Hydraulic drive practical exercises laboratory work. Laboratory work in hydraulics
Laboratory work on hydraulics - section Education, Ministry of Agriculture of the Russian Federation...
Department of Environmental Engineering,
construction and hydraulics
GPD.F.03 Hydraulics
Opd.f.02.05 hydraulics
GPD.F.07.01 Hydraulics
GPD.F.08.03 HYDRAULICS
GPD.F.07 Hydraulics and hydraulic machines
GPD.R.03 APPLIED HYDROMECHANICS
GPD.F.08 HYDROGAS DYNAMICS
Laboratory work in hydraulics
Guidelines
Ufa 2010Lab #1
MEASUREMENT OF MAIN HYDRAULIC
LIQUID CHARACTERISTICS
General information
In laboratory practice and production conditions, the following parameters are measured: level, pressure and fluid flow.
Level measurement. The simplest instrument is a glass tube connected at the lower end to an open reservoir in which the level is determined. In a tube and a tank, as in communicating vessels, the position of the liquid level will be the same.
Float level gauges are widely used (in fuel tanks, group automatic drinking bowls, various technological tanks). The working body of the device - the float - follows the measurement of the liquid level, and the readings on the scale change accordingly. The mechanical movement of the float (primary sensor) up and down can be converted into an electrical signal by means of a rheostat or an inductor and recorded by a secondary device. In this case, remote transmission of readings is possible.
Of the instruments based on indirect methods for determining the desired value, the capacitive level gauge is of the greatest interest. It uses a metal electrode as a sensor, covered with a thin layer of plastic insulation. The electrode-liquid-reservoir system, when the current is connected, forms a capacitor, the capacitance of which depends on the level of the liquid. The disadvantages of capacitive sensors include a significant dependence of readings on the state of the electrode insulation.
Pressure measurement . According to their purpose, devices for measuring atmospheric pressure (barometers), excess pressure (pressure gauges - at p ex > 0 and vacuum gauges - at p ex<0), разности давлений в двух точках (дифференциальные манометры).
According to the principle of operation, liquid and spring devices are distinguished.
In liquid devices the measured pressure is balanced by a column of liquid, the height of which serves as a measure of pressure. The piezometer is distinguished by its simple design, which is a vertical glass tube connected by its lower end to a place
pressure measurements (Fig. 1.1a).
Figure 1.1 Liquid instruments:
a) a piezometer;
b) U - shaped tube
The pressure value at the connection point is determined by the height h of the liquid rise in the piezometer: р=rgh, where r is the density of the liquid.
Piezometers are convenient for measuring small overpressures - about 0.1-0.2 at. Functionally, the possibilities are wider for two-pipe U-shaped devices (Fig. 1.1b), which are used as pressure gauges, vacuum gauges and differential pressure gauges. The glass tube of the instrument can be filled with a heavier liquid (such as mercury). Liquid instruments have a relatively high accuracy, they are used for technical measurements, as well as calibration and verification of other types of instruments.
In spring devices the measured pressure is perceived by an elastic element (tubular spring, membrane, bellows), the deformation of which serves as a measure of pressure. Widespread devices with tubular springs. In such a device, the lower open end of the oval tube (Fig. 1.2a) is rigidly fixed in the housing, and the upper (closed) end is free in space.
Under the action of the pressure of the medium, the tube tends to unbend (if p > p at) or, conversely, bend even more (if p<р ат). В показывающих приборах упругий элемент, перемещаясь, воздействует через передаточный механизм на стрелку и по шкале ведется отсчет измеряемого давления. В приборах с дистанционной передачей показаний механическое перемещение упругого элемента преобразуется в электрический (или пневматический) сигнал, который регистрируется вторичным прибором.
Figure 1.2 Spring devices:
a) with a tubular spring;
b) bellows; c) membrane
According to the accuracy class, devices with tubular single-coil springs are divided into:
Technical (for ordinary measurements - accuracy class 1.5; 2.5; 4.0);
Exemplary (for accurate measurements - accuracy class 0.16; 0.25; 0.4; 0.6; 1.0);
Control (for checking technical priors - accuracy class 0.5 and 1.0).
The accuracy class is indicated on the instrument dial; it characterizes the marginal error of the device in % of the maximum value of the scale under normal conditions (t=20°C, p=760 mm Hg).
Flow measurement. The simplest and most accurate method for determining fluid flow is volumetric using a measuring vessel. The measurement is reduced to registering the time T of filling a vessel with a known volume W. Then the flow rate is Q=W/T. In production conditions, various volumetric and high-speed meters (vane and turbine) are used as meters for the amount of liquid W. The method allows to determine the time-averaged values of Q.
a) b) in)
Figure 2.5 Liquid meters:
a− volumetric with oval gears; b− rotational;
in− high-speed with a winged turntable
To measure instantaneous flow rates in pressure pipelines, various types of flow meters are used (Fig. 1.4). Convenient for
measurements flowmeters with narrowing devices. The principle of operation of the device is based on the creation in the flow with the help of a narrowing device (for example, a diaphragm) of a difference in static pressure and its measurement with a differential pressure gauge (Fig. 1.4b). The liquid flow rate is determined by the calibration curve Q = f(h) or by the formula:
Q = mАÖ2gh, (2.2)
where m is the flow coefficient of the narrowing device;
h is the reading of the differential pressure gauge;
A is the constant of the flow meter;
where D is the diameter of the pipeline;
d is the diameter of the opening of the narrowing device.
