Influence of the flow structure formation on heat transfer processes in tubes with spiral corrugated inserts

Abstract

In order to enhance heat transfer processes in elements of power equipment with minimal energy consumption, the concept of partial structure formation of the heat transfer surface was developed. To determine the energy efficiency of partial structure formation of the heat transfer surface with transitional Reynolds numbers, the surface in the form of spiral corrugation is considered. Partial spiral corrugation due to a change in the flow structure makes it possible to increase the convective component of heat transfer with a moderate increase in friction loss in a transient flow regime. Based on direct numerical simulation of the three-dimensional non-stationary flow structure in the initial section of the tube with a spiral corrugated insert with the shock inlet and transition Reynolds number, the relationship between the structure of the disturbed non-isothermal flow and heat transfer rate on the tube surface is shown. The influence of temperature head on the growth rate of perturbations of the boundary layer in the tube, in the boundaries of which low-frequency oscillatory flow processes are formed, leading to an increase in convective heat transfer rate, is shown. The flow nature and changes in hydrodynamic and thermal parameters in the corrugated insert are investigated. The degree of influence of the spiral corrugated insert, not blocking the flow area of the tube, on the development of natural oscillations in the tube is determined. The influence of the pitch of spiral corrugation to the tube axis on the thermal and hydrodynamic processes in it is investigated. The resulting heat transfer enhancement (up to 20 %) with a simultaneous increase in friction loss (up to 7.5 %) correlates with the experimental results of other authors with similar corrugations in the given range of Reynolds numbers.