Energy storage. General information about mechanical energy storage

Mechanical Drive (MN), or mechanical energy accumulator, is called a device for pampering and storing kinetic or potential energy with subsequent returns to make useful work.

As for any type of energy storage devices (NE), characteristic modes of operation MN are charge (accumulation) and discharge (Return of energy). Storage Energy serves as an intermediate mode MN. In the charging mode, mechanical energy from an external source is supplied to the MN, and the specific technical implementation of the energy source is determined by the type MN. At the discharge of the MN, the main part of the energy stored by them is transmitted to the consumer. Some of the accumulated energy is spent on compensation for losses that occur in the discharge mode, and in most types of MN - and in storage modes.

Because in a number of accumulative installations, the time charge3 may be much superior to the discharge time (G3 "GR), it is possible to substantially exude a medium-digit" RP over medium power P3 charge MN. Thus, it is permissible to accumulate energy to accumulate energy with relatively low-power sources.

Main varieties of MN are divided into static, dynamic and combined devices.

Static Mns suck potential energy through an elastic change in the form or volume of the working fluid either by moving against the direction of gravity in the gravitational field. The solid, liquid or gaseous working fluid of these MNs has a static state in the energy storage mode, and the charge and the discharge of the NE are accompanied by the movement of the working fluid.

Dynamic Mys accumulate kinetic energy mainly in the rotating masses of solids. Conditionally - to dynamic MNs can also include accumulative devices of accelerators of charged elementary particles, in which the kinetic energy of electrons or protons, cyclically moving along closed trajectories.

Combined Mns are at the same time kinetic and potential energy. An example of a combined MN can serve as a supermarker from high-strength fibrous material having a relatively small elastic module. During the rotation of this MN in it, along with kinetic energy, the potential energy of elastic deformation is intensified. When extracting the accumulated energy from such a thing, the use of both its species is achieved.

In terms of the level of specific accumulated energy per unit of mass or the volume of the accumulating element, the dynamic inertial mys significantly exceeds some other NE varieties (for example, inductive and capacitive drives). Therefore, MN are of great practical interest for diverse applications in various industries and scientific research.

Separate species of MN found to date large-scale use in electric power industry, such as a guide - rotation of electrical stations. Charging - the discharge cycle of their work reaches tens of hours.

For inertial mines, short-term difference modes are characteristic. Energy selection from MN is accompanied by a decrease in the angular velocity of the flywheel to a permissible level. In some cases, braking can occur until the flywheel stops. The "shock" discharges, characterized by a disposable or cyclic selection of stored energy, and as a result of the large kinetic moment and the small time of the discharge of the MN, the reduction of the angular velocity of its rotor is relatively small, although the 0 powerful power can reach sufficiently high values. In this mode, many requirements are presented to ensure the strength of the shaft. Under the influence of torque in the shaft there are hazardous tangent stresses, cha. The kinetic energy of the rotor passes into the potential energy of the elastic deformations of the shaft. To overcome these difficulties in separate structures, the elastic or friction clutches are provided.

Static MN retain stored energy, being in a fixed state. The carriers of potential energy in them are elastically deformed solid bodies or compressed gases under excess pressure, as well as the masses raised to the height relative to the earth's surface. Typical examples of static MN are: stretched or compressed springs, rubber; gas-ballon batteries and pneumatic accumulators; Impact devices of various cops, for example, to climb piles using the mass energy in the raised state; Reservoirs of hydro-accumulating power plants, water tanks. We present the main energy ratios and the characteristic parameters of some typical devices.

Consider MN S. Elastic elements.

Believe Solid State Linear system, then the elastic accumulative element has a constant stiffness (or elasticity) N.= Const. Strength F.\u003d NX. proportional to linear deformation x. Perfect when charged elementary work DW.\u003d FDX.. Full stored energy

W. = J. FDX \u003d. J. NXDX \u003d NAH2 / 2-FAAH / 2, Oo.

WhereAH - resulting deformation, limited, for example, Permissible Voltage AR material; FN. = Nah -Hed strength.

Let us estimate the specific energy WYA. \u003d WJ. M, per unit mass M. \u003d YV.\u003d ysh. Springs or rod volume V. and cross section S., The material of which has the density of y and runs on the gap within the law of the throat A. \u003d XFE, Moreover X.* \u003d XFH- relative deformation, E.-module elasticity (Jung), G ^ Gp. Introducing DA \u003d EDX„ We can write down DW.\u003d FHDX* \u003d Fhdo./ E. and dwya. \u003d DW./ ysh. \u003d FDA./ Yse., From where C. \u003d F./ S. Find

WYA \u003d] (Alje) Da \u003d A2j (2je).ABOUT

For steel Springs C "\u003d 8 108 N / M "E \u003d. 2 , 1-1011 N / m2, y \u003d 7800 kg / m3, then WYA. ^200 J./ kg. AnaThe logical calculation for technical rubber gives ^ UD ^ 350 J / kg, however, due to the hysteresis character F.= F.(X.) In the "charge-discharge" cycle, the loss and heating leads TO gradual aging (destruction) of rubber, instability of the deterioration of its elastic properties.

