Machine Design

DoE funds projects to boost efficiency

Researchers at the DoE-run Pacific Northwest National Laboratory (PNNL) unveiled some of their projects aimed at reducing energy use in the U. S.

Storing solar power: Solar power is clean, but without a way to store it for at least 8 to 12 hr, it cannot be used at night. One method of storing the sun’s energy is thermal storage. It uses molten salts, but also requires expensive equipment. To solve that problem, scientists developed a metal hydride that stores up to 10 times more heat per unit of mass than salts and operates at higher tempera

tures. A PNNL team is building a demonstration project that will collect heat from the sun for 6 hr and then discharge that energy over the next 6 hr.

Lighter fuel tanks for natural gas: Natural gas is becoming more abundant and less expensive, and 150,000 vehicle use it in the U. S. (That figure climbs to 15 million for the entire world.) One problem with natural gas as a transportation fuel is that it remains a vapor, so it must be compressed and stored in a pressurized tank to boost its energy density. A PNNL team is developing lightweight fuel tanks made using superplastic forming. The process involves welding metal sheets together then blowing compressed air between them to form internal chambers. This expanded tank can be made to conform to the space available in a car while traditional tanks, looking much like scuba tanks, take up more space and are cumbersome to mount in vehicles. The new tanks should cost about $1,500 each and hold 12 MJ/kg, about twice the energy density as current natural-gas tanks.

Magnets without rare-earth metals: Magnets are critical in today’s efficient motors and wind turbines, but the most efficient of these currently rely on rare-earth magnets. Dysprosium, for example, increases a magnet’s operating temperature, which is quite high in advanced motors. A material scientist at PNNL is developing a manganese-based nanocomposite magnet that operates at up to 200°C without using any expensive dysprosium.

Better air conditioners:In humid climes, air conditioners become inefficient. To cut electrical use for cooling in hot, humid climes by up to 50%, PNNL researchers are designing a new dehumidifier that relies on a thin membrane that pulls water out of the air. The membrane is based on a thin, foil-like metal sheet coated with zeolite, a water-attracting material.

Heating and cooling electric cars: Heating and cooling in electric cars puts a load on the batteries and can significantly reduce their range. An alternative approach being evaluated at PNNL involves a molecular heat pump that uses an electrical metal organic framework to circulate heat or cooling. A 5-lb heat pump the size of a two-liter bottle could theoretically handle the heating and cooling requirements for an electrical car with little affect on mileage.

Resources: Pacific Northwest National Laboratory,

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