Use a convenient converter for converting kinematic viscosity to dynamic online. Since the ratio of kinematic and dynamic viscosity depends on the density, it must also be indicated when calculating in the calculators below.
Density and viscosity should be reported at the same temperature.
If you set the density at a temperature different from the viscosity temperature, there will be some error, the degree of which will depend on the influence of temperature on the change in density for a given substance.
Kinematic to Dynamic Viscosity Conversion Calculator
The converter allows you to convert the viscosity with the dimension in centistokes [cSt] to centipoise [cP]. Please note that the numerical values of quantities with dimensions [mm2/s] and [cSt] for kinematic viscosity and [cP] and [mPa*s] for dynamic, they are equal to each other and do not require additional translation. For other dimensions, use the tables below.
Viscosity is the most important physical constant that characterizes the operational properties of boiler and diesel fuels, petroleum oils, and a number of other petroleum products. The value of viscosity is used to judge the possibility of atomization and pumpability of oil and oil products.
There are dynamic, kinematic, conditional and effective (structural) viscosity.
Dynamic (absolute) viscosity [μ ], or internal friction, is the property of real fluids to resist shear shear forces. Obviously, this property manifests itself when the fluid moves. Dynamic viscosity in the SI system is measured in [N·s/m 2 ]. This is the resistance that a liquid exerts during the relative movement of its two layers with a surface of 1 m 2, located at a distance of 1 m from each other and moving under the action of an external force of 1 N at a speed of 1 m / s. Considering that 1 N/m 2 = 1 Pa, dynamic viscosity is often expressed in [Pa s] or [mPa s]. In the CGS system (CGS), the dimension of dynamic viscosity is [dyn·s/m 2 ]. This unit is called poise (1 P = 0.1 Pa s).
Conversion factors for calculating the dynamic [ μ ] viscosity.
| Units | Micropoise (µP) | Centipoise (cP) | Poise ([g/cm s]) | Pa s ([kg/m s]) | kg/(m h) | kg s / m 2 |
| Micropoise (µP) | 1 | 10 -4 | 10 -6 | 10 7 | 3.6 10 -4 | 1.02 10 -8 |
| Centipoise (cP) | 10 4 | 1 | 10 -2 | 10 -3 | 3,6 | 1.02 10 -4 |
| Poise ([g/cm s]) | 10 6 | 10 2 | 1 | 10 3 | 3.6 10 2 | 1.02 10 -2 |
| Pa s ([kg/m s]) | 10 7 | 10 3 | 10 | 1 3 | 3.6 10 3 | 1.02 10 -1 |
| kg/(m h) | 2.78 10 3 | 2.78 10 -1 | 2.78 10 -3 | 2.78 10 -4 | 1 | 2.84 10 -3 |
| kg s / m 2 | 9.81 10 7 | 9.81 10 3 | 9.81 10 2 | 9.81 10 1 | 3.53 10 4 | 1 |
Kinematic viscosity [ν ] is the value equal to the ratio of the dynamic viscosity of the fluid [ μ ] to its density [ ρ ] at the same temperature: ν = μ/ρ. The unit of kinematic viscosity is [m 2 /s] - the kinematic viscosity of such a liquid, the dynamic viscosity of which is 1 N s / m 2 and the density is 1 kg / m 3 (N \u003d kg m / s 2). In the CGS system, kinematic viscosity is expressed in [cm 2 /s]. This unit is called stokes (1 St = 10 -4 m 2 / s; 1 cSt = 1 mm 2 / s).
Conversion factors for calculating the kinematic [ ν ] viscosity.
| Units | mm 2 /s (cSt) | cm 2 / s (St) | m 2 /s | m 2 / h |
| mm 2 /s (cSt) | 1 | 10 -2 | 10 -6 | 3.6 10 -3 |
| cm 2 / s (St) | 10 2 | 1 | 10 -4 | 0,36 |
| m 2 /s | 10 6 | 10 4 | 1 | 3.6 10 3 |
| m 2 / h | 2.78 10 2 | 2,78 | 2.78 10 4 | 1 |
Oils and petroleum products are often characterized conditional viscosity, which is taken as the ratio of the outflow time through the calibrated hole of a standard viscometer 200 ml of oil at a certain temperature [ t] by the time of the expiration of 200 ml of distilled water at a temperature of 20°C. Nominal viscosity at temperature [ t] is denoted by the sign of WU, and is expressed by the number of conventional degrees.
