Basics of hydro and heat engineering in short. Methodical development in the discipline "Fundamentals of hydraulics, heat engineering and aerodynamics": "Basic laws of hydraulics" methodical development on the topic. conditions for the implementation of the work program of the academic discipline
MINISTRY OF AGRICULTURE AND FOOD OF THE REPUBLIC OF BELARUS
UO "GORODOKSKY STATE AGRARIAN-TECHNICAL COLLEGE"
FUNDAMENTALS OF HEATING ENGINEERING AND HYDRAULICS
correspondence course manual
in questions and answers
partI
Town
"Reviewed"
at a meeting of the methodological commission
general professional disciplines
Minutes No. _____ dated ________________
Chairman: ________
The manual is intended for students of the correspondence department of specialties 2-74 06 01 "Technical support of agricultural production processes" and 2-74 06 31 "Energy supply of agricultural production" for self-study discipline "Fundamentals of heat engineering and hydraulics".
Introduction. 5
Fuel and energy complex of the Republic of Belarus. 6
Working fluid and its parameters ... 11
Basic gas laws .. 12
Basic equations of thermodynamics. 14
Gas mixtures. Dalton's Law. sixteen
Heat capacity: its types, calculation of heat consumption for heating. eighteen
Heat capacity in processes at constant pressure and at constant volume 19
The first law of thermodynamics and its analytical expression. 21
The concept of the thermodynamic process and their types .. 22
Isochoric process. Its graph in - coordinates and basic equations 23
Isobaric process. Its plot in - coordinates and 24 basic equations
Isothermal process. Its plot in - coordinates and basic equations 26
Adiabatic process. Its plot in - coordinates and basic equations 28
Circular process. Its schedule and efficiency .. 30
The Carnot cycle and its efficiency .. 31
Water vapor. Basic definitions. 33
The process of vaporization in - coordinates. 35
The ideal cycle of a steam power plant and its efficiency .. 37
C. Their classification. 40
Ideal cycles for D.V.S. Their efficiency .. 42
Real cycles of the internal combustion engine, determination of power. 45
Heat balance and specific fuel consumption in the internal combustion engine .. 48
Operation diagram and indicator diagram of a single-stage compressor 49
Indicator diagram of a real compressor. 51
Multistage reciprocating compressors .. 53
Understanding the operation of centrifugal, axial and rotary compressors 56
Heat transfer methods. 58
Heat transfer by thermal conductivity through a single-layer flat wall 60
Thermal conductivity through a multilayer wall. 62
Thermal conductivity through cylindrical walls. 64
Convective heat transfer. 66
Heat transfer by radiation .. 67
Heat exchangers. Their types .. 70
Basics of calculating heat exchangers. 72
Complex heat transfer through a flat wall. 75
Heat transfer through a cylindrical wall. 78
Introduction
The discipline "Fundamentals of Heat Engineering and Hydraulics" provides for the study by students of the basics of thermodynamics and hydraulics, the principles of operation of boilers and drying plants, engines internal combustion, compressors, refrigerators, solar water heaters and pumps. The main energy problem facing science is to improve the technical and economic performance of heat engineering and power equipment, which will undoubtedly lead to a decrease in fuel consumption and an increase in efficiency.
Heat power engineering - the main branch of industry and agriculture, which is engaged in the transformation of natural thermal resources into thermal, mechanical and electrical energy. An integral part of heat power engineering is technical thermodynamics, which studies the physical phenomena associated with the transformation of heat into work. Calculations of heat engines and heat exchangers are made on the basis of the laws of thermodynamics. The conditions for the highest efficiency of power plants are determined. A great contribution to the development of heat engineering was made by those who created the classic works on thermodynamics.
The laws of convective and radiant heat transfer were systematized.
They laid the foundations for the design and construction of steam boilers and engines.
Knowledge of the laws of technical thermodynamics and the ability to apply them in practice makes it possible to improve the operation of heat engines and reduce fuel consumption, which is very important at the present time, when prices for hydrocarbon raw materials are increasing and consumption volumes are increasing.
