Numerical investigations of laminar flow characteristics in helically finned pipes

2011 ◽  
Vol 222 (3-4) ◽  
pp. 321-330
Author(s):  
F. Nygård ◽  
H. I. Andersson
Keyword(s):  
Laminar Flow ◽  
Flow Characteristics ◽  
Numerical Investigations

Characterizing the High Reynolds Number Regime for Deterministic Lateral Displacement (DLD) Devices

2017 ◽  
Author(s):  
Brian Dincau ◽  
Arian Aghilinejad ◽  
Jong-Hoon Kim ◽  
Xiaolin Chen
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Soft Lithography ◽  
Lateral Displacement ◽  
Flow Characteristics ◽  
Critical Diameter ◽  
Flow Rates ◽  
Deterministic Lateral Displacement ◽  
Array Configuration ◽  
High Reynolds

Deterministic lateral displacement (DLD) is a common name given to a class of continuous microfluidic separation devices that use a repeating array of pillars to selectively displace particles having a mean diameter greater than the critical diameter (Dc). This Dc is an emergent property influenced by pillar shape, size, and spacing, in addition to the suspending fluid and target particle properties. The majority of previous research in DLD applications has focused on the utilization of laminar flow in low Reynolds number (Re) regimes. While laminar flow exhibits uniform streamlines and predictable separation characteristics, this low-Re regime is dependent on relatively low fluid velocities, and may not hold true at higher processing speeds. Through numerical modeling and experimentation, we investigated high-Re flow characteristics and potential separation enhancements resulting from vortex generation within a DLD array. We used an analytical model and computational software to simulate DLD performance spanning a Re range of 1–100 at flow rates of 2–170 μL/s (0.15–10 mL/min). Each simulated DLD array configuration was composed of 60 μm cylindrical pillars with a 45 μm gap size. The experimental DLD device was fabricated using conventional soft lithography, and injected with 20 μm particles at varying flow rates to observe particle trajectories. The simulated results predict a shift in Dc at Re > 50, while the experimental results indicate a breakdown of typical DLD operation at Re > 70.

Behaviour of Fluids (Liquids and Gases, Flow and Pressure)

2011 ◽  
Author(s):  
Patrick Magee ◽  
Mark Tooley
Keyword(s):  
Laminar Flow ◽  
Average Velocity ◽  
Fluid Transport ◽  
Minimum Energy ◽  
Flow Characteristics ◽  
The Other ◽  
Transport Mode ◽  
Density Flow ◽  
Fluid Layers

A fluid can be either a liquid or a gas. Fluids exhibit different flow behaviours depending on their physical properties, in particular viscosity and density. Flow characteristics also depend on the geometry of the pipes or channels through which they flow, and on the driving pressure regimes. These principles can be applied to any fluid, and the complexity of the analysis depends on the flow regimes described in this section [Massey 1970]. Fluid flow is generally described as laminar or turbulent. Laminar flow, demonstrated by Osborne Reynolds in 1867, is flow in which laminae or layers of fluid run parallel to each other. In a circular pipe, such as a blood vessel or a bronchus, velocity within the layers nearest the wall of the pipe is least; in the layer immediately adjacent to the wall it is probably actually zero. In fully developed laminar flow, the velocity profile across the pipe is parabolic, as shown in Figure 7.1, and as discussed in Chapter 1. Peak velocity of the fluid occurs in the mid line of the pipe, and is twice the average velocity across the pipe at equilibrium, and layers equidistant from the wall have equal velocity. The importance of laminar flow is that there is minimum energy loss in the flow, i.e. it is an efficient transport mode. This is in contrast to turbulent flow, where eddies and vortices (flow in directions other than the predominant one) mean that energy in fluid transport is wasted in production of heat, additional friction and noise. The result is that the pressure drop required to drive a given flow from one end of the pipe to the other is greater in turbulent than in laminar flow. The shear stress τ, which is the mechanical stress between layers of fluid and between the fluid and the tube wall, is proportional to the velocity gradient across the tube (dv/dr) of the fluid layers. The constant of proportionality between these two variables is the dynamic viscosity, η.

Experimental and Numerical Investigations on the Leakage Flow Characteristics of Helical-Labyrinth-Brush Seals

2020 ◽  
Author(s):  
Yuanqiao Zhang ◽  
Jun Li ◽  
Dengqian Ma ◽  
Yuan He ◽  
Jingjin Ji ◽  
...  
Keyword(s):  
Pressure Drop ◽  
Rotational Speed ◽  
Static Pressure ◽  
Pressure Ratio ◽  
Flow Characteristics ◽  
Leakage Flow ◽  
Absolute Value ◽  
Numerical Investigations ◽  
Brush Seal ◽  
Speed Up

Abstract This paper numerically investigates the leakage flow characteristics of two types of HLBSs (bristle pack installed upstream or downstream of helical-labyrinth tooth named as HLBS-U and HLBS-D, respectively) at various pressure ratios (1-1.3) and rotational speeds (0-10000r/min). In parallel, the leakage flow characteristics of the HLBS-D with the constant cb of 1.0 mm are experimentally measured at the pressure ratio up to 1.3 and rotational speed up to 2000 r/min. The effective clearance of the HLBS-U is smaller than that of the HLBS-D in the case of cb=0.5mm and rotational speed n<10000r/min, and the case of cb=1.0mm. However, for the case of cb=0.5mm and n=10000r/min, and the case of cb=0.1mm, the situation is opposite. The brush seal sections of the HLBS-U and the HLBS-D offer over 55% and 65% total static pressure drop in the case of cb=1.0 mm, respectively; The brush seal sections of two HLBSs bear almost the same static pressure drop of the over 97% total static pressure drop as cb equals to 0.1 mm. The HLBS-U has lower turbulent kinetic energy upstream of the bristle pack than the HLBS-D does, which means that intensity of bristles flutter of the HLBS-U is lower. The HLBS-U possesses significantly lower absolute value of aerodynamic forces than the HLBS-D does as cb=1.0 mm.

Experimental Investigation on Flow Characteristics in a Tube-Bundle Channel

2012 ◽  
Author(s):  
Zhan Li ◽  
Guangyao Lu ◽  
Wenyuan Xiang
Keyword(s):  
Heat Exchange ◽  
Laminar Flow ◽  
Turbulent Flow ◽  
Circular Tube ◽  
Tube Bundle ◽  
Flow Characteristics ◽  
Phase Flow ◽  
Flow Friction ◽  
Annular Channels ◽  
Flow Directions

Experiments were carried out to investigate the flow characteristics with/without heat exchange in vertical and inclined tube-bundle channels. In the experiments, the influences of flow directions and heat exchange upon the flow characteristics were studied. Experiments showed that the flow friction in tube-bundle channels had relations to the flow directions, and the liquid temperature difference at the inlet and outlet of tube-bundle channels. And these influences were comparatively obvious in the laminar flow regime. In the experiments, the transition from laminar to turbulent flow was carefully observed. The flow characteristics of single phase flow through tube-bundle channels were different from those in circular tubes and those in annular channels. The flow friction in tube-bundle channel is larger than that in normal circular tube. And the transition from laminar flow to turbulent flow in tube-bundle channel is different from that in normal circular tube. The influences of flow direction and heat exchange on the friction were also studied. The results were gained to provide the basis for the further investigations on the two-phase flow in tube-bundle channels.

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