Gas accumulating The system is in a mechanically non-equilibrium state in relation to the environment: with the equality of temperature and environmental temperatures (T \u003d T0C) System pressure P\u003e P0, C, Therefore, the system can work. Elastic energy compressed in a cylinder volume V. Gas is

W. \u003d P (VDP \u003d V (P2-PI) .. (4.1)

On a unit of mass M of any compressed gas according to (4.1) there is a specific energy

WYA \u003d W / M \u003d V (P2-PL) IM \u003d ApLy. (4.2)

Based on (4.2), at k \u003d 1m3 value W.- WYSM. numerically equal to the pressure drop AR \u003d P1-P1. For example, if a /? \u003d 250 105 Pa (initial pressure P! \u003d Y5PA), then Il \u003d 25-106 J, regardless of the chemical composition of the gas. The maximum value of WYA when expanding the compressed gas to zero pressure at a given temperature according to the Mendeleev equation - Klapairone PV- Mvryt. make up

WYA.\u003d WLM \u003d RYTI ", (4.3)

Where c \u003d m / mts - molar mass (kg / kmol); Ry & ~ 8,314 KJ / (Kolol K) is a universal gas constant at TX273 K; /? "105pa; Mm - the number of kilometers in a gas mass M.

From (4.3) it can be seen that the most efficient use of light gases in MN. For the easiest gas - hydrogen (C \u003d 2 kg / kmol) at r \u003d 300 to specific energy ~ 1250 kJ / kg (or 1250 j / g). In (4.3), pressure explicitly is not included, since WYA is determined by (4.2) the ratio of overpressure gas to its density. The latter with an increase in pressure and r \u003d const increases according to the linear law (in an isothermal process PV= Const). It should be noted that appropriately appropriate for the effective use of high pressure under consideration are due to the considerations of strength substantial mass of gas cylinders, taking into account the value of WYA installation as a whole may decline almost an order of magnitude compared with FVYA from (4.2), (4.3). An assessment of the strength of cylinders can be carried out using the calculated relations of § 4.5.7.

Consider Gravitational Energy drives.

The gravistatic energy of the attraction of the Earth (at the level of ORA) is estimated quite high "UD \u003d 61.6 MJ / kg, which characterizes the work required for uniformly moving the body with a mass of MX \u003d kg from the earth's surface into the outer space (we indicate that this value Pvya is approximately more than a chemical energy of 1 kg kerosene). When lifting cargo weighing M. To height H. \u003d X.2 - XL. Spare potential energy

W. \u003d jgmdx \u003d gmh , (4.4)

Where m \u003d const, g \u003d 9,8l m / s2. According to (4.4) specific energy WYA.\u003d WJ. M.\u003d Gh. Depends only on the height H.. The stored energy is released when the cargo falls and performing relevant useful work as a result of the transition of potential energy into kinetic. The greatest specific kinetic energy in nature during falling can develop meteorites for which WYA ^ 60 MJ / kg (excluding energy costs for friction in the atmosphere).

The immediate use of gravistatic forces, with the natural masses of the natural masses, is almost impossible. However, pumping water into the raised artificial reservoirs or from underground reservoirs to the surface, it is possible to accumulate a sufficiently large amount of potential energy for large-scale applications in electric power systems. If the level difference H. \u003d 200 m, then calculated on the mass of water M \u003d 103kg stored energy in (4.4) equal to and\u003e "\u003d 1962 kJ, specific energy WYA.\u003d WJM.= 1.962 kJ / kg.

Consider inert kinetic MN.

Kinetic energy in principle can be repaired at any mass movement. For uniform progressive body movement M. with speed V. kinetic energy W.\u003d MV.2 / 2. Specific energy WYA.\u003d W./ M. \u003d V.2 J.2 Depends (quadratically) only from linear body velocity. The body moving at the first space speed of the KM / C has a specific

Energy WYAX32 MJ / kg.

For a variety of energy and transport applications, the rational of the rotational motion is rational - inertial MN (flywheels). Spare kinetic energy w \u003d j & / ~ is determined by the square of the angular velocity Q. \u003d 2NN. (P - rotation frequency) and the moment of inertia J. Flywheel relative to the axis of rotation. If the disk flywheel has a radius G. and mass M. = YV. (V.- volume, W. - material density), t °

J ^ mr2 / 2 \u003d yvr2j2 and W \u003d n2mr2n2 \u003d n2yvr2n2. Appropriate specific energy (per unit M. or V) make up FV/ M.\u003d N.* R.2N.2 , J / kg and LV0Ya.\u003d W./ V.\u003d N.2yr.2N.2 , J / m3. The values \u200b\u200bof Q and n at a given size g are limited to a linear circumferential speed V. \u003d Q..r. \u003d 2mr., associated with a permissible tearing voltage of the material AP. It is known that the voltage A in the disk or cylindrical rotor MN depends on V2. Depending on the geometric shape of metal flywheels, permissible limiting speeds on the periphery are characterized by approximately 200 to 500 m / s.

