Air Strainer Common Sense
◎Strainering Overview
strainering material
Not only effectively block dust particles , and will not form too much resistance to the airflow. Messy interwoven fibers form numerous particle barrier, a wide space between fibers allows air smooth passage.
efficiency
The ratio of the amount of CHF strainers trap dust and unstrainered air the amount is "filtration efficiency." The particles less than 0.1 m (micron) are mainly used for the spread movements, the smaller the particle, the higher the efficiency; more than 0.5 m particles are mainly used for inertial movement, the larger particles, the higher the efficiency.
resistance
Fiber makes airflow bypass, resulting in minimal resistance. The sum of numerous fibers resistance is the strainer resistance.
Strainer resistance increases with the gas flow increases, by increasing an area of strainer material, can reduce the relative wind speed through the strainer, reducing the strainer resistance.
Dynamic properties
The captured dust produces additional resistance to the airflow, so in the use, strainers resistance gradually increases. The captured dust forms a new barrier, as a result, the fitering efficiency has a slight improvement.
Most of the captured dust is gathered on the windward side of the strainer material. The larger the strainer area is and it can accommodate more dust, strainers service life is also longer.
service life
More strainer material dust, the greater the resistance. When the resistance as large as the extent of design does not allow, the strainer life is to end. Sometimes, too large resistance willl make captured dust on the strainers flying, when secondary pollution occurs, the strainer should be also scrapped.
static
If the strainer material with static or dust with static, strainer effects can be significantly improved. due to static dust changes moving trajectory and hit a barrier, static involves in stick work.
◎strainering efficiency
In the factors of determining strainering efficiency, the dust "quantity" means a variety, thus calculated and measured strainer efficiency values is different. Practically, there is the total weight of dust, dust particle number; sometimes a typical size for the amount of dust, and sometimes the amount of all the dust; also using particular method to reflect indirectly the concentrated through light amount (colorimetric), fluorescence volume (fluorescence method); a certain state instantaneous volume, but also have the dust made whole process of changing efficiency value of the weighted average.
Using different methods to test the same one strainer, the measured efficiency value will be different. To leave the testing methods, strainering efficiency is impossible.
◎strainer resistance
The strainer forms resistance to air flow. Strainer amasses dust, resistance increases, when the resistance increases to a specified value, strainers is scrapped.
The resistance of the new strainer called "the beginning of resistance"; when the corresponding strainer is scrapped, the resistance value called "final resistance."
final resistance
Final resistance selection is directly related to the service life of strainers, the system air volume range, the system energy consumption.
In most cases, the final resistance is 2 ~ 4 times of beginning resistance.
final resistance recommended value
| efficiency specifications | recommended final resistance Pa |
| G3(beginning efficiency) | 100～200 |
| G4（beginning and middle efficiency） | 150～250 |
| F5～F6（middle efficiency） | 250～300 |
| F7～F8（high and middle efficiency） | 300～400 |
| F9～H11（sub-high efficiency） | 400～450 |
| high and ultra-high efficiency | 400～600 |
The more dirty strainer resistance, the faster it grows. The final resistance value is too high does not mean that the strainer life will be significantly extended, but it will make air conditioning system air volume sharp dropping. Therefore, there is no need to set the final resistance valve value too high.
Low efficiency strainers commonly use diameter≥10 m crude fiber strainer material. As the inter-fiber gap is big, too large resistance is likely to blow away fouling on the strainer, this time, the resistance is no longer increased, but the strainering efficiency reduces to zero. Therefore, we should strictly limit below G4 strainer final resistance value.
Each strainer section shall be fitted with the resistance monitoring devices. the final resistance should be determined rely on instruments, the operator can not just rely on feeling.
◎Dust-holding volume
dust-holding volume is in a particular test conditions, the strainer accommodates particular test dust weight. Here, "specific" means:
a. standard test wind tunnel, and related test and measurement equipment;
b. the actual standard "road dust" that is much larger than atmospheric dust particles;
c. consulting by commissioning side and test side, or standard specified test method and calculation method;
d. commissioning side and test side agree to terminate the test conditions.
dust holding capacity has no directly correspond relationship with strainer actual capacity of the dust, the isolated dust holding capacity does not make any sense to users.
◎respirable particles
Large dust particles in the air are blocked by the nasal cavity, the small particles of dust may enter the trachea and lungs with air, the dust are eaten and digested by "macrophages" of trachea and lungs, those bacteria and virus are not eaten by macrophages will be destroyed by white blood cells.
Person's nose hair, secretions and mucous membranes can strainer most dust that is greater than 10 m, and only less than 10 m particles will enter the trachea and lungs with air. Therefore, the "respirable particles" is defined as "≤ 10 m particles in air."
