Lattice Boltzmann Simulation Of The Cavitation Flow And Heat Transfer In Micro-channels

The micro-channel liquid cooling technology has been widely used in the cooling of microelectronic and laser devices. However, with the increasing heat flux of electronic devices, the conventional micro-channel heat sink faces enormous challenges. It has been found that the cooling capacity of the micro-channel could be significantly improved by hydrodynamic cavitation occurring in it. Investigating the characteristics of cavitation flow in micro-channel and its effect on heat transfer have important scientific significance and practical value, and many scholars at home and abroad focus on the related research. Considering the dificiency of traditional CFD method in simulating cavitation flow and heat transfer, the present work regards micro-channels with cavitation structure as object, and firstly puts Lattice Boltzmann method coupling the pseudopotential model into the investigation on the cavitation flow and heat transfer in micro-channels. The achievements was expected to find out the cavitation conditions in micro-channel, and to reveal the characteristics of bubble formation, growth, motion, coalescence and collapse, and its effects on the heat transfer.In this paper, a general review on the basic theory of Lattice Boltzmann method is first presented, and both existing schemes for interpartical interaction forces and methods of incorporating the force term are analyzed. On this basis, the author establishes the single component multiphase Lattice Boltzmann model by using the mixed interpartical interaction forces and the exact difference method. P-R equation of state is incorporated into this model to simulate water and steam two-phase system, and both surface tension and contact angle are used as criterias to verify the reliability of the model. The results show that surface tension decreases with increasing temperature, and contact angle has a linear relation with the interaction strength between solid particles and fluid particles. This indicates that P-R equation is appropriate for gas-liquid two-phase system simulation.Based on the reliability of the model, cavitation flow inside micro-channel with rectangular restricted structure is investigated using the developed single component multiphase Lattice Boltzmann model. The cavitation flow pattern in the present paper is quite similar to experimental result in literature, which further confirms the reliability of the model. The simulation results show that cavitation first forms in the low-pressure region near the exit of the restricted structure, which accords with the real pressure distribution. The liquid film between cavitation bubble and wall is successfully simulated, and the related factors influencing the liquid film are analyzed. It is found that the fluid-solid interaction is the key to the formation of liquid film.Under the conditions of fixed pressure gradient and pressure difference respectively, the author further investigates the effec of various factors on the formation of cavitation bubble. The results indicate that, there is an optimum value for the width of the throat under fixed pressure gradient condition. Hydrodynamic cavitation easily occurs when the width of the throat approaches the optimum value, and no hydrodynamic cavitation is observed when the width of the throat deviates from the optimum value largely; There is also an optimum value for the length of exit section of micri-channel under fixed pressure difference condition. Hydrodynamic cavitation easily occurs when the length of exit section approaches the optimum value, and no hydrodynamic cavitation is observed when the length of exit section deviates from the optimum largely.With a source term, the energy equation is coupled into the single component multiphase Lattice Boltzmann model. Based on this, bubble dynamics and its effects on the heat transfer is investigated, and the processes of bubble growth and collapse in micro-channel are successfully captured. The rebound phenomenon in the collapse stage is also observed and the continuous temperature information and other parameters during the growth and collapse stages are obtained. In the present work, the coalescence of two bubbles in micro-channels is firstly simulated under static conditions. The results show that the deformations of bubbles are strongly influenced by the channel walls. The futher research indicates that there is a high-temperature wake zone at the rear of bubble during its high pressure stage, which contributes to the temperature rise of liquid. In addtion, the dynamic processes of bubble interaction and deformation are also obtained.