The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of “thickness”: for example, the syrup has a higher viscosity than water.
When we observe the water flow in the river channel, we can see that the water velocity in the middle of the river is the fastest, and the water velocity closer to the beach is slower. Similarly, when a fluid flows in a pipe, the velocity in the center of the pipe is the fastest, and the velocity closer to the pipe wall is slower.
The velocity at the pipe wall can be considered zero. This is due to the internal friction generated in the fluid when the fluid flows. That is to say, due to the existence of viscosity, the two parts (such as two layers) in the liquid move relative to each other. The fast liquid layer drags the slow liquid layer.
At the same time, the slow liquid layer uses the same size and direction. The opposite force prevents the fast liquid layer from moving. This pair of forces is also called the internal friction shear stress of the liquid.
According to experiments, the internal frictional shear stress is directly proportional to the rate of change of shear stress. The proportional coefficient is the viscosity coefficient that characterizes the fluid characteristics.
Liquid viscosity data are important in many engineering applications in the petroleum refining and petrochemical industries. The liquid viscosity is highly affected by heat.
The viscosity decreases with an increase in temperature. Most liquids suffer the exponential relationship between temperature and viscosity rather than linear form.
The more viscous the fluid, the more sensitive it is to the temperature change. Because higher temperature makes both slightly less viscous water and much lesser viscous oil, the improved viscosity contrast favors relatively the oil flow rather than water flow.
This contribution by heat enables to deploy the exploitation of the thermal recovery methods in mainly heavy oil reservoirs.
The existence of internal friction in the fluid flow will consume the mechanical energy of the flowing liquid and convert it into heat and heats up the fluid. If there is no temperature control device such as a water flow calibration device in a circulating fluid measuring device system, in order to improve the measurement accuracy, the system should be operated for a period of time, and the test should be performed after the temperature stabilizes.
Tables showing a viscosity of water at temperatures ranging from 0 to 360 °C (32 to 675 °F) – Imperial and SI Units.
| [°C] | [MPa] | [Pa s], [N s/m2] | [cP], [mPa s] | [lbf s/ft2*10-5] | [m2/s*10-6], [cSt]) |
| 0.01 | 0.000612 | 0.0017914 | 1.7914 | 3.7414 | 1.7918 |
| 10 | 0.0012 | 0.001306 | 1.306 | 2.7276 | 1.3065 |
| 20 | 0.0023 | 0.0010016 | 1.0016 | 2.0919 | 1.0035 |
| 25 | 0.0032 | 0.00089 | 0.89004 | 1.8589 | 0.8927 |
| 30 | 0.0042 | 0.0007972 | 0.79722 | 1.665 | 0.8007 |
| 40 | 0.0074 | 0.0006527 | 0.65272 | 1.3632 | 0.6579 |
| 50 | 0.0124 | 0.0005465 | 0.5465 | 1.1414 | 0.5531 |
