The density of sea water and the density of gasoline. Fuel Density Determination

One of the three aggregate states of the existence of substances is liquid. Liquid particles are arranged very compactly, which causes their high density (the densities of some liquids are given in Table 1) and low compressibility compared to gases. Structure and internal structure liquids are characterized by an ordered arrangement of particles. Due to the relatively high mobility of liquid particles, their ordering is limited to small islands (aggregates or clusters), the latter being randomly oriented relative to each other, and part of the space between them remains unfilled with matter. These formations are unstable, the connections in them are constantly destroyed and reappeared. In this case, particles are exchanged between neighboring clusters. Thus, structurally, a liquid is characterized by the presence of a labile (mobile) equilibrium due to the relative freedom of movement of particles. The formation of labile aggregates in a liquid is observed even at temperatures much higher than the crystallization temperature. As the temperature decreases, the stability of such aggregates increases and, near the crystallization temperature, liquids have a quasi-crystalline structure; the number of aggregates increases, they become larger in size and begin to orient themselves relative to each other in a certain way.

Table 1. Densities of some liquids.

Liquids are isotropic, i.e. them physical properties the same in all directions. With any, arbitrarily small forces, liquids easily change their shape, which manifests itself in fluidity. Naturally, fluidity (or its reciprocal, viscosity) for various liquids varies over a wide range. There are liquids that have a very high viscosity (for example, some bitumens), as a result of which, with a sharp application of a load - an impact - they collapse like solids. At the same time, a gradual and continuous increase in load makes it possible to detect fluidity in them.

Examples of problem solving

EXAMPLE 1

EXAMPLE 2

A table is given for the density of liquids at various temperatures and atmospheric pressure for the most common liquids. The density values ​​in the table correspond to the indicated temperatures, data interpolation is allowed.

Many substances are capable of being in a liquid state. Liquids are substances of various origin and composition that have fluidity - they are able to change their shape under the influence of certain forces. The density of a liquid is the ratio of the mass of a liquid to the volume it occupies.

Consider examples of the density of some liquids. The first thing that comes to mind when you hear the word “liquid” is water. And this is not at all accidental, because water is the most common substance on the planet, and therefore it can be taken as an ideal.

Equal to 1000 kg / m 3 for distilled and 1030 kg / m 3 for sea ​​water. Insofar as given value is closely related to temperature, it is worth noting that this "ideal" value was obtained at +3.7°C. The density of boiling water will be somewhat less - it is equal to 958.4 kg / m 3 at 100 ° C. When liquids are heated, their density usually decreases.

The density of water is close in value to various food products. These are products such as: vinegar solution, wine, 20% cream and 30% sour cream. Individual products are denser, for example, egg yolk - its density is 1042 kg / m 3. It turns out to be denser than water, for example: pineapple juice - 1084 kg / m 3, grape juice - up to 1361 kg / m 3, orange juice - 1043 kg / m 3, Coca-Cola and beer - 1030 kg / m 3.

Many substances are less dense than water. For example, alcohols are much lighter than water. So the density is 789 kg / m 3, butyl - 810 kg / m 3, methyl - 793 kg / m 3 (at 20 ° C). Certain types of fuel and oils have even lower density values: oil - 730-940 kg / m 3, gasoline - 680-800 kg / m 3. The density of kerosene is about 800 kg / m 3, - 879 kg / m 3, fuel oil - up to 990 kg / m 3.

Low density indicators are distinguished by liquids such as: turpentine 870 kg / m 3,

Any liquid has its own unique properties and characteristics. In physics, it is customary to consider a number of phenomena that are associated with these specific characteristics.

Liquids are usually divided into two main categories:

• drip or low compressibility;
• gaseous or compressible.

Figure 2. Liquid density calculation. Author24 - online exchange of student papers

These classes of liquids have fundamental differences from each other. So drop liquids differ significantly from gaseous ones. They have a certain volume. Its value will not change under the influence of any external forces. In the gaseous state, liquids can occupy the entire volume that they have. Also, a similar class of fluid can change its own volume to a large extent if it is influenced by certain external forces.

Liquids of any kind have three properties that they cannot part with:

• density;
• viscosity;
• surface tension force.

These properties are capable of influencing numerous laws of their motion, therefore they are of primary importance in the process of studying and applying knowledge in practice.

The concept of fluid density

The mass that is contained in a unit volume is called the density of the liquid. If you progressively increase the unit of pressure, then the volume of water will tend to decrease from its original value. The difference in values ​​is approximately 1 to 20000. The same order of numbers will have the volumetric compression ratio for other dropping liquids. As a rule, in practice it is found that there are no serious changes in pressure, therefore it is customary not to use the compressibility of water in practice when calculating specific gravity and density as a function of pressure.

Figure 3. Densities of various liquids. Author24 - online exchange of student papers

To calculate the density of a liquid, the concept of thermal expansion for dropping liquids is introduced. It is characterized by a coefficient of thermal expansion, which expresses the increase in the volume of a liquid with an increase in temperature by 10 degrees Celsius.

Thus, a density index is formed for a particular liquid. It is customary to take into account at different atmospheric pressure, temperature indicators. Above is a table that shows the densities of the main types of liquids.

Density of water

Water is the most common and familiar liquid. Consider the main characteristics of the density and viscosity of this substance. The density of water in natural conditions will be equal to 1000 kg/m3. This figure applies to distilled water. For sea water, the density value is slightly higher - 1030 kg / m3. This value is not finite and is closely related to temperature. Ideal performance can be recorded at a temperature of about 4 degrees Celsius. If you make calculations over boiling water at a temperature of 100 degrees, then the density will decrease quite a lot and will be approximately 958 kg / m3. It has been established that usually in the process of heating any liquids, their density goes down.