Figure 1.4 Liquid meters:
a) constant differential pressure (rotameter);
b) variable pressure drop
(with a narrowing device - a diaphragm);
c) induction
Objective
Familiarize yourself with the device, principle of operation and operation of devices for measuring the level, pressure and flow of liquid; learn the method of calibrating flowmeters.
Work order
1.3.1 Using educational literature, guidelines, posters and full-scale samples of instruments, familiarize yourself with the methods for measuring level, pressure and ... water using a measuring tank. Change Time Control...Lab #2
Experimental study of the equation
Bernoulli
General information
For a steady, smoothly varying motion of a real fluid, the Bernoulli equation has the form:
z 1 + 
, (2.1)
where z 1 , z 2 are the heights of the position of the centers of gravity of sections 1 and 2;
р 1 , р 2 - pressure in sections;
u 1 , u 2 - average flow rates in sections;
a 1 ,a 2 - coefficients of kinetic energy.
From an energetic point of view:
z is the specific potential energy of the position (geometric head);
Specific potential energy of pressure (piezometric head);
Specific kinetic energy (velocity head).
The sum z ++ = H expresses the total specific energy of the fluid (total head).
From equation (2.1) it follows that when a real fluid moves, the total head decreases downstream (H 2<Н 1). Величина h 1-2 = Н 1 - Н 2 характеризует потери напора на преодоление гидравлических сопротивлений.
A decrease in the total head in a certain way is also reflected in its components - piezometric and velocity pressures. The nature of pressure changes in a particular hydraulic system is of practical interest and can be visually studied empirically.
Objective
Experimentally confirm the validity of the equation
Bernoulli: to establish the nature of the change in total, piezometric and velocity pressures during the movement of fluid in the pipeline under study.
Experience methodology
Laboratory work can be performed on a specialized installation and a universal stand.
In the first case, piezometric and total heads are measured in the control sections of the experimental section with a steady flow of fluid, in the second case, only piezometric ones are measured, with subsequent calculation of the total heads.
Based on the experimental data, a head graph is constructed and an analysis is made of the change along the flow of the components of the Bernoulli equation.
Description of the pilot plant
A schematic diagram of a specialized installation for studying the Bernoulli equation is shown in Figure 2.1. It includes a pressure tank, ... measuring tank. The experimental section is of variable cross section (smooth ... The universal stand (Figure 2.2) has the same design scheme. Its distinguishing feature is an oblique ...Work procedure
a) the pressure tank is filled with water to a constant level; b) by briefly opening the valve of the experimental pipeline of the installation ... c) the liquid flow rate is set in the pipeline, ensuring the visibility of observations, and for a given mode ...Processing of experimental data
When working on a specialized installation, according to the measurement data, the following is calculated: - average water consumption during the experiment Q = W/T, (2.2)An analysis of the pressure graph is given. A conclusion is given on the nature of the change along the flow of total, piezometric and velocity pressures with appropriate explanations.
Test questions
1. What is the physical meaning of the Bernoulli equation?
2. Explain the concepts of geometric, piezometric and total pressure?
4. What do pressure and piezometric lines show?
5. What determines the nature of the change along the flow of total, piezometric and velocity pressures?
6. Due to what energy of a moving fluid are hydraulic resistances overcome?
Lab #3
Studying the modes of movement of liquids
General information
When a fluid moves in a pipeline (channel), two flow regimes are possible: laminar and turbulent.
The laminar regime is characterized by layered, ordered motion, in which individual layers of fluid move relative to each other without mixing with each other. A jet of paint introduced into a laminar flow of water is not washed away by the environment and looks like a stretched thread.
The turbulent regime is characterized by disordered, chaotic motion, when fluid particles move along complex, constantly changing trajectories. The presence of transverse velocity components in a turbulent flow causes intense mixing of the liquid. In this case, the colored stream cannot exist independently and disintegrates in the form of eddies over the entire cross section of the pipe.
Experiments have established that the mode of motion depends on the average speed u, pipe diameter d, fluid density r and its absolute viscosity m. To characterize the regime, it is customary to use a set of these quantities, compiled in a certain way into a dimensionless complex - the Reynolds number
where n = m/r is the kinematic viscosity coefficient.
The Reynolds number corresponding to the transition from laminar to turbulent flow is called critical and is denoted by Re cr. It should be emphasized that, due to the instability of the fluid flow at the boundary of the laminar and turbulent regimes, the value of Re cr is not strictly defined. For cylindrical pipes during the movement of water, taking into account the conditions of the flow inlet, the roughness of the walls, the presence of initial perturbations Re kr = 580-2000. In calculations, Re kr »2300 is usually taken.
At Re
In most technical applications associated with the movement of low-viscosity media (water, air, gas, steam), a turbulent regime is implemented - water supply, ventilation, gas supply, heat supply systems. The laminar regime takes place in film heat exchangers (when a condensate film drains under the influence of gravity), when water is filtered in the pores of the soil, when viscous liquids move through pipelines.
Objective
Visual observations establish the nature of the movement of the fluid under various modes; to master the methodology for calculating the pressure regime; for the pilot plant, determine the critical Reynolds number.
Description of the pilot plant
The laboratory installation (Figure 3.1) includes a pressure tank, a pipeline (with a transparent section for visual observation), a vessel with a dye, a measuring tank.
