Theoretical expression for clean air volume in cleanrooms with non-uniform environments

Abstract

Clean air volume significantly affects the cleanliness and energy consumption of a cleanroom. Traditionally, a uniform method was used to determine the cleanliness of cleanrooms, leading to high energy consumption or insecure cleanliness. To date, there exists no theoretical formula for determining the clean air volume of cleanrooms with non-uniform environments, although computational fluid dynamics can be used to verify the results according to known boundary conditions. In this study, a theoretical expression for the clean air volume in a non-uniform cleanroom environment was derived after treating the transport of particles as passive transport and using the accessibility index to describe the impact of the particle sources on the clean zone. A cleanroom in a semiconductor fab was considered as an example to demonstrate the difference between uniform and non-uniform methods, and how to use the expression to reduce the clean air volume. The following conclusions were made: 1) the clean air volume based on the non-uniform method may be significantly different from that based on the uniform method, depending on the air distributions and locations of the particle sources; 2) the clean air volume can be reduced by 51–72 % using efficient air distributions under the same cleanliness level of the clean zone; 3) lastly, the theoretical expression for the clean air volume in non-uniform environments can guide the effective decrease of the air volume.