The Influence Of Testing Environment On The Testing Result Of HEPA & ULPA Filter Scanning System

Nowadays, air purification technology is used in many fields, such as medicine, sanitation, semiconductor, precision tools. So the role of the HEPA and ULPA filter is Critical. For it, every one must be testing before being sell,which includes efficiency, resistance and leak tested. With the development of our understanding and the testing technology, the tradition way will be gradually substituted by the way of particle size efficiency. At aboard, some standards has come out, but there are no specific requirements for the testing environment ,the study on it is not referred. The design of the foreign HEPA & ULPA scanning testing system is complex and some systems need be setting in cleaning rooms. Although this can guarantee the accuracy of the test, the cost of manufacture increases as well. In China, the step of research on the filter scanning system is later. How serious the influence of testing environment on the testing results is still unknown .So this paper will research on it to give some help to develop the domestic HEPA & ULPA scanning testing system.In this paper, some calculation about the sampling speed, the sampling height and the gravitational settling of the particle has been made, according to existing academic formula and experiential formula about filter principles, and the impact of them are analyzed. Then the influence of the particle in the testing environment on testing result is analyzed. under the condition of cleaning environment and non-cleaning environment, the factors such as the distance between the sampling height, the height of the board around the filter, the small cover board which settled with the sample pipe existing, the sampling height when the board existing and the distance from the board to the board around the filter are analyzed. At last by the simulation of computational fluid dynamics (CFD), the cleaning room round the testing system and the height of board around the filter, some things about the small cover board are doing, the testing experiment is explained through studying on the airflow distribution.We can get the conclusion that the testing result in the cleaning room is better than the one in the non-cleaning room, Whether or not to a cleaning room, the sample height less than 30mm is not the main factor impacting the testing result, when the center of the filter is being scanned. But the influence of the testing environment on testing result is prominent, when the side of the filter is being scanned, which can be settled by setting up some boards around the filter, and changing the height of them and setting up a small cover board. If we only test the leak in the HEPA/ULPA filter, the particle which size is bigger than 1μm is fitter , not the particle which size is the most penetrating particulate size.