HEARING AID DRYING – Past – Present – Future

Hearing aids wet to dry

In this article we would like to inform you about the latest news in the field of hearing aid drying.

Sweat, moisture and cerumen initially adhere superficially to the hearing aids. By capillary effect (cohesion and adhesion) the mixture reaches the interior of the hearing aids and accumulates there. The cocktail of salts, acids, organic components and water leads to failures and expensive repairs, up to total loss.

Salt dry capsules

The silica gel dry capsules or tabs absorb the air humidity as well as the hearing aid humidity. Drying depends on the net salt content (weight), the temperature (°C/°F), the relative humidity (%) and a small and airtight drying can in terms of volume. Disadvantages are the hardly visible consumption process of the tabs, the continuous replacement of used tabs, chemistry as well as environmental aspects.

Electric heat dry boxes

Drying by convection of warm air has been the most common hearing aid drying method for many years. It requires the greatest possible temperature difference between the drying chamber (Ti) and room temperature (Ta). Older hearing aids were tested with an upper limit temperature of 60°C (140°F) and so was dried with approx. 50°C (122°F). This is a very effective drying process, especially for battery-operated hearing aids where the batteries can be removed during the drying process.

For the increasingly delicate hearing aids and the growing number of rechargeable hearing aids with lithium batteries, the hearing aid manufacturers specify a maximum temperature of 40°C (104°F). Convection drying is uneconomical at this low temperature difference, as it requires a very long drying time.

Charger drying

Lithium battery hearing aids and company-specific charging stations have become established in the hearing aid industry. New and at the same time critical are charging stations with an all-round function. This refers to chargers that can perform 1. charging, 2. mains-free recharging with LiPo battery, 3. drying and 4. promise hygiene. The idea is good but unfortunately the points 3. and 4. don’t work in practice. In many cases, the heating of approx. 40°C that occurs during battery charging is communicated as heating or drying, which is completely impractical in the absence of convection without supply and exhaust air ducts or even with a closed lid and can cause moisture damage to the hearing system.

Furthermore, this temperature without ventilation is the perfect breeding ground for germs and bacteria. This can significantly increase the risk of ear infections. The UV-LEDs with 275 nm, which are mostly used for hygiene, cannot reach the entire hearing aids in the charger and therefore cannot guarantee a germ reduction of 99.9%. Wavelength, intensity and above all the radiation geometry set physical limits here.

Turbo fan drying

One of the most efficient and gentle drying methods is drying by a strong air current generated by a high performance fan. In the process, the hearing aids circulate about 5 cubic meters of air per hour. The basis of drying with swirled air flow in confection is the vapour pressure gradient of the liquid. Not only is the moisture adhering to the outside evaporated, but efficient interior drying is also achieved at the boundaries of the hearing aids via water vapour partial pressure equalisation.

This turbo drying in combination with effective UV-C light (253.7 nm) ensures perfectly dried and hygienically cleansed hearing aids. This protects the hearing aids, ensures their usefulness and maintains the pleasure of hearing.

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