Design of a high-pressure circulating pump for viscous liquids
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ereas only a few of the magnetically coupled pump designs reported in the literature apply rotary action. Those no reciprocating pumps incorporate rotors shaped like a turbine, an Archimedean screw, a simple magnetic stir bar or other rotary-type pump impeller. Among those rotary-type magnetically coupled pumps, the Archimedean screw pump was designed for circulating liquids under high pressure. This rather interesting design of a screw pump consists of a helical screw shaped rotor inside a high pressure cylindrical autoclave, which is driven by an externally wound stator functioning similar to a synchronous motor. The advantage of this isochoric working Archimedean screw pump is that it avoids pulsation in the circulated fluid, which may be favorable in a supercritical fluid phase equilibria apparatus, where volume and pressure changes may lead to solute precipitation inside the pump. However, the Archimedean screw pump suffers from a very complex design and low pump efficiency. Magnetically coupled reciprocating piston pumps have been successfully used for circulating both liquids and gases in applications involving high and low pressures and temperatures. Magnetically coupled reciprocating pumps described in the literature use either solenoids or permanent magnets to drive the piston inside the pump cylinder. In some cases, the piston or parts of it are made from permanent magnets or magnetic stainless steel. The magnetically coupled pump reported by Torre et al. incorporates a permanent magnet attached to bellows instead of a piston. Both approaches using either solenoids or permanent magnets used for driving the piston have advantages and disadvantages depending on the application of the pump. Permanent magnets have the great advantage that they do not generate heat during operation. This heat generation encountered in electromagnetically driven pumps depends on the type of solenoid, the power rating, and duty cycle. Heat generation may be of concern in situations where the heat cannot be dissipated efficiently; thereby leading to challenges in phase equilibria measurements. However, a pump using permanent magnets requires an additional drive assembly involving externally moving parts to achieve linear motion. This drive assembly can consist either of a pneumatic actuator or an electric motor equipped with a mechanical transmission to convert circular to linear motion by use of either a mechanical disk-and-arm or disk-and-cable linkage, a two crank as