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Related Concept Videos

Density00:56

Density

Density is an important characteristic of substances, crucial in determining whether an object sinks or floats in a fluid. Its SI unit is kg/m3, and its cgs unit is g/cm3. The density of an object helps in identifying its composition, and also reveals information about the phase of the matter and its substructure. The densities of liquids and solids are roughly comparable, consistent with the fact that their atoms are in close contact. However, gases have much lower densities than liquids and...
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Uniform Depth Channel Flow

Uniform depth channel flow keeps fluid depth consistent along channels such as irrigation canals. In natural channels, such as rivers, approximate uniform flow is often assumed. This condition occurs when the channel’s bottom slope matches the energy slope, balancing potential energy lost from gravity with head loss due to shear stress. This balance prevents depth changes along the channel length, resulting in a steady, uniform flow.Uniform flow in open channels with a constant cross-section...
Density, Specific Weight, Specific Gravity and Compressibility of Fluid01:27

Density, Specific Weight, Specific Gravity and Compressibility of Fluid

Density, specific weight, specific gravity, and compressibility are fundamental properties of fluids. Density is the mass per unit volume, characterizing the mass of a fluid system. It influences buoyancy, pressure, flow dynamics, viscosity, thermal conductivity, and sound propagation. For instance, in pipeline design, accurate density measurements ensure that the pipeline can handle the fluid's mass.
Specific weight represents the weight per unit volume and is calculated by multiplying density...
Freezing Point Depression and Boiling Point Elevation03:12

Freezing Point Depression and Boiling Point Elevation

Boiling Point Elevation
The boiling point of a liquid is the temperature at which its vapor pressure is equal to ambient atmospheric pressure. Since the vapor pressure of a solution is lowered due to the presence of nonvolatile solutes, it stands to reason that the solution’s boiling point will subsequently be increased. Vapor pressure increases with temperature, and so a solution will require a higher temperature than will pure solvent to achieve any given vapor pressure, including one...
Freezing Point Depression and Boiling Point Elevation01:24

Freezing Point Depression and Boiling Point Elevation

When a non-volatile solute is added to a pure solvent, it results in the lowering of the freezing point of the solvent. This phenomenon is called freezing point depression. The extent to which the freezing point is lowered depends on the molality of the solute -the number of moles of solute per kilogram of solvent and the cryoscopic constant of the solvent.From the plot of chemical potential, μ, against temperature, it is evident that the μ of both solid and liquid solvents decrease with...
Coagulation01:06

Coagulation

Colloidal solids are solid particles suspended in solution. They are usually negatively charged, attracting a compact primary layer of positively charged ions, which attract more counterions to form an electrical double layer. Electrostatic repulsion between the charged double layers prevents the particles from colliding, stabilizing the colloids. These solids are often undesirable because they can contain toxins that are difficult to remove. Coagulation is a technique that helps aggregate and...

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Ice Generation and the Heat and Mass Transfer Phenomena of Introducing Water to a Cold Bath of Brine
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Density equalisation in supercooled high- and low-density water mixtures.

Niall J English1, Peter G Kusalik, John S Tse

  • 1The SEC Strategic Research Cluster and the Centre for Synthesis and Chemical Biology, School of Chemical and Bioprocess Engineering, University College Dublin, Belfield, Dublin 4, Ireland.

The Journal of Chemical Physics
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Molecular dynamics simulations reveal that high-density/low-density water interfaces rapidly equalize density, challenging the existence of distinct water states. This suggests low-density and high-density water do not coexist, even kinetically.

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Last Updated: May 8, 2026

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Area of Science:

  • Physical Chemistry
  • Computational Fluid Dynamics
  • Materials Science

Background:

  • The existence of a second critical point in water has been proposed, suggesting two distinct liquid phases: high-density liquid (HDL) and low-density liquid (LDL).
  • Previous molecular dynamics (MD) studies have explored the coexistence of these proposed water phases, often relying on assumptions of mechanical equilibrium.

Purpose of the Study:

  • To investigate the temporal evolution of high-density/low-density (HDL/LDL) water interfaces using molecular dynamics (MD) simulations.
  • To examine the behavior of water at temperatures near the predicted second critical point.
  • To challenge the 'two-liquid' model of water by analyzing interfacial density distributions.

Main Methods:

  • Performed molecular dynamics (MD) calculations on two model HDL/LDL interfaces.
  • Simulated systems at temperatures close to the predicted second critical point of water.
  • Utilized three different water models to assess the robustness of the findings.

Main Results:

  • Interfacial density equalization occurred rapidly across all simulations, irrespective of the water model used.
  • Observed a uniform density at the interface, ranging from approximately 0.99 to 1.067 g/cm³.
  • Found no evidence supporting an inhomogeneous distribution or the preferential accumulation of either HDL or LDL.

Conclusions:

  • The rapid density equalization indicates that the free energy of HDL and LDL water forms is metastable.
  • HDL and LDL water should not coexist as independent entities at thermodynamic equilibrium.
  • The findings challenge the existence of a second critical point for water and question the kinetic metastability of LDL/HDL mixtures.