples, well below 50 nm based on transmission electron microscopy. Drying caused a 50% shrinkage of pit membranes, resulting in much smaller pore constrictions. These findings suggest that pit membranes represent a mesoporous medium, with the pore space characterized by multiple constrictions. Constrictions are much smaller than previously assumed, but the pore volume is large and highly interconnected. Pores do not form highly tortuous, bent, or zigzagging pathways. These insights provide a novel view on pit membranes, which is essential to develop a mechanistic, 3D understanding of air‐seeding through this porous medium.

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Modeling Tortuosity in Thin Fibrous Porous Media Using Computational Fluid Dynamics

Cited by 17 publications

References 0 publications

On the determination of parameters required for numerical studies of heat and mass transfer through textiles – Methodologies and experimental procedures

On the determination of parameters required for numerical studies of heat and mass transfer through textiles – Methodologies and experimental procedures

An inconvenient truth about xylem resistance to embolism in the model species for refilling Laurus nobilis L.

High porosity with tiny pore constrictions and unbending pathways characterize the 3D structure of intervessel pit membranes in angiosperm xylem

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