Cross-scale modelling of transpiration from stomata via the leaf boundary layer

Background and Aims Leaf transpiration is a key parameter for understanding land surface-climate interactions, plant stress and plant structure-function relationships. Transpiration takes place at the microscale level, namely via stomata that are distributed discretely over the leaf surface with a very low surface coverage (approx. 0·2-5 %). The present study aims to shed more light on the dependency of the leaf boundary-layer conductance (BLC) on stomatal surface coverage and air speed. Methods An innovative three-dimensional cross-scale modelling approach was applied to investigate convective mass transport from leaves, using computational fluid dynamics. The gap between stomatal and leaf scale was bridged by including all these scales in the same computational model (10−5-10−1 m), which implies explicitly modelling individual stomata. Key Results BLC was strongly dependent on stomatal surface coverage and air speed. Leaf BLC at low surface coverage ratios (CR), typical for stomata, was still relatively high, compared with BLC of a fully wet leaf (hypothetical CR of 100 %). Nevertheless, these conventional BLCs (CR of 100 %), as obtained from experiments or simulations on leaf models, were found to overpredict the convective exchange. In addition, small variations in stomatal CR were found to result in large variations in BLCs. Furthermore, stomata of a certain size exhibited a higher mass transfer rate at lower CRs. Conclusions The proposed cross-scale modelling approach allows us to increase our understanding of transpiration at the sub-leaf level as well as the boundary-layer microclimate in a way currently not feasible experimentally. The influence of stomatal size, aperture and surface density, and also flow-field parameters can be studied using the model, and prospects for further improvement of the model are presented. An important conclusion of the study is that existing measures of conductances (e.g. from artificial leaves) can be significantly erroneous because they do not account for microscopic stomata, but instead assume a uniform distribution of evaporation such as found for a fully-wet leaf. The model output can be used to correct or upgrade existing BLCs or to feed into higher-scale models, for example within a multiscale framewor

An individualized digital twin of a patient for transdermal fentanyl therapy for chronic pain management.

Fentanyl transdermal therapy is a suitable treatment for moderate-to-severe cancer-related pain. The inter-individual variability of the patients leads to different therapy responses. This study aims to determine the effect of physiological features on the achieved pain relief. Therefore, a set of virtual patients was developed by using Markov chain Monte Carlo (MCMC) based on actual patient data. The members of this virtual population differ by age, weight, gender, and height. Tailored digital twins were developed using these correlated, individualized parameters to propose a personalized therapy for each patient. It was shown that patients of different ages, weights, and gender have significantly different fentanyl blood uptake, plasma fentanyl concentration, pain relief, and ventilation rate. In the digital twins, we included the virtual patients' response to the treatment, namely, pain relief. Therefore, the digital twin was able to adjust the therapy in silico to have more efficient pain relief. By implementing digital-twin-assisted therapy, the average pain intensity decreased by 16% compared to conventional therapy. The median time without pain increased by 23 h over 72 h. Therefore, the digital twin can be successfully used in individual control of transdermal therapy to reach higher pain relief and maintain steady pain relief. (Created with BioRender.com)

Integrated vegetation model for studying the cooling potential of trees in urban street canyons

Vegetation in cities provides natural cooling of the climate and is therefore increasingly integrated as an essential part of Urban Heat Island (UHI) mitigation strategies. In the present study, the influence of trees on the local climate in a street canyon is studied using an integrated vegetation model in OpenFOAM. Vegetation is modeled as porous medium providing the necessary source terms for the heat, mass and momentum fluxes. Additionally, a radiation model is developed to model the short-wave and long-wave radiative heat flux exchanges between vegetation and the surroundings. The study investigates the influence of transpirative and shaded cooling due to vegetation on the pedestrian comfort inside a street canyon. The study shows that both shading and transpiration have a direct positive influence on the temperatures measured in the street canyon. Moreover, the cooling due to shading is seen to be larger than the transpirative cooling, especially under the tree

Electrohydrodynamic drying versus conventional drying methods: A comparison of key performance indicators

Preserving fruits and vegetables by drying is a traditional yet effective way of reducing food waste. Existing drying methods are either energy-intensive or lead to a significant reduction in product quality. Electrohydrodynamic (EHD) drying is an energy-efficient low-temperature drying method that presents an opportunity to comply with the current challenges of existing drying methods. However, despite its promising characteristics, EHD drying is yet to be accepted by industry and farmers. The adoption of EHD drying is hindered due to different reasons, such as uncertainties surrounding its scalability, quality of dried product, cost of operation, and sustainability compared to conventional drying methods. To address these concerns, this study quantifies and benchmarks the Key Performance Indicators (KPIs) of EHD drying compared to the standard conventional drying methods based on lab-scale experiments. These drying methods include hot-air, freeze, microwave, and solar drying. The results show that drying food using EHD is at least 1.6, 20, and 70 times more energy-efficient than the microwave, freeze, and hot-air, respectively. Similar results could be observed for exergy efficiency. EHD drying has superior product quality compared to other drying methods. For instance, it could retain 62% higher total phenolic content with 21% less color degradation than freeze-drying. Although microwave drying resulted in significantly higher drying kinetics than other techniques, EHD performed better than solar and freeze-drying but was comparable with hot-air drying. EHD drying also shows promising results in economic performance assessment. It is the cheapest drying method after solar drying and has the highest estimated net present value (NPV) after hot-air drying. Overall, compared to the currently used drying methods for small to medium-scale drying, EHD was found to be a more exergy and energy-efficient, cost-effective, and sustainable alternative that can provide higher-quality dried products. However, its drying kinetics should be improved for industrial applications

