Laminar Flow Forced Convection Heat Transfer Of Microencapsulated Phase Change Material Slurry In Tube

MPCMs(Microencapsulated Phase Change Material slurries)is a solid-liquid two-phase fluid that can be phase-changed during the flow process.It is an efficient cooling medium.With a large heat capacity,high heat transfer efficiency,the use of a wide range,you can reduce the size of the corresponding heat exchanger or pipe and so on.With the progress of science and technology,the precision of the instrument is increasing,the size of the cooling element becomes smaller and the requirements of the cooling capacity are also increased.The application and research of MPCM are becoming more and more extensive.In this paper,the suspension made of octadecane phase change microcapsules was used as the heat transfer medium.Based on the equivalent specific heat model and modified convective heat transfer coefficient and modified Nusselt number,the MPCMs were treated with constant heat flux The convective heat transfer characteristics of the laminar flow in the tube were studied numerically.Firstly,the flow of MPCMs under different Reynolds number,mass fraction and Stephen number is simulated numerically.The results show that when MPCMs flow through the heated pipes,there are three main areas: solid state,phase transition zone and melting zone.Area,near the entrance,only the MPCM near the wall has a phase transition,along the flow direction,the phase transition zone along the pipe wall to the center of the pipeline expansion.Reynolds number,mass fraction and Stephen number are the key factors influencing the convective heat transfer size of MPCMs.When the Reynolds number is larger under the same conditions,the longer the melting zone,the higher the Nusselt number and the corrected convective heat transfer coefficient The Under the same conditions,when the mass fraction is larger,the longer the melting zone,the higher the Nusselt number and the corrected convective heat transfer coefficient.When the score is smaller,the longer the melting zone,the higher the Nusselt number and the corrected convective heat transfer coefficient.With the increase of Reynolds number,the increase of mass fraction and the decrease of Stiff's fraction,the melting starting point at the center of the pipeline is elongated along the length of the tube,and the phase transition zone becomes longer,and the Reynolds number,mass fraction and Stephen number are changed The position and size of the phase transition zone of MPCMs change the convective heat transfer effect,which makes the phase transition region bigger and the convective heat transfer effect is better.In this paper,the heat transfer characteristics of flow in MPCMs are analyzed from the microscopic point of view.The data of phase transition temperature boundary layer obtained by numerical simulation are fitted by equation.The equation with the highest fitting degree is a hexagonal polynomial.There is no practical significance in mathematical physics,so it is fitted into a straight line equation and the equation expression is written.The phase transition temperature boundary layer in the heat conduction state is transformed into the temperature boundary layer in the convective state and its expression is obtained.The result is corrected by numerical simulation and the correction factor is obtained.From the microscopic point of view,the specific melting conditions of MPCMs flowing in the tube are analyzed,and the equation expression of the phase transition temperature boundary layer in the convective state is modified,which provides a new method for studying the convective heat transfer of the MPCMs from the microscopic angle of temperature boundary layer The direction of thinking.