Physico-chemical and crystallization processes in ceramic masses with mineralizing additives determine the nature of the change in the viscosity of the resulting liquid phase, as well as the ratio of the crystalline and liquid phases, which is reflected in the change in the viscosity of the system as a whole. The use of mineralizing additives is in many cases a determining factor in improving and specifically regulating the properties of a wide range of ceramic materials. It has been established that the mineralizing effect of a number of mineralizing substances will accelerate thermal transformations in clay systems. The effectiveness of mineralizers depends on their rheological characteristics in the temperature range of firing ceramic masses. We found experimental confirmation of the assumption about the effectiveness and feasibility of using complex mineralizing additives that combine mineralizers with a low melting point and sintering accelerators with low dynamic viscosity to regulate the process of formation of a liquid phase with optimal rheological characteristics.

viscosity

mineralizing component

rheological properties

sintering

heating rate

1. Bezborodov M.A. Viscosity of silicate glasses. - Minsk: Science and Technology. - 1975. -163 p.

2. Budnikov P.P. The influence of mineralizers on the process of mullitization of clays, kaolins and synthetic masses / P.P. Budnikov, Kh.O. Govorkyan // ZHPH. - 1946. - T. XIX. - No. 10-11. - pp. 1029-1035.

3. Budnikov P.P. Reactions in mixtures of solids / P.P. Budnikov, A.M. Ginstling. - M.: Publishing house of literature. on the page, 1971. - 487 p.

4. Nikiforova E.M. Mineralizers in the ceramic industry. - Krasnoyarsk: GUTSMiZ, 2004. - 108 p.

5. Chandhuri S.P. Influence of mineraliers on the constitution of hard porcelain. Part II. Microstructures // Amer. Ceran. Soc. Bull. - 1974, 53. - No. 3. - R. 251-254.

Introduction

Physicochemical and crystallization processes in ceramic masses with mineralizing additives determine the nature of the change in the viscosity of the resulting liquid phase, as well as the ratio of the crystalline and liquid phases, which is reflected in the change in the viscosity of the system as a whole.

The use of mineralizing additives is in many cases a determining factor in improving and specifically regulating the properties of a wide range of ceramic materials. The mechanism of action of mineralizers during mineral formation reactions in ceramic disperse systems requires further serious study.

The choice of mineralizing additives comes down to the empirical selection of the composition of the sintering accelerator. This approach does not provide optimization of accepted technical solutions. There are no technological criteria and Objective assessment the effectiveness of mineralizers, which limits their use, including industrial waste. There is no generally accepted explanation for the mechanism of action of mineralizers in the mineral formation reactions of ceramic materials that occur during the formation and presence of a liquid phase.

The positive effect of mineralizers cannot be attributed only to the acceleration of the formation of the liquid phase, since it is necessary to take into account changes in other factors (viscosity, melt structure, etc.). As many researchers note, the positive effect of mineralizers is determined not only by the acceleration of the formation of the liquid phase in ceramic disperse systems, but also by the rheological properties of the liquid phase. The reduction in the viscosity of the liquid phase and the viscosity of the system as a whole, as a determining factor in the intensification of the processes of formation of ceramic dispersed structures, does not explain the mechanism of action of mineralizers.

The views according to which a decrease in the temperature of formation of the liquid phase due to and in the presence of a mineralizer is a decisive factor in activating the ongoing reactions are not confirmed.

The most acceptable views are, in our opinion, according to which the activation of processes in the mineralized liquid phase is determined by the thermorheological properties of the mineralizers themselves. However, it cannot be ruled out that only the combination of these manifestations determines the activation of the phase formation reactions of ceramic dispersed structures.

Materials and research methods

Low-grade polymineral loam of the Siberian region, characterized by a low content of clay particles, was studied. Loam is characterized by the content of clay minerals montmorillonite (d/n=1.530; 0.450; 0.255 nm), kaolinite (d/n=0.714; 0.357; 0.237 nm) and hydromica (d/n=0.998; 0.447; 0.256 nm). Due to the low content of clay particles (up to 20%), loam needs improvement and targeted regulation of its physicochemical and technological properties. Chemical composition The studied clay raw materials are given in Table 1.

Table 1 - Chemical composition of the initial clay raw materials, mass. %

The study of dynamic viscosity was carried out using the method of a body rotating in the melt on a rotational viscometer. The mineralogical composition of raw materials and sintered masses was determined on the basis of X-ray diffraction analysis data carried out on a Shimadzu XRD-6000 diffractometer. Differential thermal analysis was carried out using a Netche Q-1500 derivatograph in an air atmosphere.

