# Feasibility of Optical Flow Field Measurements of the Coolant in a Grinding Machine
## 3 Experimental Setup and Signal Processing
### Optical Setup  
The optical setup is shown in Figure 2. It is realised according to the scheme illustrated in Figure 4. A light-emitting diode (LED) panel is installed as a diffuse background illumination on the rear wall within the working area of the grinding machine for flow visualisation with shadowgraphy. It provides an illumination of 2400 lm in neutral white (colour temperature 4300 K). The distance from the LED panel to the centre of the grinding \begin{table}
\begin{tabular}{c c c c} \hline \(Q\) in L/min & \(\
u_{\text{sup,theo}}\) in m/s & \(Re\) & Flow State \\ \hline
14.9 & 5.40 & 2024 & laminar \\
26.6 & 9.64 & 3614 & transient \\
39.4 & 14.26 & 5349 & turbulent \\ \hline \end{tabular}
\end{table} 
Table 1: Experimental parameter for the volume flow \(Q\), theoretical flow velocity \(v_{\text{sup,theo}}\). Reynolds number \(Re\) and expected flow state for measurements on the supply flow with nozzle width of \(w=~{}20\) mm and height of \(h=~{}2.3\) mm. \begin{table}
\begin{tabular}{c c c c} \hline \(Q\) in L/min & \(\
u_{\text{sup,theo}}\) in m/s & \(Re\) & Flow State \\ \hline
16.0 & 14.78 & 2313 & laminar \\
26.6 & 24.63 & 3856 & transient \\
37.2 & 34.48 & 5399 & turbulent \\ \hline \end{tabular}
\end{table} 
Table 2: Experimental parameter for the volume flow \(Q\), theoretical flow velocity \(v_{\text{sup,theo}}\). Reynolds number \(Re\) and expected flow state for measurements on the fluid-tool interaction with nozzle width of \(w=~{}20\) mm and height of \(h=~{}0.9\) mm. wheel is 250 mm. For the observation, a high-speed camera of the type Pro Y4 from the company Integrated Design Tools Motion is located at a distance of \(z=60\) mm to the centre of the grinding wheel with the camera axis orientated in \(z\)-direction. A spatial resolution of 125 um/px is achieved with the 105 mm F2,8 EX macro objective from the company Sigma and the shadowgrams are recorded with a repetition rate of 13.700 Hz and an exposure time of 50 us. The exposure time is short enough to capture quasi-stationary images of the flow details. To obtain PIV measurements of the MWF supply, polyamid seeding particles with an average size of 50 um and a density of 1.03 g/cm\({}^{3}\) are filled into the MWF tank of the grinding machine. To illuminate the seeded flow, a frequency-doubled pumped Nd:YAG pulsed laser at a wavelength of 532 nm with a maximum energy per pulse of 200 mJ and a pulse length of 10 ns of the type Evergreen from the company Quantel is used. A double pulse repetition rate of 15 Hz is used with a time separation per pulse between 70 us to 100 us, which is adjusted according to the flow velocity. The laser light sheet has a width of approximately 50 mm with a sheet thickness of 1 mm. It illuminates the free MWF supply jet between the positions 50 mm to 100 mm along the \(x\)-axis and is placed in the centre axis of the free jet. The laser beam is guided into the grinding machine with a light-guiding arm, which provides the necessary flexibility and protection from contaminating MWF for the optical components. The necessary optics to form a laser light sheet are installed in the grinding machine and protected by a housing to avoid unwanted contamination by MWF droplets. For particle imaging a 5.5 Mpx sCMOS camera of the type Zyla from the company Andor with a 50 mm focal length objective of the type Planar T* 1.4/50 from the company Zeiss is used. The camera is positioned at a distance of \(z=60\) cm to the MWF jet, observing in \(z\)-direction and images are taken with a spatial resolution of 80 um/px. Figure 4: Used experimental flow measurement setup in the grinding machine: (**a**) setup in the protective housing, where the optical components such as the laser, light guiding arm and camera are installed; (**b**) arrangement of the grinding wheel and nozzle in the grinding machine; (**c**) setup for SIV measurements, consisting of the mounted camera and the LED panel. For a reduction of disturbing ambient light, a bandpass filter with a central wavelength of 532 nm and FWHM bandwidth of 4 nm is used.