Study Of Flow In Porous Media Based On Lattice Boltzmann Method

The loop heat pipe is a typical capillary force-driven two-phase flow device,which is widely applied in the aerospace field and has been valued due to its capacity of effectively cold transfer.The capillary wick in the evaporator is a core component of the loop heat pipe as it provides operation power source for the system.Heat transfer limit of the heat pipe is greatly affected by the capillary limit.With rapidly development in recent years,3D printing technology becomes suitable for manufacturing capillary wicks with complex porous structures inside.Compared with sintered capillary wicks commonly used in the engineering,3D printed wick has great advantages in the design and research of capillary wicks properties as it makes the size of pores controllable and simplifies the structure of porous media.Experimental studies,analytical calculations,and numerical simulations are three main methods for the scholars all over the world to study porous media.Among these methods,numerical simulation has received extensive attention in various fields and has developed rapidly although it doesn’t have a long history.Compared with the other two methods,it is less sensitive to the environment,more suitable for mechanism research,and has lower cost.For the study of porous media on the pore scale,lattice Boltzmann method proposed two decades ago has its own unique advantages in simulating complex boundaries and complex flows because of its mesoscopic particle background,which overcomes many deficiencies of traditional numerical simulation methods.Based on the above considerations,a 3D-printed titanium alloy capillary wick was used in this article,and lattice Boltzmann method is applied to study the basic issues of capillary flow.The work of this article includes two main parts: numerical simulation of different capillary channels and experimental research of a 3D printing titanium alloy capillary wick.Firstly,to prove the correctness of the lattice Boltzmann two-phase flow model and the program used in this article,the verification of the lid driven flow and Young-Laplace’s law were conducted.Then,physical models of a vertical single-channel model and vertical multi-channels were established,and the liquid capillary rising process in these channels under gravity was simulated,the influence of channel width,number of channels on the capillary rising process and maximum capillary rising height were studied.Based on the rules obtained above,a simplified model of a 3D printing titanium alloy capillary wick was built.The maximum capillary rising height of the liquid working fluid which had a small contact angle with the surface of the titanium alloy was calculated and the meniscus was analyzed.In order to research the capillary flow of the working fluid in the 3D printing titanium alloy capillary wick,an experimental platform was set up to observe and record the whole capillary rise process.Absolute ethanol was chosen as the working fluid in the experiment,and the contact angle between the titanium alloy capillary wick surface and ethanol was measured to be 0°.The lattice Boltzmann simulation was verified to be reliable by comparing the experimental results with the numerical simulation results.3D printing capillary wick is a special porous medium as the pores inside are regularly shaped and uniformly distributed.However,the internal structure of many other porous media is far more complex.In this article,two kinds of bended channel models were constructed.The lattice Boltzmann method was used to simulate the liquid capillary rise process in these two bended channels.And the effect of channel structure and bending rate on the capillary rise performance was analyzed.