Selection of Test Methods for Air Filters:

4.1 This standard provides three testing methods: sodium flame method, oil mist method, and counting method. For air filters and filter media, efficiency testing can be performed using any of the following three methods according to user requirements. For super air filters and filter materials, counting method should be used for efficiency testing.

4.2 Sodium flame method is used as the benchmark test method for detecting the efficiency of air filters and filter media. The counting method is used as a benchmark test method for detecting the efficiency of super air filters and filter media.

5.1.2 Measurable range of test device

The maximum measurable wind volume of the test device under standard conditions can be determined according to the user's requirements. When the original concentration of aerosols is greater than or equal to 2 mg/m3, the maximum measurable efficiency of the system should be greater than 99.999%. 5.1.3 Principle and Process of Test Equipment

The experimental device mainly consists of three parts: fogging device, air duct system, and aerosol sampling and detection device. The experimental process and the numbering of equipment, instruments, and components are shown in Figure 1.

1. Pre filter; Sampling tube before 22;

2 hoses; Sampling tube after 2023;

3 fans; 24 vent control valve;

4 valves; 25 flow meter;

5 heaters; 26 background filter;

6 high-efficiency filters; 27 three-way switching valve;

7 spray box; 28 flow meter;

8 spray; 29 way valve;

9 mixed drying section; 30 mixer;

10 buffer boxes; 31 three-way switching valve;

11 static pressure ring; 32 hydrogen filter;

12 tested filters and their fixtures; 33 regulating valve;

13 standard orifice plate; 34 flow meter;

14 valves; 35 burner;

15 regulating valve; 36 photoelectric converter;

16 minute cylinder, right,? 37 photoelectric measuring instrument;

17 pressure gauge; 38 thermometer;

18 way shut-off valve; 39 hygrometer;

19 flow meter; 40 hygrometer;

20U type pressure gauge; 41 connecting pipe.

21 inclined micro pressure gauge; Previous article: Correlation coefficient of air filter experiment

Figure 1 Schematic flowchart of sodium flame test device

Use clean compressed air to atomize the 2% sodium chloride aqueous solution in the spray box (7) through a spray (8) to form a saline droplet aerosol; Mix with clean hot air heated and filtered from fan (3). In the mixed drying section (9), the water in the droplets evaporates, and when the airflow reaches the buffer box (10), the experimental aerosol has formed a uniform dispersed solid aerosol. After the airflow flows out of the buffer box, it becomes stable

Set the process so that the velocity and concentration fields of the aerosol at the front sampling tube (22) are basically uniform. The air volume and static pressure of the air duct system are controlled by valves (4, 14), and the airflow after the test is discharged from the end of the air duct.

Aerosol sampling relies on the static pressure inside the air duct, which is pressed into the detection system through the sampling tubes (22, 23) before and after the tested filter. By changing the position of the valves (27, 29, 31), aerosols are sampled alternately before and after the filter. The original aerosol is mixed (i.e. diluted) with clean air filtered through the background filter (26) in the mixer (30) before entering the burner (35). In the burner, the sodium atoms in the aerosol are excited by the high temperature of the hydrogen flame, emitting characteristic light with a wavelength of about 589 nm, whose intensity is proportional to the mass concentration of the aerosol. The sodium intensity value is converted into a photocurrent value through a photoelectric converter (36) and detected by a digital photoelectric measuring instrument (37). The resistance of the filtering section is detected by connecting the static pressure rings (11) on both sides of the tested filter to the inclined micro pressure gauge (21). The result minus the resistance of the filter fixture is the filter resistance.

See Annex A for the structure and design requirements of the sodium flame test device, and Annex B for the structure of the spray and photometer.

The structure of the test apparatus may vary, but the test conditions and results should be consistent with the test apparatus of this standard.