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The viscosity of a fluid is a measure of its resistance to flow.

It is a property of the fluid that determines the amount of force required to move it. The higher the viscosity, the more force is required to move the fluid.

The viscosity of a fluid is affected by its temperature. The warmer the fluid, the lower its viscosity. The colder the fluid, the higher its viscosity.
The viscosity of a fluid is also affected by its pressure. The higher the pressure, the higher the fluid’s viscosity.

The viscosity of a fluid can be measured with a viscometer. A viscometer is a device that measures the resistance of a fluid to flow. The viscosity of a fluid is an important property in many applications. For example, the viscosity of a fluid can be used to determine the amount of force required to move it through a pipe.

Viscosity in physics is one of the properties of matter whereby the motion of molecules with respect to surrounding molecules encounters, due to intermolecular forces, a resistant force: in solids it is highest, but lowest in liquids and gases. If we immerse a foreign body in the fluid under consideration, it will encounter a resistance whose strength varies depending on the fluid’s degree of viscosity.
Molasses, for example, has a higher viscosity than water because it is more resistant to flow.
There are many methods one can use to measure the viscosity of a fluid, the easiest and most straightforward being to drop a sphere of a certain diameter into a transparent container containing the fluid whose viscosity one is trying to determine.

ATTENTION: the reciprocal of viscosity is called fluidity, a measure of smoothness.

Viscosity is an important factor in determining the forces that must overcome when liquids are used for lubrication and transported in pipes. It will therefore be important for us to understand what type of fluid the Besa® valve will be working with, as the friction between the walls of a pipe and the fluid flowing through it affects the valve’s discharge performance.

It controls fluid flow in processes such as spraying, injection moulding and surface coating.


Dynamic viscosity

Let us consider two planes, separated by a fluid (temperature controlled) and parallel to each other, one stationary and the other subjected to a force that pushes/pulls it parallel to the other plane.
Depending on the fluid we use to separate the two planes, and always applying the same force to move one of the two planes, we will find that the velocity of the plane varies depending on the fluid we have chosen.

Generalising we have:

A (m^2)= area of the parallel planes
y (m)= distance between the two planes
F (N)= force applied to the moving plane
u (m/s^2)= velocity of the moving plane
τ = tangential force

The tangential force will be inversely proportional to the distance between the two planes and directly proportional to the speed.
Introducing the velocity term complicates things, because only theoretically is the variation in velocity linear.

Units of measure

In the international system viscosity is measured in pascals (Pa s) which is equivalent to a poiseuille (PI), sometimes for lubricating oils the CGS system is also used, i.e. centipoise (cP)

