Symbol	Description	Unit
$Re$	Reynolds number	—
$\rho$	Fluid density	kg/m³
$v$	Flow velocity	m/s
$D$	Characteristic dimension	m
$\mu$	Dynamic viscosity	Pa·s
$P$	Pressure	Pa
$f$	Darcy friction factor	—

Common Fluids and Their Viscosity Characteristics

The following fluids are commonly encountered in engineering applications and have well-documented viscosity data available across varying temperatures and pressures.

Gases

Fluid	Dynamic Viscosity Range	Notes
Air	0.017–0.050 mPa·s	Varies significantly with temperature
Carbon Dioxide (CO₂)	0.015–0.035 mPa·s	Phase changes affect viscosity
Ethane (C₂H₆)	0.009–0.025 mPa·s	Light hydrocarbon gas
Ethylene (C₂H₄)	0.010–0.028 mPa·s	Also called ethene
Ammonia (NH₃)	0.010–0.022 mPa·s	Toxic - handle with care

Liquids

Fluid	Dynamic Viscosity Range	Notes
Benzene (C₆H₆)	0.45–0.65 mPa·s at 25°C	Carcinogenic - use alternatives
Ethanol (C₂H₅OH)	1.0–1.2 mPa·s at 20°C	Common solvent
Butane (C₄H₁₀)	0.15–0.20 mPa·s (liquid)	LPG component
Ethylene Glycol	16–25 mPa·s at 20°C	Heat transfer fluid

Pump Performance and Viscosity

Viscosity directly impacts centrifugal pump performance through hydrodynamic losses. Higher viscosity fluids experience:

Increased friction losses in the impeller
Reduced flow rates at constant head
Decreased efficiency
Higher power requirements

Rule of thumb: Pump performance corrections are typically required when kinematic viscosity exceeds 10 cSt (centistokes).

Engine and Gear Oil Selection

Oil viscosity grade selection depends on operating temperature:

Outside Temperature	SAE Grade (Engine Oil)	Viscosity Range (cSt at 100°C)
Below -30°C	0W	3.8 minimum
-30°C to 0°C	5W	3.8 minimum
0°C to 20°C	10W-30	9.3–12.5
20°C to 40°C	15W-40	12.5–16.3
Above 40°C	20W-50	16.3–21.9

Crude Oil Viscosity Correlation

Crude oil viscosity at standard conditions (20°C/68°F and 50°C/122°F) correlates with API gravity:

$\log_{10}(\nu) = A - B \cdot API$

Where:

$\nu$ = kinematic viscosity (cSt)
$API$ = API gravity of crude
$A, B$ = empirical constants varying with temperature

Typical values: Light crudes (API > 31°) have viscosities below 10 cSt, while heavy crudes (API < 22°) can exceed 100 cSt at 20°C.

Calcium Chloride Brine Properties

Calcium chloride water solutions are commonly used as refrigerants/coolants. Key properties at 25% concentration:

Property	Value
Freezing point	-30°C (-22°F)
Density	1.24 g/cm³
Specific heat	2.8 kJ/(kg·K)
Dynamic viscosity	4.2 mPa·s at 0°C

ISO Viscosity Grades for Industrial Lubricants

Industrial lubricants follow ISO VG (Viscosity Grade) classification:

ISO VG	Viscosity at 40°C (cSt)	Typical Application
22	22 ± 10%	Light hydraulic systems
32	32 ± 10%	General hydraulic systems
46	46 ± 10%	Industrial gearboxes
68	68 ± 10%	Heavy-duty gearboxes
100	100 ± 10%	Compressors
150	150 ± 10%	Extreme pressure applications
220	220 ± 10%	Heavy industrial gears
320	320 ± 10%	Very heavy loads
460	460 ± 10%	Rolling mills

References

Original Source

Source: engineeringtoolbox.com