This article investigates the colloidal study for water and ethylene glycol based nanofluids.The effects of Lorentz forces and thermal radiation are considered.The process of non-dimensionalities of governing equation...This article investigates the colloidal study for water and ethylene glycol based nanofluids.The effects of Lorentz forces and thermal radiation are considered.The process of non-dimensionalities of governing equations is carried out successfully by means of similarity variables.Then,the resultant nonlinear nature of flow model is treated numerically via Runge-Kutta scheme.The characteristics of various pertinent flow parameters on the velocity,temperature,streamlines and isotherms are discussed graphically.It is inspected that the Lorentz forces favors the rotational velocity and rotational parameter opposes it.Intensification in the nanofluids temperature is observed for volumetric fraction and thermal radiation parameter and dominating trend is noted for γ-aluminum nanofluid.Furthermore,for higher rotational parameter,reverse flow is investigated.To provoke the validity of the present work,comparison between current and literature results is presented which shows an excellent agreement.It is examined that rotation favors the velocity of the fluid and more radiative fluid enhances the fluid temperature.Moreover,it is inspected that upturns in volumetric fraction improves the thermal and electrical conductivities.展开更多
The magneto-hydrodynamics(MHD)effect is studied at different inclined angles in Rayleigh-Bénard(RB)convection inside a rectangular enclosure using the lattice Boltzmann method(LBM).The enclosure is filled with e...The magneto-hydrodynamics(MHD)effect is studied at different inclined angles in Rayleigh-Bénard(RB)convection inside a rectangular enclosure using the lattice Boltzmann method(LBM).The enclosure is filled with electrically conducting fluids of different characteristics.These characteristics are defined by Prandtl number,Pr.The considered Pr values for this study are 10 and 70.The influence of other dimensionless parameters Rayleigh numbers Ra=10^(3);10^(4);10^(5);10^(6) and Hartmann numbers Ha=0,10,25,50,100,on fluid flow and heat transfer,are also investigated considering different inclined anglesφof magnetic field by analyzing computed local Nusselt numbers and average Nusselt numbers.The results of the study show the undoubted prediction capability of LBM for the current problem.The simulated results demonstrate that the augmentation in heat transfer is directly related to Ra values,but it is opposite while observing the characteristics of Ha values.However,it is also found thatφhas a significant impact on heat transfer for different fluids.Besides,isotherms are found to be always parallel to the horizontal axis at Ra=10^(3) as conduction overcomes the convection in the heat transfer,but this behaviour is not seen at Ra=10^(4) when Ha>25.Furthermore,at Ra=10^(6),oscillatory instability appears but LBM is still able to provide a complete map of this predicted behavior.An appropriate validation with previous numerical studies demonstrates the accuracy of the present approach.展开更多
In heat exchangers, the magnitude of Nu of each duct is influenced by the temperature field, since the ratio of heat capacity rate will influence the matching status of the temperature field between contacting ducts, ...In heat exchangers, the magnitude of Nu of each duct is influenced by the temperature field, since the ratio of heat capacity rate will influence the matching status of the temperature field between contacting ducts, the total heat transfer coefficient is related with the ratio of heat capacity rate. Considering this relationship, a new method for analyzing heat exchanger is proposed - matching of temperature field. First, for a single duct with the temperature field varying exponentially along the flow direction, its Nu is calculated. Then under the hypothesis that the thermal resistance of the wall is negligible, the matching condition was set like this: both the temperature and heat flux are equal for the hot and cold fluids at the wall, so the matching relationship of parameter that describes the temperature field of the hot and cold fluids, was obtained. Finally the relationship between the total Nu and the ratio of heat capacity rate along with the ratio of inherent thermal resistance is obtained. Compared with traditional analyzing methods, the temperature matching method can be used to get the total heat transfer coefficient directly, and also be used for optimization of heat exchanger design. For a parallel flow, the optimal ratio of heat capacity rate is reciprocal to the ratio of inherent thermal resistance, and for a counter flow, the optimal ratio of heat capacity rate is zero or infinity.展开更多
文摘This article investigates the colloidal study for water and ethylene glycol based nanofluids.The effects of Lorentz forces and thermal radiation are considered.The process of non-dimensionalities of governing equations is carried out successfully by means of similarity variables.Then,the resultant nonlinear nature of flow model is treated numerically via Runge-Kutta scheme.The characteristics of various pertinent flow parameters on the velocity,temperature,streamlines and isotherms are discussed graphically.It is inspected that the Lorentz forces favors the rotational velocity and rotational parameter opposes it.Intensification in the nanofluids temperature is observed for volumetric fraction and thermal radiation parameter and dominating trend is noted for γ-aluminum nanofluid.Furthermore,for higher rotational parameter,reverse flow is investigated.To provoke the validity of the present work,comparison between current and literature results is presented which shows an excellent agreement.It is examined that rotation favors the velocity of the fluid and more radiative fluid enhances the fluid temperature.Moreover,it is inspected that upturns in volumetric fraction improves the thermal and electrical conductivities.
