Fluid-entrainment pumps

Sixties, mercury as the medium was almost completely replaced by oil. To obtain as high a vapor stream velocity as possible, he allowed the vapor stream to emanate from a nozzle with supersonic speed. The pump fluid vapor, which constitutes the vapor jet, is condensed at the cooled wall of the pump housing, whereas the fransported gas is further compressed, usually in one or more succeeding stages, before it is removed by the backing pump. The compression ratios, which can be obtained with fluid entrainment pumps, are very high if there is a pressure of 10 mbar at the inlet port of the fluid-entrainment pump and a backing pressure of 10 2 mbar, the pumped gas is compressed by a factor of 10  

Basically the ultimate pressure of fluid entrainment pumps is restricted by the value for the partial pressure of the fluid used at the operating temperature of the pump. In practice one tries to improve this by introducing baffles or cold traps. These are condensers between fluid entrainment pump and vacuum chamber, so that the ultimate pressure which can be attained in the vacuum chamber is now only limited by the partial pressure of the fluid at the temperature of the baffle. 

The various types of fluid entrainment pumps are essentially distinguished by the density of the pump fluid at the exit of the top nozzle facing the high vacuum side of the pump  

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Included in the class of fluid-entrainment pumps are not only pumps that use a fast-streaming vapor as the pump fluid, but also liquid jet pumps. The simplest and cheapest vacuum pumps are water jet pumps. As in a vapor pump (see Fig. 2.46 or 2.51), the liquid stream is first released from a nozzle and then, because of turbulence, mixes with the pumped gas in the mixing chamber. Finally, the movement of the water - gas mixture is slowed down in a Venturi tube. The ultimate total pressure in a container that is pumped by a water jet pump is determined by the vapor pressure of the water and, for example, at a water temperature of 15 °C amounts te about 17 mbar. 

Fig. 9.12 Saturation vapor pressure of pump fiuids for oii and mercuty fluid entrainment pumps...

Vacuum pumps acceptance specifications Part II (Fluid entrainment pumps) 28427 1972... 

Cavitation] [fluid vaporizes] /pump rpm too fast/suction resistance too high/ clogged suction line/suction pressure too low/liquid flowrate higher than de-sign/entrained gas. 

The inside of the reservoir generally will have baffles to prevent excessive sloshing of the fluid and to put a partition between the fluid return line and the pump suction or inlet line. The partition forces the returning fluid to travel farther around the tank before being drawn back into the active system through the pump inlet line. This aids in settling the contamination and separating air entrained in the fluid. 

Large reservoirs are desirable for cooling. A large reservoir also reduces re-circulation, which helps settle contamination, and separates entrained air. As a mle of thumb, the ideal reservoir should be two to three times the pump outlet per minute. However, due to space limitations in mobile and aerospace systems, the benefits of a large reservoir may have to be sacrificed. But they must be large enough to accommodate thermal expansion of the fluid and changes in fluid level due to system operation. 

Modifier Pump. The first feature in our adapted design is the introduction of a liquid pump via an instrument controlled VALCO (Model E04, Valeo Instruments, Houston, TX), four position selection valve. We have used an LKB Model 2150, dual piston pump for pumping modifier and entrainer fluids (LKB-Produkter AB, Bromma, Sweden). However, any suitable liquid pump could be substituted. Only pure fluids such as carbon dioxide have been introduced with the Suprex system syringe pump. With the addition of this second pump to deliver liquids, modifier is introduced directly into the extraction vessel. A wide range of alternative fluids and fluid mixtures can be rapidly selected with this dual pumping option. The criteria for selection of a modifier pump include the ability of the pump heads to withstand pressures in the range of 100 to 300 atm and interfacing capabilities, i.e. the ability to be turned on and off by the Suprex contact closure controls. 

One unique feature of the monolith reactor is the possibility of having an internal recirculation of the gas flow without the use of a pump [5,8-10]. This self-recirculation is possible due to the very low net pressure drop across the monolith. In a monolith reactor with downflow operation in slug flow regime, the fluids are not driven through the channels by an external pressure, but pulled through by gravity. This corresponds to a total superficial velocity of about 0.45 m sec . When liquid is added to the channel at a lower rate, gas will be entrained to make the total velocity 0.45 m sec. ... 

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