1 Pa s = 1 PI
1 cP = 1 mPI

Kinematic Viscosity: 1 cSt (centiStokes) = 10-6 m2/s

LiquidTemperature (ºF)Temperature (ºC)Kinematic Viscosity
CentiStokes (cSt)
Kinematic Viscosity
Seconds Saybolt Universal (SSU)
Acetaldehyde CH3CHO 6116.10.30536
Acetaldehyde CH3CHO 68200.295
Acetic acid - vinegar - 10% CH3COOH 59151.3531.7
Acetic acid - 50% 59152.2733
Acetic acid - 80% 59152.8535
Acetic acid - concentrated glacial 59151.3431.7
Acetic acid anhydride (CH3COO)2O 59150.88
Acetone CH3COCH3 68200.41
Alcohol - allyl 68201.6031.8
Alcohol - allyl 104400.90 cp
Alcohol - butyl-n 68203.6438
Alcohol - ethyl (grain) C2H5OH 68201.5231.7
Alcohol - ethyl (grain) C2H5OH 10037.81.231.5
Alcohol - methyl (wood) CH3OH 59150.74
Alcohol - methyl (wood) CH3OH 3201.04
Alcohol - propyl 68202.835
Alcohol - propyl 122501.431.7
Aluminum sulfate - 36% solution 68201.4131.7
Ammonia 0-17.80.30
Aniline 68204.3740
Aniline 50106.446.4
Asphalt RC-0, MC-0, SC-0 7725159-324737-1.5M
Asphalt RC-0, MC-0, SC-0 10037.860-108280-500
Automatic crankcase oil0-17.81295-max6M-max
Automatic crankcase oil0-17.81295-25906M-12M
Automatic crankcase oil0-17.82590-1035012M-48M
Automatic crankcase oil21098.95.7-9.645-58
SAE 20
Automatic crankcase oil21098.99.6-12.958-70
SAE 30
Automatic crankcase oil21098.912.9-16.870-85
SAE 40
Automatic crankcase oil21098.916.8-22.785-110
SAE 50
Automotive gear oil21098.94.2 min40 min
Automotive gear oil21098.97.0 min49 min
Automotive gear oil21098.911.0 min63 min
Automotive gear oil21098.914-2574-120
Automotive gear oil21098.925-43120-200
SAE 140
Automotive gear oil21098.943 - min200 min
Benzene (Benzol) C6H63201.031
Benzene (Benzol) C6H668200.74
Bone oil13054.447.5220
Bone oil21210011.665
Butyric acid n68201.6131.6
Butyric acid n3202.3 cp
Calcium chloride 5%6518.31156
Calcium chloride 25%6015.64.039
Carbolic acid (phenol)6518.311.8365
Carbolic acid (phenol)194901.26 cp
Carbon tetrachloride CCl468200.612
Carbon tetrachloride CCl410037.80.53
Carbon disulfide CS23200.33
Carbon disulfide CS268200.298
Castor oil10037.8259-3251200-1500
Castor oil13054.498-130450-600
China wood oil6920.6308.51425
China wood oil10037.8125.5580
Coconut oil10037.829.8-31.6140-148
Coconut oil13054.414.7-15.776-80
Cod oil (fish oil)10037.832.1150
Cod oil (fish oil)13054.419.495
Corn oil13054.428.7135
Corn oil2121008.654
Corn starch solution7021.132.1150
22 Baume 10037.827.5130
Corn starch solution7021.1129.8600
24 Baume 10037.895.2440
Corn starch solution7021.13031400
25 Baume 10037.8173.2800
Cotton seed oil10037.837.9176
Cotton seed oil13054.420.6100
Crude oil 48º API6015.63.839
Crude oil 48º API13054.41.631.8
Crude oil 40º API6015.69.755.7
Crude oil 40º API13054.43.538
Crude oil 35.6º API6015.617.888.4
Crude oil 35.6º API13054.44.942.3
Crude oil 32.6º API6015.623.2110
Crude oil 32.6º API13054.47.146.8
Diethyl glycol7021.132149.7
Diethyl ether68200.32
Diesel fuel 2010037.84471432.6-45.5
Diesel fuel 2013054.41.-3.97-39
Diesel fuel 3010037.86-11.7545.5-65
Diesel fuel 3013054.43.97-6.7839-48
Diesel fuel 4010037.829.8 max140 max
Diesel fuel 4013054.413.1 max70 max
Diesel fuel 601225086.6 max400 max
Diesel fuel 6016071.135.2 max165 max
Ethyl acetate CH3COOC2H359150.4
Ethyl acetate CH3COOC2H368200.49
