## 2 Harvesting System
### Theoretical Principles of Mini Wind Harvester Operation
#### 3.2.2 Work Operation inside a Closed Environment  
Figure 13 shows the test set-up diagram, which has the following elements: an air pump, a gate valve, a control valve with a gauge, a connection pipe, two pitot tubes, an anemometer, an oscilloscope, one test-bench, and the mini wind harvester. The test set-up works as follows: the air pump provides the required air flow, whose pressure gate valve controls its insertion. The pitot tubes measure the pressure value before and after the mini wind harvester, and the anemometer provides the air velocity. In addition, the oscilloscope is used to collect the data for post-processing. Table 9 shows the results of tests carried out to measure the pressure level for the different wind velocities. The table also provides the equivalent wind power for its corresponding pressure level. Where \(\gamma\) is the density of the air, A is the effective area of the wind harvester, \(\
u\) is the wind velocity, Q is the volumetric flow rate, and H is the pressure inside the pipe. With the wind power data for each flow velocity, the efficiencies, powers and losses of the harvester are obtained for the same test loads used in this work, in order to characterize the behavior of the different parts of the system. Table 10 and Figure 14 show the results for loads of 27 \(\Omega\), 11 \(\Omega\) and 100 \(\Omega\). These values are corresponded to the maximum efficiency and produced electrical power, thus, the lower mechanical losses. The best results are achieved for an impedance matching load of 27 \(\Omega\). In the 11 \(\Omega\) load condition, the load impedance is mismatched with the source, the mechanical losses increase, and the efficiency of the system begins to decrease. Finally, with a 100 \(\Omega\) load, unless the energy demand is lower, there is higher impedance mismatching, and the mechanical losses increase more than in the previous load conditions. The efficiency of the system does not reach the 11%. Figure 13: Test set-up diagram to measure wind power for the mini wind harvester model. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \(\gamma\) (g/cm\({}^{3}\)) & A (cm\({}^{2}\)) & \(\
u\) (cm/s) & Q (cm\({}^{3}\)/s) & H (mbar) & Wind Power (mW) \\ \hline
0.0013 & 8.04 & 300 & 2412 & 20 & 62.712 \\
0.0013 & 8.04 & 400 & 3216 & 36 & 150.509 \\
0.0013 & 8.04 & 500 & 4020 & 52 & 271.752 \\
0.0013 & 8.04 & 600 & 4824 & 91 & 570.679 \\
0.0013 & 8.04 & 700 & 5628 & 112 & 819.437 \\
0.0013 & 8.04 & 800 & 6432 & 142 & 1187.347 \\
0.0013 & 8.04 & 900 & 7236 & 144 & 1354.579 \\
0.0013 & 8.04 & 1000 & 8040 & 163 & 1703.676 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Measured wind power values for different wind flow ranges. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**v** & **Pressure** & **Wind Power** & **Rload** & **Elec. Power** & **Mech. Losses** & **Efficiency** \\ **(m/s)** & **(mbar)** & **(mW)** & **(\(\Omega\))** & **(mW)** & **(mW)** & **(\%)** \\ \hline  
\hline \hline \end{tabular}
\end{table} 
Table 10: Generated electric power, mechanical losses, and system efficiency values from 3 m/s to 10 m/s; from 20 mbar to 163 mbar with 27, 11 and 100 \(\Omega\) loads. Figure 14: _Cont._The presented measures of voltage, power and frequency were obtained for the impedance matching load and a varying wind flow velocity between 3 m/s and 10 m/s. However, it is likely that the mini wind harvester with 2 m/s wind velocity should be able to produce enough power. Although the harvested energy is a direct function of the pressure energy, several graphs and data are expressed as a function of the velocity of the air flow and not as a function of the pressure because in m/s the scale is linear. It is easier to interpret a linear scale of velocity between 3-10 m/s than a non-linear scale of pressure between 62-1703 mW. However, Table 9 could be used to make the conversion.