3.5.2. Ventilation Volume

When the fan works, the air volume generated by the fan is proportional to the speed of the fan blades. The ventilation volume calculation equation of the ventilator is as follows:

$$\frac{Q\_1}{Q\_2} = \frac{n\_1}{n\_2} = k \tag{15}$$

where *Q*<sup>1</sup> is the air volume of the original natural ventilator at different speeds, *Q*<sup>2</sup> is the air volume of the optimized natural ventilator at different speeds, m3/s; *n*<sup>1</sup> and *n*<sup>2</sup> are the fan speeds, rpm; and *k* is the scale factor.

When the natural ventilator and the axial fan blade rotate, the working principle of the fan system is similar to that of the fan system. The relationship between the air volume and the rotating speed is as follows, and the scale factor *k* is affected by the shape of the ventilator and the axial fan blade:

$$q = k \cdot n \tag{16}$$

where *q* is the air flow generated by the rotation of the natural ventilator and axial fan blade, r/s; *n* is the speed of ventilator, r/s; and *k* is the scale factor.

According to the analysis of the experimental results, assuming that only the ventilator was working, *q*<sup>1</sup> = *k*<sup>1</sup> · *n*1, we found the scale coefficient *k*<sup>1</sup> was 0.339. When axial fan blades are added to the ventilator, *q*<sup>2</sup> = *k*<sup>2</sup> · *n*2. We found the scale coefficient *k*<sup>2</sup> was 0.389. According to the experimental results, *k*<sup>1</sup> and *k*<sup>2</sup> are applicable to the different types of fan blade settings.

The original natural ventilator worked at 60 rpm = 1 r/s, and the wind speed in the duct was 0.33 m/s. However, when the same energy was consumed, the average rated speed of the natural ventilator, which had been optimized, was 57.06 rpm = 0.951 r/s, and the wind speed in the duct was 0.37 m/s.

Before the ventilator was optimized, the volume *q*<sup>1</sup> = *k*<sup>1</sup> · *n*<sup>1</sup> was 0.339 × 1 = 0.339 m3/s = 1200.4 m3/h. After the ventilator was optimized, the volume *<sup>q</sup>*<sup>2</sup> <sup>=</sup> *<sup>k</sup>*<sup>2</sup> · *<sup>n</sup>*<sup>2</sup> was 0.389 <sup>×</sup> 0.951 = 0.37 m3/s = 1333.2 m3/h. Then, *<sup>η</sup>* was calculated as:

$$\eta = \frac{q\_2 - q\_1}{q\_1} = \frac{1333.2 - 1200.4}{1200.4} \times 100\% = 11.1\% \tag{17}$$

The ventilation capacity of the optimized natural ventilator was increased by 11.1%.

### *3.6. Smoke Exhaust Performance of Optimized Natural Ventilator 3.6. Smoke Exhaust Performance of Optimized Natural Ventilator*

× 0.951 = 0.37 m3/s = 1333.2 m3/h. Then, *η* was calculated as: 2 1 1

*q q q*

*Fire* **2022**, *5*, x FOR PEER REVIEW 19 of 22

of fan blade settings.

the wind speed in the duct was 0.37 m/s.

η

The working conditions of fire smoke experiments using the original and optimized ventilator are shown in Table 8. The working conditions of fire smoke experiments using the original and optimized ventilator are shown in Table 8.

1333.2 1200.4 100% 11.1%

<sup>−</sup> <sup>−</sup> = = ×= (17)

fan blades are added to the ventilator, 2 22 *q kn* = ⋅ . We found the scale coefficient *k*2 was 0.389. According to the experimental results, *k*1 and *k*2 are applicable to the different types

The original natural ventilator worked at 60 rpm = 1 r/s, and the wind speed in the duct was 0.33 m/s. However, when the same energy was consumed, the average rated speed of the natural ventilator, which had been optimized, was 57.06 rpm = 0.951 r/s, and

Before the ventilator was optimized, the volume 1 11 *q kn* = ⋅ was 0.339 × 1 = 0.339

m3/s = 1200.4 m3/h. After the ventilator was optimized, the volume 2 22 *q kn* = ⋅ was 0.389

1200.4

The ventilation capacity of the optimized natural ventilator was increased by 11.1%.