Additives with a wide range of rheological properties in the firing range of ceramic materials in the form of compounds NaF, Na 2 CO 3, LiCl and KCl (dynamic viscosity h = (0.6-6) Pa×s) and cullet (h= (10-10 14) Pa×s), as well as industrial waste containing a complex of low-viscosity mineralizing components.

The most large-tonnage waste from aluminum production - gas purification sludge is represented by finely dispersed black material with a particle size from 0.071 to 1.0 mm. Microscopic examination of the sludge showed that the material consists of metamorphosed coal particles of graphite, cryolite, chiolite, corundum, fluorite, nepheline, diaspore, etc. In the diffraction pattern, graphite is recorded along lines with a value of d/n = 0.338; 0.202; 0.169 nm, corundum - d/n = 0.208; 0.255; 0.160 nm, cryolite - d/n = 0.193; 0.275; 0.233 nm. When heating sludge, an endothermic effect is observed at a temperature of 50-100 ºС, related to the removal of hygroscopic water; the exothermic effect at 90-140 ºС is associated with the adsorption of oxygen from the atmosphere by the coal mass; weak effect in the temperature range 180-300 ºС refers to the process of dehydration of aluminum hydroxide; the endothermic effect of 340 ºС is associated with the loss of water by cryolite crystalline hydrate; the intense exothermic effect at 350-600 ºС refers to the process of burning out the carbon mass; the exothermic effect with a maximum of 975 ºС refers to the crystallization of the glass phase.

The chemical composition of mixed aluminum production waste corresponds to the content of the following components, wt. %: SiO 2 - 0.68; Al 2 O 3 - 12.53; Fe 2 O 3 - 1.13; CaO - 0.73; MgO - 0.60; Na 2 O - 15.89; F - - 16.38; p.p.p. - 51.42. Aluminum production sludge is characterized by low viscosity of its mineralizing components NaF, Na 2 CO 3, Na 2 SO 4, NaHCO 3, Na 3 AlF 6, AlF 3 with each other with h 900-1000 ºС = (4.9-1.9) Pa×s.

Research results and discussion

The change in the viscosity of a ceramic system with mineralizing additives, depending on the rheological properties of the mineralizers, was established in ceramic dispersed systems made from masses based on polymineral clay with additives (mineralizers NaF, Na 2 CO 3, glass cullet, as well as industrial waste in the form of sludge) having a lower melting point optimal clay firing temperature. Curves of changes in viscosity depending on temperature and type of additive are presented in Figure 1.

Rice. 1. Changing the viscosity of garden loam with mineralizing additivesdepending on temperature: 1 - pure clay; 2 - with the addition of cullet; 3 - with Na 2 CO 3; 4 - with NaF; 5 - with the addition of sludge.

Analysis of the processes that cause anomalies in the viscosity curves indicates that with the introduction of mineralizing additives, crystallization processes undergo changes.

Thus, the appearance of the liquid phase due to eutectic melts, characterized for polymineral clay by a temperature of 875 ºС, shifts to the region of lower temperatures: with the addition of cullet by 15 ºС, Na 2 CO 3 - by 70 ºС, NaF - by 75 ºС, sludge - at 80 ºС. The beginning of the appearance of the liquid phase, which causes a monotonic decrease in viscosity for masses with NaF and cullet, coincides in temperature with the endothermic effect on the differential curve at 810 and 840 ºС, respectively, corresponding to the appearance of the mineralizer melt. The inflection point in the viscosity curve, corresponding to the transformation of dehydration products into new crystalline phases and characterized for pure clay at 925 ºС, shifts with the introduction of mineralizers to the region of lower temperatures, with the exception of the addition of cullet, which does not change the temperature at which the new phases begin to crystallize.

The addition of Na 2 CO 3 shifts this temperature by 15 ºС, NaF - by 25 ºС, sludge - by 30 ºС. The inflection in the curves corresponding to pure clay and with the additions of NaF and cullet coincides with the exothermic effect on the differential curve at 925 and 900 ºС, respectively, corresponding to the recrystallization of new phases.

The most intensive effect on the nature of crystallization processes occurring during firing of low-melting garden clay is the addition of sludge. Obviously, this is due to the fact that already at 800 ºС the combined mineralizer from the mineralizing components of the sludge has a low dynamic viscosity h = 4.9 Pa × s. The addition of sludge in the established range of activity of mineralizers and their effect on physicochemical and crystallization processes: sludge > NaF > Na 2 CO 3 > cullet, is ahead of the individual mineralizing components of sludge (NaF, Na 2 CO 3), which confirms the effectiveness of combined mineralizers.

The introduction of NaF and cullet additives leads to an increase in the intensity of the endothermic effect with a maximum of 130 ºС for garden clay and shifts the process caused by dehydration and removal of interlayer water from the montmorillonite lattice to lower temperatures: NaF - by 15 ºС, cullet - by 5 ºС.

