Introduction to Pistonless Pumps
Pistonless pumps represent an innovative area of pump design research aimed at creating pumps that have no moving parts and therefore eliminate wear that occurs in traditional positive displacement pumps. Traditional positive displacement pumps like piston pumps, diaphragm pumps, and rotary lobe pumps all use mechanical parts that move or flex to pump fluid. This motion results in friction, wear, fatigue, and ultimately failure of moving components over time.
Pistonless pumps seek to eliminate these issues by using other physical principles besides mechanical movement to displace and transfer fluids. Some pistonless pump designs under research use magnetohydrodynamics (MHD), electrohydrodynamics (EHD), thermohydrodynamics (THD), surface acoustic wave (SAW) technology, and other effects to pump liquids without mechanical parts. If successful, pistonless pumps could greatly increase pump reliability, reduce maintenance costs, and find applications where traditional pumps cannot be used due to their moving parts.
Magnetohydrodynamic (MHD) Pump Research
One area of active pistonless pump research involves magnetohydrodynamic (MHD) pumping principles. MHD involves the motion of electrically conducting fluids in the presence of crossed electric and magnetic fields. When an electrolyte fluid passes through a chamber with orthogonal electric and magnetic fields applied, the interaction of these fields exerts a body force on the fluid to displace it without internal moving parts.
Researchers have conducted computational fluid dynamics (CFD) modeling and experiments to better understand MHD pumping phenomena and optimize design parameters. Variables studied include electrode geometry, applied electric and magnetic field strengths and orientations, electrolyte properties, and chamber designs. One 2005 paper modeled an annular disk MHD pump and found optimal designs and operating conditions to maximize flow rates. Another 2010 study experimentally validated CFD models of an inductive MHD pump with different electrode shapes.
Electrohydrodynamic (EHD) Pump Research
Electrohydrodynamic (EHD) pumping is another pistonless approach being researched. EHD utilizes electric field gradients to generate bulk fluid motion and pumping. When voltage is applied between electrodes submerged in a dielectric liquid, charge separation and electric body forces are induced. With properly designed electrode geometries, this can displace the fluid in a pumping action.
Like MHD pumps, significant effort has gone into EHD pump modeling, design optimization, and experimentation. Key parameters include electrode shapes, applied voltages, liquid dielectric constants, and chamber geometries. One 2007 paper developed an analytical model of a macro-scale EHD gas pump and validated it with experiments achieving flow rates up to 10 liters/minute. A 2012 study computationally optimized the shape of coaxial cylindrical electrodes in an EHD pump, finding spiral electrode shapes enhanced pumping efficiency over parallel plates.
Surface Acoustic Wave Pump Research
Surface acoustic wave (SAW) pump technology is a very promising area of pistonless pump research that uses acoustic streaming phenomena. When high frequency surface acoustic waves propagate along a piezoelectric substrate against a liquid layer, it generates steady acoustic streaming flows within the layer that can transport and pump the fluid. SAW pumps have no moving parts and can achieve precise, low flow rate pumping needed in microfluidics applications.
Research on SAW pumps has focused on microfabrication methods, improved device designs, modeling acoustic streaming patterns, and optimizing operating frequencies. One 2010 paper describes fabrication of a SAW pump on lithium niobate and reports flow velocities over 10 mm/s. A subsequent 2012 study computationally modeled different SAW transducer geometries and interdigital electrode designs to tailor streaming profiles for pumping applications. SAW pumps show potential as truly miniature, reliable pumps without any mechanically moving components.
Other Pistonless Pump Research Approaches
Beyond MHD, EHD, and SAW approaches, other pistonless pumping mechanisms are under investigation. Thermohydrodynamic (THD) pumping utilizes localized heating and the resulting thermal expansion and fluid motion to displace liquid volumetrically, similar to a thermal pump loop. Challenges include achieving uniform, efficient heating over large volumes. One 2016 study reports a micro-thermohydrodynamic pump capable of pressures over 1 kPa and modeled heat transfer dynamics.
Other work has looked at using ultrasonic or microbubble cavitation to acoustically drive microfluidic pumping. Capillary forces and surface tension have also been harnessed in digital microfluidic systems using electrowetting on dielectric principles to manipulate discrete droplets without internal pumps. Future research directions involve further optimizing these emerging technologies through multi-physics modeling, microfabrication, and system integration efforts.
Conclusion
Pistonless pumping represents an active area of research aimed at developing truly wear-free and reliable pumps for many applications. Approaches under study utilize diverse phenomena like magnetohydrodynamics, electrohydrodynamics, surface acoustic waves, thermohydrodynamics, and more to displace fluids volumetrically without any mechanical moving parts. Significant progress has been made through computational modeling, experimentation, and microfabrication to better understand these effects and optimize emerging designs. Further development could lead to truly maintenance-free pumps suitable for microfluidics, biomedical, industrial process, and other applications where reliability, small size or integrated designs are critical. Pistonless pumps show promise to revolutionize pump technology if technical challenges are successfully overcome.
Andrew Stroud