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The Role of Circular Folds in Mixing Intensification in The The role of circular folds in mixing intensification in the small intestine: A numerical study Jinping Zha, Siyu Zou, Jianyu Hao, Xinjuan Liu, Guillaume Delaplace, Romain Jeantet, Didier Dupont, Peng Wu, Xiao Dong Chen, Jie Xiao To cite this version: Jinping Zha, Siyu Zou, Jianyu Hao, Xinjuan Liu, Guillaume Delaplace, et al.. The role of circular folds in mixing intensification in the small intestine: A numerical study. Chemical Engineering Science, Elsevier, 2021, 229, pp.116079. 10.1016/j.ces.2020.116079. hal-02975862 HAL Id: hal-02975862 https://hal.inrae.fr/hal-02975862 Submitted on 23 Oct 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Distributed under a Creative Commons Attribution - NonCommercial - NoDerivatives| 4.0 International License Chemical Engineering Science 229 (2021) 116079 Contents lists available at ScienceDirect Chemical Engineering Science journal homepage: www.elsevier.com/locate/ces The role of circular folds in mixing intensification in the small intestine: A numerical study Jinping Zha a, Siyu Zou a, Jianyu Hao b, Xinjuan Liu b, Guillaume Delaplace c, Romain Jeantet d, ⇑ Didier Dupont d, Peng Wu a, Xiao Dong Chen a, Jie Xiao a, a School of Chemical and Environmental Engineering, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou, Jiangsu Province 215123, China b Department of Gastroenterology, Beijing Chaoyang Hospital, Capital Medical University, Chaoyang District, Beijing 100024, China c UMET – Unité Matériaux et Transformations, UMR 8207 (Univ. Lille, CNRS, INRAE, Centrale Lille), 59000 Lille, France d STLO, INRAE, Institut Agro, 35042 Rennes, France highlights graphical abstract Numerical simulation of mixing in a human duodenum featuring circular folds. Tracking evolving concentration and mixing level distributions under segmentation. Mixing intensification by prominent vortices with high velocity and shear rate. Promoting mixing by tall and slim folds with enlarged segmentation amplitude, frequency and wavelength. article info abstract Article history: The inner wall of the intestine has multiscale structures whose roles, beyond the increase of surface area Received 30 April 2020 for absorption, are yet to be discovered. In this study, the mixing process in a human duodenum with cir- Received in revised form 2 August 2020 cular folds, driven by segmentation contraction, was simulated using a multiphysics model, making it Accepted 23 August 2020 possible to track the evolution of mixing level distributions and enabling quantitative evaluation of Available online 29 August 2020 the structural role of folds in mixing intensification. It was found that, in a laminar flow regime, circular folds intensify both radial and axial mixing by synergistically offering prominent and long-lasting swirls/ Keywords: vortices, high fluid velocity and high shear rates. Tall and slim folds with enlarged segmentation ampli- Small intestine tude, frequency and wavelength can enhance mixing. The maximum enhancement ratio can reach 6.18 Circular folds/Plicae circularis Segmentation under the investigated conditions. These findings will also be valuable for the improved design of biomi- Mixing metic soft-elastic reactors for the chemical and pharmaceutical industries. Process intensification Ó 2020 Elsevier Ltd. All rights reserved. Soft elastic reactor (SER) ⇑ Corresponding author. E-mail address: [email protected] (J. Xiao). https://doi.org/10.1016/j.ces.2020.116079 0009-2509/Ó 2020 Elsevier Ltd. All rights reserved. 2 J. Zha et al. / Chemical Engineering Science 229 (2021) 116079 Nomenclature 2z0 Distance between two adjacent folds (m) Symbols a Distance from pylorus to the 1st fold (m) Greek letters b The contraction starts away from the pylorus (m) a Enhancement ratio (-) c Concentration (mol/m3) C Function of time (–) 3 c0 Initial concentration (mol/m ) d Depth (m) D Diffusion coefficient (m2/s) e* Ratio of amplitude to radius (%) f Frequency (cycles/min) k Wavelength (m) hf Height of circular folds (m) l Fluid viscosity (PaÁs) I Unit tensor (–) n Ratio of height to width of a fold (–) L Length of the duodenum (m) q Density (kg/m3) M Molecular weight (g/mol) v Mixing level (%) n The index of the circular folds (–) x Distribution density of circular folds (folds/m) p Fluid pressure (Pa) P Function of position (m) Superscripts r, z, h Cylindrical coordinates (m, m, °) I System 1 (with folds) I II r ,r r-direction position of lumen wall of Systems 1 and 2, II System 2 (without folds) respectively (m) r Radius of circular folds (m) f Subscripts R Radius (m) c Characteristic R0 Radius of System 1 (m) 0 f Circular folds R Radius of System 2 (m) 0 g Glucose t Time (s) i Index of species T Cycle (s) j Index of mesh element u Fluid velocity (m/s) m Mixture V Volume (m3) v w Water g Volume ratio of glucose (–) 1 The ideally mixed