The present study discusses the thermal performance of the receiver tube,which contains a wall with various fin shapes in the parabolic trough collector.Inserted fins and bulge surfaces of the inner wall of the receiv...The present study discusses the thermal performance of the receiver tube,which contains a wall with various fin shapes in the parabolic trough collector.Inserted fins and bulge surfaces of the inner wall of the receiver tube increase the turbulent fluid flow.In pursuance of uniform distribution of heat transfer,various fin shapes such as square-shape,circle-shape,triangle-shape,and combined square-circle shapes were inserted,examined,and compared.A study of the temperature differences and fluid flow is meaningful for this project therefore finite volume method was used to investigate heat transfer.Also,hybrid Nano-Fluid AL_(2)O_(3-)CuO,TiO_(2-)Cu,and AgMgO were applied to increase thermal diffusivity.When the combined square-circle-shaped fin was inserted,the thermal peak of fluid flow in the receiver tube was lower than the other studied fin shapes by almost 1%.Besides,the hybrid nano-fluid Ag-MgO Syltherm-oil-800 has lower thermal waste in comparison to others by more than 3%.展开更多
The lattice Boltzmann method (LBM) is used to examine free convection of nanofluids. The space between the cold outer square and heated inner circular cylinders is filled with water including various kinds of nanopa...The lattice Boltzmann method (LBM) is used to examine free convection of nanofluids. The space between the cold outer square and heated inner circular cylinders is filled with water including various kinds of nanoparticles: TiO2, Ag, Cu, and A1203. The Brinkman and Maxwell-Garnetts models are used to simulate the viscosity and the effective thermal conductivity of nanofluids, respectively. Results from the performed numerical analysis show good agreement with those obtained from other numerical meth- ods. A variety of the Rayleigh number, the nanoparticle volume fraction, and the aspect ratio are examined. According to the results, choosing copper as the nanoparticle leads to obtaining the highest enhancement for this problem. The results also indicate that the maximum value of enhancement occurs at λ =2.5 when Ra = 106 while at A = 1.5 for other Rayleigh numbers.展开更多
In this paper a hydrodynamic journal sliding bearing,forming with two nonparallel surfaces that the lower surface moves with a unidirectional velocity and the upper surface is stationary shaped with exponential geomet...In this paper a hydrodynamic journal sliding bearing,forming with two nonparallel surfaces that the lower surface moves with a unidirectional velocity and the upper surface is stationary shaped with exponential geometry is verified mathematically.The values of volumetric flow rate and distribution of pressure for incompressible lubricant flow between two supports in several conditions of velocity with different variables are determined.The results indicate that by increasing the amount of constant(m),the maximum oil pressure in the bearing will face an extreme decrease,and also by increasing theαcoefficient,the rate of volumetric flow rate will decrease.展开更多
In the present work,impact of a Newtonian drop on horizontal thin fibers withcircular cross section is simulated in 2D views.The numerical simulations of the phenomenaare carried out using volume of fluid(VOF)method f...In the present work,impact of a Newtonian drop on horizontal thin fibers withcircular cross section is simulated in 2D views.The numerical simulations of the phenomenaare carried out using volume of fluid(VOF)method for tracking the free surface motion.Impacting of a Newtonian droplet on a circular thin fiber(350 um radius)investigatednumerically.The main focus of this simulation is to acquire threshold radius and velocity of adrop which is entirely captured by the fiber.The model agrees well with the experiments anddemonstrates the threshold radius decreased generally with the increase of impact velocity.Inother words,for velocity larger than threshold velocity of capture perhaps only a small portionof fluid is stuck on the solid and the rest of the drop is ejected for impact velocity smaller thancritical velocity the drop is totally captured.This threshold velocity has been determined whenthe impact is centered.展开更多
文摘The present study discusses the thermal performance of the receiver tube,which contains a wall with various fin shapes in the parabolic trough collector.Inserted fins and bulge surfaces of the inner wall of the receiver tube increase the turbulent fluid flow.In pursuance of uniform distribution of heat transfer,various fin shapes such as square-shape,circle-shape,triangle-shape,and combined square-circle shapes were inserted,examined,and compared.A study of the temperature differences and fluid flow is meaningful for this project therefore finite volume method was used to investigate heat transfer.Also,hybrid Nano-Fluid AL_(2)O_(3-)CuO,TiO_(2-)Cu,and AgMgO were applied to increase thermal diffusivity.When the combined square-circle-shaped fin was inserted,the thermal peak of fluid flow in the receiver tube was lower than the other studied fin shapes by almost 1%.Besides,the hybrid nano-fluid Ag-MgO Syltherm-oil-800 has lower thermal waste in comparison to others by more than 3%.
文摘The lattice Boltzmann method (LBM) is used to examine free convection of nanofluids. The space between the cold outer square and heated inner circular cylinders is filled with water including various kinds of nanoparticles: TiO2, Ag, Cu, and A1203. The Brinkman and Maxwell-Garnetts models are used to simulate the viscosity and the effective thermal conductivity of nanofluids, respectively. Results from the performed numerical analysis show good agreement with those obtained from other numerical meth- ods. A variety of the Rayleigh number, the nanoparticle volume fraction, and the aspect ratio are examined. According to the results, choosing copper as the nanoparticle leads to obtaining the highest enhancement for this problem. The results also indicate that the maximum value of enhancement occurs at λ =2.5 when Ra = 106 while at A = 1.5 for other Rayleigh numbers.
文摘In this paper a hydrodynamic journal sliding bearing,forming with two nonparallel surfaces that the lower surface moves with a unidirectional velocity and the upper surface is stationary shaped with exponential geometry is verified mathematically.The values of volumetric flow rate and distribution of pressure for incompressible lubricant flow between two supports in several conditions of velocity with different variables are determined.The results indicate that by increasing the amount of constant(m),the maximum oil pressure in the bearing will face an extreme decrease,and also by increasing theαcoefficient,the rate of volumetric flow rate will decrease.
文摘In the present work,impact of a Newtonian drop on horizontal thin fibers withcircular cross section is simulated in 2D views.The numerical simulations of the phenomenaare carried out using volume of fluid(VOF)method for tracking the free surface motion.Impacting of a Newtonian droplet on a circular thin fiber(350 um radius)investigatednumerically.The main focus of this simulation is to acquire threshold radius and velocity of adrop which is entirely captured by the fiber.The model agrees well with the experiments anddemonstrates the threshold radius decreased generally with the increase of impact velocity.Inother words,for velocity larger than threshold velocity of capture perhaps only a small portionof fluid is stuck on the solid and the rest of the drop is ejected for impact velocity smaller thancritical velocity the drop is totally captured.This threshold velocity has been determined whenthe impact is centered.