Liquid type

r,
cm

W,
cm 3

Δ T,
To

l,
cm

Δ W,
cm 3

β T ,
K -1

β T * ,
K -1

Alcohol

MINISTRY OF EDUCATION AND SCIENCE OF THE RUSSIAN FEDERATION Togliatti State University

Institute of Civil Engineering Department "Water supply and sanitation"

METHODOLOGICAL INSTRUCTIONS

to laboratory work on the discipline "HYDRAULICS"

for academic advisor

Togliatti 2007

UDC 532.5 (533.6)

Guidelines for laboratory work in the discipline "Hydraulics" for students of construction specialties full-time education. /Comp. Kalinin A.V., Lushkin I.A. - Togliatti: TSU, 2006.

The goals, objectives and program of laboratory work are outlined, instructions are given for preparing for work and their implementation.

Il.12. Tab. 8. Bibliography: 5 titles.

Compiled by: Kalinin A.V., Lushkin I.A. Scientific editor: Vdovin Yu.I.

Approved by the editorial and publishing section of the Methodological Council of the Institute.

© Togliatti State University, 2007

Instructions for laboratory work

The basis of the course under study is the acquisition by students of the initial skills of conducting research, understanding the results of laboratory research, presenting and defending the results. Laboratory work is carried out in the laboratories of the department "Water supply and sanitation". In the course of the work, the student has the opportunity to see and study the phenomena occurring in the liquid, to measure physical quantities, master the methodology of setting up experiments, acquire the skills of processing the data obtained as a result of the experiment, presenting the results of the study. During the laboratory work, the student must learn how to use measuring instruments.

Before conducting laboratory work, the student's knowledge of theoretical material on the topic of experimental research is monitored. Control is carried out by an academic consultant in a test form. A student is allowed to conduct laboratory work if he correctly answered 40% of the test questions.

In laboratory works No. 4 and No. 5, the student must calculate the parameters of the physical model before conducting an experimental study. The results of the calculation are presented to the academic consultant. In the event that the calculation by the student has not been performed, the student is not allowed to the pilot study.

The results of the conducted experimental study are presented in the form of a report. The report contains: the purpose of the work, the scheme of the installation, the main calculation formulas, tables of measurements and calculations, graphs, conclusions. The results of the study, after verification by an academic consultant, are used in the calculation of a short pipeline.

Description of the universal hydraulic stand GS - 3

The universal hydraulic stand (see Fig. 1) is designed for laboratory and research work, the purpose of which is to study the laws of fluid motion. The hydrostand was developed at the Department of Thermal Engineering and Thermal Engines of the Samara State Aerodynamic University.

The main elements of the hydrostand:

pressure and receiving device;

working area;

pump;

measuring devices.

On the rack 4 there is a pressure tank 2 made of stainless steel in the form of a sphere. The pressure tank has an outlet pipe 3, to which the working section 15 is attached with the help of a seal.

Water enters the pressure line from pump 9 when valve 8 is opened. During the experiment, supply valve 6 and drain valve 7 must be closed. The water flow through the working area is regulated by valve 18 at the outlet of the working area and by valve 8

Rice. 1. Scheme of the hydraulic stand

The receiving device is a tank 22 connected to the drain line 12. Above the receiving tank on the console 10, a measuring tank 20 is mounted to measure the water flow. A tray 11 is installed on the console, used to collect water and drain it into a measuring tank 20. At the bottom of the measuring tank there is a valve 21 controlled by a lever mechanism

Measuring devices are represented by a piezometric shield 13, on which seven glass tubes are mounted. The overpressure in the pressure tank is measured with a standard pressure gauge 1. When measuring the water flow, simultaneously with closing the valve on the control panel 5, an electric stopwatch is turned on. After filling with water a certain volume of the measuring tank (3 liters), the contact of the level switch closes with the simultaneous stop of the electric stopwatch.

The hydraulic stand operates in a closed circuit with pumping water from the supply tank, draining it into the receiving tank and supplying it under pressure to the supply tank.

Laboratory work No. 1 Determining the value of the viscosity coefficient of water

1. The purpose of the work: experimental determination of the value of the viscosity coefficient and density of water at a given temperature. The results of the experiment are used in the calculation of a short pipeline.

2. Work program:

2.1. Determine the viscosity of water at a given temperature using an Engle viscometer

2.2. Measure the density of the liquid with a hydrometer. 2.3. Set the dynamic viscosity of the test fluid.

3. Description of the laboratory setup and measuring instruments

Engler viscometer(Fig. 2) consists of a metal cylinder 1 with a spherical bottom with a hole. The hole is closed with a rod 2. When studying the dependence of a change in the viscosity of a liquid on temperature, the cylinder is placed in a water bath 3 with adjustable water heating.

