A numerical investigation of laminar natural double diffusive convection in an open ended vertical cylindrical annulus with unheated entry and unheated exit is performed.Both boundary conditions of uniform wall temper...A numerical investigation of laminar natural double diffusive convection in an open ended vertical cylindrical annulus with unheated entry and unheated exit is performed.Both boundary conditions of uniform wall temperature/uniform wall concentration(UWT/UWC)and uniform heat flux/uniform mass flux(UHF/UMF)are considered.Results of dimensionless induced volume rate Q,average Nusselt number Nu and Sherwood number Sh are obtained for air flow under various buoyancy ratio N,Grashof numbers due to heat and mass transfer GrT and GrM,Schmidt number Sc and combinations of unheated entry,heated section and unheated exit length.Since the flow under consideration is a boundary layer type,the governing partial differential equations was discretized to a linear system of equations by the use of an implicit finite difference method.The nonlinear convective terms are approximated by second upwind difference method for the numerical stability.The numerical results reveal that the presence of unheated entry and unheated exit severely affects the heat and mass transfer rates.The numerical solutions are found to approach asymptotically the closed form solutions for fully developed flow.Further,the present numerical results are validated with the existing solutions for pure thermal convection and are found to be in good agreement.展开更多
An experiment is carried out on the surface oscillation of buoyant-thermocapillary convection in an open cylindrical annulus. When the radial temperature difference AT reaches a critical value △Tc, a regular oscillat...An experiment is carried out on the surface oscillation of buoyant-thermocapillary convection in an open cylindrical annulus. When the radial temperature difference AT reaches a critical value △Tc, a regular oscillation appears and soon disappears on the open surface, which varies when the liquid layer＇s thickness h and temperature difference △T are varied. With growth of △T, dominant frequency of the visible oscillation will grow too but is found within certain frequencies. Driving forces, buoyance and thermocapillarity, are responsible for this phenomanon and the ＂balance＂ point is considered to exist when h is between 4.5-5.0 mm. Surface oscillation region is also found restricted within a narrow gap when Bo is smaller than 3.7.展开更多
文摘A numerical investigation of laminar natural double diffusive convection in an open ended vertical cylindrical annulus with unheated entry and unheated exit is performed.Both boundary conditions of uniform wall temperature/uniform wall concentration(UWT/UWC)and uniform heat flux/uniform mass flux(UHF/UMF)are considered.Results of dimensionless induced volume rate Q,average Nusselt number Nu and Sherwood number Sh are obtained for air flow under various buoyancy ratio N,Grashof numbers due to heat and mass transfer GrT and GrM,Schmidt number Sc and combinations of unheated entry,heated section and unheated exit length.Since the flow under consideration is a boundary layer type,the governing partial differential equations was discretized to a linear system of equations by the use of an implicit finite difference method.The nonlinear convective terms are approximated by second upwind difference method for the numerical stability.The numerical results reveal that the presence of unheated entry and unheated exit severely affects the heat and mass transfer rates.The numerical solutions are found to approach asymptotically the closed form solutions for fully developed flow.Further,the present numerical results are validated with the existing solutions for pure thermal convection and are found to be in good agreement.
基金supported by the National Natural Science Foundation of China(11032011 and 10972224)Knowledge Innovation Program of Chinese Academy of Sciences(KJCX2-YW-L08)
文摘An experiment is carried out on the surface oscillation of buoyant-thermocapillary convection in an open cylindrical annulus. When the radial temperature difference AT reaches a critical value △Tc, a regular oscillation appears and soon disappears on the open surface, which varies when the liquid layer＇s thickness h and temperature difference △T are varied. With growth of △T, dominant frequency of the visible oscillation will grow too but is found within certain frequencies. Driving forces, buoyance and thermocapillarity, are responsible for this phenomanon and the ＂balance＂ point is considered to exist when h is between 4.5-5.0 mm. Surface oscillation region is also found restricted within a narrow gap when Bo is smaller than 3.7.