The vessel with the dye is fixed by means of a tripod on the wall of the pressure tank and is equipped with a tube for supplying the dye to the water flow moving in the pipeline. The flow rate is set by the control valve and is determined using a measuring tank.
Work order
a) the pressure tank is filled with water (up to the level of the drain pipe, and the vessel is filled with dye); b) by opening the control valve in the pipeline, the flow rate is set, with ... Observations of the nature of the movement of the liquid are carried out by introducing a dye into the flow.Processing of experimental data
- according to the water temperature t (in °С) determine the kinematic coefficient of viscosity ... n = ; (3.2)Analysis of results. Work Conclusions
An analysis of visual observations of the nature of fluid motion in various modes is given. The value of the critical Reynolds number for the pilot plant and the results of the calculated determination of the regime are noted.
test questions
1. What fluid flow regimes do you know?
2. Explain the method of experimental determination of the flow regime.
3. What is the fundamental difference between a turbulent regime and a laminar one?
4. How is the flow regime determined by calculation?
5. Define the critical Reynolds number.
6. Give examples of technical systems (devices) in which: a) laminar flow; b) turbulent regime.
Lab #4
Determination of the coefficient of hydraulic
Friction
General information
A fluid flow uniformly moving in a pipe (channel) loses part of its energy due to friction on the pipe surface, as well as internal friction in the fluid itself. These losses are called head loss along the length of the flow or friction head loss.
In accordance with the Bernoulli equation, the head loss along the length of a horizontal pipe of constant diameter
h dl = , (4.1)
where are the piezometric heads in the sections under consideration.
Experiments show that the pressure loss along the length is proportional to the dimensionless coefficient l, depends on the length l and diameter d of the pipeline, the average speed u. This dependence is established by the well-known Darcy-Weisbach formula
h dl = . (4.2)
The coefficient l characterizing the friction resistance generally depends on the Reynolds number Re and the relative roughness of the pipe walls D/d (here D is the absolute size of the roughness projections). However, the effect of these quantities on the coefficient l in laminar and turbulent regimes is different.
In the laminar regime, the roughness does not affect the friction resistance. In this case, l = f(Re) and the calculation is performed according to the formula
l = 64/Re. (4.3)
In the turbulent regime, the influence of Re and D/d is determined by the value of the Reynolds number. For relatively small Re, as well as for the laminar regime, the coefficient l is a function of only the Reynolds number Re (the region of hydraulically smooth pipes). For the calculation here, the formulas of G. Blasius are applicable for Re £ 10 5:
l = 0.316/Re 0.25 , (4.4)
and formula g.K. Konakov at Re £ 3 × 10 6:
In the range of moderate Reynolds numbers l = f(Re,) and good agreement with experiment is given by the formula of A.D. Altshulya:
For sufficiently large values of Re (developed turbulent flow), the effect of viscous friction is insignificant and the coefficient l = f(D/d) is the so-called region of completely rough pipes. In this case, the calculation can be performed according to the formula of B.L. Shifrinson:
The above and other well-known empirical formulas for determining the coefficient of hydraulic friction are obtained by processing the experimental graphs. Comparing the results of calculating l using these formulas with experimental values, one can evaluate the reliability of the experiments.
Objective
To master the method of experimental determination of the coefficient of hydraulic friction; for the conditions of the experiment, establish the dependence of the coefficient of hydraulic friction on the fluid flow regime and compare the results obtained with calculations using empirical formulas.
Experience methodology
The coefficient of hydraulic friction is determined indirectly using the Darcy-Weisbach formula (4.2). At the same time, directly from experience, the head loss h dl is found from the difference in piezometric heads at the beginning and end of the investigated section of the pipeline, and the speed of movement u from the flow rate Q.
The dependence l = f(Re) is established by carrying out experiments for various modes of fluid motion and constructing an appropriate graph.
Description of the pilot plant
The laboratory setup (Figure 4.1) includes a pressure tank, an experimental pipeline and a measuring tank.
Experimental pipeline - horizontal, constant section (l = 1.2 m, d = 25 mm). There are two static pressure nipples in the section for determining pressure losses, which are connected to piezometers with the help of rubber hoses. A valve for regulating the water flow is mounted behind the measuring section.
Work procedure
a) the pressure tank is filled with water to a constant level; b) by briefly opening the valve, the installation is put into action for ... c) in the pipeline, various flow rates of the liquid are set in the range from minimum to maximum (only 5-6 ...Processing of experimental data
4.6.1 According to the measurement data, calculate: - flow rate Q, average speed u, kinematic viscosity coefficient n, Reynolds number Re (see laboratory work ...Analysis of results. Conclusion on work
test questionsLab #5
Determination of the coefficient of local
resistance
General information
In real hydraulic systems, a moving fluid loses mechanical energy in straight sections of pipes, as well as in fittings and fittings, and other local resistances. Energy losses to overcome local resistances (the so-called local pressure losses) are partly due to friction, but to a greater extent, the deformation of the flow, its separation from the walls, and the occurrence of intense vortex flows.
Local pressure losses are determined by calculation according to the Weisbach formula:
h m = z m (u 2 /2g), (5.1)
where z m is the coefficient of local resistance; showing how much of the velocity head is spent to overcome the resistance.
The value of z m in the general case depends on the type of local resistance and the flow regime. The experimental values of the coefficient for the quadratic region of the turbulent regime are given in the reference tables.
