The operating principle of the air shower transfer window

Air shower transfer Windows are commonly used equipment in clean rooms, laboratories, and other places with high cleanliness requirements. They are mainly used to remove dust particles adhering to the surface of items by high-speed clean air flow when transferring items between two areas of different cleanliness grades, avoiding cross-contamination. The core principle is to clean the surface of the items and maintain a clean environment in the areas on both sides through the process of "blowing - filtering - circulation". The following is a detailed analysis of its operating principle from two aspects: structural composition and working process.
I. Core Structure Composition
The operation of the air shower transfer window relies on the coordinated effect of the following key components:
Box body: A sealed metal or stainless steel casing that separates the two sides of the area (such as the clean area and the non-clean area) to ensure that the internal air circulation does not leak out.
Fan system: It provides the power source, usually a centrifugal fan or a multi-blade fan, used to accelerate air flow and generate high-speed airflow.
Filtration system
Primary filter: Generally located at the air inlet, it filters out larger particles in the air (such as dust and hair) to protect the subsequent high-efficiency filter.
High-efficiency filter (HEPA): Core filtration unit, with a filtration efficiency of ≥99.97% for particles ≥0.3μm, ensuring the cleanliness of the air flow used for air shower (approaching or reaching the cleanroom grade).
Blow spray nozzles: Distributed on the top, sides, or bottom of the box, arranged in a matrix, covering all surfaces of the items through high-speed airflow (such as spraying downward from the top and towards the middle from both sides).
Interlocking device: The two side doors (entrance door and exit door) are controlled by mechanical or electronic interlocking, prohibiting simultaneous opening to prevent the direct circulation of non-clean air on both sides.
Control module: It includes sensors (such as door switch sensors, differential pressure sensors) and a control panel. It can set parameters such as air shower time and wind speed, and automatically start and stop the fan.
Ii. Work Process and Principles
The operation of the air shower transfer window can be divided into the preparation stage → air shower stage, → completion stage, as detailed below
1. Preparation stage (Placing items)
The user opens the entrance door from one side (such as Area A, which has a higher cleanliness level), places the items to be delivered into the transfer window, and then closes the entrance door.
The closing of the entrance door triggers the sensor (or is manually started through the control panel), and the system enters the state ready for the air shower.
2. Air shower stage (cleaning the surface of items)
Fan startup: The control module starts the fan, drawing in external air (or circulating air) into the box.
Air filtration: The inhaled air first passes through a primary filter to remove large particles, and then is deeply purified by a high-efficiency filter (HEPA) to become a clean high-speed airflow (with a wind speed typically ranging from 20 to 25m/s, approaching the laminar flow velocity of a cleanroom).
Directional air shower: Clean air is evenly sprayed onto the surface of the object through nozzles at the top and on both sides, forming a "laminar flow" or "turbulent flow", effectively stripping off dust particles (such as microorganisms and dust) on the surface of the object.
Exhaust filtration: The dust blown off enters the exhaust channel at the bottom or back of the box with the airflow and is filtered again by the high-efficiency filter before being discharged (or recycled back to the box, depending on the design), thereby preventing pollutants from spreading to the external area.
3. Completion Stage (Item Removal)
After the air shower time (usually set to 10 to 60 seconds) is over, the control module stops the fan, and the system prompts that the air shower is complete.
The user opens the exit door from the other side (such as Area B, a lower cleanliness level or a non-clean area) (due to the interlock device, the entrance door cannot be opened at this time), takes out the cleaned items, and then closes the exit door to complete one transfer.
Iii. Key Design Points
Airflow coverage: The layout of the nozzles should ensure that all surfaces of the item (top, side, bottom) are covered by high-speed airflow to avoid cleaning blind spots.
Pressure difference control: A slight positive pressure should be maintained inside the box (relative to the areas on both sides) to prevent unfiltered air from seeping in. Some high-end models will monitor the pressure difference in real-time and automatically start the fan to compensate for leaks.
Energy-saving design: Some equipment is equipped with a "delayed shutdown" function (for example, the fan continues to run for a short time after the air shower is completed to ensure that the residual particles are removed), or a variable frequency fan is used to adjust the wind speed according to the demand.
Summary
The core of the air shower transfer window is to quickly clean the transferred items through "high-efficiency filtration + high-speed directional airflow", and combine with interlocking devices to prevent cross-contamination. Thus, in fields such as clean rooms, pharmaceuticals, electronics, and medical care, it effectively ensures the isolation of cleanliness between different areas. Its performance depends on the filtration efficiency, air flow velocity, uniformity of coverage, and the accuracy of the control system.