Zeolite is a type of hard mineral with the potential to provide a high rate of gas flow in a micro-scale gas pump. A team of scientists from the University of Michigan have published a study which showcases a zeolite gas pump which doesn’t have any moving parts and which is based on temperature variations to control the gas flow in applications like warfare agent detectors, and gas sensing breath analyzers.

Naveen Gupta and Yogesh Gianchandani are the two medical engineers who used a type of zeolite called clinoptilolite which consists of billions of nanopores that are packed more densely than other minerals meaning that it can provide a higher rate of gas flow in gas pumps.

“Unlike zeolite gas pumps, most of the traditional micropumping mechanisms have moving parts. As we go smaller in size, the ratio of the surface area to volume of the parts increases, which results in increased frictional losses of power. Larger frictional forces result in increased wear and tear in the devices, which affects the reliability of the system adversely,” said Gupta.

This gas pump is based on the thermal transpiration principle, meaning that the gas molecules flow from the cold end to the hot end of the pump. The two engineers also designed a handheld-sized pump called Knudsen pump. The gas pump consists of a thin and flexible heater in the center, while the two ends were made of two thin pieces of clinoptilolite. Also, they used perforated aluminum to keep the temperature under control, and all these pieces were sandwiched between two pieces of PVC.

After the entire device was ready, the scientists “turned it on” and the gas pump operated at 296 mW/cm² of power. In order to make the gas to enter from the both ends of the pump, the engineers put there two inlet ports, then the heater started to operate and the cold molecules started to flow through the nanopores to the heater. This process is called free molecular gas flow and, as the researchers explained, it was possible thanks to the nanopores which were getting thinner as the gas flowed and in the same time the pressure at which the gas pump could operate was getting higher.

“The free molecular regime is a name given to the gas flow conditions in which the mean free path of the gas molecules is much larger than the characteristic length of the channel. Unlike the case for the continuum gas flow regime, in the free molecular regime the gas molecules bounce against the channel walls much more frequently than they bounce against each other. Under these conditions, the wall interaction dominates and tends to cause the molecules to drift from the cold end to the warm end of the channel,” said Gupta.

In conclusion, the engineers said that they have chosen clinoptilolite because it’s one of the most abundant zeolites meaning that it’s cheap, easy to get, and in the same time it’s mechanically strong. According to the scientists, the gas pump with no moving parts could be used in various applications.

“These miniature pumps may someday be useful for a variety of applications ranging from ventilation to vacuum pumping. They may also assist as gas reservoirs and gas separation elements in miniature or handheld system diagnostic. However, the Knudsen pumping technology is still evolving and will need quite a bit of effort before it gets there,” concluded Gupta.