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Definition
Viscosity describes the internal resistance of a fluid to flow or deformation. It is one of the most important fluid properties to consider when designing a mixer. There are two common measures of viscosity: dynamic viscosity (µ) and kinematic viscosity (ν). They are related as follows:
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ν – kinematic viscosity (cSt) µ – dynamic viscosity (cP) ρ – density (g/cm3) |
Dynamic viscosity is the most relevant for mixing, as it describes the resistance of a fluid to flow under shear stress, whereas kinematic viscosity describes its resistance to flow under gravity.
Newtonian Fluids
In a Newtonian fluid, dynamic viscosity is the ratio of shear stress to velocity gradient. It remains constant whatever the shear stress and over time, as shown below:
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τ – shear stress µ – dynamic viscosity du/dy – velocity gradient |
Most fluids can be treated as Newtonian, and these are the fluids found in most mixing applications.
Falling-Ball Viscometer
A falling-ball viscometer consists of a small ball and a fixed glass tube filled with the fluid to be tested. The ball is dropped through the fluid and the time it takes to travel between two marks is measured. The dynamic viscosity is then calculated with Stokes’ law, using the densities of the fluid and of the ball.
Viscosity Cups
A viscosity cup is a cup with a precisely sized orifice in its base. The cup is filled with the liquid and the time it takes to drain through the orifice is recorded. The kinematic viscosity is then calculated with the conversion formulas or tables supplied by the manufacturer.
Viscosity cups are widely used in the paint and coatings industries.
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Rotational Viscometer
The rotational viscometer is a more sophisticated instrument. It works on the Searle principle: the torque needed to rotate a spindle in the fluid at a given speed is proportional to the viscosity of the fluid.
The spindle speed can usually be adjusted, which varies the shear applied to the fluid. Rotational viscometers can therefore measure the viscosity profile of non-Newtonian fluids, whose viscosity changes with the shear rate.
Viscosity of Common Liquids
Typical absolute viscosity of common liquids in centipoise (cP), by product category. Values are for guidance only and may vary with temperature, concentration and supplier.
| Liquid | Specific gravity at 16 °C | Absolute viscosity (cP) | Temperature (°C) | Viscosity type |
|---|---|---|---|---|
| ● Dairy Products | ||||
| Butter | 30,000 | Room temp. | ||
| Butter cream, sour | 550 | Room temp. | ||
| Butter, deodorised | 45 | 50 | N | |
| Butterfat | 20 | 65 | N | |
| Cheese, soft | 30,000 | Room temp. | ||
| Cocoa butter | 0.92 | 50 | 60 | N |
| Condensed milk | 40–80 | 40–50 | N | |
| Condensed milk, 75% solids | 1.3 | 2,160 | 20 | T |
| Cottage cheese | 30,000 | 18 | T | |
| Cream cheese | 100,000 | Room temp. | ||
| Cream, 30% fat | 1.0 | 14 | 16 | N |
| Cream, 45% fat | 0.99 | 48 | 16 | N |
