Meaning
Calculated gas transmission values convert the flow of a tracer gas like helium into a standardized air measurement to assess the integrity of a battery housing. This conversion is necessary because leak detection equipment often uses small molecules that move through cracks differently than the nitrogen and oxygen found in the atmosphere. The equivalent air leak rate provides a universal metric that engineers use to specify the sealing requirements for a pouch or prismatic cell.
It allows for the comparison of test results across different types of equipment and different test gases. This measurement applies only to the flow of gases and does not directly predict the leakage of liquid electrolytes.
Flow Transformation
Mathematical models account for the differences in viscosity and molecular mass between the tracer gas and the actual air. When a technician measures a leak with helium, the equivalent air leak rate is typically lower because helium molecules are smaller and move faster. The flow through a microscopic hole can be laminar, turbulent, or molecular depending on the pressure and the size of the opening.
Using the correct physics formula is essential to translate the raw meter reading into a meaningful air value. This process ensures that a cell which passes a helium test will also remain sealed in the real world.
Conversion Methodology
Standardized formulas like those found in the American Society for Testing and Materials guides provide the basis for these calculations. The equivalent air leak rate assumes a specific pressure differential, usually one atmosphere, between the inside and the outside of the container. Factors such as temperature and the length of the leak path are also considered when performing the conversion.
Modern leak detectors often perform this math automatically, displaying the result in units like cubic centimeters per second of air. This automation reduces the chance of human error during the quality control process.
Sealing Efficiency
Design specifications for a battery cell will state a maximum allowable value for this metric to ensure a ten year service life. If the equivalent air leak rate is too high, humidity will eventually penetrate the cell and react with the lithium salts. This ingress causes the formation of hydrofluoric acid and gas, which destroys the battery from the inside.
A low value indicates that the seals and the packaging material are functioning as a perfect barrier. Engineers use this data to validate new manufacturing techniques or to audit the performance of a production line. The metric is a cornerstone of hermeticity testing in the electronics and energy sectors.
