# A New Procedure to Design an Open Circuit Blowing Subsonic Moist-Air Wind Tunnel
## 5 Discussion  
In the present paper, a moist-air wind tunnel prototype that revealed the real behaviour of moist-air phase change in a real wind concentrator under low wind velocities has been designed and developed. The wind tunnel was designed according to the study in [7], similar to the one in [13; 14]. To reach the test conditions, temperature, relative humidity and wind speed control systems were used. Measurements were recorded using the data loggers and a digital anemometer. The wind tunnel velocity was set at 5 m/s in keeping with other authors [20; 28] who had conducted a wind tunnel test in the range of 6 to 11 m/s. This wind tunnel control system threw much light on the behaviour of wind concentrators and wind turbines under different weather conditions. Similarly, a new wind concentrator control system enabled the control of moist-air conditions at the inlet of the wind turbine and thus in energy conversion. However, some improvements, like computer control systems, must be developed for such types of wind tunnels. Figure 26: Simulation of wind concentrator velocity (point 3) at 100%. Figure 25: Moist air relative humidity (m/s): \(p=101\),328 Pa, \(T=292.8\) K, \(V=5\) m/s. In consequence, this system may be a laboratory test that emulates the behaviour of a low-speed wind turbine that receives moist air from a nozzle that improves the wind energy conversion based on the moist air phase change. In this sense, point 1 of Figure 9 represents the wind and points 2 and 3 let us understand the real conditions in the nozzle inlet (point 2) and nozzle throat (point 3). Furthermore, in Figures 18-20, an expansion process that makes a reduction in moist air temperature and an increase in the relative humidity when reaching from point 2 to point 3. These results were validated with CFD simulations, which are shown in Figures 22-25, but, as it can be appreciated, in accordance with the nozzle design, the 3D distribution of the relative humidity and temperature is not homogeneous in each point but getting an average value in agreement with sampled data. It must be highlighted that the phase change process was obtained partially when the weather conditions reached 95% (something so common during the night in some Galician regions in the winter season). In consequence, although in point 3, an increase in moist-air velocity was updated, sampled data showed that this increase was not as high as expected. This is because the energy released from moist air depends on its phase change, and it can only be reached when the relative humidity is 100% in this section. This need for 100% relative humidity inside the nozzle implies an outdoor air relative humidity of 98%, which is a too high value for an open wind tunnel based on adiabatic saturation of the air. Despite this, 98% of relative humidity can be obtained in humid areas in outdoor conditions in the Galician winter season during certain periods of time. Once the CFD simulations were validated with the average value of the prototype, it is possible to understand what may happen if 100% of relative humidity is obtained inside the nozzle by more simulations. In consequence, an outdoor air velocity was simulated at 100% in this situation, as shown in Figure 26.  
From Figure 26, it is evident that this model, in accordance with its original design, shows a clear increase in moist-air velocity in the lower section from 5 m/s of outdoor air. It also reveals a constant proportionality value with respect to the outdoor air from 5 to 14 m/s. From this last value, a really significant increase to 24 m/s was obtained. The sensibility at the time to sample moist air pressure in Pa proved to be really complicated due to electronic devices not letting us be accurate enough, and differential manometers were needed (certified by the calibration certificate by the seller). The number of decimal points employed to sample this variable was adequate to sample inlet and outlet conditions of air in the nozzle.