| Cream, 50% fat | 0.98 | 112 | 16 | N |
| Cream, 50% fat | 55 | 32 | N | |
| Cream, clotted | 20,000 | Room temp. | ||
| Cream, double | 120 | Room temp. | ||
| Cream, single | 50 | Room temp. | ||
| Cream, sour | 15,200 | Room temp. | ||
| Milk | 1.02–1.05 | 2 | 18 | N |
| Milk whey, 48% sugar | 800–1,500 | 40 | T | |
| Milk, condensed | 6,000 | Room temp. | ||
| Milk, evaporated | 6,100 | Room temp. | ||
| Processed cheese | 30,000 | 18 | T | |
| Whey | 800–1,500 | Room temp. | ||
| Whole egg | 150 | 4.5 | T | |
| Yoghurt | 3,000–8,000 | Room temp. | ||
| ● Fish & Animal Oils | ||||
| Bone oil | 0.92 | 48 | 54 | N |
| Cod oil | 0.93 | 32 | 38 | N |
| Lard | 0.96 | 62 | 38 | N |
| Lard oil | 0.91–0.93 | 40–47 | 38 | N |
| Sperm oil | 0.88 | 24 | 38 | N |
| Whale oil | 0.93 | 25–39 | 38 | N |
| ● Food Products | ||||
| Apple sauce | 1.1 | 500 | 80 | T |
| Baby food | 1,400 | 93 | T | |
| Batter | 29,500 | 30 | T | |
| Beer | 18 | Room temp. | ||
| Beet sauce | 1,950 | 76 | T | |
| Biscuit cream premix | 29,200 | 18 | T | |
| Brewer’s yeast | 368 | 18 | T | |
| Broth mix | 430 | 18 | T | |
| Carob bean sauce | 1,500 | 30 | T | |
| Chocolate | 280 | 49 | T | |
| Chocolate syrup | 2,250 | Room temp. | ||
| Citrus fruit pulp | 1.27 | 600 | 20 | T |
| Coffee liquor 30–40 | 10–100 | 20 | T | |
| Corn syrup | 15,000 | Room temp. | ||
| Custard | 1.6 | 1,500 | 85–90 | T |
| Edible oil | 0.9 | 65 | 20 | N |
| Fruit juice | 1.04 | 55–75 | 18 | N |
| Gelatine | 1,200 | Room temp. | ||
| Gelatine, 37% solids | 1,190 | 43 | T | |
| Glucose | 1.3 | 4,300–8,600 | 25–30 | T |
| Gravy slurry | 1.0 | 110 | 80 | T |
| Honey | 1,800–3,000 | Room temp. | ||
| Icing | 10,000 | Room temp. | ||
| Jam | 8,500 | Room temp. | ||
| Jam garnish | 8,440 | 16 | T | |
| Malt extract | 1.4 | 3,000 | 60 | T |
| Malt extract 80 | 9,500 | 18 | T | |
| Maple syrup | 150–300 | Room temp. | ||
| Mayonnaise | 5,000–20,000 | Room temp. | ||
| Mincemeat | 100,000 | 30 | T | |
| Molasses | 5,000–10,000 | Room temp. | ||
| Mousse mix | 1,200 | 5 | T | |
| Orange juice concentrate | 30 °Brix | 630 | 20 | N |
| Pancake batter | 2,200 | Room temp. | ||
| Peanut butter | 150,000–250,000 | Room temp. | ||
| Pectin | 300 | 38 | N | |
| Rice pudding | 10,000 | 100 | T | |
| Salad cream | 1,300–2,600 | 18 | T | |
| Sorbitol | 1.29 | 200 | 20 | N |
| Soya bean slurry | 5,000–10,000 | 50–90 | T | |
| Spaghetti sauce | 1,000 | Room temp. | ||
| Starch solution 25% | 300 | Room temp. | ||
| Sugar syrup, sucrose | 1,210 | Room temp. | ||
| Tomato juice | 180 | Room temp. | ||
| Tomato ketchup | 1,000 | 30 | T | |
| Tomato ketchup | 1,000 | Room temp. | ||
| Tomato paste 30 | 195 | 18 | T | |
| Tomato purée | 50,000 | Room temp. | ||
| Tomato sauce | 2,600 | Room temp. | ||
| Vinegar | 12–15 | 20 | N | |
| Yeast slurry | 20 | 18 | T | |
| ● Fuel & Lubricating Oils | ||||
| Fuel oil no. 4 | 12 | Room temp. | ||
| Hydraulic oil | 30–120 | Room temp. | ||
| Lubricating oil | 60–200 | Room temp. | ||
| Machine oil, heavy | 600 | Room temp. | ||
| Machine oil, light | 150 | Room temp. | ||
| Motor oil SAE 10 | 50 | Room temp. | ||
| Motor oil SAE 20 | 125 | Room temp. | ||
