Study On Characteristics Of Flow And Heat Transfer In Heat Dissipation Model Through Porous Foam Metal

Porous foam metal has the characteristics of small density,big specific surface area and high mechanical strength.It can be used for heat dissipation equipment to improve the heat transfer performance of the heat sink and reduce the volume of the heat sink.In this paper,based on the cooling of electronic chip,the internal flow characteristics and heat transfer characteristics of the porous foam metal heat dissipation model were simulated and experimentally studied.Firstly,in order to highlight the characteristics of the foam metal radiator,the traditional rectangular fins with the same parameters?the same volume and heat transfer area?was used as the comparison and reference.The steady-state convective heat transfer problem based on three-dimensional laminar flow was numerically simulated,and the calculation results of the rectangular heat dissipation model were analyzed in three aspects:heat transfer characteristics?temperature field and convective heat transfer strength?,flow characteristics?velocity field and resistance characteristics?,comprehensive performance evaluation?temperature uniformity of heating plate and radiator efficiency?.Secondly,the generation and characteristics of the three-dimensional random foam model were introduced,and the uniformity of the model was verified by the consistency of local porosity.Numerical simulations of similar foam geometries with different porosity were also performed.And analysis method of the results was consistent with the structured fins.The performance evaluation index of the porous model was proposed,and the optimal porous structure within the research range?porosity ranges from 25%to 85%?was sought.Then,taking the foam geometry with a porosity of 65%as the research object,the convective heat transfer problem of the foam metal in the heat dissipation model of the constant power heating plate was studied experimentally.The reliability of the simulation to a certain extent was verified by comparing two parameters which are the temperature of the measuring point on the bottom plate and the pressure loss of the fluid with the numerical results.Finally,the mechanism of heat transfer enhancement of foam metal was explained from the boundary layer theory and field synergy theory respectively,which is of great significance for improving the heat dissipation performance of the radiator and guiding the design of compact heat exchange equipment.The results show that:?1?The inlet flow has a great influence on the temperature uniformity of the bottom plate of the straight rib radiator,and the porous material can improve the uniformity of the temperature of the bottom plate.For porous structures with different porosity,too high or too low porosity will adversely affect the uniformity of the temperature of the bottom plate.?2?The local Nusselt Number Nu_x of the rectangular fins in the flow direction is always reduced,and the overall trend of the Nu_x of the porous structure is also lowered,but rising trend occurs in some local positions.The convective heat transfer coefficient of the porous foam heat exchanger is significantly higher than that of the structured fins under the same conditions,showing good heat transfer superiority.?3?There is a good linear relationship between lg Nu and lgRe for rectangular fins,and the relationship between Fanning friction factor f and Re is fitted.There is a complex flow inside the porous metal,and?p is also proportional to Re,and the relationship between?p and?at different flow rates is fitted.?4?For the foam metal heat dissipation model,the cooling effect of the heated base plate deteriorates as the porosity increases,but the fluid pressure drop is significantly reduced.?5?Under the condition of the same heat exchange area and volume,the convective heat transfer coefficient of the foam structure at 0.1L/min is 3331.96 W/?m²·K?.The convective heat transfer coefficient of the rectangular fins at 0.3L/min is 2873.56 W/?m²·K?.All shows that the heat transfer performance of the foam metal is significantly higher than that of the straight fin.The index(h/?p^1/3)of comprehensive evaluation for flow and heat transfer indicates that the porous structure with a porosity of 55%has the best performance.?6?The mechanism of enhanced heat transfer of porous foam metal is to periodically break the boundary layer,increase fluid disturbance and mixing,reduce the angle between the direction of temperature gradient and the direction of velocity vector,and improve the synergy between temperature field and velocity field.