Objective
To master the method of experimental determination of the coefficient of local resistance; determine empirically the coefficient z m for the investigated local resistance, establish its dependence on the Reynolds number and compare the data obtained with the tabular ones.
Experience methodology
The coefficient of local resistance is determined by an indirect method using dependence (5.1). At the same time, local head losses hm are found from ...Description of the pilot plant
The installation for the experimental determination of the coefficient of local resistance (Figure 5.1) includes a pressure tank, a pipeline with the investigated local resistance and a measuring tank. Static pressure nipples are installed on the pipeline in front of the local resistance and behind it, which are connected to piezometers with the help of rubber hoses. There is a valve to control the flow of water.
Work procedure
a) the pressure tank is filled with water to a constant level; b) check the absence of air in the piezometers (the water levels in them when closed ... c) in the pipeline set various water flow rates in the range from minimum to maximum (only 5-6 ...Processing of experimental data
According to the measurement data, the following is calculated: - average flow rate Q = W / T and average flow rate u = Q / w (where w is the cross-sectional area ...Analysis of results
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The workshop presents descriptions of sixteen laboratory works in the discipline "Hydraulics", each of which includes a brief theory, guidelines for implementation and control questions. Reference material is included in the appendix. The glossary of terms consists of the concepts used and their definitions.
For students studying in the specialty 19060365 "Service of transport and technological machines and equipment (Motor transport)" and 19050062 "Operation of vehicles".
FOREWORD
The study of hydraulics by students of motor transport specialties provides for a certain amount of laboratory work. This collection contains descriptions of laboratory work and guidelines for their implementation.
The purpose of the laboratory workshop is to consolidate the material of the lecture course by students, develop the skills of independent work with devices during experiments, teach methods for determining the parameters of a moving fluid and performing calculations, as well as the ability to draw conclusions based on the results obtained.
Each job has 2 hours to complete. Since, when studying the discipline, part of the sections was transferred to students for independent study, the methodological instructions for each work briefly outline the theoretical material.
INTRODUCTION
Hydraulics is a technical science that studies the mechanical properties, laws of equilibrium and movement of fluids. The term "liquid" covers both droplets, practically incompressible liquids, and gaseous or compressible media.
The theoretical approach is based on the Euler continuity principle, according to which a liquid is considered not as a collection of its discrete material particles, but as a continuum, i.e. a continuous or continuous material medium that allows unlimited divisibility of its particles. Such a view of the structure of a substance is admissible if the dimensions of the volumes in which the phenomenon under study is considered are large enough compared to the dimensions of the molecules and their mean free path.
In hydraulics, experimental methods of research are widely used, which makes it possible to correct theoretical conclusions that deviate from real phenomena.
The main sections of practical hydraulics are: flow through pipes, outflow of fluid from holes and through nozzles, interaction of flow with obstacles, movement in porous media (filtration), and hydraulic machines.
LABORATORY WORKS
Topic 1. STUDY OF PHYSICAL PROPERTIES
LIQUIDS
Objective: master methods for measuring density, thermal expansion, viscosity and surface tension of liquids.
General information
A substance that is in a liquid state of aggregation (liquid phase) is called a liquid. The liquid state of aggregation is intermediate between the solid state, which is characterized by the preservation of its volume, the formation of a surface, the possession of a certain tensile strength, and the gaseous state, in which the substance takes the form of a vessel where it is enclosed. At the same time, the liquid has only its inherent property - fluidity, i.e. the ability to plastically or viscously deform under the action of any (including arbitrarily small) stresses. Fluidity is characterized by the value, inverse viscosity.
The main characteristics of a liquid are density, compressibility, thermal expansion, viscosity, and surface tension.
Density of a homogeneous substance is called the mass ratio m liquid to its volume W:
ρ = m/ W.
Compressibility- the property of a liquid to reduce volume under the action of uniform pressure. She's rated compressibility factor p, showing the relative decrease in the volume of liquid Δ W/W with increasing pressure Δ ρ per unit:
βρ = (Δ W/W)/Δ ρ .
thermal expansion- the property of a liquid to change volume when heated - is characterized, at constant pressure, coefficient of volumetric thermal expansion T, which is equal to the relative volume increment Δ W/W in case of temperature change T one degree:
β T =(Δ W/W)/Δ T.
As a rule, when heated, the volume of the liquid increases.
Viscosity(internal friction) - the property of fluid bodies to resist the movement of one of their parts relative to another. She is being evaluated dynamic viscosity coefficient , which has the dimension of Pa∙s. It characterizes the resistance of a liquid (gas) to the displacement of its layers.
Along with dynamic viscosity, calculations often use kinematic viscosity coefficientν, which is determined by the formula
ν = μ /ρ
and measure m 2 / s or stokes (1 St = 1 cm 2 / s).
The coefficients of dynamic and kinematic viscosity are determined by the type of fluid, do not depend on the flow velocity, and decrease significantly with increasing temperature.
Surface tension- thermodynamic characteristic of the interface between two phases, determined by the work of reversible isothermal formation of a unit area of this surface. In the case of a liquid interface, surface tension is considered as a force acting per unit length of the surface contour and tending to reduce the surface to a minimum for given phase volumes. Characterized surface tension , J / m 2 \u003d N / m. The work of forming a new surface is spent on overcoming the forces of intermolecular cohesion (cohesion) during the transition of substance molecules from the bulk of the body to the surface layer. The resultant of intermolecular forces in the surface layer is not equal to zero and is directed inside the phase in which the adhesion forces are greater. Thus, surface tension is a measure of the uncompensated intermolecular forces in the surface (interfacial) layer, or the excess of free energy in the surface layer compared to the free energy in the volumes of the phases.
