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The Basic Concept for Microfluidics-Based Devices
Published in Raju Khan, Chetna Dhand, S. K. Sanghi, Shabi Thankaraj Salammal, A. B. P. Mishra, Advanced Microfluidics-Based Point-of-Care Diagnostics, 2022
A Reynolds number is a dimensionless quantity that helps in predicting the type of flow of a fluid. This concept was introduced in 1851 by George Stokes and popularized in 1883 by Osborne Reynolds, a British engineer, and physicist from the University of Manchester. A Reynolds number is the ratio of internal forces to viscous forces when a fluid is subjected to relative internal momentum owing to the differences in fluid velocities of individual layers. The detailed derivation of a Reynolds number is deduced in the latter half of the chapter. Re=InterialForceViscousForce=ρvDμ=uDv
Introduction to the Continuum Fluid
Published in Tasos C. Papanastasiou, Georgios C. Georgiou, Andreas N. Alexandrou, ViscousFluid Flow, 2021
Tasos C. Papanastasiou, Georgios C. Georgiou, Andreas N. Alexandrou
Flows of highly viscous liquids are characterized by a vanishingly small Reynolds number and are called Stokes or creeping flows. Most flows of polymers are creeping flows [6]. The Reynolds number also serves to distinguish between laminar and turbulent flow. Laminar flows are characterized by the parallel sliding motion of adjacent fluid layers without intermixing, and persist for Reynolds numbers below a critical value that depends on the flow. For example, for flow in a pipe, this critical value is 2,100. Beyond that value, eddies start to develop within the fluid layers that cause intermixing and chaotic, oscillatory fluid motion, which characterizes turbulent flow. Laminar flows at Reynolds numbers sufficiently high that viscous effects are negligible are called potential or Euler flows. The Stokes number is zero in strictly horizontal flows and high in vertical flows of heavy liquids. The capillary number appears in flows with free surfaces and interfaces [7]. The surface tension, and thus the capillary number, can be altered by the addition of surfactants to the flowing liquids.
Physical and Chemical Factors Governing the Behavior of Physiological Regulators and Control Systems
Published in Robert B. Northrop, Endogenous and Exogenous Regulation and Control of Physiological Systems, 2020
Several physiological systems involve fluid dynamics in their descriptions. These include the respiratory system, the regulatory systems for intraocular pressure and cerebrospinal fluid pressure, and systems involving the circulatory system (e.g., blood pressure regulation, short term and long term). In the simplified descriptions of fluidic systems below, we assumed that laminar flow conditions are present (i.e., there is no turbulence). Laminar flow is generally present when the Reynolds number is less than 1000. The Reynolds number of a fluid flowing in a cylindrical tube is given by: () Re=ρv¯rη
Influence of the Refrigerant on the Performance of a Heat Pump with Gas Bearings
Published in Heat Transfer Engineering, 2023
Huaqi Lian, Yulong Li, Chengjun Rong
The model is based on the following assumptions [33]:The flow in the gas film is isothermal, as the gas film is very thin, and the heat is conducted away by bearing surface quickly.The gas viscosity is constant, as the gas temperature is constant.The mass flow rate into the orifices is equal to the mass flow rate out of the gas film.The flow is laminar, as the Reynolds number of the flow is low.The gravity and the inertial force are neglected, and the side flow is neglected.The flow is steady.
A review on the progress and development of thermoelectric air conditioning system
Published in International Journal of Green Energy, 2023
Manoj Sasidharan, Mohd Faizul Mohd Sabri, Sharifah Fatmadiana Wan Muhammad Hatta, Suriani Ibrahim
The flow behavior and characteristics play an important role in determining the performance of thermoelectric cooling (Ma 2004). Table 3 shows various approaches that make extensive use of experimental and numerical methods while using other methods. Some studies have used conserved laminar flows in the micro channel heat sinks and turbulent flows in the feed tubes (manifolds) (Baby and Balaji 2013). The review found that studies with the laminar flow were the most prevalent. Figure 14 compares studies with laminar flow to those with laminar-turbulent or turbulent flow. It is generally understood that heat sink performance is better with laminar flow because the heat sink channel cannot be short enough with turbulence. The laminar Reynolds number ranges from 100 to 2300, and several studies have investigated the turbulent flow. According to some studies, heat sinks perform better in turbulent flows and a strong pump is required.
MVU-Net: a multi-view U-Net architecture for weakly supervised vortex detection
Published in Engineering Applications of Computational Fluid Mechanics, 2022
Liang Deng, Jianqiang Chen, Yueqing Wang, Xinhai Chen, Fang Wang, Jie Liu
Generalizability. In the 3D experiments, we verify the generalizability at three different situations. Firstly, we use different time-steps in the same unsteady simulation for training and testing. Secondly, we adopt different flow conditions of half cylinder for training ( and 640) and testing ( and 6400). The Reynolds number helps predict flow patterns in different fluid flow situations. At low Reynolds numbers, flows tend to be dominated by laminar (sheet-like) flow, while at high Reynolds numbers flows tend to be turbulent. As the Reynolds number increases, the vortex structures become very complex and rich. Thirdly, we use two new cases (double delta wing and turbulent boundary layer), which is totally different from the training cases, to verify the performance of our method. These three kinds of cases evaluate the generalizability of our method from the aspects of time-steps, flow conditions, and object shapes in flow field.