## 5 Experiment Measurement and Analysis
### Performance Analysis and Comparison of Reference Fan and Optimal Fan  
The rotating speed of the stand fan is fixed at 900 rpm during the CFD simulation. Therefore, for comparison, the test results should be measured by using fan law to match with the operating speed of 900 rpm. As explained in the last paragraph, there are four sets of experimental results obtained for comparing to each other. As a result, the test outcome shows that the max flow velocity at the monitoring surface of the reference fan is 2.83 m/s (see Table 5). Even the enhancement in the flow rate is 48% greater than that of the reference fan, however, the max velocity of the redesign fan #1 and optimal fan are reduced to 2.15 and 2.76 m/s, respectively. Clearly, the velocity profiles generated by the optimal rotor are more flat and uniformly distributed under the constraint (higher flow rate and smaller peak velocity). In addition, the air speed drops significantly from the center of the rotor to the circumferential ring, where the velocity decreases to ignorable values of less than 0.1 m/s. This kind of velocity pattern can be observed for all the test fan sets; however, the reference fan has the fastest decline trend among the test fans in this experimental program. In addition, as indicated in Figure 11, the velocity distributions generated by the optimal impeller (including the optimal fan and redesign #1 fan) are smoother, but it becomes quite fluctuated when the air stream passes through the reference protective cover. On the other hand, the flow distribution generated by the optimal fan is flat and extended to a wide region; thus, there is a small velocity (less than 1 m/s) near the outer edge of the protective cover (see Figure 11b). Furthermore, after improving both the impeller and protective cover, the experimental flow rate of the optimal fan enlarges from 1590 up to 2455 CFM (see Table 5), which represents a 54% increase compared with the reference fan under the same rotating speed. Besides, the flow rate of redesign fans #2, which is constructed by integrating the reference impeller and optimal protective cover, is slightly better (2.9% enhancement) than the original reference fan although its max flow velocity is 2.53 m/s, which is a little less than the reference fan's. It is concluded that the optimal protective cover can make the flow distribution more uniform even under a concentrated outflow by the reference impeller. The simulation deviations for all testing samples are in a range between approximately 10% and 16% (see Table 5) while the experimental and simulation results have the same tendency overall. In addition, the distribution tendency of simulated flow velocity is consistent with the experimental result. Thus, the simulation error is still within an acceptable range and considered as having a good reliability. Figure 10: Mockups of the optimal impeller and protective cover. (**a**) Impeller; (**b**) protective cover. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Cases**} & \multicolumn{3}{c}{**Max Flow Rate**} & \multicolumn{3}{c}{**Tested Energy Consumption**} & \multirow{2}{*}{**Max Test**} \\ \cline{2-2} \cline{4-7}  & **CFD (CFM)** & **Test (CFM)** & **Deviation (\%)** & **Power (Wait)** & **Efficiency (CFMWat0)** & **Percentage (\%)** & **Velocity (m/s)** \\ \hline Reference fan & 1436 & 1590 & 10.7 & 29.1 & 54.6 & - & 2.83 \\ Redesign fan #1 & 2017 & 2341 & 16.1 & 50.9 & 46.0 & -16 & 2.15 \\ Redesign fan #2 & 1470 & 1636 & 11.3 & 29.1 & 56.2 & 3 & 2.76 \\ Optimal fan & 2126 & 2455 & 15.4 & 50.9 & 48.3 & -13 & 2.53 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The performance comparison between the test and CFD results of the reference fan and the redesign fans under 900 rpm. In general, for the human body, exposure to 1 m/s wind speed is considered as the more comfortable situation. After checking the velocity distribution for the optimal fan, its flow field distribution is quite uniform and symmetrically extended in all directions (see Figure 11).