Kinematic viscosity is a goal for evaluating the activity of petroleum products, an important goal for liquid petroleum, and a major goal for identifying changes in the quality of petroleum during transportation and use. Accurately measuring the kinematic viscosity of oil can tightly control the quality of oil. After discussion, it was found that there are many factors that affect the kinematic viscosity. Key points include analyzing the effects of factors such as constant temperature oil bath temperature, capillary viscometer coefficient, and different orientations of viscometer devices on the kinematic viscosity, and drawing corresponding conclusions to provide a basis for oil quality judgment.
For measuring the kinematic viscosity of oil products, the liquid petroleum of lubricating oil is generally measured using the GB/T265 method. For dark colored oil products, the countercurrent method is generally used. Kinematic viscosity is a characteristic within a fluid that prevents its relative activity, reflecting the liquid's activity performance under flow conditions. The unit commonly used is m ²/ s. It is an important goal to measure the performance of oil products. The classification and classification of oil products are based on their kinematic viscosity measured at temperatures of 40 ℃ and 100 ℃. The higher the viscosity, the thicker the oil film, and the better the lubrication performance; The lower the viscosity, the greater the frictional resistance, the higher the degree of wear, and the more unfavorable it is for mechanical movement. Moreover, kinematic viscosity is a condition where, at a stable temperature, a certain volume of liquid is measured and flows through a calibrated glass capillary viscometer under the action of gravity. The product of the capillary coefficient of the viscometer and the active time is the kinematic viscosity of the liquid measured at that temperature.
Factors affecting the measurement of oil viscosity in motion: capillary viscometer coefficients
Capillary viscometers have different coefficients and corresponding activity times depending on their measurement scale. The same type of testing liquid moves at different times in capillary viscometers with different coefficients. When the moving liquid exceeds a certain speed, it becomes turbulent and does not conform to laminar flow conditions. A small coefficient capillary viscometer increases the frictional force between the liquid and the inner wall of the viscometer, Lengthening the speed of liquid movement in a hardness tester will cause the measured kinematic viscosity value to be higher. Capillary viscometers with high viscosity coefficients have larger internal diameters, lower friction between the fluid and the inner wall of the viscometer, shorter fluid movement time in the salinity tester, resulting in lower measured kinematic viscosity and a simple turbulent phenomenon, which increases the measurement error of the viscometer. Moreover, capillary viscometers with high coefficients are difficult to maintain constant temperature during measurement, which increases errors. Therefore, the longer the liquid is active in the viscometer, the better. A capillary viscometer with suitable coefficients should be selected based on the properties of the liquid.
The influencing factors of measuring the viscosity of oil products in motion - the orientation of the viscometer device
According to the rules of using a viscometer, when measuring the kinematic viscosity of a liquid, it is necessary to adhere to the fact that the reading line of the capillary viscometer is relatively horizontal. Therefore, when measuring, it is necessary to ensure that the capillary viscometer is in a straight state and that there are no bubbles in the liquid inside the capillary to avoid increasing errors. To determine whether the capillary viscometer is in a straight state, a plumb line can be used to clamp it from the front, back, left, and right sides. When the viscometer is skewed, its reading may be large due to the observer's different orientations
Or small, and when the capillary viscometer is skewed, it will increase the contact area between the liquid and the viscometer, increase the friction force, and make the result measurement inaccurate. After experimental verification, it was found that when the capillary viscometer is skewed towards the coarse tube direction, the measured results are slightly smaller; When skewed towards the capillary direction, the measured results are biased, therefore, when measuring the kinematic viscosity, it is necessary to ensure that the viscometer is in a straight state.
The Factors Influencing the Measurement of Kinematic Viscosity of Oil Products - Moisture
When measuring the kinematic viscosity of oil products, if the sample contains water or if the viscometer contains water inside, due to the immiscibility between the oil and water, water is suspended in the oil product. Once the sample comes into contact with the viscometer, water will automatically approach the inner wall of the viscometer, adding resistance to the sample's movement, causing the sample to linger in the viscometer for a longer period of time than without water, resulting in an overestimation of the results of kinematic viscosity measurement. Therefore, when using a capillary viscometer to measure the kinematic viscosity, it is necessary to ensure that the sample does not contain any water, and it is not necessary to ensure that the inner wall of the viscometer is clean and dry, in order to reduce errors in measuring the viscosity.
The Influence Factor of Oil Product Kinematic Viscosity Measurement - Temperature
The condition of oil is related to the content of unsaturated fatty acids inside it. The higher the content of unsaturated fatty acids, the more severe the coagulation of the oil; The less unsaturated fatty acids it contains, the lower the cohesion of the oil. In addition, temperature has a significant impact on the kinematic viscosity of oil products. The higher the temperature, the lower the kinematic viscosity of oil products; The lower the temperature, the higher the kinematic viscosity of the oil. Therefore, in the measurement of viscosity, it is necessary to clearly determine the temperature corresponding to the viscosity of the oil. The temperature should be kept constant according to the standard rules and time. If the temperature is unstable, it will also affect the measurement results. Moreover, it has been proven through practice that if the temperature changes between positive and negative 0.1 ℃, the viscosity measurement results of the oil will also have a large deviation.
Factors affecting the measurement of oil kinematic viscosity - other factors
The capillary viscometer needs to be calibrated on time because long-term use can affect its accuracy. To avoid increased errors caused by human error, it is necessary to calibrate it on time. A stopwatch is also classified as a measuring tool and should be regularly checked to see if it is within its validity period. The stopwatch must be accurate.
Precautions for measuring the kinematic viscosity of oil products
The main factors affecting the measurement of oil viscosity in motion include temperature, moisture, the orientation and model selection of the viscometer device. When using a constant temperature bath, it is necessary to ensure that the temperature of the oil is in a stable state. Temperature deviation has a significant impact on the measurement of the oil viscosity meter, and the selection of viscosity meter coefficients must be suitable to minimize friction during the activity process and keep it within a certain scale. In addition, it is necessary to clean the viscometer well and ensure that the inside of the viscometer is clean and free of moisture before measurement. The most crucial thing is to use a plumb line to calibrate the orientation of the capillary device when installing a viscosity gauge, so that it is in a straight state. The operation of manual instruments must be carried out under the guidance of technical personnel and skilled measurement personnel to avoid human errors and inaccurate test results.