The Role of Short Chain Fatty Acids in Irritable Bowel Syndrome

Wenxi Jian,Jiali Wu,Shefeng Zhu,Linying Xin,Chaohui Yu,Zhe Shen 대한소화기 기능성질환∙운동학회 2022 Journal of Neurogastroenterology and Motility (JNM Vol.28 No.4

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder that is characterized by abdominal pain and disordered bowel habits. The etiology of IBS is multifactorial, including abnormal gut-brain interactions, visceral hypersensitivity, altered colon motility, and psychological factors. Recent studies have shown that the intestinal microbiota and its metabolites short chain fatty acids (SCFAs) may be involved in the pathogenesis of IBS. SCFAs play an important role in the pathophysiology of IBS. We discuss the underlying mechanisms of action of SCFAs in intestinal inflammation and immunity, intestinal barrier integrity, motility, and the microbiota-gut-brain axis. Limited to previous studies, further studies are required to investigate the mechanisms of action of SCFAs in IBS and provide more precise therapeutic strategies for IBS.

Experimental study on the Influence of Heating Surface Inclination Angle on Heat Transfer and CHF performance for Pool Boiling

Chenglong Wang,Panxiao Li,Dalin Zhang,Wenxi Tian,Suizheng Qiu,G.H. Su,Jian Deng 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.1

Pool boiling heat transfer is widely applied in nuclear engineering fields. The influence of heating surface orientation on the pool boiling heat transfer has received extensive attention. In this study, the heating surface with different roughness was adopted to conduct pool boiling experiments at different inclination angles. Based on the boiling curves and bubble images, the effects of inclination angle on the pool boiling heat transfer and critical heat flux were analyzed. When the inclination angle was bigger than 90°, the bubble size increased with the increase of inclination angle. Both the bubble departure frequency and critical heat flux decreased as the inclination angle increased. The existing theoretical models about pool boiling heat transfer and critical heat flux were compared. From the perspective of bubble agitation model and Hot/Dry spot model, the experimental phenomena could be explained reasonably. The enlargement of bubble not only could enhance the agitation of nearby liquid but also would cause the bubble to stay longer on the heating surface. Consequently, the effect of inclination angle on the pool boiling heat transfer was not conspicuous. With the increase of inclination angle, the rewetting of heating surface became much more difficult. It has negative effect on the critical heat flux. This work provides experimental data basis for heat transfer and CHF performance of pool boiling.

A dryout mechanism model for rectangular narrow channels at high pressure conditions

Gongle Song,Yu Liang,Rulei Sun,Dalin Zhang,Jian Deng,G.H. Su,Wenxi Tian,Suizheng Qiu 한국원자력학회 2020 Nuclear Engineering and Technology Vol.52 No.10

Adryoutmechanism model for rectangular narrow channels at high pressure conditions is developed byassuming that the KelvineHelmholtz instability triggered the occurrence ofdryout. This model combinesthe advantages of theoretical analysis and empirical correlation. The unknown coefficients in thetheoretical derivation are supported by the experimental data. Meanwhile, the decisive restriction of theexperimental conditions on the applicability of the empirical correlation is avoided. The expression ofvapor phase velocity at the time ofdryoutis derived, and the empirical correlation of liquidfilm thicknessis introduced. Since the CHF value obtained from the liquidfilm thickness should be the same as thevalue obtained from the KelvineHelmholtz critical stability under the same condition, the convergentCHF value is obtained by iteratively calculating. Comparing with the experimental data under thepressure of 6.89e13.79 MPa, the average error of the model is 15.4% with the 95% confidence interval[-20.5%, 10.4%]. And the pressure has a decisive influence on the prediction accuracy of this model.Compared with the existingdryoutcode, the calculation speed of this model is faster, and the calculationaccuracy is improved. This model, with great portability, could be applied to different objects andworking conditions by changing the expression of the vapor phase velocity when the dryout phenom-enon is triggered and the calculation formula of the liquidfilm.©2020 Korean Nuclear Society, Published by Elsevier Korea LLC. This is an open access article under theCC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).1. IntroductionThe plate type fuel element has the advantages of compactstructure, high power per unit volume, low central temperature,high burnup, low heat storage and good safety. It is an advanceddesign structure of the new integrated pressurized water reactorcore. The coolantflow channel of the plate type fuel element is atypical rectangular narrow channel, which has compact structure,small temperature difference of heat transfer, simple surface pro-cessing, smoothness of heat transfer surface. Besides, it is not easyto produce impurities and pollute the heat transfer surface todeteriorate heat transfer with the high-speedfluid. Due to theabove characteristics, the rectangular narrow channel is widelyused in thefields of chemical, nuclear energy, electronic devicecooling, refrigeration and others. The research on the thermal hy-draulic properties of rectangular narrow channels has become a hotresearch topic [1,2].Critical heatflux (CHF) is the most important thermal hydrauliclimit parameter to ensure reactor core safety. When the criticalboiling occurs, theflow boiling mechanism of the coolant changes,the heat transfer coefficient decreases, and the heat transfer on thesurface of the nuclear fuel element deteriorates. In severe cases, thefuel element can be burned and even cause the radioactive leakage.It is generally believed that in region of the annularflow, CHF iscaused by liquidfilm drying, and the CHF model establishedaccordingly is called dryout model. Due to the wide range of quality(about 0.1e1.0) corresponding to the annularflow pattern, dryout isof great significance for the safety analysis and transient process ofboiling water reactors and pressurized water reactors. In recentyears, the dryout model has received much attention [3,4].In rectangular narrow channels, bubble growth is limited, and*Corresponding author.**Corresponding author.E-mail addresses:dlzhang@mail.xjtu.edu.cn(D. Zhang),dengjian_npic@163.com(J. Deng).Contents lists available atScienceDirectNuclear Engineering and Technologyjournal homepage:www.elsevier.com/locate/nethttps://doi.org/10.1016/j.net.2020.03.0181738-5733/©2020 Korean Nuclear Society, Published by Elsevier Korea LLC. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Nuclear Engineering and Technology 52...

Experimental study on vertically upward steam-water two-phase flow patterns in narrow rectangular channel

Zhou, Jiancheng,Ye, Tianzhou,Zhang, Dalin,Song, Gongle,Sun, Rulei,Deng, Jian,Tian, Wenxi,Su, G.H.,Qiu, Suizheng Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.1

Experiments of vertically upward steam-water two-phase flow have been carried out in single-side heated narrow rectangular channel with a gap of 3 mm. Flow patterns were identified and classified through visualization directly. Slug flow was only observed at 0.2 MPa but replaced by block-bubble flow at 1.0 MPa. Flow pattern maps at the pressure of 0.2 MPa and 1.0 MPa were plotted and the difference was analyzed. The experimental data has been compared with other flow pattern maps and transition criteria. The results show reasonable agreement with Hosler's, while a wide discrepancy is observed when compared with air-water two-phase experimental data. Current criteria developed based on air-water experiments poorly predict bubble-slug flow transition due to the different formation and growth of bubbles. This work is significant for researches on heat transfer, bubble dynamics and flow instability.