Accumulated energy, in particular for a thin riming flywheel, W.\u003d MV. /2 (M.- Miss of the rotating rings). Specific energy WYA.\u003d W./ M. \u003d V.2 /2 does not depend on the size of the ring and is determined by the ratio of the parameters of the OR / in its material (see § 4.5.1, where it is shown that V.2 \u003d Opj.Y). It should be noted that a similar pattern for WYA ~ AVJU also takes place in inductive energy storage (see ch. 2), although they differ significantly from the physical nature. In general, in the manufacture of storage elements MN, it is necessary to apply materials with elevated GP / Y values\u003e 105 J / kg. The most appropriate materials are high-strength alloyed steel, titanium alloys, as well as light aluminum alloys (type "Dural") and magnesium alloys (type "electron"). Applying metal materials, you can get the specific energy of the MN to WM \u003d 200-300 to J / kg.

Forwarding flywheels with particularly large specific energies (supermarkets) Tone-fiber materials theoretically can provide the following levels of the WYA indicator: glass filaments 650 kJ / kg, quartz yarns - 5000 kJ / kg, carbon fibers (with diamond structure) -15000 kJ / kg . The threads (or the tapes made of them) and the adhesive are forming a composite design, the strength of which is lower than that of the source fibers. Taking into account the elements of fastening in real super - flywheels, the values \u200b\u200bof the Jew less specified are practically achieved, but still relatively higher than in other varieties of MN. Supermanhovikov admit circumferential speeds to V. "1000 m / s. The technical implementation of such devices requires the provision of special conditions. For example, the installation of a flywheel in a vacuum casing is necessary, since the specified values V. Correspond to supersonic speeds in the air (the number of Maha Ma\u003e 1), which in the general case can cause a number of unacceptable effects: the appearance of air seals and shock waves, a sharp increase in aerodynamic resistance and temperature.

Multilayer fibrous supermarkets have sufficiently high reliability and safer in operation than solid flywheels. With unacceptable loads caused by inertial forces, only the most stressful outer layers of the fiber composite design of the supermanovka are destroyed, while the destruction of the massive flywheel is accompanied by an expansion of its broken parts.

The combination of static and dynamic MN properties takes place in various devices. The simplest of them is the oscillating pendulum. The cyclic process of mutual transformation of potential energy into kinetic can be maintained sufficiently long, if you compensate for the loss in the pendulum mechanism.

Consider illustrative examples of MN, in charge of the charge at the same time, kinetic and potential energy. They demonstrate the principal possibilities of joint practical use of both types of accumulated mechanical energy. In fig. 4.1, but The cargo is shown M, Rotating around the center ABOUT On an absolutely rigid string length / deflected from the vertical position to the corner of the CP. Line speed V. corresponds to the rotational motion of m around the circle of the radius G. Potential energy of cargo WN.\u003d GMH due to his rise to height H. As a result of deviation. The kinetic energy of the cargo is 1fk \u003d 0.5 MV2 . The force f \u003d f "+ Fr. Its inertial component is equal to FK \u003d MV LR\u003e Gravitational value components F T. \u003d GM.. Since f "/ FR \u003d R2 / RG \u003d TG (D, postolo WN./ WK. \u003d 2h./ Rtg.^>. If you are passing ^! What a \u003d / (L - COSCP) and R \u003d / SINCP, then / g / g \u003d (1 - COSCP) / SIN. In this way, W."L. LFK \u003d 2COSCP / (L + COS (P), and in the case of CP-\u003e 0 We obtain WN / WK-\u003e 1. Therefore, at small CPs, the stored energy FV \u003d JVK + WN can be distributed to equal parts (WN wn can be increased If we secure the cargo on the elastic suspension (rod or string).

Another example of joint accumulation W.„ and WK. serves rotating fine-concrete flywheel (Fig. 4.1, b), which has elasticity (rigidity) N. The tension in the rim ^ p \u003d nai is proportional to the elastic elongation A / \u003d 2l (Mr.0) caused by inertial forces AFR. \u003d AMV2 / g, distributed Nome On the circumference of the rim by the radius of the equilibrium of the rim element weighing 2 dm \u003d 2 (l // 2l;) d (p determined by the 2A / V \u003d \u200b\u200b2A / 7 ratio (() SINACP ^ AI ^ ACP, where 0,5 MV2 \u003d 2K.2 (R. - R.0 ) N.. Consequently, the kinetic energy rim LVK. \u003d 2N.2 (R. - R.0 ) N.. Since stored potential energy)