When you enter a modern cleanroom, you can barely feel the wind, yet the air flows with extreme precision and strictness. This invisible “airflow organization” determines the success of production processes ranging from smartphone chips to life-saving pharmaceuticals. A cleanroom is not a “sealed box,” but a dynamic, controlled aerodynamic system. Its core secret lies in using scientifically designed airflow to remove contaminants faster than they are generated and settle.
Two Core Airflow Modes in Cleanrooms
The airflow organization in cleanrooms is mainly divided into two types: unidirectional flow and non-unidirectional (turbulent) flow. The choice directly depends on the ISO level and process requirements the cleanroom needs to achieve.
What is Unidirectional Flow?
Unidirectional flow, formerly known as “laminar flow,” is the hallmark of the highest level of cleanrooms. Its principle is simple yet powerful: air flows parallel in a single direction (vertical or horizontal) at a uniform cross-sectional velocity (typically 0.3-0.5 m/s), like a giant, invisible “air piston” sweeping across the entire work area.
- Working Principle: Clean air filtered by HEPA /ULPA filters is evenly delivered from the entire ceiling or one wall, flowing vertically or horizontally towards the opposite return air wall or floor grille. This parallel airflow carries away particles generated during operation along the shortest path with almost no diffusion, preventing contaminants from spreading in all directions.
- Visual Imagining: You can imagine it as a drop of ink falling into a smoothly flowing river; the ink will be immediately carried away by the current in a straight line, without contaminating upstream or to the sides.
- Typical Applications: ISO Class 1-5 cleanrooms. Such as semiconductor lithography areas, aseptic injection filling lines, high-precision micro-assemblies, etc., in critical areas where even a single speck of dust could cause product failure.
What is Non-unidirectional Flow (Turbulent Flow)?
For most environments that don’t require extreme cleanliness, a more economical and flexible non-unidirectional flow design is employed. Here, the airflow direction is turbulent and uneven.
Working Principle: Clean air is supplied through a limited number of HEPA filter outlets, mixed and diluted with indoor air, and then exhausted through multiple return air vents located in the lower part of the room. Its core purification logic is not “immediate removal,” but “rapid dilution and mixing.” By continuously supplying a large volume of clean air, the concentration of pollutants generated indoors is diluted to below acceptable standards.
Visual Implication: Imagine lighting an incense stick in a room and then turning on several fans to blow in fresh air; the smoke gradually mixes with the fresh air, eventually reducing the smoke concentration throughout the room to a very low level.
Typical Applications: ISO Class 6-8 cleanrooms. Examples include medical device assembly areas, pharmaceutical packaging areas, food production workshops, and as buffer corridors before high-level cleanrooms.
Engineering Details of Airflow Design: Pressure Differential, Ventilation, and Layout
Beyond the macroscopic airflow pattern, several key engineering parameters collectively constitute the “immune system” of a cleanroom:
- 1. Pressure Differential Control: A cleanroom must always maintain positive pressure over adjacent areas with lower cleanliness levels. This means that when the door is open, clean air overflows, effectively preventing the backflow of contaminated air from outside. This pressure differential is typically precisely controlled between 5-20 Pascals, equivalent to the weight of a piece of paper in your hand, yet crucial.
- 2. Air Change Rate: This is a key indicator of the air renewal rate in a cleanroom. In an ISO 5 unidirectional flow cleanroom, the concept of “air change rate” translates to continuous airflow; while an ISO 7 turbulent flow cleanroom may require 50-60 air changes per hour. In contrast, a typical office only requires 2-3 air changes per hour.
- 3.Equipment and Personnel Layout – Reducing Turbulence: In unidirectional flow cleanrooms, the placement of any large equipment or operators must be carefully planned to avoid obstructing critical airflow surfaces or creating downstream vortex zones. Ideally, personnel and equipment should be positioned downstream of the airflow.
Furthermore, Munich engineers believe that airflow design must be integrated with heat load control, humidity management, and energy efficiency. Trenntech, a leading HEPA/ULPA supplier, has found in its experience with such projects that the most efficient systems often strike the optimal balance between theoretical cleanliness requirements, actual operating costs, and long-term reliability. In this era where the microscopic level determines success or failure, controlling airflow is as important as controlling production quality.