In relation to hydromica-kaolinite-montmorillonite garden clay, a significant decrease in the dissociation temperature of CaCO 3 in the presence of mineralizers and a shift of the decarbonization zone to lower temperatures was established, as evidenced by a shift in the maximum of the endothermic effect corresponding to this process and characterized by a maximum peak of 805 ºC for clay by 55-60 ºС when adding NaF and by 20-25 ºС when adding cullet.

The melting point of NaF mineralizers and cullet is higher than the dissociation temperature of calcium carbonate CaCO 3, which suggests that the interaction reactions between the mineralizer and calcium carbonate occur in the solid phase with the formation of solid solutions that contribute to the deformation of the crystal lattices of the reacting components and increase their reactivity.

The formation of solid solutions is explained by an increase in the amplitude of vibration of Na + ions around its geometric center at 600-700 ºС and the proximity of its ionic radius to the radius of Ca 2+, which creates conditions for the introduction of the Na + ion into crystal lattice CaCO 3, CaO. Thermograms immediately after the endothermic effect of CaCO 3 dissociation revealed endothermic effects at temperatures of 810, 840 ºС in masses with NaF mineralizers and cullet, respectively, which may be due to the appearance of the liquid phase at temperatures below the melting point of the mineralizer due to the formation of low-melting eutectics of the mineralizer and carbonate calcium. This observation is quite consistent with the data of N.A. Toropov, indicating the formation of a liquid phase in the NaF-CaCO 3 system at 400-600 ºС. The peak of the endothermic effect, which is significantly more intense in intensity, associated with the appearance of the liquid phase in masses containing NaF, characterizes a more active process of its formation in comparison with the mass of clay and cullet, which is associated with the lower viscosity of the liquid phase formed by the NaF mineralizer in clay during the period of calcite dissociation and, as a consequence, an increase in the amount of melt due to the activation of the process of dissolving calcium carbonate in it.

The established significant decrease in the intensity of the peak of the endothermic effect associated with the dissociation of calcite in the mass of clay and NaF is caused by its overlap with the exothermic reaction of the formation of calcium silicates, which is a consequence of the direct acceleration of the effect of hydromica and montmorillonite clay and the mineralizers they contain on the dissociation of carbonates.

Judging by the above data, the mineralizing effect of a number of substances leads to the acceleration of thermal transformations in clay systems, increasing their reactivity, and the effectiveness of the influence of mineralizers on these processes depends on their rheological characteristics in the temperature range of firing of ceramic masses.

We found experimental confirmation of the assumption about the effectiveness and feasibility of using complex mineralizing additives that combine mineralizers with a low melting point and sintering accelerators with low dynamic viscosity in the firing temperature range of ceramic materials to regulate the process of formation of a liquid phase with optimal rheological characteristics.

The results of studies of the rheological properties of complex mineralizer additives (Fig. 2, 3), coinciding with the data of Bondarenko N.V. , indicate the possibility of reducing the melting temperature of the melt by combining mineralizing additives with different rheological properties.

Rice. 2. Dependence of the viscosity of the complex additiveon temperature and composition (mass, %): 1 - LiCl 100; 2 - KCl 100; 3 - LiCl 10, KCl 90; 4 - LiCl 30, KCl 70; 5 - LiCl 50, KCl 50; 6 - LiCl 70, KCl 30.

Rice. 3. Dependence of the viscosity of the complex additive cullet -NaFon temperature and composition (wt.%): 1 - cullet 100; 2 - NaF 100;

3 - cullet 50, NaF 50; 4 - cullet 75, NaF 25; 5 - cullet 25, NaF 75.

As follows from Fig. 2, the most effective from the point of view of assessing its rheological properties, in comparison with pure LiCl and KCl additives, is a combined mineralizing additive in a combination of LiCl and KCl 1:1, forming a melt at the melting temperature of LiCl, at the same time the viscosity of the complex additive approaches the viscosity KCl. Also very effective is a combined mineralizing additive that combines a low-viscosity NaF additive (h 1000º C = 2 Pa×s) and a high-viscosity cullet additive (h 800º C = 10 9 Pa×s), forming a melt at a temperature 130 ºC lower than the melting point of NaF. At the same time, the viscosity of the combined mineralizer approaches the viscosity of NaF (h 870º C =4 Pa×s). In accordance with the established patterns, it is obvious that it is possible to activate individual high-viscosity additives characterized by the onset of softening in the region of fairly low temperatures 575-875 ºС (Erklese, calcium borate, cullet, frit, zeolite) already in this temperature range.

