SBIR-STTR Award

As stated in the solicitation, the Air Force spends $4.5 billion annually on aircraft maintenance related to corrosion. A significant fraction of this expenditure could be saved by a Corrosion Mitigation System (CMS) that both limited a shelter's indoor relative humidity to less than 50% while capturing airborne chloride particles. However, these functions, particularly humidity control, can be expensive to implement with conventional dehumidifiers. Liquid desiccant dehumidifiers are uniquely suited to efficiently control indoor humidity. Since a liquid desiccant can dehumidify air without over-cooling the air, the high latent loads of an active aircraft shelter in a humid locale can be met without excessive (and wasteful) sensible cooling. Furthermore, a liquid-desiccant CMS has the potential to capture airborne chloride particles as it absorbs moisture. Recent advances can significantly reduce the energy use and improve the O & M characteristics of a liquid-desiccant CMS. The proposed work will study (1) liquid desiccant conditioners that use membranes to prevent droplet carryover, (2) two-stage regenerators that can almost halve the thermal energy required by the CMS, and (3) non- corrosive alternatives to the traditional lithium chloride. The major deliverable for the proposed work is a recommended configuration for a liquid-desiccant CMS that could be field tested in a second phase of work.

Benefit:
If successful, the Corrosion Mitigation System (CMS) developed in the proposed work will provide the Air Force an effective means to significantly reduce maintenance costs for aircraft. The liquid desiccant technology that is the focus of this work can also be used for humidity control in standard HVAC applications. This close sharing of technology will lead to advances crossing over in both directions between the CMS and HVAC fields.

Keywords:
liquid desiccant, corrosion mitigation, humidity control,chloride control, membrane liquid desiccant conditioners, liquid desiccant dehumidifiers

The Air Force spends $4.5 billion annually on aircraft maintenance related to corrosion.The source of this corrosion frequently is airborne chlorides that settle on metal parts and sensitive avionics and then absorb moisture from the air to create an electrolyte that promotes galvanic corrosion.The proposed work will design, fabricate and test a Corrosion Mitigation System (CMS) that supplies at least 75 lb/min of deeply dried and highly filtered air to parked or stored aircraft and aerospace ground equipment (AGE).The CMS will apply a technology that integrates liquid-desiccant contactors into a compressor-based, direct-expansion (DX) air conditioner to produce a system that can deliver air with a dewpoint that is more than 10 degree F lower than the air conditioners suction temperature (i.e., the proposed system will deliver deeply dried air with a dewpoint of 32 degree F while operating with a 44 degree F evaporator suction temperature.The high suction temperature reduces the work performed by the compressor leading to very low power requirements that are projected to be 40% to 50% below those of commercially available systems that perform a similar function. Once proven at the smaller scale, the liquid-desiccantCMS technology can be scaled up to become a highly efficient means of maintaining larger shelters at relative humidity below 40%.The technology will also be very competitive in the segment of the HVAC market that addresses humidity problems within buildings;

Benefit:
In addition to reducing the high maintenance cost imposed by chloride-induced corrosion, the technology at the core ofa liquid-desiccant CMS will have import HVAC applications.High humidity frequently leads to an uncomfortable and unhealthy indoor environment.While corrosion may be less of a problem, humidity-induced mold can lead to very large maintenance bills for building owners.A version of the liquid-desiccant CMS thatdelivers large volumes of dry ventilation air could be a much lower cost alternative to technologies now used to control indoor humidity in very humid climates.