The density of water is also quite close to that of a number of common foods. It can be compared with wine, vinegar solution, skim milk, cream, sour cream. Some types of products have higher density values. However, there are many among food and drink products that can significantly yield to classical water. Among them, alcohols are usually distinguished, as well as petroleum products, including fuel oil, kerosene and gasoline.

If it is necessary to calculate the density of some gases, then the equations of state are used ideal gases. This is necessary in cases where the behavior of real gases differs significantly from the behavior of ideal gases and the liquefaction process does not occur.

The volume of a gas usually depends on pressure and temperature values. Pressure differences, which cause significant changes in the density of gases, occur when moving at high speeds. Usually incompressible gas manifests itself at speeds that exceed one hundred meters per second. The ratio of the fluid velocity to the speed of sound is calculated. This allows you to correlate many indicators when confirming the density of a substance.

Viscosity of liquids

Viscosity is another property of any liquid. This is the state of a fluid that is capable of resisting shear or other external force. Real liquids are known to have similar properties. It is defined as internal friction during the relative movement of fluid particles that are nearby.

There are not only easily mobile liquids, but also more viscous substances. The first group usually includes air and water. In heavy oils, resistance occurs on a different level. Viscosity can characterize the degree of fluidity of a liquid. Also, such a process is called the mobility of its particles, and it depends on the density of the substance. The viscosity of liquids in the laboratory is determined by viscometers. If the viscosity of a liquid depends to a greater extent only on the applied temperature, then it is customary to distinguish between several basic parameters of substances. As the temperature increases, the viscosity of the dropping liquid tends to decrease. The viscosity of a gaseous liquid only increases under similar conditions.

The force of internal friction in liquids arises when the velocity of the gradient is proportional to the area of ​​the layers that carry out friction. In this case, friction in liquids is usually distinguished from the process of friction in other solids. AT solids the friction force will depend on the normal pressure, and not on the area of ​​the rubbing surfaces.

Anomalous and ideal fluids

There are two types of liquids, based on their internal characteristics:

• abnormal fluids;
• ideal liquids.

Definition 1

Anomalous fluids are those fluids that do not obey Newton's law of viscosity. Such liquids are able to start moving after the moment of shear stress when passing the limit threshold at a minimum. This process is also called initial shear stress. These fluids cannot move at low stresses and experience elastic deformations.

Ideal fluids include an imaginary fluid that is not subject to any compression and deformation, that is, it is devoid of the property of viscosity. For its calculation it is necessary to enter certain correction factors.

Goals of the work:

to give students an idea of ​​the methodology for determining the density of petroleum products;

to teach students to take into account the value of density in the operations of accounting for the consumption of fuel and lubricants.

Under fuel densityρ understand its mass per unit volume. The dimension of density in the SI system of units is expressed in kg/m 3 . The density of oil products depends on temperature, i.e., with its increase, the density decreases, and with a decrease, it increases. Density can be measured at any temperature, but the result of the measurement must be brought to a temperature of +20 °C, which is taken as standard when assessing the density of fuels and oils.

Bringing the measured density to the density at a standard temperature of +20 ° C is carried out according to the formula

ρ 20 = ρ t + γ(t + 20),

where ρ - fuel density at test temperature, kg/m 3 ; γ - average temperature correction, kg/m 3 -deg (Table 2); t- temperature at which fuel density was measured, °C.

The values ​​of corrections for density are given in Table. 2.

table 2

Average temperature corrections for the density of oil products

Reporting on researched oil products

Accounting for petroleum products at oil depots, fuel depots of motor vehicles, mechanization bases and gas stations, as well as wholesale purchase and transportation of fuels and lubricants are carried out in mass units, i.e. the receipt is carried out in weight units - kilograms and tons (kg, t), and the consumption is taken into account in volumetric units - liters (l).

Therefore, the system of accounting and reporting, as well as calculations in the preparation of requests for supply, should provide for the conversion of quantities from mass units to volume units and vice versa. In addition, the control of the presence of fuel residues in the tanks of filling stations (gas stations), their retail sale and release when filling tanks of vehicles, their consumption rates are also established and produced in volume units, i.e. in liters (l).

Because of this, it is necessary to recalculate from mass units to volume units and vice versa, for which it is necessary to know the density of received and issued oil products.

The recalculation is carried out as follows: the amount of gasoline in mass units, kg G t = V t ρ t,

where V t- the amount of gasoline in volume units, l; ρ t- density of gasoline at the same temperature, kg/l.

With the reverse calculation and the same notation V t = G t / ρ t.

Thus, absolute density substance is the amount of mass contained in a unit volume. It has the dimension kg / m 3 in the SI system.

Density measurement with oil densimeters

In warehouses and filling stations, the density of petroleum products is measured using oil densimeter(hydrometer), which is a hollow glass float with a ballast at the bottom and a thin glass tube at the top, in which the density scale is placed. The measuring set includes densimeters with various limits of density scales, which allow practically determining the density of all types of fuels and oils (Fig. 3-4).

Densimeters are graduated in g / cm 3, therefore, to express the density of the product in the SI system, it is necessary to recalculate the measurement result by multiplying by 1000.

Rice. 4. Determination of the density of gasoline a - aerometer: 1 - thermometer scale; 2 - density scale (p, g / cm 2); b - oil densimeter: 1 - oil densimeter