Laminar flow-over designs

It is clear from Figure 11.12 that the slicing and replacing mechanism occurs in isolation and is not accompanied by either shearing or extension, both of which would deform the fluid elements. However, it is possible to create this distributive mixing action during laminar flow over appropriately designed... 

While designers of fluid power equipment do what they can to minimize turbulence, it cannot be avoided. For example, in a 4-inch pipe at 68°F, flow becomes turbulent at velocities over approximately 6 inches per second (ips) or about 3 ips in a 6-inch pipe. These velocities are far below those commonly encountered in fluid power systems, where velocities of 5 feet per second (fps) and above are common. In laminar flow, losses due to friction increase directly with velocity. With turbulent flow, these losses increase much more rapidly. 

The basic equations for filmwise condensation were derived by Nusselt (1916), and his equations form the basis for practical condenser design. The basic Nusselt equations are derived in Volume 1, Chapter 9. In the Nusselt model of condensation laminar flow is assumed in the film, and heat transfer is assumed to take place entirely by conduction through the film. In practical condensers the Nusselt model will strictly only apply at low liquid and vapour rates, and where the flowing condensate film is undisturbed. Turbulence can be induced in the liquid film at high liquid rates, and by shear at high vapour rates. This will generally increase the rate of heat transfer over that predicted using the Nusselt model. The effect of vapour shear and film turbulence are discussed in Volume 1, Chapter 9, see also Butterworth (1978) and Taborek (1974). 

Because of the sensitivity of PCR assays, it is most important to minimise the potential danger of cross-contamination. Ideally, PCR laboratories should consist of two separate rooms, each containing their own equipment (e.g., pipetors). One room should be dedicated to the setting up of RT reactions and PCR assays only. Both laboratories should use aerosol-resistant tips to prevent carry-over of sample within the barrel of the pipet. Post-PCR tubes should never be opened in the room used to set up PCRs as this is probably the most potent source for potential contamination. A laminar-flow cabinet, particularly one designed for PCR, should be considered a requirement for a PCR room in situations where a large number of samples will be processed. 

In contrast, stabilization of boundary layer by contouring the airfoil surface to achieve favourable pressure gradient as a passive way is found to be practical and attractive. The resultant section is known as the Natural Laminar Flow (NLF) airfoil and this is an area which has been under renewed investigation over the last three decades. Early efforts of designing... 

Centrifugal Force. Robertson et al40 designed an apparatus in which the centrifugal force vector was perpendicular to the membrane surface but opposite (and parallel) to the flux vector. Solutions of casein and dextran (60,400 dal-tons) were passed over the membrane in laminar flow. When the apparatus was spun, centrifugal field strengths from 100 to 600g resulted in flux improvement factors of 3 to 16. 

Micro fuel cell designs without polymeric membranes can overcome some PEM-related issues such as fuel crossover, anode dry-out or cathode flooding. In these membraneless laminar flow-based fuel cells (LF-EC) two or more liquid streams merge into a single microfluidic channel. The stream flows over the anode and the cathode electrodes placed on opposing side walls within the channel. The reaction of fuel and oxidant takes place at the electrodes while the two liquid streams and their liquid-liquid interface provide the necessary ionic transport [122,123]. 

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