Continuous flow of supercritical fluid: Upon reaching the proper pressure, the outlet of the first vessel and inlet of the second vessel open simultaneously so that one fills as the other empties.
High pressures and temperature considerations challenge designers of syringe, membrane, and dual-piston pumps that are typically used to deliver supercritical fluids such as carbon dioxide. High pressures tend to cause leaks, which reduce efficiency. Temperature plays a key role in all supercritical pumping because these fluids have a much lower viscosity than normal liquids. If the pump-head temperature rises above the liquid's critical temperature, it tends to leak, requiring complicated heading and cooling systems.
To overcome these challenges, researchers developed a new supercritical pumping technology that uses temperature to create pressure within two high-pressure vessels. When fluids are subjected to higher temperatures, they expand, creating more pressure, which is used to move the liquid. Independently heating and cooling two high-pressure vessels connected in parallel allows increased pressure to discharge liquid from the heated vessel, while fluid flows into the cooler vessel.
An electronic circuit switches power to a heating element off and on in response to preset pressure values to control temperature. This simple pumping technology is low cost, and quiet since it requires no moving parts, according to Janusz Pawliszyn of the University of Waterloo (Ontario, Canada). The design is suitable for applications in pharmaceutical manufacturing, wastewater treatment, food and beverage manufacturing, and laboratory processes.
Martjin Rasser, Yet2.com, 17 Monsignor O'Brien Hwy., Cambridge, MA 02141; Tel: (617) 557-3800 Ext. 127; Fax: (617) 523-8232; E-mail: [email protected].
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