Вариант 1
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Turbine
device
A
steam or gas turbine is a heat engine that converts the potential energy of a
gas or steam into Ek, and Ek into mechanical energy from the rotation of the
shaft.
Spring
turbine classification
Turbines
are classified according to the following characteristics: 1. By the number of
stages;-
one-stage;-
two-stage;2.the
movement of the steam flow:-
axial turbines;-
radial, in which steam flows in a plane perpendicular to the axis of rotation;3.
By the number of bodies (cylinders):-
one-family building;-
double body;-
multi-hull;4.
By steam distribution:-
choke - one or more unused valvesdelivered
in parallel to all nozzles;-
nozzle - here the steam consists of several common nozzlesgoes
to the nozzle;-
bypass - unused steam to the first stage injectorsand
skip other steps to the next stepsreaches
through;5.
By the principle of steam operation:-
active turbines;-
jet turbines;6.
By the nature of the thermal process:-
condensing turbines with a recuperative intake;-
condensing turbines with one or two regulators;-
back pressure turbines;7.According
to the parameters of unused steam:-
medium pressure turbines, P0 = 34.3 bar, t = 4350C; 0-
high pressure turbines, P0 = 88 bar, t = 535 C;-
high pressure turbines, P0 = 127.5 bar, t = 5650C;-
turbines operating under pressure exceeding critical parameters,P0
= 235.5 bar, t = 5600C, steam intermediate heating t = 5650C;
Turbine
marking
K
- 800 - 240;
The
first letter K is the type of turbine, depending on the nature of the thermal
process (condensing turbines with regeneration);
T
- condensing turbines with steam heating regulators;
PT
- condensing turbine with double regulator, production and heating;
R,
PR - turbines with back pressure and capacity regulators;
The
second character (800 MW) is the rated power of the turbine, MW. Third
character (240 bar) - superheated steam pressure
Questions
1) How many stages of turbines are divided?
2) How many steam are divided on the principle of
operation and what are they called?
3) What is the labeling of turbines?
4) What housings are divided by the number of housings
(cylinders)?
5) What are the types of thermal processes?
6) How to define condensing turbines with steam heating
regulator?
When calculating pressure pipelines, the main task is either to determine the throughput (flow rate), or the pressure loss in a particular section, as well as along the entire length, or the diameter of the pipeline at a given flow rate and pressure loss.
In practice, pipelines are divided into short and long. The first includes all pipelines in which the local head losses exceed 5 ... 10% of the head losses along the length. When calculating such pipelines, pressure losses in local resistances must be taken into account. These include, for example, volumetric transmission oil lines.
The second includes pipelines in which local losses are less than 5 ... 10% of head losses along the length. They are calculated without taking into account local losses. Such pipelines include, for example, main water pipelines, oil pipelines.
Considering the hydraulic scheme of long pipelines, they can also be divided into simple and complex. Simple pipelines are called series-connected pipelines of one or different cross-sections that do not have any branches. Complex piping refers to pipe systems with one or more branches, parallel branches, etc. The so-called ring pipelines are also complex.
6.1. Simple pipeline of constant cross-section
The liquid moves through the pipeline due to the fact that its energy at the beginning of the pipeline is greater than at the end. This difference in energy levels can be created in several ways: by pump operation, difference in liquid levels, gas pressure.
Consider a simple pipeline of constant cross-section, which is located arbitrarily in space (Fig. 6.1), has a total length l and diameter d, and also contains a number of local resistances (valve, filter and check valve). In the initial section of the pipeline 1-1, the geometric height is equal to z1 and the excess pressure P1, and in the final section 2-2, respectively, z2 and P2. Due to the constancy of the pipe diameter, the flow velocity in these sections is the same and equal to ν.
Figure: 6.1. Simple pipeline diagram
Let us write the Bernoulli equation for sections 1-1 and 2-2. Since the velocity in both sections is the same and α1 = α2, the velocity head can be ignored. Thus we get
or
The piezometric height on the left-hand side of the equation will be called the required head Нпр. If this piezometric height is specified, then it is called the available head Hsp. This head consists of the geometric height Hpot, to which the liquid rises, the piezometric height at the end of the pipeline and the sum of all head losses in the pipeline.
Let's call the sum of the first two terms a static head, which we represent as some equivalent geometric height
and the last term Σh - as a power function of the flow rate
Σh = KQm
then
Hпотр = Hст + KQm
where K is a quantity called pipeline resistance;
Q - liquid flow rate; m is the exponent, which has different meanings depending on the flow regime.
For a laminar flow, when local resistances are replaced by equivalent lengths, the resistance of the pipeline is
where lcalc = l + leq.
The numerical values of the equivalent lengths leq for various local resistances are usually found empirically.
For a turbulent flow, using the Weisbach-Darcy formula and expressing the velocity in terms of the flow rate, we obtain
Using these formulas, you can build a curve of the required head depending on the flow rate. The greater the flow rate Q, which must be provided in the pipeline, the more required the required head Нpr. In a laminar flow, this curve is depicted by a straight line (Figure 6.2, a), in a turbulent flow, by a parabola with anwith an exponent equal to two (Figure 6.2, b). .
