Related Concept Videos
01:22Couette Flow
Couette flow represents the flow of fluid between two parallel plates, with one plate fixed and the other moving with a constant velocity. This configuration allows for a simplified analysis using the Navier-Stokes equations, which govern fluid motion under conditions of viscosity and incompressibility. For Couette flow, the assumptions include a steady, laminar, incompressible flow with a zero-pressure gradient in the flow direction. This flow type is beneficial for understanding shear-driven...
01:24Turbulent Flow
Turbulent flow is characterized by unpredictable fluctuations in velocity and pressure, which result in a chaotic fluid movement distinct from the orderly patterns of laminar flow. While laminar flow is governed by smooth, parallel layers with minimal mixing, turbulent flow exhibits highly irregular, three-dimensional patterns. This behavior arises due to instabilities in the fluid's velocity profile, and amplifies as the flow velocity increases. Minor disturbances, known as turbulent spots,...
01:30Bernoulli's Equation for Flow Along a Streamline
Bernoulli's equation relates the energy conservation in a fluid moving along a streamline. The equation applies to incompressible and inviscid fluids under steady flow. For such a flow, Newton's second law is applied to a small fluid element, which experiences forces due to pressure differences, gravity, and velocity variations. The force balance leads to the following form of Bernoulli's equation:
01:16Bernoulli's Equation for Flow Normal to a Streamline
Bernoulli's equation for flow normal to a streamline explains how pressure varies across curved streamlines due to the outward centrifugal forces induced by the fluid's curvature. The pressure is higher on the inner side of the curve, near the center of curvature, and decreases outward to balance these centrifugal forces.
The pressure difference depends on the fluid's velocity and radius of curvature. The pressure variation is minimal in flows with nearly straight streamlines. However, the...
The pressure difference depends on the fluid's velocity and radius of curvature. The pressure variation is minimal in flows with nearly straight streamlines. However, the...
01:17Steady, Laminar Flow Between Parallel Plates
Understanding steady, laminar flow between parallel plates is essential for analyzing and designing flow in narrow rectangular channels, commonly found in various water conveyance and drainage systems. The Navier-Stokes equations govern fluid motion and are generally challenging to solve due to their nonlinearity. However, simplifications are possible in certain cases, like the steady laminar flow between parallel plates. For this scenario, we assume steady, incompressible, laminar flow.
01:28Irrotational Flow
Irrotational flow is characterized by fluid motion where particles do not rotate around their axes, resulting in zero vorticity. For a flow to be irrotational, the curl of the velocity field must be zero. This imposes specific conditions on velocity gradients. For instance, to maintain zero rotation about the z-axis, the gradient condition:
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Related Experiment Video
Updated: Jun 25, 2026
08:34
Cryogenic Liquid Jets for High Repetition Rate Discovery Science
Published on: May 9, 2020
Generation of protosnowflakes in supersonic flow.
Lawrence S Bartell1, Paul J Lennon
1Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA. lbart@umich.edu
The Journal of Chemical Physics
|March 5, 2009
Summary
Researchers created ice nanocrystals at 200 K, mimicking upper atmosphere snowflake precursors. The rapid ice nucleation kinetics at this temperature are key, suggesting similar properties to natural snowflake nuclei.
Area of Science:
- Atmospheric science
- Materials science
- Physical chemistry
Background:
- Snowflake nuclei form in the upper atmosphere under specific temperature and pressure conditions.
- Laboratory studies of ice nucleation kinetics have historically been limited by slow reaction rates.
- Understanding ice crystal formation is crucial for atmospheric modeling and weather prediction.
Purpose of the Study:
- To investigate the formation and properties of ice nanocrystals generated under conditions relevant to atmospheric processes.
- To explore the kinetics of ice nucleation at approximately 200 K and compare them to existing laboratory data.
- To determine if laboratory-generated ice nanocrystals resemble precursors of atmospheric snowflakes.
Main Methods:
- Generating minuscule liquid water drops in supersonic flow via condensation of supersaturated water vapor.
Main Results:
- Ice nanocrystals with diameters of approximately 24 nm were successfully generated at 200 K.
- Ice nucleation kinetics were observed to be 20 orders of magnitude faster than in previous laboratory studies.
- The nanocrystals were identified as slightly denser cubic ice, flattened with 111 planes perpendicular to their thin direction.
Conclusions:
- Temperature, not the mode of generation, is the critical factor for rapid ice nucleation kinetics.
- The generated ice nanocrystals exhibit properties suggesting they are plausible precursors to atmospheric snowflakes.
- The structure of the ice nanocrystals, particularly the 111 planes, may act as templates for subsequent hexagonal ice growth.