⒈ dust holding capacity

Filter dust holding capacity is not scrapped accommodate the weight of atmospheric dust, which is a filter in a specific test conditions to accommodate the weight of a particular test dust. Here the "specific" means:

Standard test wind tunnel, and related test and measurement equipment;

Atmospheric dust particles much larger than the actual standard "road dust";

Commissioning party agreed with the experimental side, or standards for test methods and calculation methods;

The agent and the agreed termination of the filter test conditions.

Dust holding capacity and actual capacity dust filter has no direct correspondence between the weight, encouraging dust holding capacity data for the user does not make any sense. For example, a test filter dust holding capacity of 600g, the actual use of it may hold 2.5kg of atmospheric dust; another of dust holding capacity of 900g, into your hands it may only 1.5kg Douzhu dust. Only test conditions and dust are the same, according to the amount of data to estimate the dust filter which will only last longer than some of the other.

Specialized laboratories and filter manufacturers in assessing the general ventilation filters products, you want to filter dust destructive test, which is designed according to the relevant test criteria to evaluate the whole process of the test filter average efficiency, dust holding capacity is Such test data obtained in a batch of data. How long insistence on laboratory filters dust test, the test could exploit looked at historical data to compare the pros and cons of a filter only difficult for outsiders to find out the number of dust holding capacity of practical significance.

Some European and American standards required test termination conditions are:

Resistance reaches 2 times the initial resistance or higher;

Instantaneous filtration efficiency is lower than the highest efficiency value of 85%. Most of the resistance of the filter instead of falling, only with fluffy crude fiber (≧ 10μm) material low efficiency filters may be the second case. Obviously, the test set at the higher end of the resistance, the resulting value greater dust holding capacity. Therefore, the principal and the experimenter to terminate the experiment clearly defined conditions, otherwise there is no dust holding capacity data much sense.

European Eurovernt4 / 9 standard termination test resistance 450Pa, this data is much higher than two times the initial resistance, but that is not the efficiency test dust holding capacity test.

Chinese standard only provides for "coarse" filters dust test, the purpose is to obtain efficiency in mind but heavy dust holding capacity. When discussing dust holding capacity with others, you have to know each other then to say which country.

European and American standard test known as ASHRAE dust to dust, the main component of "AC fine ash", that is Arizona desert dust in a particular location (ArizonaRoadDust), the AC fine ash mixed with a certain percentage of fine carbon black and short fiber since become ASHRAE dust. China has been specified with the Loess Plateau, dust, Japanese regulations with their own "off East Clay."

⒉ stick dust force

Two objects come into contact, a tiny between the surface gravity, it is not familiar gravity, not magnetism, static electricity is not, it is a molecule with molecule, molecules and the force between molecules, the textbook call it "Van der Waals force" or "van der Waals forces."

From a micro perspective, a single atom or molecule of the negatively charged electron cloud has a center, there are positively charged nuclei centers, when these two centers do not coincide, there is a dipole. Single dipole may be changing, it may be relatively stable, but multiple dipole get together, they will produce gravity on the surrounding objects. This attraction is very weak, and its magnitude smaller than the bond of 1 to 2 orders of magnitude. His role is also very narrow range, close to the big attraction disappears; short distance (> 7?) When the electron cloud overlap adjacent molecules and mutually exclusive

Chalk on a blackboard to stay, because van der Waals force can deal with those powders; chalk blackboard stick will not be because of gravity compared with the van der Waals force is negligible.

Dust in the air collide, 因范德瓦尔斯 force as one, with Chengdu University of dust particles. Indoor dust hit the wall and stay where the wall "fade" or the formation of black stains. Rough surface due to a large contact surface with the dust, the dust stick more easily.

The filter in the filter medium is a maze, outside of which there is more dust than usual chance of crash barriers, and because of the filter media everywhere in the van der Waals force to stay.