Ethyl bromide C2H5Br68200.27
Ethylene bromide68200.787
Ethylene chloride68200.668
Ethylene glycol7021.117.888.4
Formic acid 10%68201.0431
Formic acid 50%68201.231.5
Formic acid 80%68201.431.7
Formic acid concentrated68201.4831.7
Formic acid concentrated77251.57cp
Freon -117021.10.21
Freon -127021.10.27
Freon -217021.11.45
Fuel oil 17021.12.39-4.2834-40
Fuel oil 110037.8-2.6932-35
Fuel oil 27021.13.0-7.436-50
Fuel oil 210037.82.11-4.2833-40
Fuel oil 37021.12.69-5.8435-45
Fuel oil 310037.82.06-3.9732.8-39
Fuel oil 5A7021.17.4-26.450-125
Fuel oil 5A10037.84.91-13.742-72
Fuel oil 5B7021.126.4-125-
Fuel oil 5B10037.813.6-67.172-310
Fuel oil 61225097.4-660450-3M
Fuel oil 616071.137.5-172175-780
Gas oils7021.113.973
Gas oils10037.87.450
Gasoline a6015.60.88
Gasoline a10037.80.71
Gasoline b6015.60.64
Gasoline b10037.8
Gasoline c6015.60.46
Gasoline c10037.80.40
Glycerin 100%68.620.36482950
Glycerin 100%10037.8176813
Glycerin 50% water68205.2943
Glycerin 50% water140601.85 cp
Ink, printers10037.8550-22002500-10M
Ink, printers13054.4238-6601100-3M
Insulating oil7021.124.1 max115 max
Insulating oil10037.811.75 max65 max
Jet Fuel-30.-34.47.952
Lard oil10037.841-47.5190-220
Lard oil13054.423.4-27.1112-128
Linseed oil10037.830.5143
Linseed oil13054.418.9493
Methyl acetate68200.44
Methyl acetate104400.32 cp
Methyl iodide68200.213
Methyl iodide104400.42 cp
Menhaden oil10037.829.8140
Menhaden oil13054.418.290
Molasses A, first10037.8281-50701300-23500
Molasses A, first13054.4151-1760700-8160
B, second10037.81410-13.2M6535-61180
B, second13054.4660-3.3M3058-15294
C, blackstrap10037.82630-55M12190-255M
C, blackstrap13054.41320-16.5M6120-76.5M
Naphthalene2121000.78 cp
Neatstool oil10037.849.7230
Neatstool oil13054.427.5130
Olive oil10037.843.2200
Olive oil13054.424.1
Palms oil10037.847.8
Palms oil13054.426.4
Peanut oil10037.842200
Peanut oil13054.423.4
Petroleum ether6015.631(est)1.1
Propionic acid3201.52 cp31.5
Propionic acid68201.13
Propylene glycol7021.152241
Quenching oil100-12020.5-25
Rapeseed oil10037.854.1250
Rapeseed oil13054.431145
Rosin oil10037.8324.71500
Rosin oil13054.4129.9600
Rosin (wood)10037.8216-11M1M-50M
Rosin (wood)20093.3108-4400500-20M
Sesame seed oil10037.839.6184
Sesame seed oil13054.423110
Sodium chloride 5%6820109731.1
Sodium chloride 25%6015.62.434
Sodium hydroxide (caustic soda) 20%6518.34.039.4
Sodium hydroxide (caustic soda) 30%6518.310.058.1
Sodium hydroxide (caustic soda) 40%6518.3
Soya bean oil10037.835.4165
Soya bean oil1305.419.6496
Sperm oil10037.521-23110
Sperm oil13054.415.278
Sulphuric acid 100%682014.5676
Sulphuric acid 100%140607.2 cp
Sulphuric acid 95%682014.575
Sulphuric acid 60%68204.441
Sulphuric acid 20%3M-8M
Sulphuric acid 20%650-1400
Tar, coke oven7021.1600-176015M-300M
Tar, coke oven10037.8141-3082M-20M
Tar, gas house7021.13300-66M2500
Tar, gas house10037.8440-4400500
Tar, pine10037.8559200-300
Tar, pine13255.6108.255-60
Toluene140600.38 cp
Triethylene glycol7021.140400-440
Triethylene glycol185-205
Varnish, spar6820313
Varnish, spar10037.8143
Water, distilled68201003831
Water, fresh6015.61.1331.5
Water, fresh13054.40.55
Water, sea1.1531.5
Whale oil10037.835-39.6163-184
Whale oil13054.419.9-23.497-112
Xylene-o104400.623 cp