Relative viscosity is measured in degrees VU (°VU) (if the test is carried out in a standard viscometer according to GOST 6258-85), Saybolt seconds and Redwood seconds (if the test is carried out on Saybolt and Redwood viscometers).
You can transfer viscosity from one system to another using a nomogram.
In petroleum dispersed systems, under certain conditions, in contrast to Newtonian fluids, the viscosity is a variable dependent on the shear rate gradient. In these cases, oils and oil products are characterized by effective or structural viscosity:
For hydrocarbons, the viscosity essentially depends on their chemical composition: it increases with increasing molecular weight and boiling point. The presence of side branches in the molecules of alkanes and naphthenes and an increase in the number of cycles also increase the viscosity. For various groups of hydrocarbons, the viscosity increases in the series alkanes - arenes - cyclanes.
To determine the viscosity, special standard instruments are used - viscometers, which differ in the principle of operation.
Kinematic viscosity is determined for relatively low-viscosity light petroleum products and oils using capillary viscometers, the operation of which is based on the fluidity of a liquid through a capillary according to GOST 33-2000 and GOST 1929-87 (viscometer type VPZh, Pinkevich, etc.).
For viscous petroleum products, the relative viscosity is measured in viscometers such as VU, Engler, etc. The outflow of liquid in these viscometers occurs through a calibrated hole in accordance with GOST 6258-85.
There is an empirical relationship between the values of conventional °VU and kinematic viscosity:
The viscosity of the most viscous, structured petroleum products is determined on a rotational viscometer according to GOST 1929-87. The method is based on measuring the force required to rotate the inner cylinder relative to the outer one when filling the space between them with the test liquid at a temperature t.
In addition to standard methods for determining viscosity, sometimes non-standard methods are used in research work, based on measuring viscosity by the time the calibration ball falls between the marks or by the decay time of the vibrations of a solid body in the test liquid (Geppler, Gurvich viscometers, etc.).
In all standard methods described, the viscosity is determined at a strictly constant temperature, since the viscosity changes significantly with its change.
Viscosity versus temperature
The dependence of the viscosity of petroleum products on temperature is a very important characteristic both in oil refining technology (pumping, heat exchange, settling, etc.) and in the use of commercial petroleum products (draining, pumping, filtering, lubrication of rubbing surfaces, etc.).
As the temperature decreases, their viscosity increases. The figure shows viscosity versus temperature curves for various lubricating oils.
Common to all oil samples is the presence of temperature regions in which a sharp increase in viscosity occurs.
There are many different formulas for calculating viscosity as a function of temperature, but the most commonly used is Walter's empirical formula:
Taking the logarithm of this expression twice, we get:
According to this equation, E. G. Semenido compiled a nomogram on the abscissa axis of which, for ease of use, temperature is plotted, and viscosity is plotted on the ordinate axis.
Using a nomogram, you can find the viscosity of an oil product at any given temperature if its viscosity at two other temperatures is known. In this case, the value of the known viscosities is connected by a straight line and continues until it intersects with the temperature line. The point of intersection with it corresponds to the desired viscosity. The nomogram is suitable for determining the viscosity of all types of liquid petroleum products.
For petroleum lubricating oils, it is very important during operation that the viscosity be as little dependent on temperature as possible, since this ensures good lubricating properties of the oil over a wide temperature range, i.e., in accordance with the Walter formula, this means that for lubricating oils, the lower the coefficient B, the higher the quality of the oil. This property of oils is called viscosity index, which is a function of the chemical composition of the oil. For various hydrocarbons, the viscosity varies with temperature in different ways. The steepest dependence (large value of B) for aromatic hydrocarbons, and the smallest - for alkanes. Naphthenic hydrocarbons are close to alkanes in this respect.
There are various methods for determining the viscosity index (VI).
In Russia, VI is determined by two values of kinematic viscosity at 50 and 100°C (or at 40 and 100°C - according to a special table of the State Committee for Standards).
When certifying oils, IV is calculated according to GOST 25371-97, which provides for the determination of this value by viscosity at 40 and 100°C. According to this method, according to GOST (for oils with VI less than 100), the viscosity index is determined by the formula:
For all oils with v 100 ν, v 1 And v 3) is determined according to the GOST 25371-97 table based on v 40 And v 100 this oil. If the oil is more viscous ( v 100> 70 mm 2 /s), then the quantities included in the formula are determined by special formulas given in the standard.
It is much easier to determine the viscosity index from nomograms.