In certain circumstances, the static electricity is also involved in the process of capturing dust. If the filter media with a static, filter effect will be significantly improved, static electricity is one of the reasons to change the trajectory of dust hit an obstacle, the second is the force of static electricity 比范德瓦尔斯 easier to stick dust. Dust can also be artificially with static electricity, so they are easily adsorbed by other objects, such as household and industrial use electrostatic filter electrostatic precipitator.

⒊ filter resistance

Filter formed on the airflow resistance. Filter fouling, resistance increases, when the resistance increases as large as a specified value, the filter scrapped
The resistance of the new filter called "initial resistance", corresponding to the resistance value of the filter scrapped "end resistance."

Design, often requires a representative value of the resistance to air flow accounting system design, the resistance value "design resistance", the preferred method is to take initial resistance and end resistance averages.

Determine the final resistance

Final choice of resistance is directly related to the life of the filter, the system air volume range, the system energy consumption.
Under normal circumstances, the final resistance selection is empty out the designer thing. Experienced engineers can change the original design according to the situation of the final resistance value.

Some designers will forget to tell the user that his chosen end resistance value; sometimes the user will change filters or other models from other vendors. At this time, the engineer to determine the final resistance value.

In most cases, the use of live filters final resistance is the initial resistance of 2 to 4 times.

The dirtier the filter, faster growth and resistance. High end resistance value does not mean that the service life of the filter will be significantly extended, but it will make the air conditioning system air volume plummeted. Therefore, there is no need to end resistance values ​​given too high. Some test standard specifies test termination condition is when the resistance is "initial resistance of two-fold or higher," with the actual conditions of use of this provision does not matter much.

Low efficiency filters often use crude fiber diameter ≧ 10μm filter. Since a large gap between the fibers, the resistance is too large it is possible to disperse the dust on the filter, this time, the resistance is no longer increased, but the filtration efficiency is reduced to zero. Therefore, the following must be strictly limited G4 filters final resistance value.

The following are some suggestions of the final resistance, it comes from experience, not much reason to talk about.
End resistance values ​​in Table 1-1 filtration efficiency specifications recommended final resistance (Pa)
G3 (coarse) 100-200
G4150-250
F5-F6 (in effect) 250-300
F7-F8 (High efficiency) 300-400
F9-H11 (Asia and efficient) 400-450
Efficient and very efficient 450-600

Filter to end resistance, may mean to immediately replace the filter, it may mean that plans to do tomorrow, next week or next month to replace the filter. Final resistance depends on how you look at the user site-specific regulations and experience of the operator.

Resistance Monitoring

Should be installed on each filter segment resistance monitoring devices. The resistance will depend instrument to determine, not only by the operators feeling.

Cheapest resistance monitoring device is a U-shaped tube manometer. Inclined tube manometer beautiful than the U-shaped tube, the accuracy is also higher. Analog pressure table grades and prices are higher. Differential pressure transmitter can be turned into resistance current or voltage signal, and then lost control system.

In addition to reading the resistance monitoring device, the alarm device should be added the final resistance. The easy way is to draw on the red bar differential pressure gauge; insurance is to use differential pressure switch.

⒋ filtration efficiency

The air filter of the "filtration efficiency" is the amount of dust captured the dust content of the original ratio:

Efficiency significance deceptively simple, but it is because of the meaning and value of the different test methods are quite different.

Factors in determining the filtration efficiency, the dust "quantity" meaning varied, whereby the calculated and measured values ​​out of the filter efficiency also varied. Practice, the total weight of dust, the number of particles of dust; sometimes a typical size for the amount of dust, but also the amount of all the dust particle; as well as with a specific method the concentration profile to reflect the amount of light (colorimetric France), the amount of fluorescence (fluorescence method); has a state of the instantaneous volume, but also dust test the efficiency of the whole process of change in the value of the weighted average volume.

Only filters use the same method for testing the type, the measured value is not the same efficiency. Each country, the manufacturers use test methods are not uniform, the filter effect is very different interpretation and expression. Leave the test methods, filtration efficiency will be impossible.