state wf Width of circular folds (m) Y Mass fraction (–) 1. Introduction It has been widely accepted that this multiscale structure can drastically increase the absorption area (Martini et al., 2012). Nev- Food provides the body with essential nutrients and energy so ertheless, whether these structures can contribute to digestion and that normal human physiological activities can be maintained. Effi- absorption, other than to increasing the area, has not yet been rig- cient digestion and absorption processes are critical for human orously investigated. From the chemical engineering perspective, health. After being ingested, food is further digested by the stom- nutrient molecules need to overcome mass transfer resistance in ach and then enters the small intestine where the chyme is mixed the lumen (i.e., cavity within the tube) before their arrival at the and reacts with intestinal fluids that include enzymes, bile and villi surface where the absorption takes place. The intestinal wall pancreatic juices. Carbohydrates, proteins and fats are converted movement drives fluid convection and mixing in the lumen, effec- into absorbable nutrient molecules in the intestine. Driven by tively reducing mass transfer resistance and, hence, positively con- intestinal motility, the nutrients are then transferred to the wall tributing to digestion and absorption. It will be interesting and of the intestine and eventually absorbed (Hall, 2016; Marieb and meaningful to investigate whether the structure of the intestinal Keller, 2018). inner wall can lead to mixing intensification. If the answer is yes, It should be noted that both digestion and absorption in then how much intensification can be achieved? This study was humans essentially take place in the small intestine. The small motivated by this scientific question, with the aim of quantita- intestine has been a focus of research for many years because of tively revealing the role of circular folds in mixing intensification. its importance in the digestive process (Bayliss and Starling, Many experimental and simulation efforts have been devoted to 1899). However, our understanding of the digestion and absorp- the study of the small intestine. Intestinal motility causes chyme to tion process in this organ is far from complete due to the high com- mix with intestinal secretions, and the measurement of motion plexity of the system. In addition to complex motility, the structure patterns began as of 1899 and perhaps even earlier. Researchers of the intestinal wall demonstrates hirarchical and multiscale fea- at the time used a graphic method and discovered a number of tures (Marieb and Keller, 2018; Martini et al., 2012). The duode- intestinal movements (Bayliss and Starling, 1899). The two major num, for example, is a 25-cm-long cylindrical tube with a ones are segmentation movement (i.e., mixing contraction) and diameter of 4 cm (Martini et al., 2012). Plicae circularis (i.e., circu- peristalsis (i.e., propulsive contraction). The 3rd type is pendular lar folds) – submucosa protrudes with a maximum height of about movement (i.e., longitudinal contraction) (Lentle and Janssen, 8 mm – are distributed along the inner wall of the tube (Standring, 2011), which is not well-known. The segmentation, as opposed 2008). The surface of the circular folds is covered with finger-like to peristalsis, was observed to be the main form of movement dur- bumps, referred to as villi. The height of a villus is only around ing the post-prandial period since residence time values should be 1 mm. In addition, micrometer-scale microvilli form a brush border longer than the time needed to achieve acceptable mixing on the villi surface. The microvilli secrete specific enzymes to (Husebye, 1999; Lentle and de Loubens, 2015; Sarna et al., 1983). enable the digestion of carbohydrates and proteins (Hall, 2016). The real-time motion of the intestinal tract can be illustrated using J. Zha et al. / Chemical Engineering Science 229 (2021) 116079 3 spatiotemporal maps (Lentle and de Loubens, 2015). Tremendous CFD model. The success of this work verified that it’s feasible to efforts have been made as well to characterize the physical and model the intestinal wall movement by the moving mesh method. chemical properties of the gastrointestinal contents and intestinal These preliminary efforts demonstrate the role of the intestinal structures. Extensive measurements have been made of the length inner surface structure in promoting mass transfer in the lumen. and width of the intestine, the viscosity of the chyme, the ampli- However, compared to the rat system, the human duodenum is tude and frequency of the contraction wave, etc. These valuable much larger and features large circular folds in addition to small data provide a solid base for the further study of the gastrointesti- villi and microvilli.
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