Investigation On Slip Behavior Of Viscous Fluid In Simulated Oral Environment

With the aging of population and various diseases is going to be a major concern in social,dysphagia has become a common disease that affects the quality of life of patients.And dysphagia will directly affect the patient’s ability to swallow,so the viscous fluid which is easy to swallow can provide a better choice for them.Therefore,carrying out investigation on slip behavior of viscous fluids in simulated oral environment will provide theoretical and technical basis for the development of functional food for patients with dysphagia.Firstly,the squeeze model and Reynolds equation under the tongue and upper palate micro gap were established,and the flow rate change was obtained by numerical method;By using the DHR-2 rheometer,non-Newtonian fluid’s viscosity which was changed with shear rate was studied,then the influencing factors of fluid flow were explored.The results showed that the reciprocal of the square of Newtonian fluid flow was linearly related to the load and viscosity ratio and time.The prepared non-Newtonian fluid was approximately a power-law fluid,and its viscosity was increased with the increase of fat and protein content,however,the rate of nonNewtonian fluid flow was first higher then lower than the equivalent Newtonian fluid,by changing the content of fat and protein in the diet could reduce the risk of choking during meals.Secondly,the slip model under the micro gap of the tongue and upper palate was established.According to the severity of the patient’s dysphagia,the working condition parameters corresponding to the grade of the dysphagia were classified.By using finite element analysis,the change of fluid pressure distribution,friction coefficient and their influencing factors were studied.The results showed that the pressure of the fluid from the center of the tongue along the sliding direction first increased and then decreased,and the pressure along the direction perpendicular to the sliding direction changed gradually and then decreased sharply.As the level of dysphagia increased,the dysphagia became slight,the fluid pressure increased while the friction coefficient changed sharply and then gradually decreased.Patients with more severe dysphagia had an increased friction coefficient,leading to excessive saliva secretion and reducing the comfort.Friction coefficient changed sharply and then gradually decreased while the initial fluid height increased.Choosing small mouthfuls could get better comfort when people were swallowing fluid food.Compared with the difference in the level of dysphagia,the change of the initial fluid height had less effect on the friction coefficient.Finally,in order to explore the lubrication mechanism of viscous fluid in the oral environment of patients with severe dysphagia,it was planned to carry out a friction test investigation of viscous fluid between the tongue and the upper palate under low speed,light load and micro gap,that is by preparing different mass fractions of glucose syrup solution,various viscosity foods which were suitable for patients could be obtained;Using PDMS and glass to simulate the tongue and upper palate friction pair,the friction test of the viscous fluid based on the reciprocating sliding module was carried out on the MFT-5000 rubbing rig to explore the influencing factors of the average friction coefficient and lubrication mechanism of the fluid.The results showed that the glucose syrup solution with a mass fraction in the range of 20% to 60% could be approximated as a Newtonian fluid,and its viscosity increased with the increase of glucose syrup mass fraction;The average friction coefficient decreased with the increase of slip velocity and fluid viscosity,but it first increased and then increased with the increase of external load.So by changing the solute content in the solution and swallowing rehabilitation training could improve the comfort.As for patients with severe dysphagia,their oral environment was mainly in the state of mixed lubrication or fluid lubrication.As the mass fraction of glucose syrup increased,the critical values of mixed lubrication and fluid lubrication in the Stribeck curve increased sequentially.Therefore,choosing a thin fluid for swallowing could help the fluid to be in a fluid-lubricated state and enhance the comfort.In addition,in view of the time-consuming data processing after the friction test,a data processing system based on the sliding module of the MFT-5000 rubbing rig was designed.The system could realize the stage division and graphic display of the original data,the comparison display after the selection of multiple effectiveness of the friction coefficient,and the acquisition of some parameters of the sample attributes,which greatly improved its processing efficiency and accuracy,and also provided a reference for data processing of other modules.