Hospital operating room air conditioning filter knowledge what?
The efficiency of the filter was tested by sodium flame method according to GB 6165-85. The air volume of the test efficiency is the same as that of the test resistance, and the results show that the efficiency of the filter is not less than 99.99%
High-Efficiency Particulate AirFilter, HEPA Filter can remove low concentration submicron particles with extremely high collection efficiency (≥99.97%). It was used by the United States Atomic Energy Commission in the 1940s to remove radioactive dust in experimental reactors (Anglenetal., 2003), has now become the world’s nuclear industry to prevent radioactive aerosol pollution of the atmosphere is widely used as an important environmental protection equipment. Reducing the resistance of HEPA filters can significantly reduce the construction and operation costs of ventilation systems. It is one of the core tasks of theoretical and experimental research on filtration to study the relationship between resistance and other structural parameters and to reduce filter resistance (Fu Haiming et al., 2003).
Theoretical and experimental studies on filtration began in the early 20th century. In 1922,Freundlich proposed that the maximum permeability of aerosol particles existed within the radius of 0.1-0.2 μm (Spurny, 1997). Since then, many scholars at home and abroad have carried out a large number of studies on the theory of air filtration, and given the calculation formula of filter resistance, but there is a large deviation between the calculated results and the measured data (Lin Zhongping, 1998; Xu Zhonglin,1998).Thomas(2001) et al. conducted experimental and simulation studies on filter resistance under unsteady conditions. So far, the existing theory can not be directly used to guide the production practice of filters. In this paper, the structural form of HEPA filter is improved by experiments, the structural parameters of HEPA filter are found out when the resistance is lowest, and the relationship between the structure and resistance of HEPA filter is discussed. It is of great significance for the development of high performance air HEPA filter and the discussion of filtration theory.
2. Theoretical analysis
The resistance of HEPA filter is divided into two parts: the resistance of filter material and the resistance of structure.
2. 1 Resistance of filter material
At present, people used Darcy’s law to study the resistance of filtered materials. According to the filtration theory, the pressure difference between the two ends of the porous medium follows Darcy’s law at low flow rate and small Reynolds number:
Filter structural resistance
2. 2. There are few theoretical studies on the structural resistance of filters. Structural resistance is divided into two parts, one is the air flow into and out of the filter, due to the sudden change of ventilation area (in the air, the air expansion) caused by the energy loss; Part of it is the energy loss caused by the blocking and friction of the filter materials and separators when the air flows in the filter. Structural resistance can be calculated by studying the flow of air in the airflow channel of the filter.
2. 3 Through the experiment to determine the reasonable structure parameters of HEPA filter
When the filter (air filter manufacturer)material, shape size and ventilation volume of the filter are fixed, increasing the filter material area of the filter can reduce the speed of air passing through the filter material. According to formula (1), the filter resistance will be reduced. At the same time, the measures taken to increase the filter media area (such as reducing the spacing of filter paper pleats, increasing the depth of filter paper pleats) often lead to the increase of structural resistance. The result of the combined action is the existence of the optimal structural parameters, so that the total resistance of the filter is the lowest. The existing theory is unable to obtain accurate structural parameters to minimize the resistance of HEPA filters, therefore, through experimental research. Optimization of the structural parameters of HEPA filters with the lowest resistance can guide the production and development of filters. In this paper, the relationship between the structure and the resistance of the filter is studied from three aspects: the pleat spacing, pleat depth and pleat shape of the filter material.
3. Materials andmethods
The experimental filters were flat-plate compact HEPA filter and HEPA filter with partition board, and the filtration materials were imported and domestic HEPA glass fiber filter paper (filter paper A and filter paper B, respectively, were used in this paper).