All the amount of dust in the air is "total suspended particles" and the exclusion larger than 10 m particles, the remaining is the "respirable particles", is labeled TM10 technically. We often hear the "respirable particles" is the TM10. If removes more than 5 m particles, the remaining "respirable particles" is TM5.
respirable particles and Health Effects
| concentration mg/m3 | Health Effects | |
| TSP | respirable particles | |
| >0.29 | >0.20 | Threshold concentration of immune function changes, the prevalence of respiratory disease begin to increase. |
| 0.21 | 0.15 | the average daily maximum allowable air concentration in residential area. |
| <0.16 | <0.11 | not cause immune function changes of pupil below threshold concentration, does not cause respiratory tract disease rates increased. |
◎Chemical Strainer
CHF chemical strainers remove gaseous pollutants in the air. In the ventilation and air conditioning field, CHF chemical strainers use activated carbon as the main strainer material. Chemical Strainer typical applications areas are: chip factory, the nuclear industry, airports, environmental protection, museums, and so on. Some household appliances also use chemical strainer material.
Principles of chemical filtration
CHF Chemical Strainer selective absorbs harmful gas molecules, not remove impurities mechanically like ordinary strainers.
There are a large number of invisible micro in activated carbon materials, most of tiny hole diameter is between the 5Å ~ 500Å, the unit material micropore total surface area is up to 700 ~ 2300m2 / g, that is, in a grain size activated carbon particles, the inner pore surface area is equivalent to a large living room wall size.
No apparent adsorption of chemical reactions known as physical adsorption, this adsorption depends mainly on the van der Waals force. High boiling point in the air (at room temperature or higher) free molecules contact with activated carbon, some in the micropores form liquid and due to capillary theory to stay there, some filled with molecular size equivalent porous become ensemble with the material. Atmospheric nitrogen, oxygen, carbon dioxide, hydrogen, argon and other major components are with very low boiling point, activated carbon can not adsorb them. Ordingary activated carbon is a hydrophobic material, so the water vapor adsorption capacity is also limited. In addition, activated carbon can also adsorb some air-borne microbes and kill them
Through chemical treatment to use hazardous materials and chemical reaction of the adsorbed gases, said as chemical adsorption. Activated carbon capture gas molecules by Van der Waals force, the chemical composition of materials and contaminants reaction to form solid ingredients or harmless gases. The main method of chemical treatment is evenly mixed with specific reagents in activated carbon, therefore, activated carbon with chemical treatment, also known as "impregnated carbon"
In using process, the adsorption capacity will continue to weaken, when reduced to a certain extent, strainers are scrapped. If only physical adsorption, using heating or water vapor fumigation methods to enable harmful gases from the activated carbon and make it regenerated.
activated carbon materials
activated carbon materials are divided into particles carbon, fiber carbon, carbon powder.
Carbon fiber is made from carbon-containing organic fibers. Its aperture is small (<50Å), adsorption capacity is large, fast adsorption, faster regeneration. The commonly used fiber materials are Phenolic substrates, plant fiber, polyacrylonitrile, pitch.
Adsorption performance
Adsorption capacity. the maximum amount of unit activated carbon adsorbs pollutant is called adsorption capacity. The adsorption capacity of different materials will be different; the adsorption capacity of the same materials to different gas will be different; temperature, background concentrations change, the adsorption capacity also changes.
Retention time. The air stays length in the activated carbon layer is known as Retention time. The longer the stay, the more adequate absorption. In order to maintain sufficient residence time, carbon layer should be thick enough, strainer wind speed should be as low as possible
Service Life. The new activated carbon adsorption efficiency is high, the efficiency in the use reduces constantly, when the strainer downstream harmful gas gets close to the allowed concentration limit, the strainer is scrapped. The using time before the scrap, also known as the effective protection time.
Selectivity. Generally speaking, in the physical adsorption that are easily adsorbed are: large molecular gas, high boiling point gases, volatile organic gases. If the activated carbon with chemical impregnation, you can also clear the gas that is difficult to deal with normally, or highlight adsorption capacity of certain types of gas.
activated carbon strainers Selection
The main factors of affecting activated carbon strainer adsorption effects and service life are: the type and concentration of pollutants, airflow retention time in the strainer material, air temperature and humidity.
When in the actual selection, you should based on the pollutant type, concentration and processing blowing rate and other conditions to determine the strainer form and activated carbon types.
CHF activated carbon strainer upstream and downstream should have a good dust strainer, its efficiency specifications shall not be less than F7. The upstream activated carbon strainer prevents dust from clogging material; downstream activated carbon strainer stops their own dust.