An even more convenient nomogram for finding the viscosity index was developed by G. V. Vinogradov. The definition of VI is reduced to the connection of known viscosity values at two temperatures by straight lines. The point of intersection of these lines corresponds to the desired viscosity index.
The viscosity index is a generally accepted value that is included in oil standards in all countries of the world. The disadvantage of the viscosity index is that it characterizes the behavior of the oil only in the temperature range from 37.8 to 98.8°C.
Many researchers have noticed that the density and viscosity of lubricating oils to some extent reflect their hydrocarbon composition. A corresponding indicator was proposed that links the density and viscosity of oils and is called the viscosity-mass constant (VMC). The viscosity-mass constant can be calculated by the formula of Yu. A. Pinkevich:
Depending on the chemical composition of the VMK oil, it can be from 0.75 to 0.90, and the higher the VMK oil, the lower its viscosity index.
At low temperatures, lubricating oils acquire a structure that is characterized by yield strength, plasticity, thixotropy or viscosity anomaly, which are characteristic of dispersed systems. The results of determining the viscosity of such oils depend on their preliminary mechanical mixing, as well as on the flow rate, or on both factors at the same time. Structured oils, like other structured petroleum systems, do not follow the Newtonian fluid flow law, according to which the change in viscosity should depend only on temperature.
An oil with an unbroken structure has a significantly higher viscosity than after its destruction. If the viscosity of such an oil is reduced by destroying the structure, then in a calm state this structure will be restored and the viscosity will return to its original value. The ability of a system to spontaneously restore its structure is called thixotropy. With an increase in the flow velocity, more precisely, the velocity gradient (curve section 1), the structure is destroyed, and therefore the viscosity of the substance decreases and reaches a certain minimum. This minimum viscosity remains at the same level even with a subsequent increase in the velocity gradient (section 2) until a turbulent flow appears, after which the viscosity increases again (section 3).
Viscosity versus pressure
The viscosity of liquids, including petroleum products, depends on external pressure. Changing the viscosity of oils with increasing pressure is of great practical importance, since high pressures can occur in some friction units.
The dependence of viscosity on pressure for some oils is illustrated by curves, the viscosity of oils with increasing pressure changes along a parabola. Under pressure R it can be expressed by the formula:
In petroleum oils, the viscosity of paraffinic hydrocarbons changes least of all with increasing pressure and slightly more naphthenic and aromatic. The viscosity of high-viscosity oil products increases with increasing pressure more than the viscosity of low-viscosity ones. The higher the temperature, the less the viscosity changes with increasing pressure.
At pressures of the order of 500 - 1000 MPa, the viscosity of oils increases so much that they lose their liquid properties and turn into a plastic mass.
To determine the viscosity of petroleum products at high pressure, D.E. Mapston proposed the formula:
Based on this equation, D.E. Mapston developed a nomogram, using which known quantities, for example ν 0 And R, are connected by a straight line and the reading is obtained on the third scale.
Viscosity of mixtures
When compounding oils, it is often necessary to determine the viscosity of the mixtures. As experiments have shown, the additivity of properties is manifested only in mixtures of two components that are very similar in viscosity. With a large difference in the viscosities of the mixed oil products, as a rule, the viscosity is less than that calculated according to the mixing rule. Approximately, the viscosity of a mixture of oils can be calculated if we replace the viscosities of the components with their reciprocal - mobility (fluidity) ψ cm:
Various nomograms can also be used to determine the viscosity of mixtures. The ASTM nomogram and the Molin-Gurvich viscosigram have found the greatest application. The ASTM nomogram is based on the Walther formula. The Molin-Gurevich nomogram was compiled on the basis of the experimentally found viscosities of a mixture of oils A and B, of which A has a viscosity of °VU 20 = 1.5, and B has a viscosity of °VU 20 = 60. Both oils were mixed in different ratios from 0 to 100% (vol.), and the viscosity of the mixtures was established experimentally. The nomogram shows the values of viscosity in units. units and in mm 2 / s.
Viscosity of gases and oil vapors
The viscosity of hydrocarbon gases and oil vapors is subject to other laws than for liquids. As the temperature rises, the viscosity of gases increases. This pattern is satisfactorily described by the Sutherland formula:
Viscosity measures the internal resistance of a fluid to the force that is used to make that fluid flow. Viscosity is of two types - absolute and kinematic. The first is usually used in cosmetics, medicine and cooking, and the second is more often used in the automotive industry.