Fig 2. Engler viscometer

The principle of operation of the hydrometer (see Fig. 3) is based on the use of the law of Archimedes, according to which the force of Archimedes acts vertically upwards on a body placed in a liquid. The magnitude of this force depends on the density of the liquid. The greater the density of the liquid in which the body is placed, the greater will be the Archimedes force that will push the body out of the liquid. It is possible to put marks on the body in the form of a float, corresponding to different values ​​of density, and depending on how much such a “float” will be visible above the surface of the liquid, judge the density of this liquid.

Rice. 3. Hydrometer

4. Order of performance of work:

4.1. Pour ≈ 250 cm 3 of the investigated liquid into cylinder 1 and place a measuring vessel under the hole.

4.2. With rod 2 we open a hole in the cylinder, at the same time turning on the stopwatch.

4.3. Determine the time τ 1 outflow from the cylinder of 200 cm3 of the investigated liquid at room temperature. The experiment is repeated at least 3 times.

4.4. Carefully wipe the cylinder and pour it into it with the bottom hole closed ≈ 250 cm 3 reference liquid (distilled water).

4.6. Determine the expiration time τ 2 reference fluid.

4.7. To determine the density ρ, the liquid under study is poured into a tall measuring cup. We lower the hydrometer into the glass and determine the density of the liquid using the hydrometer scale.

4.8. We determine the average expiration time τ 1sr and τ2sr

τ cf = τ " + τ " + ... + τ n , n

where n is the number of measurements. 4.9. Calculating degrees Engler

° E \u003d τ 1sr.

τ 2sr

4.10. We determine the coefficient of kinematic viscosity ν according to the Ubelode formula

ν = (0.0732° Oe − 0.0631 ° Oe) .

4.11. We find the dynamic viscosity coefficient μ using the formula

ν = μ ρ .

4.12. The results of measurements and calculations are summarized in Table 1 and are used in the calculation of a short pipeline

Table 1

5. Conclusions

Viscosity of the test liquid

Laboratory work No. 2 Study of the laws of fluid motion

1. The purpose of the work: Experimental confirmation of the conclusions made during the study of the topic "Fundamentals of fluid dynamics and kinematics", the acquisition of skills in constructing a pressure line and a piezometric line of a short pipeline.

2. Work program:

2.1. Determine the pressure H at three points on the axis of the pipe, find the pressure loss. 2.2. Determine the flow velocity on the axis of the pipe.

2.3. Construct graphs of changes in the total head H and hydrostatic head H p along the length of the pipe.

3. Description of the installation. Laboratory work is carried out in the laboratory of hydraulics of the Department of V&V. The working section of the hydraulic stand, on which the work is carried out, is an inclined metal pipe of variable cross section (Fig. 4). Piezometric tubes and Pitot tubes are installed in sections 1-1, 2-2, 3-3, 4-4 and 5-5 to measure the static and total pressures of the liquid. The liquid flow rate in the pipe is controlled by a valve located at the end of the working section of the stand.

Rice. 4. Scheme of the working section of the hydrostand

4. Order of performance of work:

4.1. We turn on the installation.

4.2. We open the valve at the end of the working section of the stand.

4.3. We measure the distance between pipe sections l and the ordinate z in each section.

4.3. After the air bubbles come out of the tubes, we record the readings of the piezometers

and Pitot tubes in all sections.

4.4. Turn off the installation.

4.5. Determine the energy loss between sections

h w 1− 2 = H 1 − H 2 , h w 2− 3 = H 2 − H 3 etc.,

where h w 1 - 2 - head loss between sections 1-1 and 2-2; h w 2 - 3 - pressure loss between sections 2-2 and 3-3; H 1, H 2, H 3 - Pitot tube readings in sections 1-1, 2-2 and 3-3.

4.6. We find the measured velocity head in each section

where H i - readings of the Pitot tube in the corresponding section; H pi - readings of the piezometric tube in the corresponding section.

4.7. Determine the flow velocity on the axis of the pipe

υ = 2gh υ .

4.8. The research results are recorded in table 2. Table 2

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

Lab #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 static pressure difference 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

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

Work procedure

Processing of experimental data

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 Re kr - turbulent.

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

Processing of experimental data

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 fluid 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

Processing of experimental data

Analysis of results. Conclusion on work

Lab #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

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

Processing of experimental data

Analysis of results

What will we do with the received material:

If this material turned out to be useful to you, you can save it to your page on social networks:

Read also:

• 0

  Amount of movement Amount of movement of a system of material points

  2022-04-04 06:51:15

• 0

  Eccentric tension - compression

  2022-04-04 06:51:15

• 0

  Examples Determine if a sequence is infinitesimal

  2022-04-04 06:51:15