At present great attention is given to a problem of research of hydrodynamics and heat exchange in pulsating flows. Experimental studies for the flow in smooth channels show that pulsation of fluid flow significantly affects heat transferring and can be accompanied by both reduction and increasing in the intensity of heat exchange. However, at the present day, there is little reliable information about the effect of a pulsating flow on heat transferring in channels with discrete roughness. Thus, detection of regularities in heat exchanging processes of such flows in discretely rough channels is an actual problem for today. In this paper the results of numerical simulation of heat exchange in smooth and discrete-rough channels with a pulsating motion of fluid in them are presented. It is revealed that in the pulsating flow the instantaneous values of the heat exchange coefficient change with the change in the instantaneous values of the Reynolds numbers. Three zones of influence of the pulsing flow on the heat exchange in the channels are established. In the first area, with the Strouhal numbers 0 < Sh < 2, increasing in the average value of heat exchange in 10-15 % is observed. In the second area 2 < Sh < 4.3, its decreasing in 10-15 %. In the third area, 4.3 < Sh < 6, the average value of the heat exchanging value becomes almost the same as for the case of a stationary flow.
Obtaining information about pulsating turbulent flow structure and identifying the heat transfer processes laws of such flows in the channels today is an urgent task. Identification of the physical causes of various factors that affect the flow structure and heat transfer in the channels can allow controlling of these processes. The numerical solution of the task is performed in the Flow Simulation software, in which the movement and heat transfer of fluids are modelled by using the Navier-Stokes equations. In this work is used a model of a periodically pulsating fluid flow with sinusoidal velocity pulses. The considered frequency range of the flow pulsations in the channel is from 0 up to 100 Hz. The obtained calculation results with the flow pattern visualization make it possible to identify the flow features at given pulsations in the channel with respect to the stationary regime. The results of the numerical solution showed that flow pulsations significantly affect the heat transfer in the channels. At a flow pulsation frequency in the channel 0 < f < 40, in comparing with the stationary mode, the Nusselt criterion increases by 10-15 %. At a frequency of 40 < f < 100, the Nusselt criterion decreases by 10-15 %. The results of visualization of flow patterns in a discretely rough channel showed that the presence of vortex zones and zones of return flows leads to the destruction of the boundary layer and, as a consequence, to intensification of the heat transfer process.
We prove a statement on the averaging of a hyperbolic initial-boundary-value problem in which the coefficient of the Laplace operator depends on the space L 2 -norm of the gradient of the solution. The existence of the solution of this problem was studied by Pokhozhaev. In a space domain in R n , n ≥ 3, we consider an arbitrary perforation whose asymptotic behavior in a sense of capacities is described by the Cioranesku-Murat hypothesis. The possibility of averaging is proved under the assumption of certain additional smoothness of the solutions of the limiting hyperbolic problem with a certain stationary capacitory potential.
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