Nondestructive measurement of fruit and vegetable quality

We review nondestructive techniques for measuring internal and external quality attributes of fruit and vegetables, such as color, size and shape, flavor, texture, and absence of defects. The different techniques are organized according to their physical measurement principle. We first describe each technique and then list some examples. As many of these techniques rely on mathematical models and particular data processing methods, we discuss these where needed. We pay particular attention to techniques that can be implemented online in grading lines

Advanced computational modelling for drying processes - a review

Drying is one of the most complex and energy-consuming chemical unit operations. R&D efforts in drying technology have skyrocketed in the past decades, as new drivers emerged in this industry next to procuring prime product quality and high throughput, namely reduction of energy consumption and carbon footprint as well as improving food safety and security. Solutions are sought in optimising existing technologies or developing new ones which increase energy and resource efficiency, use renewable energy, recuperate waste heat and reduce product loss, thus also the embodied energy therein. Novel tools are required to push such technological innovations and their subsequent implementation. Particularly computer-aided drying process engineering has a large potential to develop next-generation drying technology, including more energy-smart and environmentally-friendly products and dryers systems. This review paper deals with rapidly emerging advanced computational methods for modelling dehydration of porous materials, particularly for foods. Drying is approached as a combined multiphysics, multiscale and multiphase problem. These advanced methods include computational fluid dynamics, several multiphysics modelling methods (e.g. conjugate modelling), multiscale modelling and modelling of material properties and the associated propagation of material property variability. Apart from the current challenges for each of these, future perspectives should be directed towards material property determination, model validation, more complete multiphysics models and more energy-oriented and integrated "nexus" modelling of the dehydration process. Development of more user-friendly, specialised software is paramount to bridge the current gap between modelling in research and industry by making it more attractive. These advanced computational methods show promising perspectives to aid developing next-generation sustainable and green drying technology, tailored to the new requirements for the future society, and are expected to play an increasingly important role in drying technology R&D. © 2014 Elsevier Ltd.publisher: Elsevier articletitle: Advanced computational modelling for drying processes – A review journaltitle: Applied Energy articlelink: http://dx.doi.org/10.1016/j.apenergy.2014.06.027 content_type: article copyright: Copyright © 2014 Elsevier Ltd. All rights reserved.status: publishe

A novel plant cell division algorithm based on ellipse/ellipsoid fitting

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Convective drying of fruit: Role and impact of moisture transport properties in modelling

© 2016 Elsevier Ltd 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.publisher: Elsevier articletitle: Convective drying of fruit: Role and impact of moisture transport properties in modelling journaltitle: Journal of Food Engineering articlelink: http://dx.doi.org/10.1016/j.jfoodeng.2016.08.013 content_type: article copyright: © 2016 Elsevier Ltd. All rights reserved.status: publishe

Moisture barriers to control drying of fresh-cut fruit: Quantifying their impact by modeling

© 2016 Institution of Chemical Engineers Moisture barriers are applied as functional interfaces between food products and their environment to control or limit the moisture exchange, a typical example being edible films. Hygrothermal continuum modeling is used to obtain insight on the impact of moisture barriers on the fruit dehydration process. The effects of moisture permeability and thickness of the barrier on the drying process are quantified, by looking into the drying kinetics and the internal moisture transport. Barriers are found to induce a smaller drying rate and a higher product temperature, but lead to more spatially-uniform drying within the sample. The sensitivity of the total drying time to the barrier's permeability is also found to be dependent on the permeability of the fruit tissue itself. The presence of a barrier significantly reduced the sensitivity of the drying time to an increase in air speed, thus convective transfer coefficients. Such hygrothermal simulations are a promising way to tailor moisture barriers to a specific application, in terms of optimal barrier permeability and thickness, to obtain the required drying characteristics.publisher: Elsevier articletitle: Moisture barriers to control drying of fresh-cut fruit: Quantifying their impact by modeling journaltitle: Food and Bioproducts Processing articlelink: http://dx.doi.org/10.1016/j.fbp.2016.10.016 content_type: article copyright: © 2016 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.status: publishe