The values of density, compressibility coefficients, volumetric thermal expansion, kinematic viscosity and surface tension at a temperature of 20°C are given in Table. Clause 3.1 of the application.
Description of the device to study
physical properties of the liquid
The device for studying the physical properties of a liquid contains 5 devices made in one transparent case (Fig. 1), on which the parameters necessary for processing the experimental data are indicated. Devices 3-5 begin to operate after turning the device 180 about. Thermometer 1 indicates the ambient temperature and therefore the temperature of the liquids in all appliances.
Rice. 1. Diagram of the device:
1 - thermometer; 2 - hydrometer; 3 – Stokes viscometer;
4 – capillary viscometer; 5 - stalagmometer
1.1. Coefficient definition
thermal expansion of the liquid
Thermometer 1 (Fig. 1) has a glass container with a capillary filled with thermometric liquid and a scale. The principle of its operation is based on the thermal expansion of liquids. A change in the ambient temperature leads to a corresponding change in the volume of the thermometric liquid and its level in the capillary. The level indicates the temperature value on the scale.
The coefficient of thermal expansion of a thermometric fluid is determined based on a thought experiment. It is assumed that the ambient temperature has increased from the lower (zero) to the upper limit value of the thermometer and the liquid level in the capillary has increased by l.
To determine the coefficient of thermal expansion, it is necessary:
2. Calculate the volume increment of the thermometric fluid
Δ W = π r 2 l,
where r is the radius of the thermometer capillary (indicated on the thermometer).
3. Taking into account the initial (at 0°С) volume of thermometric liquid W(the value is given on the thermometer) find the coefficient of thermal expansion β T = (Δ W/W)/Δ T and compare it with the reference value β T* (Table P. 3.1). Enter the values of the quantities used in the table. one.
Table 1
|
Liquid type |
r, |
W, |
Δ T, |
l, |
Δ W, |
β
T , |
β
T *
, |
Alcohol |
|
|
|
|
|
|
|
1.2. Measuring the density of a liquid with a hydrometer
Hydrometer 2 (Fig. 1) is used to determine the density of a liquid using the float method. It is a hollow cylinder with a millimeter scale and a weight at the bottom. Thanks to the load, the hydrometer floats in the liquid under study in a vertical position. The immersion depth of a hydrometer is a measure of the density of a liquid and is read from a scale along the upper edge of the liquid meniscus around the hydrometer. In conventional hydrometers, the scale is graduated in terms of density.
In the course of work, the following operations must be performed:
1. Measure the immersion depth h hydrometer on a millimeter scale on it.
2. Calculate the density of the liquid using the formula
ρ = 4m/(πd 2 h),
where m and d– mass and diameter of the hydrometer (values are given on the hydrometer).
This formula is obtained by equating the gravity of the hydrometer G = mg and buoyant (Archimedean) force F A = ρ gW, where the volume of the submerged part of the hydrometer W = hpd 2 /4.
3. Compare the experimental density value with reference value * (Table P. 3.1). The values of the quantities used are summarized in Table. 2.
table 2
Results of observations and calculations
|
Faculty of Engineering and Physics of High Technologies Department of Physical Methods in Applied Research M.V. Valdin Guidelines to the laboratory workshop on hydraulics Teaching aid Ulyanovsk UDC 532.5 (075.8) BBq 30.123 i73 Published by decision of the Academic Council of the Faculty of Engineering and Physics of High Technologies of Ulyanovsk State University Reviewers: Doctor of Technical Sciences, Professor of the Department of Oil and Gas Business and Service P.K. Germanovich Candidate of Physical and Mathematical Sciences, Associate Professor of the Department of Physical Methods in Applied Research Yu.N. Zubkov Vyaldin M.V. In 99 Guidelines for a laboratory workshop on hydraulics.- Ulyanovsk: UlGU, 2014.- 48s. The workshop on hydraulics provides for the implementation of 9 laboratory works, two of which are aimed at studying the design and principle of operation of two laboratory stands "Hydrostatics" and "Hydrodynamics", the rest cover the practical determination of hydrostatic pressure, the density of an unknown liquid, the pressure force on the horizontal and vertical walls of the vessel, hydraulic resistance along the length of the pipe and on a sudden expansion; study of fluid flow during outflow in Venturi pipes and visual observation of laminar and turbulent flow regimes of a one-dimensional fluid flow. The manual is intended for students of the Faculty of Engineering and Physics of High Technologies. Ulyanovsk State University, 2014 Vyaldin M.V., 2014 Introduction……………………………………………………………………...4 Measurements, measurement errors and presentation of experimental data………………………………………………………………………………….4 Lab #1 The study of the laboratory stand "HYDROSTATICS GS" …………………8 Lab #2 Determination of hydrostatic pressure …………………………………..11 Lab #3 Determination of the density of an unknown liquid …………………………......14 Lab #4 Determination of the fluid pressure force on flat walls ………………..17 Lab #5 The study of the laboratory stand "HYDRODYNAMICS GD" ………………21 Lab #6 Determination of head loss in a round pipe ………………………………...28 Lab #7 Determination of head loss due to sudden expansion ………………….....34 Lab #8 Experimental construction of Bernoulli diagrams ………………………..39 Lab #9 Observation of flow regimes and determination of flow parameters…. …….43 Introduction Hydraulics as a science is one of the most important in terms of the practical application of knowledge both in production and in everyday life, and a modern engineer