Correcting the Periodic Optical Distortion for Particle-Tracking Velocimetry in Corrugated-Plate Heat Exchangers

Abstract

To improve current methods for the experimental validation of numerical simulations in corrugated-plate heat exchangers (CPHEs), a full-field quantitative velocimetry of fluid flow is required. This paper investigates the application of particle-tracking velocimetry (PTV) to modified CPHEs. For this, an experimental CPHE unit with a transparent, corrugated upper plate was built. We show that by viewing through a corrugated, refractive interface, a complex periodic optical distortion is introduced, that affects and corrupts the estimated particle trajectories. As this problem cannot be addressed using existing calibration techniques, we propose a novel calibration algorithm for periodic optical distortion. The algorithm relies on the automatic detection of nonlinear distortion using a checkerboard target place within the CPHE unit. The calibration is first made on a coarse grid and subsequently refined by a set of low-order periodic basis functions in order to seize the periodic nature of the deformation field. The proposed algorithms have been applied to a test case with known, uniform particle velocities in order to demonstrate the performance. When applied to a real case, a reduction in the systematic positional error by 35 % was demonstrated.