Conclusion

A change in the viscosity of ceramic disperse system from masses based on polymineral clay with mineralizing additives depending on the thermorheological properties of the mineralizers. The nature of the changes in crystallization processes that cause anomalies in the viscosity curves has been revealed.

The possibility of increasing the efficiency of high-viscosity additives and transferring their thermorheological properties to the optimal range by combining them with low-viscosity mineralizers has been experimentally proven. A combination of highly viscous additives having low temperature softening with low-viscosity mineralizers, leads to a decrease in viscosity and maintaining a low softening temperature.

Reviewers:

• Tolkachev V.Ya., Doctor of Technical Sciences, Professor, Chief Technologist of the CPC of Sibirsky Element LLC, Krasnoyarsk.
• Stupko T.V., Doctor of Technical Sciences, senior researcher, head of the Department of Chemistry, Krasnoyarsk State Agrarian University, Krasnoyarsk.

Bibliographic link

Even if you use the most modern motor oil, its properties change as the vehicle operates.

As you know, all oils contain functional additives designed to improve and maintain certain properties (in Russia they are usually called additives). When operating in an engine, these additives are destroyed under the influence of thermal and mechanical loads. The oil molecules themselves undergo changes. When all these changes reach a certain limit, it is necessary to replace motor oil.

One of the key characteristics that allows you to set the timing of an oil change is the change in viscosity, on which the ability of the oil to perform its functions greatly depends. A change in viscosity of just 5% is already perceived by specialists as a signal, and a change of 10% is considered a critical level.

It is important to understand that the change in viscosity does not occur abruptly. This is a gradual process that occurs throughout the life of the vehicle between oil changes. The main reasons leading to changes in viscosity are presented in the table.

Common causes of changes in motor oil viscosity

Changes associated with oil contamination must be eliminated either through diagnostics and repairs at stations Maintenance, or a change in driving style.

The most interesting changes occur at the molecular level. They are interesting because they cannot be completely avoided, since they are of a fundamental, natural nature. But these changes can be contained.

The reasons leading to an increase in viscosity will be discussed in a separate article devoted to the anti-wear properties of oils. Here we will focus on the reverse process. Here are the most likely consequences of a decrease in engine oil viscosity:

Reduced oil film thickness on the surfaces of rubbing parts and, as a result, excessive wear, increased sensitivity to mechanical impurities, rupture of the oil film under high loads and when starting the engine.

An increase in friction force in engine elements operating in mixed and boundary friction modes (piston rings, gas distribution mechanism) will lead to excessive fuel consumption and heat generation.

It is known that the SAE J300 standard approves four methods for determining the viscosity of motor oil. Since the effects of viscosity reduction are mainly felt while the engine is running, the most appropriate method would be to determine the HTHS viscosity.

This parameter, which stands for high-temperature viscosity at high shear rate (High-Temperature High-Shear rate viscosity), is usually determined under conditions as close as possible to the operating conditions of the oil in a friction pair piston ring- cylinder wall. By the way, similar conditions exist on the surface of the camshaft cams and in the bearings crankshaft at high engine loads. The temperature when determining the viscosity of HTHS is + 150 °C, and the shear rate is 1.6 * 10 6 1/s. To make it easier to imagine the last value, we will give several fantastic everyday examples in which the shear rate has a similar value: painting a fence with a roller at a speed of 160 km/s, squeezing water out of a 10 ml syringe with a needle in 1/10 of a second, spreading oil for 200,000 pieces of bread by one person in 1 minute.

So, it is the HTHS viscosity that is most closely related to both the protective properties of the oil and the fuel consumption of a running engine. The last statement is confirmed by research (Figure 1).

Picture 1.
Relationship between fuel consumption and engine oil properties
(P.I. Lacey, SAE Technical Paper 2001-01-1904)

In the VMPAUTO laboratory, using an Anton Paar MCR 102 rheometer, HTHS viscosity can be measured under “milder” conditions than those provided for in the standards: it is still possible to achieve a shear rate of 10 5 1/s at +150 °C. However, even with such an approximation, interesting results can be obtained.

Figure 2 shows the results of determining the HTHS viscosity in full synthetic oil Shell Helix ULTRA AV-L 5W-30, used in the VW GOLF 1.6 2006 model. The new oil had an HTHS viscosity of 3.62 mPa*s. But after 8000 km of HTHS operation, the viscosity dropped by 0.16 mPa*s (-4.4%), that is, it had already approached the “signal” 5% level for specialists. This means that all the negative consequences described above may begin to appear in the very near future.

At the beginning of 2013, the scientific and technical department of VMPAUTO began developing a new generation multifunctional additive for motor oils. Its name is “P14”. In the spring of 2014, full-scale tests began on vehicles of various classes.