must know the methods for studying hydraulic phenomena and diagnosing the condition of pipelines. Therefore, students should know the device of various pressure, density, viscosity, liquid flow meters, as well as the units of measurement of these quantities, both in systems of units in SI and CGS, and in non-systemic units of measurement. To calculate many of the quantities under study, it is important to be able to use Internet resources to search for the corresponding tabular data (for example, kinematic viscosity is often confused with dynamic viscosity, because they do not know the formula for the relationship between these quantities and, accordingly, do not pay attention to units of measurement and prefixes indicated in the tables). Taking readings from hydraulic instruments also presents some difficulties: for example, rotameter readings are given in divisions, and in order to convert these readings to the SI system, you must be able to use the graph of flow (in divisions) from flow (in liters / hour). When performing laboratory work, it should be remembered that some of the connecting pipes in the "Hydrostatics" stand are open, and the change in pressure (excess and vacuum pressure) should be done smoothly and taking into account the inertia of the liquid. Measurements, measurement errors and presentation of experimental data. In the laboratory of hydraulics, direct and indirect measurements are made. Measurement is understood as a comparison of the measured value with another value, taken as a unit of measurement. For direct measurements (for example, temperature, pressure, etc.), measuring instruments (thermometer, pressure gauge) are used, calibrated in the appropriate units of measurement. With indirect measurements, the desired value is determined from the results of direct measurements of other quantities that are associated with the measured value by a certain functional dependence (for example, P = P 0 +ρgh, ρ = m/V, ρ = P/gh). When measuring any quantities, three sequential operations are performed: selection, testing and installation of devices (in our case, the stands are prepared for work by a technician-engineer); observation of indications and their countdown for each mode; calculation of the desired value from the measurement results and evaluation of the error. The true value of the measured quantity cannot be determined with absolute certainty. Each measurement gives the value of a certain quantity X with some error ∆X, called the absolute error. Measurement errors are: systematic, random and misses. A systematic error is such an error that remains constant or regularly changes when repeated measurements of the same value are carried out. In any measuring device there is one or another systematic error that cannot be eliminated, but which can be taken into account. Random errors are errors that cannot be prevented. Usually they are taken into account in multiple measurements and they obey statistical laws. Misses and gross errors are excessively large errors that clearly distort the measurement result. With the laboratory measurement method, several measurements of the quantity are made and the arithmetic mean of the obtained values is calculated, in contrast to the technical method, in which a single measurement of the investigated quantity is allowed. Sources of errors can be: measuring instruments (instrumental error), observer (readout errors), environment (environmental error), measurement technique and result processing technique (mathematical processing error). The total error ∆X for direct measurements is determined after finding the random error and estimating the systematic error. In the simplest cases, ∆X (absolute error) is determined by the error of the measuring instruments. For example, for a pressure gauge, the absolute error is taken to be equal to half the price of the smallest division. The division price is determined by the ratio of the difference between the nearest digital values on the instrument scale to the number of divisions between them. To evaluate the accuracy of indirect measurements, first determine the relative error ε = ∆X/Xav., where Khsr. - the arithmetic mean of the values of the quantity, then the recording of the measurement results will be as follows: X = Xav. ± ∆Х, and ∆X is determined through the relative error ε, which is found by the differentiation rule. Table 1 (see Appendix) provides formulas for calculating the relative error of values for the most common functional dependencies. Here are some cases of calculating the relative error of indirect measurements of Y: Let the function be given by the expression Y = A + B, and the absolute measurement errors ∆A, ∆B, then Y +∆Y = (A ± ∆A) + (B ± ∆B), therefore, ∆Y = ∆A +∆B, then the relative error will be determined as follows ∆Y/Y = ∆Y/(A+B) = (∆A + ∆B)/(A + B); If Y = A * B, then ∆Y/Y = ∆A/A + ∆B/B, or ε Y = ε A + ε B . If the calculation formulas include constants, for example, the number π \u003d 3, 14 some physical constants, for example, g \u003d 9.83 m / s 2, tabular data, then they are taken with such accuracy that the number of significant digits after the decimal point they were one more than the number of significant digits in the values of the measured quantities. An example of calculating the relative error of measuring absolute pressure. Initial formula: Р = Р 0 + ρgh, so the functional dependence is similar to Y = A + B, i.e. ∆P/P = (∆P 0 +∆(ρgh))/ (P 0 + ρgh), where ∆(pgh) is calculated according to the example of the second functional dependence ∆(ρgh)/ρgh = ∆p/p + ∆g/g + ∆h/h, whence ∆(ρgh) = (εp + εh)*ρgh. Rules for calculating errors and presenting experimental data. Since the accuracy of the determined physical quantity is determined by measurement, and not by calculation, the