Local Heat Transfer Dependency on Thermal Boundary Condition in Ribbed Cooling Channel Geometries

Abstract

The present study is geared toward quantifying the effects of imposed thermal boundary condition in cooling channel applications. In this regard, tests are conducted in a generic passage, with evenly distributed rib type perturbators at 90 deg, with a 30% passage blockage ratio and pitch-to-height ratio of 10. Uniform heat-flux is imposed on the external side of the slab which provides Biot number and solid-to-fluid thermal conductivity ratio around 1 and 600, respectively. Through infrared thermometry measurements over the wetted surface and via an energy balance within the solid, conjugate heat transfer coefficients are calculated over a single rib-pitch. The local heat extraction is demonstrated to be a strong function of the conduction effects, observed more dominantly in the rib vicinity. Moreover, the aero-thermal effects are investigated by comparing the findings with analogous aerodynamic literature, enabling heat transfer distributions to be associated with distinct flow structures. Furthermore, the results are contrasted with the iso-heat-flux wetted boundary condition test case. Neglecting the thermal boundary condition dependence, and thus the true thermal history of the boundary layer, is demonstrated to produce large errors in heat transfer predictions.

Influence of the thermal boundary conditions on the heat transfer of a rib-roughened cooling channel using LES

“…For the practical case of a real turbine blade, assuming a coolant temperature of 900 K and a metal temperature at the material limit of 1200 K 5 and a Biot number of order unity, we obtain a temperature difference in the blade of around 10 K. Locally, this value may be larger due to larger local enhancement factor differences. Since the life of a turbine blade is reported to be half for an increased temperature of 30 K, this temperature difference demonstrates the severe impact of the applied boundary condition on the design application.…”

“…The relative bulk flow temperature (or temperature ratio) T∞ΔT was assumed to have only a small effect on the heat transfer in the experiments 5,15 and it is assumed that the Nusselt number depends only on the Reynolds number, the conductivity ratio between fluid and solid and the Biot number: Nu=f(Re,K,Bi).…”

“…The applied configuration models the experimental facility of Ç akan, 14 Cukurel, 5,15 which was a simplified model of an internal rib-roughened aircraft gas turbine blade cooling passage with a pitch to rib ratio of 10 and a blockage ratio of 0.3 ( Table 1 summarizes dimensions). The cooling passage was scaled up by a factor of 15 with respect to real engine conditions.…”

“…Experimental studies did recently indicate a conjugate effect. 5 An objective of this study is whether this experimental observation can be found to be true numerically via LES, while bypassing real conjugate computations by applying different flux boundary conditions and thus reducing the computational cost.…”

Direct Simulation of Internal Flow Transient Liquid Crystal Experiments

“…Another consideration is what effect does the transient change in the thermal boundary layer has on the local heat transfer coefficient, which in a transient TLC experiment will be continually changing. Cukurel and Arts [13] demonstrated this is significant by comparing two steady state cases of an iso-heat flux and a convective boundary condition. This has led to strategies applying three point non-linear corrections when applying steady state CFD to determine local heat transfer coefficients [14].…”