Heat Transfer in Turbulent Boundary Layers of Pipe Flow: A Wavelet Transforms Approach

Abstract

Transport of energy in turbulent boundary layers of pipe is characterised by two simulatneous, complimentary processes vis-a-vis turbulent advection and conduction. Both the aforementioned processes are manifestations of passive scalar transport in the turbulent boundary layer. Since passive scalar transport is intimately related to flow structure evolution, a wavelet based method is used to characterise flow structure evolution. This work deals with the calculation of turbulent advective and conductive heat fluxes for a high temperature heat transfer molten salt FLiNaK.Heat transfer of a molten fluoride salt, FLiNaK with a eutectic composition of 46.5 %LiF-11.5 %NaF-42 %KF (mol %) in the turbulent boundary layer of pipe is characterised by the transport of passive scalar (Temperature). Energy coupled large eddy simulation (LES) were carried out to obtain transient velocity and temperature (passive scalar) data in the domain. Two complimentary fluxes namely turbulent advective and conductive are a manifestation of this passive scalar distribution. Calculation of conductive flux from the aforementioned transient velocity and temperature data is relatively straightforward which involves knowledge of thermal conductivity (k), whose temperature dependence is well documented [1]. But, the calculation of turbulent advective flux involves knowledge of local heat transfer coefficient (HTC), which has a extremely complex dependence on evolution of local turbulent flow structures. We deal with this issue using multi-scale wavelet methodology namely Wavelet transform modulus maxima (WTMM) [2,3], to disseminates the flow struc-