Absolute viscosity and kinematic viscosity
Absolute viscosity fluid, also called dynamic, measures the resistance to the force that makes it flow. It is measured regardless of the properties of the substance. Kinematic viscosity, on the contrary, depends on the density of the substance. To determine the kinematic viscosity, the absolute viscosity is divided by the density of that fluid.
Kinematic viscosity depends on the temperature of the liquid, therefore, in addition to the viscosity itself, it is necessary to indicate at what temperature the liquid acquires such a viscosity. Engine oil viscosity is usually measured at 40° C (104° F) and 100° C (212° F). During oil changes in automobiles, auto mechanics often take advantage of the property of oils to become less viscous as temperatures rise. For example, to remove the maximum amount of oil from the engine, it is preheated, as a result, the oil flows out easier and faster.
Newtonian and non-Newtonian fluids
Viscosity varies in different ways, depending on the type of liquid. There are two types - Newtonian and non-Newtonian fluids. Newtonian fluids are liquids whose viscosity will change regardless of the force that deforms it. All other liquids are non-Newtonian. They are interesting in that they deform at different rates depending on the shear stress, that is, the deformation occurs at a higher or, conversely, lower rate, depending on the substance and on the force that presses on the liquid. The viscosity also depends on this deformation.
Ketchup is a classic example of a non-Newtonian fluid. While it's in the bottle, it's almost impossible to get it out with little force. If, on the contrary, we apply great force, for example, we begin to shake the bottle strongly, then the ketchup will easily flow out of it. So, a large stress makes ketchup fluid, and a small one has almost no effect on its fluidity. This property is unique to non-Newtonian fluids.
Other non-Newtonian fluids, on the contrary, become more viscous with increasing stress. An example of such a liquid is a mixture of starch and water. A person can safely run through a pool filled with it, but will begin to sink if he stops. This is because in the first case the force acting on the fluid is much greater than in the second. There are non-Newtonian fluids with other properties - for example, in them, the viscosity varies not only depending on the total amount of stress, but also on the time during which the force acts on the liquid. For example, if the overall stress is caused by a greater force and acts on the body for a short period of time, rather than being distributed over a longer period with less force, then a liquid, such as honey, becomes less viscous. That is, if honey is stirred intensively, it will become less viscous compared to stirring it with less force, but for a longer time.
Viscosity and lubrication in engineering
Viscosity is an important property of liquids that is used in everyday life. The science that studies the fluidity of liquids is called rheology and is devoted to a number of topics related to this phenomenon, including viscosity, since viscosity directly affects the fluidity of various substances. Rheology generally studies both Newtonian and non-Newtonian fluids.
Engine oil viscosity indicators
The production of engine oil takes place with strict observance of the rules and recipes, so that the viscosity of this oil is exactly what is needed in a given situation. Before selling, manufacturers control the quality of the oil, and mechanics in car dealerships check its viscosity before pouring it into the engine. In both cases, the measurements are carried out differently. In the production of oil, its kinematic viscosity is usually measured, and mechanics, on the contrary, measure the absolute viscosity, and then translate it into kinematic. In this case, different measuring devices are used. It is important to know the difference between these measurements and not to confuse kinematic viscosity with absolute viscosity, as they are not the same.
To get more accurate measurements, engine oil manufacturers prefer to use kinematic viscosity. Kinematic viscosity meters are also much cheaper than absolute viscosity meters.
For cars, it is very important that the viscosity of the oil in the engine is correct. In order for car parts to last as long as possible, friction must be reduced as much as possible. To do this, they are covered with a thick layer of engine oil. The oil must be sufficiently viscous to remain on the rubbing surfaces as long as possible. On the other hand, it must be fluid enough to pass through the oil passages without a noticeable reduction in flow rate, even in cold weather. That is, even at low temperatures, the oil should remain not very viscous. In addition, if the oil is too viscous, then the friction between the moving parts will be high, which will lead to an increase in fuel consumption.
Motor oil is a mixture of different oils and additives such as antifoam and detergent additives. Therefore, knowing the viscosity of the oil itself is not enough. It is also necessary to know the final viscosity of the product and, if necessary, change it if it does not meet accepted standards.
Oil change
With use, the percentage of additives in engine oil decreases and the oil itself becomes dirty. When the contamination is too high and the additives added to it have burned off, the oil becomes unusable, so it must be changed regularly. If this is not done, then dirt can clog the oil channels. The viscosity of the oil will change and will not meet standards, causing various problems such as clogged oil passages. Some repair shops and oil manufacturers advise changing oil every 5,000 kilometers (3,000 miles), but car manufacturers and some auto mechanics say that changing oil every 8,000 to 24,000 kilometers (5,000 to 15,000 miles) is sufficient if the car is in good condition and in good condition. condition. Changing every 5,000 kilometers is suitable for older engines, and now advice for such a frequent oil change is a publicity stunt that forces car enthusiasts to buy more oil and visit service centers more often than is actually necessary.