Historically, engage ventilation and clean room filters are a group of people, engage in automotive filters is another group of people, in addition to engaging in dust, engage in liquid filtration, they are all using various methods, each of said The efficiency. When the air filter factory mix the sale of automotive filters, or when the air filter dust plant development when they themselves will inevitably be what he said filtration efficiency confused.

In order to save the ice to reduce misunderstanding abroad there are some efficient methods with code indicates that those test method code that is clear, but also to determine the efficiency indicators, Country 2.1 "filtration efficiency labeling" and 2.2 "filter efficiency specifications comparison." Today, the worlds filter manufacturers are crowding the Chinese market, domestic manufacturers for users of all backgrounds to sell products, but also arbitrary use efficiency labeling. Efficiency and efficiency of various numerical terms the users, designers and production plant Yunshanwuzhao.

In addition, there is a filter theory "single fiber efficiency", which can be greater than 100% is a geometric meaning, as detailed in the book next to the content on the filtration theory. A little careless, people will engage in theoretical issues in terms of efficiency Yun Cai.

In this chaotic situation, if you must know the specific efficiency value, please do not forget to provide for specific test methods and computational efficiency.

⒌ filtering mechanism

⑴ collide and stick

Dust particles in the air, or to do with the flow inertial motion, or do no regular exercise, or subject to some kind of field force and movement. When the movement of the particles hit the obstacle, the obstacle between the surface particles of the van der Waals force that they stick together.

⑵ fiber filter material

Filter material should be able to: only effectively intercept dust particles, without the formation of the airflow too much resistance. Non-woven fibrous material and especially paper that meets this requirement. Messy interwoven fibers form numerous road barrier against dust, wide space between the fibers allow airflow smoothly.

⑶ principle of inertia

Large particles in the gas stream as inertial motion. Obstacle bypass airflow, particle deviate due to inertia on the flow direction and hit an obstacle. Larger particles, the stronger the force of inertia, the greater the likelihood of collision obstacle, so the filtering effect is better.

⑷ diffusion theory

Small particles do not rule Brownian motion. Do the math on the random motion used when handling mass transfer in the "diffusion" theory, so there is a diffusion theory says. The smaller the particle, the more intense exercise without rules, the impact of obstacles more opportunities, so the filtering effect is better.

⑸ efficiency increases with the size of dust particles only

The amount of the filter and the dust collecting filter is not the amount of dust in the air ratio of "filtration efficiency." Less than 0.1μm (micron) particles mainly for diffusion, the larger particles, the higher the efficiency; greater than 0.5μm particles mainly for inertial motion, the larger particles, the higher the efficiency.
In between 0.1 ~ 0.5μm, the efficiency has a lowest point, the particle size of the dust filter difficult.

⑹ resistance

Fiber bypass the airflow generated smiling resistance. Numerous fiber resistance is the sum of the resistance of the filter.

Filter resistance with the gas flow rate increased with the increase, by increasing the area of ​​the filter material, filter material can reduce the relative speed to reduce the filter resistance.

⑺ dynamic performance

The dust is captured additional resistance to flow, so the use of gradually increasing resistance of the filter. The captured dust and filter media into one to form a new obstacle, therefore, a slight improvement in filtration efficiency.

Fights gather dust caught in the filter material on the windward side. Filtration area is larger, the dust can be accommodated, the more the longer the life of the filter.

⑻ filter scrapped

The more dust filter, the greater the resistance. When the resistance is large enough to allow the extent of design, filter life will end. Sometimes, too much resistance would have been captured on the filter dust scattering appears this danger, the filter should also scrapped.

⑼ electrostatic

If the filter material with electrostatic or dust with static electricity, filter effects can be significantly improved.

The reason: Electrostatic dust changed the trajectory and crashed into the barrier, static electricity stick to the work involved.