| Motor oil SAE 30 | 200 | Room temp. | ||
| Motor oil SAE 40 | 320 | Room temp. | ||
| Motor oil SAE 50 | 540 | Room temp. | ||
| Motor oil SAE 60 | 1,000 | Room temp. | ||
| Motor oil SAE 70 | 1,600 | Room temp. | ||
| ● Glycol Products | ||||
| Diethylene glycol | 1.12 | 32 | 21 | N |
| Ethylene glycol | 1.12 | 18 | 21 | N |
| Ethylene glycol | 16 | Room temp. | ||
| Glycol | 20 | Room temp. | ||
| Propylene glycol | 1.04 | 52 | 21 | N |
| Triethylene glycol | 1.12 | 40 | 21 | N |
| ● Industrial Products | ||||
| Acetate glue | 1,200–1,400 | 20 | T | |
| Alkyd resins | 500–3,000 | Room temp. | ||
| Antifreeze | 15 | Room temp. | ||
| Benzine | 5 | Room temp. | ||
| Caulking compound | 5,000,000–10,000,000 | Room temp. | ||
| Caustic soda 50% | 45 | Room temp. | ||
| Cleaning emulsions | 1,500 | Room temp. | ||
| Cresol crystals | 10 | 18 | T | |
| Diesel | 14 | Room temp. | ||
| Dipropylene glycol | 107 | Room temp. | ||
| Epoxy resin | 5,000–10,000 | Room temp. | ||
| Glue, gun grade | 5,000–50,000 | Room temp. | ||
| Glue, pourable | 3,000–5,000 | Room temp. | ||
| Glycerine 100% | 1.26 at 20 °C | 648 | 20 | N |
| Isopropyl alcohol | 2 | Room temp. | ||
| Isopropyl alcohol | 1.11 | 1.9 | 85 | N |
| Kerosene | 10 | Room temp. | ||
| Lacquer, 25% solids | 3,000 | 18 | T | |
| Methyl ethyl ketone | 4 | Room temp. | ||
| NaOH 20% | 1.22 | 1 | 18 | N |
| NaOH 30% | 1.33 | 1 | 18 | N |
| NaOH 40% | 1.43 | 20 | 18 | N |
| Paraffin | 10 | Room temp. | ||
| Petrol | 8 | Room temp. | ||
| Plastisol | 2.5 | 28,000 | 18 | T |
| Polyester | 1.1 at 30 °C | 3,000 | 30 | T |
| Polyester resin | 3,000 | Room temp. | ||
| Polyglycerine caprinate | 6,000–7,000 | Room temp. | ||
| Polyisobutylene | 1.09 at 85 °C | 12,500 | 85 | T |
| Polymer solution | 20,000 | Room temp. | T | |
| Polyol, non-pigmented | 500–5,000 | Room temp. | ||
| Polypropylene | 240,000 | 50 | T | |
| Potassium hydroxide | 67 | Room temp. | ||
| Printing ink | 550–2,200 | 38 | T | |
| Printing ink, liquid | 550–2,200 | Room temp. | ||
| Putty | 100,000,000 | Room temp. | ||
| PVA resin | 65,000 | Room temp. | ||
| Resin solution | 880 | 24 | T | |
| Resin solution | 7,100 | Room temp. | ||
| Resin, pourable | 880–975 | Room temp. | ||
| Sulphonic acid | 1.04 | 125 | 30 | T |
| Titanium dioxide | 5,000 | Room temp. | ||
| Toluene | 6 | Room temp. | ||
| Triacetate dope | 48,000–60,000 | 40 | T | |
| ● Paints & Varnishes | ||||
| Lacquer, 25% pigments | 3,000 | Room temp. | ||
| Lacquer, water-based | 900 | Room temp. | ||
| Latex neoprene | 5,000 | Room temp. | T | |
| Latex paint | 750 | Room temp. | T | |
| Paint, water-based | 2,400 | Room temp. | ||
| Varnish | 320 | Room temp. | ||
| ● Pharmaceuticals | ||||
| Blood | 10 | Room temp. | ||
| Detergents | 1,470 | 70 | T | |
| Glycerine | 1,000–2,000 | Room temp. | ||
| Hand cream | 8,000 | Room temp. | ||
| Hand lotion | 5,000 | Room temp. | ||
| Latex emulsion | 1.0 | 200 | 24 | T |
| Liquid soap | 85 | Room temp. | ||
| Paraffin emulsion | 1.2 | 3,000 | 18 | T |
| Petroleum jelly | 64,000 | Room temp. | ||
| Shampoo | 3,000–5,000 | Room temp. | ||
