Pulsating flow, effect

The effect of pulsating flow on pitot-tube accuracy is treated by Ower et al., op. cit., pp. 310-312. For sinusoidal velocity fluctuations, the ratio of indicated velocity to actual mean velocity is given by the factor /l + AV2, where X is the velocity excursion as a fraction of the mean velocity. Thus, the indicated velocity would be about 6 percent high for velocity fluctuations of 50 percent, and pulsations greater than 20 percent should be damped to avoid errors greater than 1 percent. Tne error increases as the frequency of flow oscillations approaches the natural frequency of the pitot tube and the density of the measuring fluid approaches the density of the process fluid [see Horlock and Daneshyar, y. Mech. Eng. Sci, 15, 144-152 (1973)]. 

In a previous paper (16) the hardware design of the SEC/Viscometer system used in this work has been described. The effects of operational variables, e.g. pump pulsations, flow rate and flow irregularities on the performance of the viscometer and the enhancement of the signal-to-noise ratio by using mechanical dampers also has been described. Our current work has focused on the development, implementation and application of automated data... 

Vetter, G., Notzon, S. Effect of pulsating flow on Coriolis mass flowmeters. Flow Measurement and Instumentation 5 (1994) 4, 263-273. 

The parameter of the EPR 6, 0 < 6 < 1, characterizes the portion of the duct s cross-section occupied by the EPR. The calculations show that its increase does not decelerate the frequently oscillating medium which also differs from the low-frequency case. The effects of the easily penetrable roughness on a pulsating flow can be classified, in summary, depending on either the EPR is used for controlling the pulsating flow or, conversely, pressure pulsations are used to influence the flow in a duct with the EPR ... 

Belleville et al. [54] give a full description of the chemical nature of the fouling species. The use of enzymes to enhance the filter ability might also be effective for raising the economy in the application of ceramic membranes [55]. Another means of achieving economical operation could be flux enhancement by the application of pulsating flow as outlined by Jaffrin et al. [56,57]. The simultaneous introduction of pulses, and a rise in circulation velocity from 3 to 4.37 m/s and of the transmembrane pressure from 1 to 4.5 bar, increases the flux from 351/m h to 501/m h. 

The peristaltic pump is by far the most common propulsion device in flow analysis, due to its low cost and easy incorporation into multichannel flow systems. It delivers a pulsating flow (Fig. 3.4b) as a result of the vector sum of two effects. The first is the main action of the roller, which accounts for the main constant flow, whereas the second relates to the roller lift-off from the platen, which accounts for the slight sinusoidal fluctuations (ripple) on the main flow. 

A steady concentration of the reactant is not observed when the confluent reagent stream is not properly added. Pronounced differences in matrix composition (e.g., colour and suspended matter), flow rates and viscosity of the carrier and confluent streams may result in a pulsed addition of the confluent stream. The effect is random, but if the fluid-propelling device is a peristaltic pump, it is characterised by a typical frequency, dictated by the rotation speed of the peristaltic pump. A pulsating flow is then established, leading to undulations in the recorded peak. The effect is reduced if the involved streams converge with similar mean linear velocities. As the effect is characterised by a constant frequency, the modulated signal (ripple) is easily filtered out. 

Breakage of drops in a turbulent gas flow occurs due to the inertial effect caused by a significant difference of density of liquid and gas, and also due to difference of pulsation velocities, i.e. velocities of turbulent pulsations flowing around a drop, at opposite ends of the drop. Breakage of a drop thus occurs due... 

The microbial rating is generally used for membrane filters that are used in the sterilisation industry and is expressed as the ability of the filters to sterilise liquids. The filter permeability is the expression of resistance to flow provided by the filter media. This direct method establishes the permeability and can provide flow and pressure drop data with respect to fluid temperature and viscosity, filter size, and time. The effect of pulsating flow is the loosening of fine particles by agitating the filter. 

Mixing in stratified laminar flow relies on molecular diffusion. Therefore, mixing time for liquids is in the order of seconds in microchannels with diameters in the range of about 100 pm. A very simple method to disturb the fluid flow consists in superimposing a pulsating flow in the inlet of the channels. Glasgow and Aubry [50] used a simple T-shaped mixer to demonstrate the effective flow disturbance at very low Re (>0.3) by varying the inlet flow in a sine wave fashion. 

The normal comse of SSE is only realized at a definite range of input parameters. Outside the range there occms some disturbances in the normal process a discontinuous movement of the extrudate without an essential change of its shape (the stick-shp effect) the imstable flow of the polymer in the paraxial zone of the extrudate resulting in polymer tin-bidity the pulsating flow with a considerable deformation of extrudate shape and the occurrence of spiral-like cracks on its surface. 

A flow measurement is always accompanied by noise. This noise is attenuated somcwhnt by the wide proportional band of the eontroller and passed on to the valve. If the noise is of any magnitude, the valve may be stroked sufficiently to introduce actual changes in flow. The nonlinear function is an efficient noise filter, in that, it rejects small-amplitude signals. The result is smoother valve motion and a more stable loop. Figure 5.22 shows comparative records for linear and nonlinear control of a noisy flow loop. The nonlinear controller has proven to be quite effective on pulsating flows too, where the disturbance is periodic rather than random. 

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