Hydrodynamics analysis in micro-channels of a viscous coupling using gamma-ray computed tomography

In this work, high-resolution gamma-ray computed tomography (HireCT) was applied for the first time on a viscous coupling to visualize the internal working fluid distribution. The HireCT measurement system comprises a ¹³⁷Cs isotopic source and a gamma-ray detector arc operated in single photon counting mode. It is able to produce cross-sectional images of dense objects with a spatial resolution of about 2 mm. To scan fast rotating parts time-averaged rotation-synchronized CT scanning mode was employed in these experiments. The analyzed viscous coupling (Visco^® clutch of MAHLE Behr) mainly consists of a driven primary disc and a secondary housing with an engine cooling fan mounted on it. The viscous coupling is assembled within an experimental rig. Its primary and secondary parts are axially assembled and a working liquid is pumped into engaged radial ring profiles to provide a defined torque transfer. The internal ring channel width, where the working liquid is to be observed, is considerably lower than one millimeter. Although the HireCT measurement system is not able to resolve these micro-channels, the working liquid can be successfully visualized via its phase contrast. Investigations have been performed at different filling levels corresponding to different transmission slips of the test viscous coupling. Moreover, both radial and tangential liquid distributions for different operational steady states could be determined. Finally, the obtained experimental data were compared to results from computational fluid dynamics (CFD) simulations in some operating points and were in good agreement.