As engine design improves, so does the distance a car can travel without an oil change. Therefore, in order to decide when it is worth pouring new oil into the car, be guided by the information in the operating instructions or the car manufacturer's website. Some vehicles also have sensors that monitor the condition of the oil - they are also convenient to use.
How to choose the right engine oil
In order not to make a mistake with the choice of viscosity, when choosing an oil, you need to take into account what kind of weather and for what conditions it is intended. Some oils are designed to work in cold or, conversely, in hot conditions, and some are good in any weather. Oils are also divided into synthetic, mineral and mixed. The latter consist of a mixture of mineral and synthetic components. The most expensive oils are synthetic, and the cheapest are mineral oils, since they are cheaper to produce. Synthetic oils are becoming more and more popular due to the fact that they last longer and their viscosity remains the same over a wide range of temperatures. When buying synthetic motor oil, it is important to check if your filter will last as long as the oil.
The change in viscosity of engine oil due to changes in temperature occurs in different oils in different ways, and this dependence is expressed by the viscosity index, which is usually indicated on the packaging. Index equal to zero - for oils, the viscosity of which is most dependent on temperature. The less the viscosity is affected by temperature, the better, which is why motorists prefer oils with a high viscosity index, especially in cold climates where the temperature difference between hot engine and cold air is very large. At the moment, the viscosity index of synthetic oils is higher than that of mineral oils. Blended oils are in the middle.
In order to keep the viscosity of the oil unchanged longer, that is, to increase the viscosity index, various additives are often added to the oil. Often these additives burn out before the recommended oil change date, meaning the oil becomes less usable. Drivers using oils with these additives are forced to either regularly check whether the concentration of these additives in the oil is sufficient, or change the oil frequently, or be content with oil with reduced qualities. That is, oil with a high viscosity index is not only expensive, but also requires constant monitoring.
Oil for other vehicles and mechanisms
Viscosity requirements for oils for other vehicles are often the same as those for automotive oils, but sometimes they differ. For example, the requirements for the oil that is used for a bicycle chain are different. Bicycle owners usually have to choose between a thin oil that is easy to apply to the chain, such as an aerosol spray, or a thick one that sticks well and lasts on the chain. Viscous oil effectively reduces friction and is not washed off the chain when it rains, but quickly becomes dirty, as dust, dry grass and other dirt get into the open chain. Thin oil does not have these problems, but it has to be reapplied frequently, and inattentive or inexperienced cyclists sometimes don't know this and ruin the chain and gears.
Viscosity measurement
To measure viscosity, devices called rheometers or viscometers are used. The former are used for liquids whose viscosity varies depending on environmental conditions, while the latter work with any liquids. Some rheometers are a cylinder that rotates inside another cylinder. They measure the force with which the fluid in the outer cylinder rotates the inner cylinder. In other rheometers, liquid is poured onto a plate, a cylinder is placed in it, and the force with which the liquid acts on the cylinder is measured. There are other types of rheometers, but the principle of their operation is similar - they measure the force with which the liquid acts on the moving element of this device.
Viscometers measure the resistance of a fluid that moves within a measuring instrument. To do this, the liquid is pushed through a thin tube (capillary) and the resistance of the liquid to movement through the tube is measured. This resistance can be found by measuring the time it takes for the liquid to move a certain distance in the tube. Time is converted to viscosity using calculations or tables available in the documentation for each device.
Viscosity of liquids
Dynamic viscosity, or coefficient of dynamic viscosity ƞ (Newtonian), is determined by the formula:
η = r / (dv/dr),
where r is the viscous drag force (per unit area) between two adjacent fluid layers, directed along their surface, and dv/dr is the gradient of their relative velocity, taken in a direction perpendicular to the direction of motion. The unit of dynamic viscosity is ML -1 T -1, its unit in the CGS system is poise (pz) \u003d 1g / cm * s \u003d 1dyn * s / cm 2 \u003d 100 centipoise (cps)
Kinematic viscosity is determined by the ratio of the dynamic viscosity ƞ to the fluid density p. The dimension of the kinematic viscosity is L 2 T -1, its unit in the CGS system is stokes (st) \u003d 1 cm 2 / sec \u003d 100 centistokes (cst).