According to Figure 22, when the fire was small (15 × 5 × 4 cm), the effects of the optimized and original ventilators on temperature reduction were approximately the same. This is because the thermal pressure driving force was not enough to drive the optimized ventilator when the fire was small. Therefore, the temperature did not show an obvious downward trend. According to Figure 22, when the fire was small (15 × 5 × 4 cm), the effects of the optimized and original ventilators on temperature reduction were approximately the same. This is because the thermal pressure driving force was not enough to drive the optimized ventilator when the fire was small. Therefore, the temperature did not show an obvious downward trend.

**Figure 22.** Temperature change of ventilator before and after optimization in the case of a fire environment (fire scale: 15 × 15 × 4 cm). **Figure 22.** Temperature change of ventilator before and after optimization in the case of a fire environment (fire scale: 15 × 15 × 4 cm).

However, Figure 23 shows that the optimized ventilator markedly reduced the temperature under the thermal pressure driving force of the fire. However, Figure 23 shows that the optimized ventilator markedly reduced the temperature under the thermal pressure driving force of the fire. *Fire* **2022**, *5*, x FOR PEER REVIEW 20 of 22

**Figure 23.** Temperature change of ventilator before and after optimization in fire environment (fire scale: 20 × 20 × 4 cm). **Figure 23.** Temperature change of ventilator before and after optimization in fire environment (fire scale: 20 × 20 × 4 cm).

The hot pressure driving force generated by the flame makes the ventilator rotate at a higher speed. Therefore, if the optimized ventilator is used for smoke exhaust, the tem-

To further apply an unpowered ventilator in different buildings or tunnels and quickly exhaust smoke during building and tunnel fires, in this study, we conducted a series of experiments to investigate its ventilation and smoke exhaust performance. Our

(1) After adding a set of axial fan blades below the natural ventilator, the rotational speed of the ventilator decreased at the same power, but the ventilation volume of the ventilator increased, and the ventilation performance of the ventilator was en-

(2) At the same speed, with increasing numbers of axial flow fan blades and increasing fan blade angle, the air volume of the ventilator first increased and then decreased. When the number of fans was five and the angle was 25°, the air volume of the ventilator was the largest and the ventilation effect was the best. Compared to adding backward curved fan blades, the ventilator with forward curved blades produced a

The natural ventilator constructed in this study was a swirling natural ventilator 6. This type of unpowered ventilator was also used in the smoke exhaust experiments. Therefore, we conclude that this type of ventilator is more suitable for selected flow natural ventilators, and the optimized natural ventilator is suitable for smoke exhaust from buildings or tunnels. However, in other scenes (such as factories), the optimized unpowered ventilator has not been tested, which is a future research direction for natural venti-

larger air volume and a better ventilation effect at the same wind speed. (3) When the wind speed at the fan outlet reached 5.179 m/s, the original ventilator rotated at the rated speed of 60 rpm. When the same wind speed acted on the optimized ventilator, the speed was 57.06 rpm; the speed was reduced by 4.5 rpm. The air volume was increased by 11.1%, and the energy consumption was reduced by 2.952 J. (4) The optimized ventilator could quickly exhaust he fire smoke in an actual experiment and lower the temperature of the ventilator without consuming energy. Therefore, the optimized ventilator can be installed in buildings or tunnels to quickly exhaust

exhaust the smoke faster, and the smoke exhaust efficiency of the ventilator will be im-

proved.

**4. Conclusions** 

hanced.

fire smoke.

lator smoke exhaust.

conclusions are summarized as follows:

The hot pressure driving force generated by the flame makes the ventilator rotate at a higher speed. Therefore, if the optimized ventilator is used for smoke exhaust, the temperature in the air duct will decrease faster, the temperature generated by the flame can exhaust the smoke faster, and the smoke exhaust efficiency of the ventilator will be improved.