As can be seen from Fig. 2, the addition of “P14” had virtually no effect on the HTHS viscosity of the new engine oil (-1.4%). At the same time, adding “P14” to the oil after 8000 km made it possible not only to restore the HTHS viscosity value to the initial value, but also to slightly increase it (+3.0%), giving the engine oil a new “viscosity potential” for further trouble-free operation. Measurement of HTHS viscosity 7500 km after applying “P14” (+5.5%) shows that even before the next change of engine oil, its protective characteristics remain unchanged high level: there was neither a critical drop nor an increase in this most important parameter.

Figure 2.
HTHS viscosity of engine oil at + 150 °C and a shear rate of 10 5 1/s.
Each value is the average of 100 measurements.

During the year at seasonal change temperature, the viscosity of transported oil changes (Fig. 1.20). If the oil temperature increases from t 1 to t 2, the viscosity of the oil decreases. This leads to a decrease in the hydraulic resistance of the pipeline (H 2 Q 1).

Let us consider the effect of changes in oil viscosity on the magnitude of PS backwaters. Let us assume that the same number of pumps of the same type is installed at all stations, the head pressure at the head pumping station is h P, and the residual pressure at the final point is h OST. Let us assume for simplicity that the oil pipeline consists of one operational section N E = 1, and the number of substations is n (Fig. 1.21).

Pumping station pressure in winter period will be

in summer

, (1.59)

where H1, H2 are the total pressure losses in the pipeline, respectively, in winter and summer.

Rice. 1.20. Combined characteristics of the pipeline and substation

when oil viscosity changes

Rice. 1.21. Influence of seasonal changes in oil viscosity

by the amount of backwaters in front of the substation

From the starting point of the route profile, we will plot the values ​​of H 1 and H 2 on a vertical scale, then we will connect the vertices of the segments with straight lines to the point z K +h OC. The resulting lines correspond to the position of the hydraulic slope lines in the winter i 1 and summer i 2 periods.

Let's imagine that the pipeline route is an ascending straight line AB. As can be seen from the constructions, when arranging stations, such a route will be divided into equal sections of length L/n. In this case, the lines of hydraulic slopes i 1 and i 2 will intersect line AB at the same points. This suggests that with a monotonic profile of the oil pipeline route, changes in oil viscosity do not affect the amount of backwater at the inlet of intermediate substations.

In real conditions, the route profile can be very rough, then the distances between pumping stations will be unequal (l 1 ¹l 2 ¹l 3 ¹l n). Let us consider the change in the headwater in front of the substation in this case.

The amount of backwater DH C in front of the s-th substation can be found from the pressure balance equation

where a=m M ×a M and b=m M ×b M .

The flow rate in expression (1.61) is determined from the pressure balance equation for the oil pipeline as a whole (1.37), which allows us to write

. (1.62)

After substituting (1.62) into (1.61), we obtain

As follows from expression (1.63), only one factor depends on the viscosity value , because .

Let us introduce the following notation:

;

– average distance between pumping stations on the section to the s-th substation;

– arithmetic average distance between substations;

Taking into account the adopted simplifications, expression (1.63) can be represented in the form

Where
.

The F value is directly proportional to the change in oil viscosity: as the viscosity decreases, the F value also decreases.

If the condition L cf is satisfied< l ср(С) , то при уменьшении вязкости подпор на с-й ПС возрастает. В противном случае при L ср >l av(C) the backwater at the s-th substation decreases and may turn out to be less permissible value DH min (Fig. 1.21). In the case of station placement according to hydraulic calculations at minimum oil temperature (t 1 =t min, n 1 =n max), it is necessary to analyze the operation of each stage in the summer.

In the summer, if the strength of the pipe allows, you can increase the pressure on the hydraulic pump by turning on an additional booster pump connected in series.

1.10. Regulation of oil pipeline operating modes

The operating modes of the oil pipeline are determined by the flow and pressure of the substation pumps at the given point in time, which are characterized by the conditions of the material and energy balance of the pumping stations and the pipeline. Any imbalance leads to a change in the operating mode and necessitates regulation.

The main factors influencing the operating modes of the “substation – pipeline” system include the following:

§ changes in the rheological parameters of oil due to seasonal changes in temperature, as well as the influence of the content of water, paraffin, dissolved gas, etc.;

§ technological factors - changes in pump parameters, turning them on and off, the presence of oil reserves or free containers, etc.;

§ emergency or repair situations caused by damage to the linear part, failures of substation equipment, or triggering of limit protection.

Some of these factors act systematically, some periodically. All this creates conditions under which the operating modes of the “substation – pipeline” system continuously change over time.