numerical value of the measurement result is rounded to a figure of the same order as the error value. Extra digits for integers are replaced by zeros, and decimal fractions are discarded. Example: (103221 ± 245) Pa - before rounding; (103220 ± 250) Pa - after rounding when calculating the liquid pressure. If the zero-replaced or discarded digits are less than 5, then the remaining digits are not changed. And if this figure is greater than 5. Then the subsequent remaining digits increase by one. Example: (846.45 ± 0.13) kg / m 3 - before rounding; (846.5 ± 0.1) kg / m 3 - after rounding when calculating the density of an unknown liquid. If the digit being replaced by zero or discarded is equal to 5 (with subsequent zeros), then rounding is performed as follows: the last digit in the rounded number remains unchanged. If it is even, and increases by one if it is odd. Example: (184, 256 ± 0.127) H - before rounding; (184.26 ± 0.13)N or (184.3 ± 0.1) - after rounding when calculating the fluid pressure force on flat horizontal and vertical walls. When presenting the final result of measurements, it is convenient to use the record of a numerical value in the form of a decimal fraction multiplied by the required power of 10. For example, when recording the value of atmospheric pressure: 101 239 Pa \u003d 101.239 * 10 3 Pa \u003d 101.24 kPa. In most cases of experimental study of hydraulic phenomena, it is advisable to present the obtained dependences in the form of a graph. Comparing the theoretical curve with the experimental one, it is determined whether the results of the experiment agree with the expected value. In some cases, it is proposed to superimpose the experimental section of the graph on the theoretical curve. In this case, the behavior of the curve section should be taken into account precisely within the limits of the measured value that are displayed on the theoretical curve. For convenience, the chosen scale in constructing the experimental dependence should coincide with the scale of the theoretical dependence. For example, when superimposing a graph of the dependence of hydraulic resistance on the Re number on the Murin graph, the experimental section is only a tenth of the theoretical curve (and there are a whole lot of them on the Murin graph). Therefore, the correct coincidence of the experimental section with one of these curves will allow, in the continuation of this curve, to determine the equivalent relative roughness of the inner surface of the pipe. Experimental points on graph paper are presented in the form of crosses and the curve is drawn not for all points, but within the limits of errors, so that above and below this curve the number of points according to their total distance from the experimental line is approximately the same. The general form of the experimental curve should be similar to the form of the theoretical dependence or the form of the corresponding part of the theoretical curve. Lab #1 STUDY OF THE LABORATORY STAND "HYDROSTATICS GS" Objective: to study the device and principle of operation of the laboratory stand "Hydrostatics"; write down the formula for determining absolute pressure, write down the formula for determining excess pressure using a battery of piezometers; know the density of liquids in piezometers; determine the division value of piezometers and pressure gauges; express their meaning in the SI system. Brief theory. The stand consists of a working table 1 (Fig. 1), a tank 2 fixed on it and a shield 3 with a P3 battery pressure and vacuum gauge. A shield of wall-mounted piezometers 4 is fixed next to the table. The tank is ¾ filled with working fluid. With the help of compressor 5 and vacuum cleaner 6, located on the bottom shelf of the table, excess or vacuum pressure can be created under the tank cover. The required mode is provided by the control unit 7 and valves B1 and B2. The air pressure in the tank is recorded by mechanical devices - the MN1 pressure gauge and the VN vacuum gauge. On the front and side walls of the tank there are flanges, to which two tested flat walls 9 are attached through bellows 8 - vertical and horizontal. Rulers with scales are fixed on the flanges, which serve to determine the displacement of the walls. The legs of the P3 battery pressure and vacuum gauge are filled with liquid (in the general case, liquids can be different). The left end of the battery pressure gauge is filled with air and connected to the upper part of the tank, and the right end is open to the atmosphere (Fig. 2). On the wall panel of piezometers 4, there is a piezometer P1 connected to the part of the tank filled with the working fluid, and a U-shaped pressure and vacuum gauge P2 filled with the investigated fluid with an unknown density. One end of the pressure vacuum gauge P2 is connected to the upper (air) part of the tank, and the other end is connected to a mechanical device - the MN2 pressure gauge. Valves V5 and V3 are used to block the P2 pressure and vacuum gauge when conducting experiments on pressure or vacuum exceeding the measurement limits of this liquid device. Valves B8 and fitting 10 are used to fill the tank with working fluid and empty it. Rice. 1. Laboratory stand "Hydrostatics GS". The laboratory bench "GS" is designed to perform laboratory work No. 2.3.4 to determine the hydrostatic pressure, the density of an unknown liquid and the pressure force of the liquid on flat vertical and horizontal walls. Test questions. What is the laboratory stand "Hydrostatics GS" intended for? What is the principle of operation of the stand based on? List the main elements of the laboratory stand. What pressure meters are used in the stand? What is the scale division value of a battery of piezometers? What is the scale division value of wall piezometers?
