Fluid motion pumping

Lubricity. In any mechanical seal design, there is rubbing motion between the dynamic seal faces. This rubbing motion is often lubricated by the fluid being pumped. Most seal mauufac turers hmit the speed of their seals to 90 ft/sec (30 m/sec). This is primarily due to centrifugal forces acting on the seal, which tends to restrict the seal s axial flexibihty. 

The chip micro reactor ([R 6]) was only one part of a complex serial-screening apparatus [20]. This automated system consists of an autosampler (CTC-HTS Pal system) which introduces the reactant solutions in the chip via capillaries. A pumping system (p-HPLC-CEC System) serves for fluid motion by hydro dynamic-driven flow. A dilution system [Jasco PU-15(5)] is used for slug dilution on-chip. The detection system was a Jasco UV-1575 and analysis was carried out by LC/MS (Agilent 1100 series capLC-Waters Micromass ZQ). All components were on-line and self-configured. 

As the disk spins, it pumps fluid to the surface. For laminar flow, analytical solutions describing the fluid motions have been obtained. In modeling the system the disk is assumed to be immersed in a large volume of electrolyte with the counterelectrode far away. 

Pumping Fluid motion Liquid-solid-gas Liquid-liquid-solid Liquid-liquid-gas Liquid-liquid-gas-solid Heat transfers... 

Convection is called forced convection if Ihe fluid is forced to flow over the surface by external means such as a fan, pump, or the wind. In contrast, convection is called natural (or free) convection if the fluid motion is caused by buoyancy forces that are induced by density differences due to the variation of temperature in the fluid (Fig. 1 33). For example, in the absence of a fan, heat transfer from the surface of the hot block in Fig. 1-32 is by natural convection since any motion in the air in this case is due to the rise of Ihe warmer (and thus lighter) air near the surface and the fall of the cooler (and thus heavier) air to fill its place. Heat transfer between the block and the surrounding air is by conduction if the temperature difference between Ihe air and the block is not large enough to overcome the resistance of air to movement and thus to initiate natural convection currents. 

Convection is classified as natural (or free) and forced convection, depend ing on how the fluid motion is initiated. In forced convection, the fluid is forced to flow over a surface or in a pipe by external means such as a pump or a fan. In natural convection, any fluid motion is caused by natural means such as the buoyancy effect, which manifests itself as the rise of warmer fluid and the fall of the cooler fluid. Convection is also classified a.s external and internal, depending on whether the fluid is forced to flow over a surface or in a pipe. 

In Chapters 7 and 8, we considered heat transfer by forced convection, where a fluid was forced to move over a surface or in a tube by external means such as a pump or a fan. In this chapter, we consider natural convection, where any fluid motion occurs by natural means such as buoyancy. The fluid motion in forced convection is quite noiicenhle, since a fan or a pump can transfer enough momentum to the fluid to move it in a certain direction. Tlie fluid motion in natural convection, however, is often not noticeable because of the low velocities involved. 

Very often fluid motion near the solid is not only the result of the temperature gradient, but also the result of some outside forces. In such cases, heat transfer is by forced convection. Here, a pressure gradient appears as a result of an external force exerted by a pump, for example. Fluid mixing takes place as a result of the... 

Circulation times are measures of the average bulk fluid motion generated by the liquid pumping of the impeller in a stirred tank. Measurements of circulation and mixing times help us to understand the scalar transport in the tank. 

Convection, sometimes identified as a separate mode of heat transfer, relates to the transfer of heat from a bounding surface to a fluid in motion, or to the heat transfer across a flow plane within the interior of the flowing fluid. If the fluid motion is induced by a pump, a blower, a fan, or some similar device, the process is called forced convection. If the fluid motion occurs as a result of the density difference produced by the temperature difference, the process is called free or natural convection. 

Specifically, theoretical equations and correlations of data are presented for evaluating the local rate of heat transfer between the surface of a body and an encompassing fluid at different temperatures and in relative motion. Forced convection requires either that the fluid be pumped past the body, as for a model in a wind tunnel, or the body be propelled through the fluid, as an aircraft in the atmosphere. The methods presented apply equally to either situation when velocities are expressed relative to the body. Gravity forces are usually negligible under these conditions. Further, the contents of this chapter are confined to those conditions where the fluid behaves as a continuum. 

The flow in an anchor agitated vessel has been studied in detail by Peters and Smith . The impeller promotes fluid motion close to the vessel wall but the region near the shaft may be relatively stagnant. In addition, there is little top-to-bottom turnover. In order to promote a top-to-bottom motion a helical ribbon may be used and often a screw is added to the shaft to obtain motion in the central regions of the vessel. This combined impeller system would have a ribbon pumping upward near the wall of the vesel with the screw, twisted in the opposite sense, pumping downwards near the shaft. 

Magnetic pumps are pumps using electromagnetic or magnetic fields to actuate and control fluid motion in microchannels. The application of electromagnetic or magnetic forces is a flexible way of manipulating fluids in lab-on-a-chip devices. 

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