| 60 | 0.0199 | 0.000466 | 0.46602 | 0.9733 | 0.474 |
| 70 | 0.0312 | 0.0004035 | 0.40353 | 0.8428 | 0.4127 |
| 80 | 0.0474 | 0.000354 | 0.35404 | 0.7394 | 0.3643 |
| 90 | 0.0702 | 0.0003142 | 0.31417 | 0.6562 | 0.3255 |
| 100 | 0.101 | 0.0002816 | 0.28158 | 0.5881 | 0.2938 |
| 110 | 0.143 | 0.0002546 | 0.25461 | 0.5318 | 0.2677 |
| 120 | 0.199 | 0.000232 | 0.23203 | 0.4846 | 0.246 |
| 140 | 0.362 | 0.0001966 | 0.19664 | 0.4107 | 0.2123 |
| 160 | 0.618 | 0.0001704 | 0.17043 | 0.3559 | 0.1878 |
| 180 | 1 | 0.0001504 | 0.15038 | 0.3141 | 0.1695 |
| 200 | 1.55 | 0.0001346 | 0.13458 | 0.2811 | 0.1556 |
| 220 | 2.32 | 0.0001218 | 0.12177 | 0.2543 | 0.1449 |
| 240 | 3.35 | 0.0001111 | 0.11106 | 0.232 | 0.1365 |
| 260 | 4.69 | 0.0001018 | 0.10181 | 0.2126 | 0.1299 |
| 280 | 6.42 | 0.0000936 | 0.09355 | 0.1954 | 0.1247 |
| 300 | 8.59 | 0.0000859 | 0.08586 | 0.1793 | 0.1206 |
| 320 | 11.3 | 0.0000783 | 0.07831 | 0.1636 | 0.1174 |
| 340 | 14.6 | 0.0000703 | 0.07033 | 0.1469 | 0.1152 |
| 360 | 18.7 | 0.0000603 | 0.06031 | 0.126 | 0.1143 |
| Temperature | Pressure | Dynamic viscosity | Kinematic viscosity | ||
| [°F] | [psi] | [lbf s/ft2 *10-5] | [lbm/(ft h)] | [cP], [mPa s] | [ft2/s*10-5] |
| 32.02 | 0.9506 | 3.7414 | 4.3336 | 1.7914 | 1.9287 |
| 34 | 0.0962 | 3.6047 | 4.1752 | 1.7259 | 1.8579 |
| 39.2 | 0.118 | 3.2801 | 3.7992 | 1.5705 | 1.6906 |
| 40 | 0.1217 | 3.234 | 3.7458 | 1.5484 | 1.6668 |
| 50 | 0.1781 | 2.7276 | 3.1593 | 1.306 | 1.4063 |
| 60 | 0.2563 | 2.3405 | 2.7109 | 1.1206 | 1.2075 |
| 70 | 0.3634 | 2.0337 | 2.3556 | 0.9737 | 1.0503 |
| 80 | 0.5076 | 1.7888 | 2.0719 | 0.8565 | 0.925 |
| 90 | 0.6992 | 1.5896 | 1.8411 | 0.7611 | 0.8234 |
| 100 | 0.9506 | 1.4243 | 1.6497 | 0.682 | 0.7392 |
| 110 | 1.277 | 1.2847 | 1.488 | 0.6151 | 0.6682 |
| 120 | 1.695 | 1.1652 | 1.3496 | 0.5579 | 0.6075 |
| 130 | 2.226 | 1.062 | 1.23 | 0.5085 | 0.5551 |
| 140 | 2.893 | 0.9733 | 1.1273 | 0.466 | 0.5102 |
| 150 | 3.723 | 0.895 | 1.0366 | 0.4285 | 0.4706 |
| 160 | 4.747 | 0.8279 | 0.9589 | 0.3964 | 0.4367 |
| 170 | 6 | 0.7698 | 0.8916 | 0.3686 | 0.4074 |
| 180 | 7.52 | 0.7192 | 0.833 | 0.3444 | 0.382 |
| 190 | 9.349 | 0.6745 | 0.7813 | 0.323 | 0.3596 |
| 200 | 11.537 | 0.63 | 0.7297 | 0.3016 | 0.3371 |
| 212 | 14.71 | 0.5881 | 0.6812 | 0.2816 | 0.3163 |
| 220 | 17.203 | 0.5619 | 0.6508 | 0.269 | 0.3032 |
| 240 | 25.001 | 0.505 | 0.585 | 0.2418 | 0.275 |
| 260 | 35.263 | 0.4575 | 0.5299 | 0.2191 | 0.2515 |
| 280 | 49.286 | 0.4176 | 0.4837 | 0.2 | 0.232 |
| 300 | 67.264 | 0.384 | 0.4448 | 0.1839 | 0.2157 |
| 350 | 134.73 | 0.3202 | 0.3708 | 0.1533 | 0.1853 |
| 400 | 247.01 | 0.275 | 0.3185 | 0.1317 | 0.1648 |
| 450 | 422.32 | 0.2404 | 0.2785 | 0.1151 | 0.1504 |
| 500 | 680.56 | 0.2126 | 0.2463 | 0.1018 | 0.1398 |
| 550 | 1045 | 0.1888 | 0.2187 | 0.0904 | 0.1322 |
| 600 | 1542.1 | 0.1673 | 0.1937 | 0.0801 | 0.127 |
| 625 | 1851.2 | 0.1562 | 0.1809 | 0.0748 | 0.1252 |
| 650 | 2207.8 | 0.1438 | 0.1666 | 0.0689 | 0.1239 |
| 675 | 2618.7 | 0.1292 | 0.1496 | 0.0619 | 0.123 |