# A Study on the Improvement of Filter Performance to Remove Indoor Air Pollution
## 1 Introduction  
Indoor air quality has a very important influence when it becomes difficult to go outdoors. There are many sources of indoor air pollution. When food is cooked, a large number of pollutants are generated in a short time. In general residential spaces, most of the structures are connected to the kitchen and the living space, so the hood plays an important role in preventing the diffusion of indoor pollution and properly discharging it to the outdoors. The filter mounted on the hood is an important research topic [1; 2; 3; 4; 5]. The hood filter has a great influence on the pressure loss and collection efficiency, depending on the shape. The typical shapes used for the filter are the mesh-type and the baffle-type [6; 7; 8]. A mesh-type filter is suitable for home use because it has low pressure loss and noise and uses a small-capacity fan. The baffle-type filter has the advantage of high collection efficiency; therefore, it is advantageous to use in restaurants and factories. However, the pressure loss is high, making the vibration large and the fan capacity increased [6; 7; 8; 9; 10; 11; 12]. The study of filters has been conducted in various ways using computational fluid dynamics (CFD) [3; 4; 13; 14]. One type of baffle-types, the chevron-type filter, has high efficiency, but the pressure loss is also very high. Table 1 shows the shapes of generally used hood filters. The mesh-type filter is widely used for home use. It is less efficient but less noisy, so it is suitable for indoor use. Baffle-type filters and complex-type filtersare generally used for restaurants and industrial purposes. This is because restaurants or industrial sites that generate a lot of oil-mist and dust require high efficiency even if some noise is generated. The cyclonic-type filter has the advantage of high collection efficiency. However, the disadvantages are that it generates a lot of noise and vibration due to high pressure loss, and it is difficult to design for everyday use [14; 15]. [PERSON] reported in their master's thesis that the chevron filter had a collection efficiency of 93% and a pressure loss of 6.35 mmAq [14]. Based on the previously studied shape, the structure is simplified to reduce the pressure loss and study the shape with high dust-collection efficiency. According to [PERSON], the simulation technology was secured by copying the shape of the thesis [14]. A preliminary simulation was conducted by removing the protrusion to reduce the high-pressure loss, and a simple filter was proposed by removing the shape of the high-pressure section and selected as the basic shape. In order to increase the contact time of the physical filter, the Coanda effect was applied. The Coanda effect is a phenomenon in which a fluid flows along a wall due to the surrounding pressure and the viscosity of the fluid when it flows along a curved surface. When the fluid flows along the wall and deviates from a certain pressure, flow separation occurs. By using the Coanda effect, the contact time of the filter was increased to improve the collection efficiency. Using this phenomenon, various home appliances have been released [16; 17; 18; 19; 20]. However, the Coanda effect alone cannot dramatically improve the collection efficiency. Therefore, by applying the shape of the sub-filter under the main filter, the efficiency according to the shape is compared, and an optimal filter improvement is proposed. The purpose of this study is to propose an optimal filter with high efficiency and low pressure loss, and to secure the reliability of the simulation through the experiment. To select the optimum filter shape and secure reliability, wind tunnel device fabrication and experiments are conducted to compare the simulation results with the experimental results to achieve an error rate of 10% or less.