基金The second author would like to acknowledge to the North South University for the partial support as a Research Assistant(Grant No.NSU-RP-18-067)。
文摘The magneto-hydrodynamics(MHD)effect is studied at different inclined angles in Rayleigh-Bénard(RB)convection inside a rectangular enclosure using the lattice Boltzmann method(LBM).The enclosure is filled with electrically conducting fluids of different characteristics.These characteristics are defined by Prandtl number,Pr.The considered Pr values for this study are 10 and 70.The influence of other dimensionless parameters Rayleigh numbers Ra=10^(3);10^(4);10^(5);10^(6) and Hartmann numbers Ha=0,10,25,50,100,on fluid flow and heat transfer,are also investigated considering different inclined anglesφof magnetic field by analyzing computed local Nusselt numbers and average Nusselt numbers.The results of the study show the undoubted prediction capability of LBM for the current problem.The simulated results demonstrate that the augmentation in heat transfer is directly related to Ra values,but it is opposite while observing the characteristics of Ha values.However,it is also found thatφhas a significant impact on heat transfer for different fluids.Besides,isotherms are found to be always parallel to the horizontal axis at Ra=10^(3) as conduction overcomes the convection in the heat transfer,but this behaviour is not seen at Ra=10^(4) when Ha>25.Furthermore,at Ra=10^(6),oscillatory instability appears but LBM is still able to provide a complete map of this predicted behavior.An appropriate validation with previous numerical studies demonstrates the accuracy of the present approach.
基金supported by the National Basic Research Program of China"973"Program)(Grant No.2011CB710705)the strategic priority research program of the Chinese Academy of Sciences(Grant No.XDA03010500)
文摘In heat exchangers, the magnitude of Nu of each duct is influenced by the temperature field, since the ratio of heat capacity rate will influence the matching status of the temperature field between contacting ducts, the total heat transfer coefficient is related with the ratio of heat capacity rate. Considering this relationship, a new method for analyzing heat exchanger is proposed - matching of temperature field. First, for a single duct with the temperature field varying exponentially along the flow direction, its Nu is calculated. Then under the hypothesis that the thermal resistance of the wall is negligible, the matching condition was set like this: both the temperature and heat flux are equal for the hot and cold fluids at the wall, so the matching relationship of parameter that describes the temperature field of the hot and cold fluids, was obtained. Finally the relationship between the total Nu and the ratio of heat capacity rate along with the ratio of inherent thermal resistance is obtained. Compared with traditional analyzing methods, the temperature matching method can be used to get the total heat transfer coefficient directly, and also be used for optimization of heat exchanger design. For a parallel flow, the optimal ratio of heat capacity rate is reciprocal to the ratio of inherent thermal resistance, and for a counter flow, the optimal ratio of heat capacity rate is zero or infinity.
