## 4 Results and Discussion
### Heat Recovery  
Energy saving is vital in today's conditions. Energy production costs are increasing due to the decrease in energy resources, and most energy production methods negatively affect the environment. Studies in this field focus on saving energy by developing energy models. However, it is clear that recovering the spent energy and, if possible, converting this gained energy to its original form or reusing it as a different type of energy, will be much more efficient than pure energy saving. In this study, a comprehensive heat recovery system was developed for heat recovery from the coolant used in the metalworking process (this system is registered with the patent number 201922131). The heat energy obtained  
Figure 8: Energy consumptions for 15 \({}^{\circ}\)C coolant temperature. Figure 9: Energy consumptions for 20 \({}^{\circ}\)C coolant temperature. is used for heating domestic water and workshop. The energy obtained is measured instantly with the help of a data logger integrated into the system. An example of energy calculation is shown in Table 3. Data obtained from the data logging system are used in these calculations. The recovered heat energy can be calculated using Formula (1):  
\[\mathrm{Q}=\dot{m}\cdot\mathrm{c}\cdot\left(\mathrm{t}\aas@@fstack{\prime}7 -\ \mathrm{t}6\right)/60000\ (\mathrm{kW}) \tag{1}\]  
where \(\dot{m}\) and \(\mathrm{c}\) are, respectively, the mass flow rate and specific heat of the water (\(4182\ \mathrm{j}/\mathrm{kg}^{\circ}\mathrm{C}\)). In order to calculate the heat energy recovered using this Equation, the temperature and flow rates in the system were measured. The mass flow rate is calculated according to the following relation:  
\[\dot{m}=\rho\frac{V}{t} \tag{2}\]  
Here, \(\rho\) is the density of water (\(1000\ \mathrm{kg}/\mathrm{m}^{3}\)), \(V\) is the volume (lt) passing through the line in the measurement intervals, and \(t\) is the time between two measurement intervals. The \(t6\) and \(t7\) are the temperature values read from the temperature sensors numbered 6 and 7 placed at the inlet and outlet of the heat exchanger. The average energy is found by averaging the instantaneous energies obtained from the line on the recovery system at the same time intervals throughout the experiment period. Total energy is found by multiplying the average energy obtained per unit time by the total experiment time. Sample data calculation is shown in Table 4. \begin{table}
\begin{tabular}{c c c} \hline
**Calculated Average Energy** & **Total Working Time** & **Total Energy** \\
**(kWh)** & **(h)** & **(kWh)** \\
2.093 & 0.37 & 0.767 \\ \hline \end{tabular}
\end{table} 
Table 4: Sample data calculation. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline
**Time** & **Date** & **t6** & **t7** & **t8** & **t9** & **t10** & **Flow Meter** & **Calculated Flow** \\
18:48:00 & 9 October 2023 & 32.3 & 34 & 15.1 & 18.9 & 28.2 & 24.08 & 2.852 \\
18:49:54 & 9 October 2023 & 32.2 & 33.7 & 14.8 & 18.8 & 28.2 & 23.52 & 2.458 \\
18:50:55 & 9 October 2023 & 32.1 & 33.5 & 14.6 & 18.7 & 28.2 & 22.96 & 2.23  
each variable on heat recovery. According to the results, the feed rate emerges as the most influential parameter affecting heat recovery, with a \(p\)-value of 0.062. Figure 11 illustrates the S/N analysis graphs for heat recovery. In these graphs, the optimal value for each parameter corresponds to the highest signal-to-noise ratio. Based on the analysis, the ideal settings at a coolant temperature of 15 \({}^{\circ}\)C are as follows: an emulsion ratio of 7.5%, a feed rate of 0.04 mm/rev, and a spindle speed of 398 rpm. Furthermore, by examining the variation between the maximum and minimum S/N ratios of the parameters, the parameter exhibiting the largest difference is identified as the most influential. Consequently, the feed rate is determined to have the most significant impact on heat recovery. This finding aligns with the results obtained from variance analysis.