From the pressure balance equation it follows that all control methods can be divided into two groups:

q methods related to changing the parameters of pumping stations

§ change in the number of operating pumps or their connection diagram;

§ regulation using replaceable rotors or machined impellers;

§ regulation by changing the pump shaft rotation speed;

q methods related to changing pipeline parameters

§ throttling;

§ bypassing part of the liquid into the suction line (bypassing).

Changing the number of operating pumps. This method is used when it is necessary to change the flow rate in an oil pipeline. However, the result depends not only on the pump connection diagram, but also on the type of pipeline characteristics (Fig. 1.22).

1 – pump characteristics; 2 – pressure characteristic of the substation with a series connection of pumps; 3 – pressure characteristic of the substation with parallel connection of pumps; 4, 5 – characteristics of the pipeline; 6 – h-Q characteristic pump in series connection; 7 – h-Q characteristic of the pump in parallel connection

Let us consider, as an example, a parallel and series connection of two identical centrifugal pumps when operating on a pipeline with different hydraulic resistance.

As can be seen from the graphical constructions (Fig. 1.22), a series connection of pumps is advisable when working on a pipeline with a steep characteristic. In this case, the pumps operate with a higher flow rate (Q B >Q C) than with a parallel connection, as well as with a higher total pressure and efficiency. Parallel connection of pumps is more preferable when operating on a pipeline with a flat characteristic (Q F >Q E, HF >H E, h F >h E).

Adjustment via replaceable rotors. Most modern mainline pumps are equipped with replaceable rotors for reduced flow 0.5Q NOM and 0.7Q NOM. In addition, the NM 10000-210 pump is equipped with a replaceable rotor for 1.25 Q NOM.

Replaceable rotors have specific characteristics (Fig. 1.23).

Rice. 1.23. Characteristics of a pump with replaceable rotors

The use of replaceable rotors is economical at the initial stage of oil pipeline operation, when not all pumping stations have been built and the pipeline has not been brought to its design capacity (phased commissioning of the oil pipeline). The effect of installing replaceable rotors can also be obtained with a long-term reduction in pumping volume.

Turning of impellers along the outer diameter widely used in oil pipeline transport. Depending on the speed coefficient n S, wheel turning can be performed within the following limits: at 60< n S <120 допускается обрезка колес до 20%; при 120< n S <200 – до 15%; при n S =200¼300 – до 10%.

Recalculation of the pump characteristics when turning the impeller is performed using similar formulas:

where Q З, H З and N З - flow, pressure and power consumption corresponding to the factory diameter of the impeller D З;

Q У, H У and N У - the same with a reduced diameter of the impeller D У.

The control method by turning the impeller can be effectively used when the pumping mode has been established for a long time. It should be noted that reducing the diameter of the impeller beyond permissible limits leads to a disruption of the normal hydrodynamics of flow in the working parts of the pump and a significant decrease in efficiency.

Changing the pump shaft speed– a progressive and economical method of regulation. The use of smooth control of the rotation speed of pump rotors at the substations of main oil pipelines facilitates the synchronization of station operation, completely eliminates the turning of impellers, the use of replaceable rotors, and also avoids hydraulic shocks in the oil pipeline. This reduces the start-up and stop time of pumping units. However, due to technical reasons, this method of regulation has not yet found widespread use.

The method of changing the rotation speed is based on similarity theory

(1.66)

where Q 1, H 1 and N 2 – flow, pressure and power consumption corresponding to the rotational speed of the impeller n 1;

Q 2, H 2 and N 2 - the same at the impeller rotation speed n 2.

As the rotation speed decreases, the pump characteristic will change and the operating point will shift from position A 1 to A 2 (Fig. 1.24).

Rice. 1.24. Combined characteristics of an oil pipeline and a pump when changing the shaft speed

In accordance with (1.66), when recalculating the pump characteristics from rotation speed n 1 to frequency n 2, we obtain the following relations:

Changing the pump shaft rotation speed is possible in the following cases:

§ use of engines with variable speed;

§ installation of couplings with an adjustable slip coefficient (hydraulic or electromagnetic) on the pump shaft;

§ the use of current frequency converters while simultaneously changing the supply voltage of electric motors.

It should be noted that it is impossible to change the rotation speed within a wide range, since this significantly reduces the efficiency of the pumps.

Method throttling in practice it is used relatively often, although it is not economical. It is based on partially blocking the flow of oil at the outlet of the pumping station, that is, on the introduction of additional hydraulic resistance. In this case, the operating point from position A 1 shifts towards decreasing flow rate to point A 2 (Fig. 1.25).

