Forced Fluid Flow Research Articles

Combined free and forced convective heat transfer and fluid flow in a rotating curved circular tube

A study is made of the combined free and forced convective heat transfer and fluid flow in a rotating curved circular tube for the fully developed flow with the thermal boundary condition of constant heat flux per unit length of tube. The heat-transfer and flow-friction characteristics are determined by the five non-dimensional parameters, i.e. the radius ratio B, the Prandtl number Pr, a parameter Ro which represents the effects of Coriolis forces, the Grashof number Gr 2 and the Dean number K 1. The governing equations are solved by finite difference method, and the results of computations are presented for the axial velocity and temperature distributions, the streamlines and isothermals, the local f and Nu, and the mean f and Nu. The effects of B is minor. Pr has substantially no effect on f, but increases Nu greatly when a strong secondary current is present. The increase in the last three parameters of secondary-flow-inducing forces enhance both f and Nu significantly. The rate of increase in f and Nu due to the force parameters is higher for a circular tube than for rectangular tubes. Their effects commence to be pronounced at smaller values of them which are Ro ≈ 2, Gr 2 ≈ 100 and K 1 ≈ 100, while those for a square tube are Ro ≈ 10, Gr 2 ≈ 1000 and K 1 ≈ 100.

Self-similar problems of convective diffusion in the presence of heterogeneous chemical reactions with allowance for thermal diffusion effects

A number of studies have been made of the problem of the effect of a temperature gradient on mass transfer in a forced viscous fluid flow. The question of allowing for thermal diffusion effects has been examined in connection with flow around bodies [1–4], duct flow [5], and jet flows [6,7]. Recently, in addition to the problem of thermal diffusion separation, the attention of investigators has been claimed by the problem of taking into account the effect of thermal diffusion on mass transfer in a convective flow in the presence of chemical reactions on the flow surfaces [4].

Origin of the equiaxed zone in small ingots

It is deduced by thermal analysis that no entirely new crystals are nucleated in the interior of an ingot at any time after pouring. By comparing the conditions for columnar growth in ingots and in unidirectional solidification experiments, it is concluded that in the ingot, sufficient constitutional supercooling for nucleation might occur if it were not prevented by the presence of crystals in the liquid. At low pouring temperatures, most of the equiaxed grains are nucleated as separate crystals at the time of pouring. When the superheat is higher, the main process for the origin of the equiaxed zone appears to be a multiplication mechanism operating by local remeiting. Dynamic procedures used during unidirectional solidification and conventional ingot freezing permit one to conclude that the main mechanism operating to refine the equiaxed structure, as a function of imposed disturbances (mechanical or forced fluid flow) is a multiplication mechanism, most likely the process of detachment of dendritic arms by remeiting.