LearnChemE

#### Properties of Fluids: Screencasts

Defines fluids and describes some characteristics of fluids.

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Explains two fluid properties: density and bulk modulus.

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Explains two fluid properties: vapor pressure and surface tension.

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##### Important Equations:

Density $$\rho$$ of an ideal gas can be calculated by rearranging the ideal gas law.

$\rho = \frac{RM}{RT}$

where $$P$$ is pressue, $$M$$ is molecular mass, $$R$$ is the gas constant, and $$T$$ is the absolute temperature.

Specific volume $$v$$:

$v = \frac{1}{\rho}$

Specific gravity $$(SG)$$ is a dimensionless form of density. It compares the density of the material of interest to a reference material, which is most commonly water.

$SG = \frac{\rho_f}{\rho_{ref}}$

where $$\rho_f$$ is the density of the material of interest and $$\rho_{ref}$$ is the density of the reference material.

Specific weight $$(\gamma)$$:

$\gamma = \rho g$

where $$g$$ is the acceleration due to gravity.

The bulk modulus $$(E_v) )\ is a fluid property that describes that compressibility of the fluid. $E_v = -V \frac{dP}{dV} = \rho \frac{dP}{d\rho}$ where \(V$$ is volume, $$dP$$ is differential pressure, $$dV$$ is differential volume, and  $$d \rho$$ is differential density.

Surface tension $$(\sigma)$$ is tensile force at interfaces that can be derived for a fluid droplet in an immiscible fluid.

$\Delta P = \frac{2\sigma}{r}$

where $$\Delta P$$ is a pressure change, and $$r$$ is the radius of the droplet.

One of the common effects of the surface tension is capillary rise. The height of capillary rise $$(h)$$ can be derived as follows:

$h = 2\sigma \cos(\frac{\theta}{\gamma r})$

where $$\theta$$ is the contact angle between the liquid and the capillary tube and $$r$$ is the radius of the capillary tube.