Rice. 1.25. Combined characteristics of substation and pipeline when regulated by throttling and bypass

The feasibility of using the method can be characterized by the value of throttling efficiency h DR

. (1.68)

With an increase in the value of the throttled pressure h DR, the value of h DR decreases. The total efficiency of the pump (PS) is determined by the expression h=h 2 ×h DR. The throttling method is appropriate to use for pumps with a flat pressure characteristic. In this case, energy losses for throttling should not exceed 2% of energy costs for pumping.

Method of bypassing part of the liquid into the suction line of pumps ( bypass ) is mainly used at headends. When the valve on the bypass line (bypass) is opened, the pressure pipeline is connected to the suction pipeline, which leads to a decrease in resistance after the pump and the operating point moves from position A 1 to A 3 (Fig. 1.25). Flow Q B =Q 3 -Q 2 goes through the bypass, and flow Q 2 enters the main line.

Bypass efficiency is

. (1.69)

In practice, bypass is rarely used due to its inefficiency. The bypass control method should be used for steeply falling pump characteristics. In this case, it is more economical than throttling.

Viscosity called the ability of a fluid to resist shear forces. This property of a liquid manifests itself only when it moves. Let us assume that a certain amount of liquid is enclosed between two flat unlimited parallel plates (Fig. 2.1); the distance between them is P; the speed of movement of the upper plate relative to the lower one is υ.

Experience shows that the layer of liquid immediately adjacent to the wall sticks to it. It follows that the speed of movement of the fluid adjacent to the bottom wall is zero, and to the top wall – υ. The intermediate layers move at a speed that gradually increases from 0 to υ.

Rice. 2.1.

Thus, there is a difference in speed between adjacent layers, and mutual sliding of the layers occurs, which leads to the manifestation of the force of internal friction.

To move one plate relative to another, it is necessary to apply a certain force G to the moving plate, equal to the resistance force of the fluid as a result of internal friction. Newton found that this force is proportional to speed And, contact surfaces S and inversely proportional to the distance between the plates n , i.e.

where μ is the proportionality coefficient, called dynamic viscosity (or dynamic viscosity coefficient).

To further clarify this dependence, it should be related to the infinitesimal distance between the layers of liquid, then

where Δ υ is the relative speed of movement of neighboring layers; Δ P - the distance between them. Or at the limit

The last expression represents Newton's law for internal friction. The plus or minus sign is taken depending on the sign of the velocity gradient dv/dn.

Since τ = T/S there is a tangential shear stress, then Newton’s law can be given a more convenient form:

The tangential stress arising in a fluid is proportional to the velocity gradient in the direction perpendicular to the velocity vector and the area along which it acts.

The proportionality coefficient µ characterizes the physical properties of the liquid and is called dynamic viscosity. From Newton's formula it follows that

The physical meaning of the coefficient p follows from this expression: if , then µ = τ.

In hydrodynamics, the quantity

called kinematic viscosity (kinematic viscosity coefficient).

Dynamic viscosity µ decreases with increasing temperature, and increases with increasing pressure. However, the influence of pressure for dropping liquids is negligible. The dynamic viscosity of gases increases with increasing temperature, but changes only slightly with changes in pressure.

Newton's law for internal friction in liquids differs significantly from the laws of friction in solids. In solids there is static friction. In addition, the friction force is proportional to normal pressure and depends little on the relative speed of movement. In a fluid that obeys Newton's law, in the absence of a relative velocity of movement of the layers, there is no friction force. The friction force does not depend on pressure (normal stress), but depends on the relative speed of movement of the layers. Liquids that obey Newton's law are called Newtonian. However, there are liquids that do not obey this law (anomalous liquids). These include various types of emulsions, colloidal solutions, which are heterogeneous bodies consisting of two phases (solid and liquid).

Thus, clay solutions used in drilling oil wells and some types of oils do not obey Newton’s law near their pour point. Experiments have established that in such liquids movement occurs after the tangential stresses reach a certain value called initial shear stress.

For such liquids, a more general dependence for τ is valid (Bingham’s formula):

where τ0 is the initial shear stress; η – structural viscosity.

Thus, these liquids at voltage τ< τ0 ведут себя как твердые тела и начинают течь лишь при τ ≥ τ0. В дальнейшем градиент скорости пропорционален не т, а разнице τ -τ0.

Graphically, the relationship between and τ is depicted by curve 1 for Newtonian liquids and curve 2 for anomalous liquids (Fig. 2.2).

Rice. 2.2. Addictiondv/dn from shear stress

When structural fluids move through a pipeline, three modes of their movement are observed: structural, laminar, turbulent.

Structural. To start movement, a certain initial pressure drop in the pipeline Δ is required R 0, after which the liquid separates from the walls and begins to move as one whole (like a solid).