The fluidity φ is the reciprocal of the dynamic viscosity. The latter for liquids decreases with decreasing temperature approximately according to the law φ \u003d A + B / T, where A and B are characteristic constants, and T denotes the absolute temperature. The values for A and B for a large number of liquids were given by Barrer.
Water viscosity table
Data of Bingham and Jackson, reconciled to the national standard in the USA and Great Britain on July 1, 1953, ƞ at 20 0 С=1.0019 centipoise.
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Temperature, 0 С |
Temperature, 0 С |
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Table viscosity of various liquids Ƞ, cps
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Liquid |
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Bromobenzene |
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Formic acid |
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Sulfuric acid |
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Acetic acid |
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Castor oil |
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Provence oil |
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carbon disulfide |
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Methyl alcohol |
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Ethanol |
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Carbonic acid (liquid) |
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Carbon tetrachloride |
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Chloroform |
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ethyl acetate |
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Ethyl formate |
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Ethyl ether |
Relative viscosity of some aqueous solutions (table)
The concentration of solutions is assumed to be normal, which contains one gram equivalent of a solute per 1 liter. Viscosity are given in relation to the viscosity of water at the same temperature.
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Substance |
Temperature, °С |
Relative viscosity |
Substance |
Temperature, °С |
Relative viscosity |
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Calcium chloride |
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Ammonium chloride |
Sulfuric acid |
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Potassium iodide |
hydrochloric acid |
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Potassium chloride |
sodium hydroxide |
Table viscosity of aqueous solutions of glycerin
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Specific gravity 25°/25°С |
Weight percent glycerin |
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Viscosity of liquids at high pressures according to Bridgman
Table relative viscosity of water at high pressures
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Pressure kgf / cm 3 |
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Table of relative viscosities of various liquids at high pressures
Ƞ=1 at 30 ° С and pressure 1 kgf/cm 2
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Liquid |
Temperature, ° С |
Pressure kgf / cm 2 |
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carbon disulfide |
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Methyl alcohol |
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Ethanol |
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Ethyl ether |
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Viscosity of solids (PV)
Viscosity table for gases and vapors
Dynamic viscosity of gases usually expressed in micropoises (mpuses). According to the kinetic theory, the viscosity of gases should not depend on pressure and change in proportion to the square root of the absolute temperature. The first conclusion turns out to be generally correct, with the exception of very low and very high pressures; The second conclusion requires some corrections. To change ƞ depending on the absolute temperature T, the formula is most often used:
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gas or steam |
Sutherland's constant, C |
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Nitrous oxide |
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Oxygen |
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water vapor |
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Sulphur dioxide |
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Ethanol |
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Carbon dioxide |
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Carbon monoxide |
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Chloroform |
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Table viscosity of some gases at high pressures (mcpz)
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Temperature, 0 С |
Pressure in atmospheres |
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Carbon dioxide |
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To determine the kinematic viscosity, the viscometer is selected so that the flow time of the oil product is at least 200 s. Then it is thoroughly washed and dried. A sample of the product to be tested is filtered through a filter paper. Viscous products are heated to 50–100°C before filtration. In the presence of water in the product, it is dried with sodium sulfate or coarsely crystalline table salt, followed by filtration. The required temperature is set in the thermostatic device. The accuracy of maintaining the selected temperature is of great importance, so the thermostat thermometer must be installed so that its reservoir is approximately at the level of the middle of the viscometer capillary with simultaneous immersion of the entire scale. Otherwise, a correction for a protruding column of mercury is introduced according to the formula:
^T = Bh(T1 – T2)
- B is the coefficient of thermal expansion of the working liquid of the thermometer:
- for a mercury thermometer - 0.00016
- for alcohol - 0.001
- h is the height of the protruding column of the working fluid of the thermometer, expressed in divisions of the thermometer scale
- T1 - set temperature in the thermostat, °C
- T2 is the ambient air temperature near the middle of the protruding column, °C.
The determination of the expiration time is repeated several times. In accordance with GOST 33-82, the number of measurements is set depending on the expiration time: five measurements - with an expiration time of 200 to 300 s; four from 300 to 600 s; and three for expiration times greater than 600 s. When taking readings, it is necessary to monitor the constancy of temperature and the absence of air bubbles.
To calculate the viscosity, the arithmetic mean of the flow time is determined. In this case, only those readings are taken into account that differ by no more than ± 0.3% for accurate and ± 0.5% for technical measurements from the arithmetic mean.
