Abstract
The problem of convective heat transfer in the initial section of a pipe with a corrugated section was considered at transient Reynolds numbers. Influence on the intensity of heat exchange and the magnitude of hydraulic resistance of geometric parameters (wavelength and amplitude) of the corrugated insert, variability of the thermophysical properties of the heat carrier and the direction of the heat flow was estimated. Threshold value of the corrugation wavelength (L/R 0 >0.6) was determined for the Reynolds number range under consideration for which there was a significant growth of heat exchange. Influence of the gradient of the dynamic viscosity coefficient on flow stability and intensification of heat exchange in internal flows was demonstrated. Influence of Reynolds and Prandtl numbers on local heat transfer, hydraulic resistance and flow structure was determined. It was established that the use of corrugated surfaces is ineffective at Reynolds numbers less than 2000. It was shown that heat exchange in a pipe can be raised to 30 % with an increase in hydraulic resistance of 1.05 times in the range of Reynolds numbers 2·10 3 ...1.4·10 4 with the use of a nonencumbering corrugation.
Highlights
IntroductionIntensification of heat exchange processes in the elements of power equipment at equal heat exchange areas and equal velocities of the same coolant (that is, when the Reynolds and Prandtl numbers are equal) is determined by the structure of the coolant flow on the heat exchange surfaces
Intensification of heat exchange processes in the elements of power equipment at equal heat exchange areas and equal velocities of the same coolant is determined by the structure of the coolant flow on the heat exchange surfaces
The flow structure is understood as thickness of the dynamic boundary layer or flow conditions in the boundary layer or spatial and time scales of the vortex perturbations in the boundary layer and intensity of these perturbations
Summary
Intensification of heat exchange processes in the elements of power equipment at equal heat exchange areas and equal velocities of the same coolant (that is, when the Reynolds and Prandtl numbers are equal) is determined by the structure of the coolant flow on the heat exchange surfaces. Heat exchange can be intensified by realization of Reynolds analogy through increase of stresses on the streamlined surface and thereby intensity of the vortex structures in the boundary layer. This process is energy-consuming [1]. Corrugation is a special case of this method; it ensures a significant increase of efficiency of the heat exchange equipment by intensifying vortex perturbations on streamlined surfaces. Intensity of heat removal and growth of hydraulic resistance accompanying corrugation depend in a quite complicated way on geometric parameters of the corrugated surface when the Reynolds and Prandtl numbers vary
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