Laminar. With increasing pressure drop Δ R the speed of fluid movement will increase and a laminar flow regime will begin to develop near the walls. As the speed further increases, the region of the laminar regime will expand, then the structural regime completely turns into laminar.

Turbulent. With a further increase in speed, the laminar regime becomes turbulent (see paragraph 6.1).

Dependence of viscosity on temperature and pressure. Viscometers

The viscosity of a droplet liquid depends largely on temperature and, to a lesser extent, on pressure. The dependence of viscosity on pressure is neglected in most cases. For example, at pressures up to 50–105 Pa, the viscosity changes by no more than 8.5%. The exception is water at a temperature of 25°C - its viscosity decreases slightly with increasing pressure. Another feature of water is that its density increases with a decrease in temperature to +4°C, and with a further decrease in temperature (from +4 to 0°C) it decreases. This explains the fact that water freezes from the surface. At a temperature of about 0°C, it has the lowest density, and layers of liquid having the same temperature as the lightest float to the surface, where water freezes if its temperature is less than 0°C.

At atmospheric pressure, the viscosity of water depending on temperature is determined by the Poiseuille formula

Where v – kinematic viscosity; µ – dynamic viscosity; ρ is the density of water at a given temperature; t – water temperature.

The viscosity of a liquid is determined using instruments called viscometers. For liquids more viscous than water, an Engler viscometer is used. This device consists of a container with a hole through which, at a temperature of 20°C, the time for draining distilled water is determined. T 0 and liquid T , the viscosity of which needs to be determined. Ratio of quantities T And T 0 is the number of conventional Engler degrees:

After determining the viscosity of the liquid in conventional Engler degrees, the kinematic viscosity (cm2/s) is found using the empirical Ubellode formula

The v values ​​obtained using this formula are in good agreement with experimental data.

During the year, with seasonal changes in temperature, the viscosity of transported oil changes (Fig. 1.20). If the oil temperature increases from t 1 to t 2, the viscosity of the oil decreases. This leads to a decrease in the hydraulic resistance of the pipeline (H 2 Q 1).

Let us consider the effect of changes in oil viscosity on the magnitude of PS backwaters. Let us assume that the same number of pumps of the same type is installed at all stations, the head pressure at the head pumping station is h P, and the residual pressure at the final point is h OST. Let us assume for simplicity that the oil pipeline consists of one operational section N E = 1, and the number of substations is n (Fig. 1.21).

The pressure of the pumping station in winter will be

in summer

where H1, H2 are the total pressure losses in the pipeline, respectively, in winter and summer.

Rice. 1.20. Combined characteristics of the pipeline and substation

when oil viscosity changes

Rice. 1.21. Influence of seasonal changes in oil viscosity

by the amount of backwaters in front of the substation

From the starting point of the route profile, we will plot the values ​​of H 1 and H 2 on a vertical scale, then we will connect the vertices of the segments with straight lines to the point z K +h OC. The resulting lines correspond to the position of the hydraulic slope lines in the winter i 1 and summer i 2 periods.

Let's imagine that the pipeline route is an ascending straight line AB. As can be seen from the constructions, when arranging stations, such a route will be divided into equal sections of length L/n. In this case, the lines of hydraulic slopes i 1 and i 2 will intersect line AB at the same points. This suggests that with a monotonic profile of the oil pipeline route, changes in oil viscosity do not affect the amount of backwater at the entrance of intermediate substations.

In real conditions, the route profile can be very rough, then the distances between pumping stations will be unequal (l 1 l 2 l 3 l n). Let us consider the change in the headwater in front of the substation in this case.

The amount of backwater H C in front of the s-th substation can be found from the pressure balance equation

where a=m M a M and b=m M b M .

The flow rate in expression (1.61) is determined from the pressure balance equation for the oil pipeline as a whole (1.37), which allows us to write

. (1.62)

After substituting (1.62) into (1.61), we get

As follows from expression (1.63), only one factor depends on the viscosity value, since.

Let us introduce the following notation:

;

– the average distance between pumping stations on the section to the s-th substation;

– arithmetic average distance between substations;

Taking into account the adopted simplifications, expression (1.63) can be represented in the form

Where .

The F value is directly proportional to the change in oil viscosity: as the viscosity decreases, the F value also decreases.

If the condition L cf is satisfied< l ср(С) , то при уменьшении вязкости подпор на с-й ПС возрастает. В противном случае при L ср >l av(C) the backwater at the s-th substation decreases and may be less than the permissible value H min (Fig. 1. 21). In the case of station placement according to hydraulic calculations at minimum oil temperature (t 1 =t min,  1 = max), it is necessary to analyze the operation of each stage in the summer.

In the summer, if the strength of the pipe allows, you can increase the pressure on the hydraulic pump by turning on an additional booster pump connected in series.