Heat-transfer coefficients on surfaces exposed to convection environments are often measured by transient techniques such as transient liquid crystal or infrared thermography. In these techniques, the surface temperature is measured as a function of time, and that measurement is used with the exact solution for unsteady, zero-dimensional (0-D) or one-dimensional (1-D) heat conduction into a solid to calculate the local heat-transfer coefficient. In using the 0-D or 1-D exact solutions, these transient techniques assume that the heat-transfer coefficient is independent of time, that the free-stream or bulk temperature characterizing the convection environment is a constant, and that the conduction into the solid is 0-D or 1-D. In this study, CFD conjugate analyses were performed to examine the errors invoked by these assumptions for a problem, where the free-stream/bulk temperature and the heat-transfer coefficient vary appreciably along the surface and where conduction into the solid may not be 0-D or 1-D. The problem selected to assess these errors is flow and heat transfer in a channel lined with a staggered array of pin fins. This conjugate study uses 3-D steady and unsteady RANS closed by the shear-stress transport (SST) turbulence model for the gas phase (wall functions not used) and the Fourier law for the solid phase. The errors are assessed by comparing the heat-transfer coefficients predicted by the 3-D CFD with those predicted by the 0-D and 1 -D exact solutions, where the surface temperatures needed by the exact solutions were taken from the 3-D CFD solution.
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