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During gastrointestinal endoscopy, endoscopy is pushed into human digestive tract with the aid of outside force, which may cause a series of complications due to repeatedly inserting, rotating, pushing and retrieving operation. These are serious friction damage problems that few studies have focused on. In this paper, the friction behavior between the front-tip of gastroscopy and esophageal wall tissue during endoscopy was studied by using a UMT-II Micro-Tribometer. Fresh porcine esophagus of different anatomical sites (thoracic, abdominal and cervical esophagus) and layers in vitro was chosen as the tissue samples. The normal force was from 0.2 to 1.0 N, the sliding speed was from 0.1 to 0.9 mm/s, and the unidirectional sliding displacement was 22 mm to simulate the endoscopy manipulation. Results showed that the typical “stick-slip” phenomena appeared in the process of the front-tip sliding on the esophageal internal surface, which was related to the alternating deformation, recovery as well as the energy dissipation of esophageal tissue. The friction coefficient decreased with the increasing normal load and increased with the increasing sliding speed. Since the physiological structure and mechanical property of esophagus were diverse in different anatomical sites and layers, there would be a lower friction coefficient in the thoracic esophagus compared with the cervical and abdominal esophagus. Besides, the friction coefficient in intact esophagus was larger than that in layered esophagus. The results can provide the basic data for safety operation and damage control during gastrointestinal endoscopy. [ABSTRACT FROM AUTHOR]

Abstract: Non-premixed turbulent reacting flow in a methane-fuelled coaxial jet combustor has been studied numerically employing Reynolds Averaged Navier–Stokes (RANS) models. A local extinction approach for treating chemical reaction kinetics within the eddy dissipation concept (EDC) has been examined. It applies a database of pre-calculated chemical time scales, which contains the influence of chemical kinetics that is otherwise time-consuming to calculate. Simulations were carried out using standard k-epsilon, RNG k-epsilon and k-Omega SST turbulence models by open-source CFD-toolbox OpenFOAM. The results were compared to available numerical results and experimental data for predicting velocity, and temperature fields. All simulations were conducted with a reasonable number of meshes to demonstrate the accuracy of different turbulent RANS models in OpenFOAM solver which has a wide range of engineering applications in such type of flows. [Copyright &y& Elsevier]