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Automotive Desiccant Bags
Moisture destroys automotive thermal systems. In AC loops, water reacts with refrigerants to form acids that corrode components. In electric vehicles (EVs), humidity compromises battery cooling circuits, triggering isolation faults. Automotive desiccant bags are engineered components designed to prevent these specific failures across OEM production and the global supply chain.
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The Role of Desiccants in Automotive Systems
Desiccant bags serve two functions:
- Active system protection: Integrated directly into AC and EV cooling loops to continuously filter impurities and trap moisture from refrigerants and oils.
- Passive asset preservation: Bulk moisture absorption to protect completely knocked down (CKD) kits during shipping.
Critical Applications and Material Selection
The physical format of the desiccant dictates line speed, machinery compatibility, and patient experience.
AC and Refrigeration Circuits
In mobile air conditioning (MAC), moisture causes ice formation at the expansion valve and lubricant hydrolysis. This is critical in modern systems: water reacts with the chemically unstable HFO-1234yf refrigerant to produce highly corrosive hydrofluoric acid.
- Media Selection: Molecular sieves (XH-7 and XH-9 grades) are mandatory. They selectively trap 2.8-angstrom water molecules while physically excluding larger refrigerant molecules, maintaining high capacity even at temperatures exceeding 100°C.
- Integration: Bags are shaped to fit receiver-driers or accumulators, acting as depth filters to trap compressor wear sludge.
Electric Vehicle (EV) Thermal Management
Vented EV battery housings draw in humid air during thermal cycling. If moisture degrades the highly hygroscopic Polyol Ester (POE) oils in the cooling loop, altered conductivity will trigger ECU isolation faults.
- Performance Requirement: Desiccant pads in EV cooling reservoirs must achieve moisture uptake rates exceeding 20% by weight at low humidity to maintain dielectric strength over a 15-year service life.
Logistics and CKD Shipping
Fluctuating temperatures in shipping containers cause condensation that flash-rusts metal components. High-capacity calcium chloride desiccants or silica gel bags absorb up to 300% of their weight to protect CKD kits, while 1g–5g silica sachets prevent lens fogging in headlamp assemblies.
Engineering Specifications and Design Features
A burst bag in a sealed loop requires a complete system flush and compressor replacement. The physical packaging must survive the operating environment.
Materials and Burst Strength
Bags use non-woven polyester or PP blends to withstand constant compressor pressure pulsations.
- Filtration: The fabric must act as a 20–40 micron depth filter, trapping debris without shedding internal fibers.
- Tensile Strength: Seams must exceed 12.5 N/25mm tensile force.
Weld and Seal Integrity
Ultrasonic or thermal welding is used instead of adhesives to withstand road vibration.
- Peel Strength: ≥7.1 N/25mm (90°) and ≥21 N/25mm (180°).
- Thermal Shock: Welds must not delaminate across extremes of -40°C to 110°C.
Chemical Compatibility
The entire assembly must remain chemically inert when exposed to R134a, R1234yf, PAG oils (conductive), and POE oils (non-conductive).
Molecular Sieve vs. Silica Gel
Feature | Molecular Sieve (XH Grades) | Silica Gel (Type A) |
Primary Use | Active AC Systems, EV cooling | CKD Storage, Headlamps |
Low RH Capacity | High (adsorbs rapidly at <10% RH) | Low (requires higher RH) |
Temp Stability | Retains moisture up to 225°C | Releases moisture above 60°C |
Selectivity | High (excludes refrigerants) | Low (absorbs refrigerants) |
In an AC system running at 80°C, silica gel physically releases trapped moisture back into the refrigerant, causing acid formation. Molecular sieves permanently lock water away.
