چكيده به لاتين
Internal combustion engines exhaust valves, especially in turbocharged engines, are subjected to enhanced thermal load so that to remove heat faster and more from valve head, valve is manufactured hollow and sodium with high thermal conductivity is put in valve so that it is liquid in engine operation condition. In this research, problem goes far beyond and copper particles are used in valve cavity that its conductivity is more than sodium. Aim of doing this research is to know how heat transfer is enhanced or weakened after adding copper particles to sodium and air in the cavity. Two methods can be used to analyze the problem; 1.Eulerian-spatial approach with heterogeneous mixture model and 2.Lagrangian-particle approach. When there are sodium and air in the cavity, Eulerian approach and consequently continuum medium equations or Navier-Stokes equations with volume of fluid method for phase separation, are used. To adding copper particle to sodium and air medium, according to Maxwell and Einstein equations, heterogeneous mixture model is applied. Calculations are performed by first method (Eulerian-spatial approach with heterogeneous mixture model) in multiphase model and volume of fluid part of Ansys Fluent 19.2 software. Copper particle are added to sodium and air by 1,2,3 and 4 percent volume fraction to investigate change of conduction heat transfer magnitude in direction of valve stem. To investigate role of copper particle in heat transfer, it was revealed that increasing conductivity and increasing viscosity act opposite each other, such that increasing particle volume fraction can enhance conduction to a threshold that depend on geometry, boundary condition and fluid properties; in such a way that one percent volume fraction increase conduction in valve stem direction to about 5.8 percent but with a further increase in particle volume fraction, viscosity effects, cause slowing down the material movement and therefore decreasing heat transfer. Therefore regarding optimum limit is necessary that make desirable the conductivity and viscosity resultant in heat transfer enhancement.
