# Feasibility of Optical Flow Field Measurements of the Coolant in a Grinding Machine
## 5 Conclusions and Outlook  
In this study, the feasibility of optical measurements of the MWF flow in a grinding process is investigated for a simplified setup without workpiece. For this purpose, two different measurement methods (SIV and PIV) were implemented in a grinding machine. The majority of the presented flow field measurements is based on characteristic flow structures, which are visualised with shadowgraphy and used as flow tracers for SIV. The validity of this method is shown by comparison measurements of the supply flow with PIV reference measurements. The standard deviations for the velocity measurements of the _MWF free supply jet_ are determined from the measurement series, neglecting outliers. For PIV, a maximum standard deviation of 4% results, independent of the measurement arrangement. In comparison, the measurements for SIV showed a maximum standard deviation of 6% for the top view and 11% for the side view, respectively. The superposition of visualized fluid structures in different depths, combined with the change in shape of these structures, results in a significantly increased random deviation, especially in the side view. Nonetheless, the measurement results provide a first impression of the MWF flow, in particular of the average flow velocity, which is one of the most important parameters for the grinding process. In addition, the use of a theoretical velocity from the continuity equation is confirmed. Furthermore, the velocity measurements offer the possibility to detect unforeseen (e.g., pressure-related) geometric deviations of the nozzle geometry by a comparison of the theoretical and the measured velocity fields. Systematic measurement deviations of the supply flow velocity are revealed, necessitating further investigations in order to provide an appropriately resolved measurement of the MWF supply flow behaviour along the jet axis. Measurement deviations are most likely contributed by the light deflection at the curved surface of the liquid-air phase transition. The measured velocity flow fields after the _interaction with the grinding wheel_ are verified by the plausibility of the visualised flows. The velocity changes that occur as a result of the interaction at the grinding wheel agree in magnitude and direction with the circumferential velocity of the grinding wheel. Only the flow in direct contact with the grinding wheel is not measurable due to the absence of visualisable fluid structures. Further research on the measurability of the flow in relation to the illumination conditions is therefore recommended. The obtained results prove the feasibility of quantitative SIV-based flow velocity field measurements for the MWF supply flow as well as for the MWF flow after the grinding wheel interaction. This is a key step to the future understanding of the connection between the cooling properties of fluid dynamics and thus, to the ongoing development of optimised cooling in the grinding process. In future investigations, the influence of a workpiece on the measurability of the flow directly in front of and behind the interaction zone has to be examined. For this purpose, a grinding setup with variable grinding gap will be used. When the fluid interacts with the grinding gap, not all of the fluid is coupled into the cooling process and the non-coupled portion bounces off the workpiece and tool. This results in a highly atomised backflow that affects the observation of the flow, and its impact on the flow measurement has to be determined. Furthermore, investigations to estimate the local mean fluid concentrations in the droplet regions of the MWF flow field are of interest, since the concentrations also influence the cooling performance. For this purpose, an approach to determine the concentrations from the captured shadowgram image intensities in the droplet regions will be tested. Conceptualisation: [PERSON], C.V., D.S. and A.F. ; investigation: [PERSON] and L.S., supervision: [PERSON] and A.F. ; visualisation: [PERSON], writing original draft: B.E.