The hood is the research object.
As shown, the multi-blade centrifugal fan of the range hood is a double-sided air intake structure, and is composed of an impeller, a volute, a shroud and a built-in motor. The specific structural parameters of the impeller are as follows: the inner diameter of the impeller is Di=204mm, the outer diameter of the impeller is D2=240mm, the number of blades is Z=60 pieces, and the blades are single-arc-shaped thick blades, which are distributed along the circumference, and the blade thickness is 0.5. Mm, the blade inlet angle is negative = 72., the blade exit angle is up to 170., the leaf center angle
The aerodynamic performance test is to ensure that the other structure of the range hood is unchanged under the strong speed U=1070r/min), and the aerodynamic performance test of the range hood with the blade outlet angle of 160, 170 and 180 is carried out. By measuring the indoor atmospheric pressure, atmospheric temperature, relative humidity and the static pressure in the decompression cylinder and the input power of the main motor under each working condition, the above measurement results are converted, and finally the fan is obtained in different working conditions. Under the range hood air volume, full pressure and full pressure efficiency.
The range hood noise test is carried out in a semi-anechoic chamber. The height of the bottom of the range hood is higher than 1.3 m. During the test, it is necessary to ensure that the inlet and outlet of the range hood and the multi-blade centrifugal fan have no other components to hinder the flow. Eliminate vibration and noise on the ground and other components. The test test device is as shown, and the noise measurement uses a hand-held sound level meter.
3 is the flow-to-pressure efficiency performance curve of the range hood of the multi-blade centrifugal fan blades.
It can be seen that when the blade exit angle is reduced, the total pressure efficiency of the range hood is increased in the range of 0~10 m3/min compared with the original impeller, and the air volume specified in the national standard is 7 m3/min. The total efficiency of the range hood is the highest, increasing by about 2.43%. When the flow rate is greater than 10m3/min, the total pressure efficiency of the range hood is lower than that of the original impeller. In contrast, increasing the blade exit angle, the total pressure efficiency of the range hood is lower than that of the original impeller in the full flow area.
When the air volume specified by the national standard is 7m3/min, the efficiency is reduced by 0.6%. This is mainly because the blade exit angle is too large, which leads to an increase in the flow velocity in the impeller flow passage, thereby increasing the friction loss of the gas flow.
The outlet angle of the blade for the multi-blade centrifugal fan is 160., 170. (original impeller), 180. At the same speed 1070r/min, the range hood flow - full pressure, flow - static pressure performance curve. And it shows that in most air volume ranges, the static pressure and full pressure of the range hood under standard conditions will increase to different degrees with the increase of the blade exit angle. In the national standard, the air volume is 7m3/min, and ft=180. The standard static pressure of the range hood is the largest, which is 32Pa higher than that of the original hood, which is 39Pa higher than that of the range hood using 0 2=160. According to the national standard, the maximum air volume of the range hood is the volume of gas delivered per unit time when the static pressure value is zero. It shows that compared with the original range hood, the maximum flow rate after the impeller exit is slightly decreased.
Table 1 Comparison of the performance of the range hood under different blade outlet installation angles Table angle Maximum static pressure / Pa maximum air volume Standard static pressure / Pa full pressure efficiency / % noise / dB The data obtained from Table 1 shows that at the strong speed n = At 1070r/min, when the blade exit angle is reduced, the sound level of the range hood A is reduced by about 1.2dB compared with the range hood using the original impeller (le=170.), and the noise reduction effect is better; the blade exit angle is improved. At the same time, the sound level of the range hood A is increased by 1.1 dB. According to the analysis, the blade curvature is too large due to the excessive exit angle of the blade, the flow in the volute is deteriorated, and the eddy current intensity is intensified, causing large noise.
4 Conclusions The experimental study method was used to investigate the influence of the exit angle of the multi-blade centrifugal fan blades on the overall aerodynamic performance of the range hood. In the course of the experiment, only the change of the installation angle of the blade outlet was considered, and the matching of the impeller design with the volute and the change of the pressure of the flue pipe network were not considered. The study found that the smaller the exit angle of the blade is, the higher the full pressure efficiency of the range hood is in the range of small flow conditions. In the range of large flow conditions, the full-pressure efficiency of the range hood of 2=160. is slightly reduced. When the air volume is specified as 7m3/min, the range hood of the team = 160. has the highest total pressure efficiency, reaching 26.17%, and the efficiency is increased by about 2.43%. The static pressure and full pressure of the range hood will follow the blade outlet. The angle increases with different degrees. When the blade exit angle is greater than 170., the maximum air volume of the range hood does not increase significantly with the increase of the blade exit angle. However, as the blade exit angle increases, the oil smoke increases. The noise of the machine is constantly increasing.
Despite the maximum air volume and static pressure flow field of the range hood of ft=160., the interaction between the external flow field and the groove surface is mainly in the near wall area, small pressure gradient and zero pressure gradient, drag reduction effect exists, medium or strong Under the pressure gradient, there is still controversy about whether the drag effect of the groove surface still exists or disappears.
The drag reduction effect of the trench is mainly at the bottom of the trench, and there is no drag reduction effect near the apex of the trench. The direction and direction of the groove, the traditional view that the downstream flow reduction effect is good, but the lateral groove drag reduction effect is not obvious, but it is also reported that the suspension balance test can be obtained, the vertical flow to the imitation small size groove can be obtained 10.2% drag reduction effect.
In view of the research content of drag reduction, combined with fluid machinery, the following research ideas are proposed: For the current research examples, the geometric parameters of riblets are determined under given conditions to achieve the effect of rent reduction.
Starting from the flow parameters of the fluid machine, the CFD software is used for the simulation calculation to determine the geometric characteristic parameters of the groove surface ribs that achieve the drag reduction effect.
Under the given riblets geometry parameters, the changes of other parameters are discussed, and the drag reduction effect can still be achieved in a large range.
After determining the geometric parameters, determine the allowable range of variation of each parameter by changing the fluid mechanical speed, pressure, speed and other parameters to ensure that there is a minimum drag reduction requirement.
From the stability point of view, it can maintain such drag reduction effect for a long time, and study the groove surface failure mechanism.
Study the corrosion wear mechanism of microscopic surfaces and predict the failure time of microscopic surfaces. Study the microscopic surface forming process to guide the manufacture of overcurrent components.
(Finish)
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