Figure 6.2. Dependences of the required heads on the liquid flow rate in the pipeline
The slope of the curves of the required pressure depends on the resistance of the pipeline K and increases with an increase in the length of the pipeline and a decrease in the diameter, as well as with an increase in local hydraulic resistance.
The value of the static head Нst is positive when the liquid moves upward or into a cavity with increased pressure, and negative when the liquid is lowered or moves into a cavity with a reduced pressure. The point of intersection of the required pressure curve with the abscissa axis (point A) determines the flow rate when the fluid moves by gravity. The required head in this case is zero.
Sometimes, instead of curves of the required pressure, it is more convenient to use the characteristics of the pipeline. The characteristic of the pipeline is the dependence of the total head loss (or pressure) in the pipeline on the flow rate:
Σh = f(q)
6.2. Simple piping connections
Figure: 6.3. Series connection of pipelines
When liquid is supplied through such a composite pipeline from point M to point N, the flow rate of liquid Q in all series-connected pipes 1, 2 and 3 will be the same, and the total pressure loss between points M and N is equal to the sum of the pressure losses in all series-connected pipes. Thus, for a serial connection, we have the following basic equations:
Q1 = Q2 = Q3 = QΣhM-N = Σh1 + Σh2 + Σh3
These equations determine the rules for constructing the characteristics of a series connection of pipes (Figure 6.3, b). If the characteristics of each pipeline are known, then the characteristics of the entire series M-N connection can be plotted from them. To do this, add the ordinates of all three curves.
Parallel connection. Such a connection is shown in Fig. 6.4, a. Lines 1, 2 and 3 are horizontal.
Figure: 6.4. Parallel piping connection
We denote the total heads at points M and N, respectively, HM and HN, the flow rate in the main line (i.e., before branching and after merging) - through Q, and in parallel pipelines through Q1, Q2 and Q3; total losses in these pipelines through Σ1, Σ2 and Σ3.
It is obvious that the flow rate of the liquid in the main line
Q = Q1 = Q2 = Q3
Выразим потери напора в каждом из трубопроводов через полные напоры в точках М и N :
Σh1 = HM - HN; Σh2 = HM - HN; Σh3 = HM - HN
Hence we conclude that
Σh1 = Σh2 = Σh3
those. head losses in parallel pipelines are equal to each other. They can be expressed in general terms through the corresponding costs as follows
Σh1 = K1Q1m; Σh2 = K2Q2m; Σh3 = K3Q3m
where K and m - are determined depending on the flow regime.
The following rule follows from the last two equations: to construct the characteristics of the parallel connection of several pipelines, one should add the abscissas (flow rates) of the characteristics of these pipelines with the same ordinates (Σ h). An example of such a construction is given in Fig. 6.3, b.
Branched connection. A branched connection is a set of several simple pipelines that have one common section - the place where the pipes branch (or close).
Figure: 6.5. Branched pipeline
Let the main pipeline has a branch in section M-M, from which, for example, three pipes 1, 2 and 3 of different diameters depart, containing different local resistances (Fig. 6.5, a). The geometric heights z1, z2 and z3 of the end sections and the pressures P1, P2 and P3 in them will also be different.
As with parallel pipelines, the total flow rate in the main pipeline will be equal to the sum of the flow rates in each pipeline:
Q = Q1 = Q2 = Q3
Writing down the Bernoulli equation for the section M-M and the final section, for example, the first pipeline, we obtain (neglecting the difference in velocity heights)
Denoting the sum of the first two terms by Hst and expressing the third term in terms of the flow rate (as was done in Section 6.1), we obtain
HM = Hст 1 + KQ1m
Similarly, for the other two pipelines, you can write
HM = Hст 2 + KQ2mHM = Hст 3 + KQ3m
Таким образом, получаем систему четырех уравнений с четырьмя неизвестными: Q1, Q2 и Q3 и HM.
Writing down the Bernoulli equation for the section M-M and the final section, for example, the first pipeline, we obtain (neglecting the difference in velocity heights)
Denoting the sum of the first two terms by Hst and expressing the third term in terms of the flow rate (as was done in Section 6.1), we obtain
Similarly, for the other two pipelines, you can write
Thus, we obtain a system of four equations with four unknowns: Q1, Q2 and Q3 and HM.
The construction of the curve of the required head for a branched pipeline is performed by adding the curves of the required heads for the branches according to the rule of adding the characteristics of parallel pipelines (Fig. 6.5, b) - by adding the abscissas (Q) with the same ordinates (HM). The curves for the required head for the branches are marked with numbers 1, 2 and 3, and the total curve for the required head for the entire branch is marked with the letters ABCD. The graph shows that the condition for supplying fluid to all branches is the inequality HM> Hst1.