| Soap solution | 1.03 at 60 °C | 82 | 60 | T |
| Soap, Arylan | 1.0 at 40 °C | 630 | 60 | T |
| Toothpaste | 70,000–100,000 | 18 | T | |
| Wax | 0.9 | 500 | 93 | T |
| ● Vegetable Oils | ||||
| Castor oil | 0.96 | 580 | 27 | N |
| Chinawood oil (tung oil) | 0.94 | 300 | 21 | N |
| Coconut oil | 0.93 | 55 | 24 | N |
| Corn oil | 0.92 | 28 | 57 | N |
| Cottonseed oil | 0.88 | 62 | 24 | N |
| Linseed oil | 30–70 | Room temp. | ||
| Linseed oil, raw | 0.93–0.94 | 29 | 38 | N |
| Oleic acid | 40 | Room temp. | ||
| Olive oil | 0.91 | 40 | 38 | N |
| Palm oil | 0.92 | 43 | 38 | N |
| Peanut oil | 0.92 | 38 | 38 | N |
| Peanut oil | 100 | Room temp. | ||
| Sesame oil | 94 | Room temp. | ||
| Soya bean oil | 0.93 | 60 | 24 | N |
| Turpentine | 0.86 | 2 | 16 | N |
| Vegetable oil | 40 | Room temp. | ||
N Newtonian T Thixotropic (non-Newtonian) 1 cP = 1 mPa·s Source: Euromixers
Viscosity Cup Conversion Table
Efflux time in seconds for each viscosity cup, against kinematic viscosity in centistokes (cSt). Read across from your cup and flow time to find the viscosity. Scroll sideways to see all values.
| Cup type \ cSt | 1 | 2 | 3 | 4 | 7.5 | 10 | 15 | 20 | 25 | 30 | 40 | 50 | 60 | 70 | 80 | 90 | 100 | 125 | 150 | 175 | 200 | 225 | 250 | 275 | 300 | 325 | 350 | 375 | 400 | 500 | 600 | 700 | 800 | 900 | 1000 | 1250 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Shell cups | ||||||||||||||||||||||||||||||||||||
| ‘Ultra Low’ cup | 53 | 68 | 84 | |||||||||||||||||||||||||||||||||
| Shell cup #1 | 17 | 21.5 | 26 | 35 | 46 | 57 | ||||||||||||||||||||||||||||||
| Shell cup #2 | 18.3 | 22 | 30.4 | 39 | 47 | 56 | ||||||||||||||||||||||||||||||
| Shell cup #2.5 | 19 | 25 | 30 | 35.6 | 46.6 | 57 | ||||||||||||||||||||||||||||||
| Shell cup #3 | 18.6 | 22 | 28.6 | 35 | 42 | 48 | 55 | |||||||||||||||||||||||||||||
| Shell cup #3.5 | 17.5 | 20 | 24.6 | 29.2 | 34 | 38.4 | 43 | 47.8 | 59.4 | |||||||||||||||||||||||||||
| Shell cup #4 | 18 | 21 | 24 | 27 | 30 | 37 | 45 | 52 | 60 | |||||||||||||||||||||||||||
| Shell cup #5 | 16 | 20 | 24 | 28 | 32 | 36 | 40 | 44 | 48 | 52 | 56 | 60 | 64 | |||||||||||||||||||||||
| Shell cup #6 | 17.5 | 19 | 20.5 | 22.5 | 24 | 25 | 31.5 | 37.5 | 44 | 50 | 56.5 | 63 | 78 | |||||||||||||||||||||||
| Zahn cups | ||||||||||||||||||||||||||||||||||||
| Zahn cup #1 | 30.5 | 32 | 35 | 38 | 42 | 45 | 52 | 60 | 68 | |||||||||||||||||||||||||||
| Zahn cup #2 | 18 | 19 | 20 | 22.5 | 25 | 28 | 30 | 34 | 38 | 43 | 53 | 63 | 72 | |||||||||||||||||||||||
| Zahn cup #3 | 17 | 19.5 | 22 | 24.5 | 27 | 30 | 32 | 35.5 | 38 | 41 | 43 | 45 | 48.5 | 58 | 70 | |||||||||||||||||||||
| Zahn cup #4 | 17 | 18 | 19.5 | 21 | 22.5 | 24 | 26 | 28 | 30 | 32 | 38 | 45 | 51 | 54 | 65 | 70 | ||||||||||||||||||||
| Zahn cup #5 | 17 | 18.5 | 20 | 21 | 22.5 | 27 | 31 | 35 | 40 | 45 | 49 | 60 | ||||||||||||||||||||||||
| Ford / ISO / DIN / AFNOR cups | ||||||||||||||||||||||||||||||||||||
| Ford cup #3 | 32 | 37 | 40 | 43 | 53 | 63 | 73 | 83 | 93 | 103 | 113 | 120 | 130 | |||||||||||||||||||||||
| Ford cup #4 | 20 | 22 | 25 | 28 | 35 | 40 | 48 | 55 | 62 | 70 | 76 | 82 | 90 | 98 | 103 | |||||||||||||||||||||
