Analytical And Numerical Investigations Of Flow Characteristics Of Annular Microchannels

With the rapid development of MEMS,the application of microscale correlation consequently is applied for various fields.For the microchannel exchangers and reactors are gradually developing towards the tendency of miniaturization and integration,which means that the entrance effect cannot be neglected.Especially for mini-channels,the entrance length accounts for a large ratio of the entire length,so the entrance influence cannot be neglected.However,the research on the entrance section is not enough at present,and there are some basic problems.The study of entrance effect will lay a foundation for the application and development of modern high technology,which has important engineering value and academic significance.The engineering background of the current investigation is based on the application of tubular heat exchanger and micro-reactor.CFD software ANSYS Fluent was used to study the pressure drop and friction of laminar flow in annular microchannel,including the velocity distributions and flow characteristics in the developed region and the fully developed region.In this work,the inner-outer diameter ratio of microchannels（0.05<r^*<1）and Reynolds number（25<Re<2000）on the friction factor and the entrance length are mainly analyzed.The numerical simulation results obtained in this paper are in good agreement with the theoretical exact solution.the f_appRe value in the annular microchannel is larger in the entrance area,and gradually decreases with the increase of the dimensionless axial distance,and then reaches a stable value,and the flow reaches the fully developed stage.The apparent friction factor and the inlet length of the annular channel decrease with the increase of the inner-outer diameter ratio and Reynolds number.In addition,the dimensionless entrance length is a function of the Reynolds number and the ratio of inner and outer diameters.In addition,in this paper,the asymptotic analysis method is applied.And according to the simulation results,proposing models for predicting the f_appRe value of the annular channel and for calculating the entrance length of the annular microchannel.These models and relations can predict the distribution of friction and pressure drop of the annular microchannel and,can provide a basis for further research and which is benefit to engineering practice and application.It is of great significance for the research of tube heat exchangers and micro-reactors.