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
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 effects of viscous dissipation on thermal entrance heat transfer in a parallel plate channel filled with a saturated porous medium,is investigated analytically on the basis of a Darcy model.The case of isothermal ...The effects of viscous dissipation on thermal entrance heat transfer in a parallel plate channel filled with a saturated porous medium,is investigated analytically on the basis of a Darcy model.The case of isothermal boundary is treated.The local and the bulk temperature distribution along with the Nusselt number in the thermal entrance region were found. The fully developed Nusselt number, independent of the Brinkman number, is found to be 6. It is observed that neglecting the effects of viscous dissipation would lead to the well-known case of internal flows,with Nusselt number equal to 4 93.A finite difference numerical solution is also utilized. It is seen that the results of these two methods, analytical and numerical, are in good agreement.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
At high altitudes, power of an internal combustion engine reduces due to air density reduction. In turbocharged diesel engine this issue affects the performance of the compressor and can result in unstable operation o...At high altitudes, power of an internal combustion engine reduces due to air density reduction. In turbocharged diesel engine this issue affects the performance of the compressor and can result in unstable operation of the turbocharger if the power is not decreased by engine actuator. Mainly for testing the effects of altitude in the test room, air throttle valve and combustion air handling unit were used to reduce the suction air pressure. Easier and cheaper solution to consider effect of altitude on engine performance is to mask part of the air filter to reduce the suction pressure. In this paper, pressure drop against 0%, 26%, 52%, 66% and 74% of air filter hole’s masking for different mass flow rates has been studied by computational fluid dynamics. The analysis output mass flow rate-pressure diagram for the air filter, will be used as input data in the GT-Power software which is a one-dimensional computational fluid dynamics software and the effect of masking on altitude and performance at different revolutions per minute of the engine is investigated. Also, an experimental and computational fluid dynamics study was carried out to predict altitude against different proportions of air filter hole’s masking at 1000 rpm. The predicted results are validated by comparing with those of experimental data. A good agreement between the predicted and experimental values ensures the accuracy of the numerical predictions with the present work.展开更多
<span style="font-family:Verdana;">Accord</span><span style="font-family:Verdana;">ing</span><span style="font-family:Verdana;"> to </span><span sty...<span style="font-family:Verdana;">Accord</span><span style="font-family:Verdana;">ing</span><span style="font-family:Verdana;"> to </span><span style="font-family:Verdana;">the </span><span style="font-family:Verdana;">study of basic Rankin thermal cycle, the steam exh</span><span style="font-family:Verdana;">aust pressure of a typical steam turbine toward </span><span style="font-family:Verdana;">the </span><span style="font-family:Verdana;">condenser, plays a great rol</span><span style="font-family:Verdana;">e</span><span style="font-family:Verdana;"> in the efficiency and the net output power of </span><span style="font-family:Verdana;">the </span><span style="font-family:;" "=""><span style="font-family:Verdana;">steam turbine, so most surface conden</span><span style="font-family:Verdana;">sers </span></span><span style="font-family:Verdana;">that</span><span style="font-family:Verdana;"> are working in thermal power plants are kept at va</span><span style="font-family:;" "=""><span style="font-family:Verdana;">cuum condition so that the maximum power of thermal cycle can be achieved. The </span><span style="font-family:Verdana;">vacuu</span><span style="font-family:Verdana;">m pressure at condenser leads to </span></span><span style="font-family:Verdana;">the </span><span style="font-family:Verdana;">entering of air </span><span style="font-family:Verdana;">and Non-</span><span style="font-family:Verdana;">condensable gases from turbine gland seals to condenser so that the special air ejection equipment is being used to take apart air from steam and vent it to out of condenser.</span><span style="font-family:;" "=""> </span><span style="font-family:Verdana;">In this study</span><span style="font-family:Verdana;">,</span><span style="font-family:Verdana;"> a special steam and air separator mechanism in </span><span style="font-family:Verdana;">an </span><span style="font-family:Verdana;">evacuating system called </span><span style="font-family:Verdana;">“</span><span style="font-family:Verdana;">Aircoole展开更多
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 effects of viscous dissipation on thermal entrance heat transfer in a parallel plate channel filled with a saturated porous medium,is investigated analytically on the basis of a Darcy model.The case of isothermal boundary is treated.The local and the bulk temperature distribution along with the Nusselt number in the thermal entrance region were found. The fully developed Nusselt number, independent of the Brinkman number, is found to be 6. It is observed that neglecting the effects of viscous dissipation would lead to the well-known case of internal flows,with Nusselt number equal to 4 93.A finite difference numerical solution is also utilized. It is seen that the results of these two methods, analytical and numerical, are in good agreement.
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.
文摘At high altitudes, power of an internal combustion engine reduces due to air density reduction. In turbocharged diesel engine this issue affects the performance of the compressor and can result in unstable operation of the turbocharger if the power is not decreased by engine actuator. Mainly for testing the effects of altitude in the test room, air throttle valve and combustion air handling unit were used to reduce the suction air pressure. Easier and cheaper solution to consider effect of altitude on engine performance is to mask part of the air filter to reduce the suction pressure. In this paper, pressure drop against 0%, 26%, 52%, 66% and 74% of air filter hole’s masking for different mass flow rates has been studied by computational fluid dynamics. The analysis output mass flow rate-pressure diagram for the air filter, will be used as input data in the GT-Power software which is a one-dimensional computational fluid dynamics software and the effect of masking on altitude and performance at different revolutions per minute of the engine is investigated. Also, an experimental and computational fluid dynamics study was carried out to predict altitude against different proportions of air filter hole’s masking at 1000 rpm. The predicted results are validated by comparing with those of experimental data. A good agreement between the predicted and experimental values ensures the accuracy of the numerical predictions with the present work.
文摘<span style="font-family:Verdana;">Accord</span><span style="font-family:Verdana;">ing</span><span style="font-family:Verdana;"> to </span><span style="font-family:Verdana;">the </span><span style="font-family:Verdana;">study of basic Rankin thermal cycle, the steam exh</span><span style="font-family:Verdana;">aust pressure of a typical steam turbine toward </span><span style="font-family:Verdana;">the </span><span style="font-family:Verdana;">condenser, plays a great rol</span><span style="font-family:Verdana;">e</span><span style="font-family:Verdana;"> in the efficiency and the net output power of </span><span style="font-family:Verdana;">the </span><span style="font-family:;" "=""><span style="font-family:Verdana;">steam turbine, so most surface conden</span><span style="font-family:Verdana;">sers </span></span><span style="font-family:Verdana;">that</span><span style="font-family:Verdana;"> are working in thermal power plants are kept at va</span><span style="font-family:;" "=""><span style="font-family:Verdana;">cuum condition so that the maximum power of thermal cycle can be achieved. The </span><span style="font-family:Verdana;">vacuu</span><span style="font-family:Verdana;">m pressure at condenser leads to </span></span><span style="font-family:Verdana;">the </span><span style="font-family:Verdana;">entering of air </span><span style="font-family:Verdana;">and Non-</span><span style="font-family:Verdana;">condensable gases from turbine gland seals to condenser so that the special air ejection equipment is being used to take apart air from steam and vent it to out of condenser.</span><span style="font-family:;" "=""> </span><span style="font-family:Verdana;">In this study</span><span style="font-family:Verdana;">,</span><span style="font-family:Verdana;"> a special steam and air separator mechanism in </span><span style="font-family:Verdana;">an </span><span style="font-family:Verdana;">evacuating system called </span><span style="font-family:Verdana;">“</span><span style="font-family:Verdana;">Aircoole