Test
6.1. What is a short pipeline?
a) a pipeline in which linear head losses do not exceed 5 ... 10% of local head losses;
b) a pipeline in which local head losses exceed 5 ... 10% of head losses along the length;
c) pipeline, the length of which does not exceed 100d;
d) a pipeline of constant cross-section without local resistance.
6.2. What is a long pipeline?
a) pipeline, the length of which exceeds 100d;
b) a pipeline in which linear head losses do not exceed 5 ... 10% of local head losses;
c) a pipeline in which local head losses are less than 5 ... 10% of head losses along the length;
d) a pipeline of constant cross-section with local resistances.
6.3. What types are long pipelines divided into?
a) on parallel and serial;
b) simple and complex;
c) straight and curved;
d) into branched and compound.
6.4. What are the simple pipelines?
a) series-connected pipelines of one or different sections without branches;
b) parallel-connected pipelines of the same section;
c) pipelines that do not contain local resistance;
d) series-connected pipelines containing no more than one branch.
6.5. What pipelines are called complex?
a) series pipelines, in which the bulk of energy losses are local resistances;
b) parallel connected pipelines of different sections;
c) pipelines with local resistance;
d) pipelines forming a pipe system with one or more branches.
6.6. What is a pipeline characteristic?
a) dependence of the pressure at the end of the pipeline on the fluid flow rate;
b) the dependence of the total head loss on pressure;
c) the dependence of the total head loss on the flow rate;
d) the dependence of the resistance of the pipeline on its length.
6.7. Static head Hst is:
a) the difference between the geometric height Δz and the piezometric height in the final section of the pipeline;
b) the sum of the geometric height Δz and the piezometric height in the final section of the pipeline;
c) the sum of piezometric heights in the initial and final sections of the pipeline;
d) the difference in speed heights between the final and initial sections.
6.8. If we write the Bernoulli equation for a simple pipeline, then the piezometric height on the left side of the equation is called
a) the required pressure;
b) available pressure;
c) full pressure;
d) the initial pressure.
6.9. The required head curve reflects
a) dependence of energy losses on pressure in the pipeline;
b) the dependence of the resistance of the pipeline on its throughput;
c) the dependence of the required pressure on the flow;
d) the dependence of the driving mode on the flow rate.
6.10. The required pressure is
a) the head obtained in the final section of the pipeline;
b) the head that must be communicated to the system to achieve the required pressure and flow rate in the final section;
c) the pressure spent on overcoming the local resistance of the pipeline;
d) the head reported to the system.
Вариант
3
Task 1. Find a pair
https://learningapps.org/display?v=pt314mxin20
Task 2. Test
4.1. Hydraulic resistance is
a) the resistance of the fluid to a change in the shape of its channel;
b) resistance that prevents the free passage of liquid;
c) pipeline resistance, which is accompanied by fluid energy losses;
d) resistance at which the speed of fluid movement through the pipeline decreases.
4.2. What is the source of energy loss in a moving fluid?
a) density;
b) viscosity;
c) fluid consumption;
d) changing the direction of movement.
4.3. What types are hydraulic resistances divided into?
a) linear and quadratic;
b) local and non-linear;
c) nonlinear and linear;
d) local and linear.
4.4. Does the mode of fluid movement affect the hydraulic resistance
a) affects;
b) does not affect;
c) affects only under certain conditions;
d) in the presence of local hydraulic resistance.
4.5. Laminar flow regime is
a) a mode in which liquid particles move haphazardly only at the walls of the pipeline;
b) a mode in which liquid particles in the pipeline move haphazardly;
c) the regime in which the liquid retains a certain structure of its particles;
d) a mode in which liquid particles move layer by layer only at the walls of the pipeline.
4.6. Turbulent fluid flow is
a) the mode in which the particles of the liquid retain a certain order (move in layers);
b) a mode in which liquid particles move in the pipeline haphazardly;
c) the mode in which the particles of the liquid move both layer by layer and unsystematically;
d) a mode in which liquid particles move layer by layer only in the center of the pipeline.
4.7. Under what mode of fluid movement in the pipeline does the pulsation of velocities and pressures occur?
a) in the absence of fluid movement;
b) when calm;
c) with turbulent;
d) with laminar.
4.8. At what mode of fluid movement in the pipeline is there a pulsation of velocities and pressures in the pipeline?
a) with laminar;
b) at high-speed;
c) with turbulent;
d) in the absence of fluid movement.
4.9. With laminar fluid flow in the pipeline, the following phenomena are observed
a) pulsation of speeds and pressures;
b) absence of pulsation of speeds and pressures;
c) velocity pulsation and no pressure pulsation;
d) pressure pulsation and absence of velocity pulsations.
4.10. During turbulent movement of liquid in a pipeline, the following phenomena are observed
a) pulsation of speeds and pressures;
b) absence of pulsation of speeds and pressures;
c) velocity pulsation and no pressure pulsation;
d) pressure pulsation and absence of velocity pulsations.