| ISO cup #4 | 26 | 33 | 39 | 46 | 53 | 60 | ||||||||||||||||||||||||||||||
| DIN cup #4 | 20 | 22 | 24 | 26 | 28 | 30 | 35 | 40 | 46 | 50 | 56 | 61 | 71 | |||||||||||||||||||||||
| AFNOR cup #4 | 20 | 22 | 24 | 26 | 28 | 30 | 35 | 40 | 46 | 50 | 56 | 61 | 71 | |||||||||||||||||||||||
| Norcross cups | ||||||||||||||||||||||||||||||||||||
| Norcross cup #1 | 31 | 36 | 40 | 53 | 70 | 87 | ||||||||||||||||||||||||||||||
| Norcross cup #2 | 19 | 23 | 28 | 34 | 45 | 55 | 67 | 76 | ||||||||||||||||||||||||||||
| Norcross cup #3 | 17 | 20 | 25 | 30 | 35 | 40 | 45 | 50 | 55 | 68 | 79 | |||||||||||||||||||||||||
| Norcross cup #4 | 18 | 22 | 27 | 32 | 36 | 40 | 44 | 48 | 53 | 57 | 61 | 65 | 68 | 85 | ||||||||||||||||||||||
| Norcross cup #5 | 20 | 22 | 26 | 31 | 36 | 41 | 45 | 50 | 62 | |||||||||||||||||||||||||||
Values in seconds. Source: Euromixers.
Effect on Mixing
Viscosity is one of the most important factors to consider when designing a mixer for a given application.
The higher the viscosity, the more energy is needed for mixing, which means larger impellers and more powerful motors. For highly viscous products, a close-clearance impeller such as a gate or helical ribbon impeller may be needed to mix the whole tank volume properly.
Laminar and Turbulent Mixing
Low-viscosity mixing almost always takes place in turbulent flow. Mixing is then governed by inertial forces rather than molecular diffusion, and is achieved by the many eddies created by the impeller.
Impellers such as hydrofoils and pitched-blade turbines are used for low-viscosity mixing because they give high pumping capacity and create strong turbulence in the vessel.
High-viscosity mixing, by contrast, takes place mainly in laminar flow: viscous forces dominate and suppress turbulence, and molecular diffusion is the main mixing mechanism. To promote diffusion, laminar mixing aims to “cut and fold” the fluid, increasing the interfacial area between the different fluids.
Anchor and helical ribbon impellers are used here, because their large contact area with the fluid enhances this “cut and fold” action throughout the tank.
The chart below shows the suitable viscosity range for each type of standard impeller.
Table of Impeller Types and Their Appropriate Operating Viscosities
Mixing Non-Newtonian Fluids
Mixing non-Newtonian fluids properly can be difficult. If you have a non-Newtonian application and need help choosing a mixer, contact us: our application engineers will be happy to help.
Static Mixers
Viscosity affects in-line static mixers in the same way as agitated tanks. At low viscosity, mixing is driven by turbulent eddies; at high viscosity, it always relies on molecular diffusion and on the same “cut and fold” principle as the agitated tanks described above.
Different mixing elements are used for low- and high-viscosity fluids, following the same principles as tank impellers. The higher the viscosity, the larger and more complex the elements inside the pipe must be to mix evenly across the whole pipe diameter. This increases the pressure drop and therefore the pump power required: as with agitated tanks, high-viscosity fluids need more power to mix.