Rice. 2. Hydraulic scheme of the stand "Hydrostatics GS". What is the division value of mechanical pressure gauges? Express this value in the SI system. What liquid is poured into the battery of piezometers? Specify its density. What liquids are poured into wall piezometers? Indicate what is the density of the liquid in the P1 piezometer. What liquid and to what level is the tank filled? Why? How is the excess and combined pressure and vacuum pressure in the tank determined by a battery of desktop piezometers? Write a formula. Specify two main modes of operation of the stand. What devices are used to create these modes and where are they located? What methods of determining hydrostatic pressure are the most accurate. Lab #2 DETERMINATION OF HYDROSTATIC PRESSURE. Objective - students mastering the methods of measuring hydrostatic, gauge and vacuum pressures in two modes. In preparation for work, in the process of performing work and in processing the results of experiments, the student must: Familiarize yourself with various pressure measuring devices; Determine the hydrostatic pressure in three ways in two modes; Determine the pressure under the tank cap according to the readings of the piezometer and the battery pressure and vacuum gauge and compare them with the readings of a mechanical device in two modes; Determine the absolute error of hydrostatic pressure measurement by all three methods for all modes. n1.docFEDERAL AGENCY FOR EDUCATION Biysk Technological Institute (branch) state educational institution higher professional education "Altai State Technical University them. I.I. Polzunov" A.I. Roslyakov, L.V. Lomonosov LABORATORY WORKSHOP for hydraulics, hydraulic machines and hydraulic drives courses "Hydraulics", "Hydraulics and hydraulic machines", "Fundamentals of hydraulics and hydraulic drive" for students of specialties: TM-151001, VUAS - 170104, AT - 190603, APCP - 240706, MAPP-260601, TGV - 270109 Publishing house of the Altai State Technical Universitythem. I.I. Polzunova Reviewer: Head of the Department of MAHIPP BTI AltSTU Professor Kunichan V.A. The work was prepared at the department "Heat and gas supply and ventilation, processes and apparatuses of chemical technology" Roslyakov, A.I. Laboratory workshop on hydraulics, hydraulic machines and hydraulic roprivodam: guidelines for laboratory work on the courses "Hydraulics", "Hydraulics and hydraulic machines", "Fundamentals of hydraulics and hydraulic drive" for students of specialties: TM -151001, VUAS - 170104, AT - 190603, APCP - 240706, MAPP -260601, TGV - 270109 / A.I. Roslyakov, L.V. Lomonosov. – Alt. state tech. un-t, BTI. - Biysk: Alt. state tech. un-ta, 2009. - 137 p. © A.I. Roslyakov, L.V. Lomonosov, 2009 © BTI AltSTU, 2009 DETERMINATION OF THE FORCE OF HYDROSTATIC PRESSURE 6 1.1 Purpose of work: 6 1.3 Background 6 1.5 Installation description 9 1.7 Processing of experimental data 12 1.8 Security questions 12 2.1 Purpose of work: 15 2.3 Background 15 2.3.1 Modes of movement of a real fluid 15 2.7 Processing of experimental data 21 6.2 Lab preparation: 56 INTRODUCTION The purpose of the workshop is to consolidate the theoretical material in the course of hydraulics, to acquire skills in working with instrumentation and other research equipment. LABORATORY WORK No. 1. DETERMINATION OF THE FORCE OF HYDROSTATIC PRESSURE(4 HOURS)1.1 Purpose of work:- to determine empirically the force of hydrostatic pressure and its center of pressure; – build a diagram of hydrostatic pressure. - learn the definitions of the main concepts and terms of the topic Basic terms and concepts: - absolute peace; – vacuum; – hydrostatics; - pressure; is an ideal liquid; - overpressure; - mass forces; – density; are surface forces; – level surface; - balance; – free surface; - center of pressure. 1.3 Theoretical backgroundAll external and internal forces acting on a liquid are continuously distributed either over its volume (mass forces), or on the surface ( superficial). As a result of the action of external forces, a normal stress arises inside a fluid at rest, equal to the limit to which the ratio of the force to the area (Figure 1.1) on which it acts tends, when the size of the area tends to zero, i.e. when contracting the site to a point hydrostatic pressure called normal stresses arising in a liquid under the action of external forces . It is characterized by two properties: – - the value of pressure at a given point is the same in all directions, that is, it does not depend on the angle of inclination of the platform on which it acts. The value of hydrostatic pressure (see figure 1.1) depends on the depth of immersion ( h) of the considered point in the liquid volume, the specific gravity of the liquid and the pressure in the volume above the free surface and is calculated according to the basic equation of hydrostatics:
where - specific gravity of the liquid, equal to the product of density and free fall acceleration, N/m 3 . G Figure 1.2 - Diagram hydrostatic pressure The resulting points are connected by a straight line. As a result, a diagram of excess hydrostatic pressure on a flat vertical wall is obtained in the form of a triangle. The plot of absolute pressure is constructed similarly. However, in practice, the forces arising from the action of the fluid on various walls are more important. For example, the force of hydrostatic pressure ( F) of a liquid on a flat wall immersed in a liquid (see Figure 1.1) is equal to the product of the surface area S on the value of hydrostatic pressure R with at a depth h c immersion of the center of gravity of the considered surface: Thus, the resulting force consists of two components: – strength
– strength F c weight pressure at the immersion depth of the center of gravity
PressureR 0 , applied to the free surface, is transmitted to all points of the liquid throughout the volume in all directions without changing the value(Pascal's law), that is, the same at any point in the considered volume of liquid. Therefore, the component
where I with- the moment of inertia of the site S relative to the axis passing through its center of gravity, m 4; h with is the immersion depth of the center of gravity of the site, m; S is the area of the site under consideration, m2. Point of application of the resultant force F hydrostatic pressure is between the points D and C. - installation for the experiment; Did not find an answer to your question? Look at here
|
, (1.1)
=
p a. The second point is at the bottom, where the pressure 
pressure in the volume above the free surface:
;
.
applied at the center of gravity (point With) of the site under consideration. On the contrary, the weight pressure (see formula (1.1) and Figure 1.1) is directly proportional to the immersion depth. Therefore, the point of application of the component F c(dot D) will be located in the center of the overpressure diagram (triangle) located below the center of gravity of the site. Point shift amount D relative to the center of gravity is determined by the formula
, (1.3)
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