Question 1
Fuel and energy complex of the Republic of Belarus
The top priority of the energy policy of the Republic of Belarus, along with the stable supply of the country with energy carriers, is the creation of conditions for the functioning and development of the economy with the most efficient use of fuel and energy resources.
The RB's own reserves of fuel and energy resources are insufficient and amount to approximately 15-20% of the consumed amount. There is a sufficient amount of peat and wood, brown coal, shale is quite low-calorie.
Oil production in the Republic of Belarus is about 2 million tons per year. Gas about 320-330 thousand tons of fuel equivalent. The rest of the energy resources are purchased abroad, mainly from Russia.
Energy prices have risen significantly. So for 1000m3 of gas 115u. That is, oil - for one ton 230 cu. e. The Republic of Belarus buys about 22 billion of natural gas and about 18 million of oil a year. To ensure that the country's energy security does not depend on one supplier, negotiations are underway with Azerbaijan, the Middle East, Venezuela, which in the future will sell hydrocarbon raw materials in the form of oil.
At present, the government and the Energy Conservation Committee are heavily emphasizing the use of local fuels, and by 2010 they must reduce the consumption of purchased energy resources by 20-25%.
Peat.
More than 9000 peat deposits have been explored in the republic with a total area within the boundaries of the industrial depth of the deposit of 2.54 million hectares and initial peat reserves of 5.65 billion tons. To date, the remaining geological reserves are estimated at 4.3 billion tons, which is 75% from the original.
The main reserves of peat lie in the deposits used agriculture(1.7 billion tons and 39% of the remaining reserves) or classified as nature conservation objects (1.6 billion tons or 37%).
Peat resources included in the developed fund are estimated at 260 million tons, which is 6% of the remaining reserves. The reserves recoverable during field development are estimated at 110-140 million tons.
Oil shale.
Forecasted reserves of oil shale (Lyubanskoe and Turovskoe deposits) are estimated at 11 billion tons, commercial reserves - 3 billion. T.
The most studied is the Turovskoye deposit, within which the first mine field with reserves of 475-697 million tons has been previously explored, 1 million tons of such shale is equivalent to about 220 thousand. here. Calorific value - 1000-1500 kcal / kg, ash content -75%, resin yield 6 - 9.2%, sulfur content 2.6%
In terms of its quality indicators, Belarusian oil shale is not an efficient fuel due to its high ash content and low calorific value. They require preliminary thermal processing to yield liquid and gaseous fuels. Taking into account the fact that the cost of the products obtained is higher than world prices and oil, as well as taking into account the environmental damage due to the occurrence of huge ash dumps and the content of carcinogenic substances in ash. Extraction of shale and the forecast period is impractical.
Brown coals.
The total reserves of brown coal are 151.6 million tons
Explored in detail and prepared for industrial development two deposits of the Zhitkovichi field: Severnaya (23.5 million tons) and Naidinskaya (23.1 million tons), two other deposits (Yuzhnaya - 13.8 million tons and Kolmenskaya - 8.6 million tons). t) were previously explored.
The use of brown coal is possible in combination with peat in the form of briquettes.
The estimated cost of coal reserves is estimated at 2 tons of fuel equivalent. in year.
Firewood.
In general, in the republic, the annual volume of centralized procurement of firewood and sawmill waste is about 0.94 - 1.00 million tons of fuel equivalent. t. Part of the firewood goes to the population through self-procurement, the volume of which is estimated at the level
0.3-0.4 million tons of fuel equivalent
The republic's maximum possibilities for using firewood as fuel can be determined based on the natural annual growth of wood, which is approximately estimated at 25 million cubic meters. m or 6.6 million tons of oil equivalent. tons per year (if you burn everything that grows), including in polluted areas. Gomel region - 20 thousand cubic meters m or 5.3 thousand tons of fuel equivalent To use wood from these areas as fuel, it is necessary to develop and introduce technologies and equipment for gasification. Taking into account the fact that by 2015 it is planned to double the harvesting of wood for the production of thermal energy, the projected annual volume of wood fuel by 2010 may increase to 1.8 million tons of fuel equivalent.
Renewable energy sources.
The potential capacity of all watercourses in Belarus is 850 MW, including technically available - 520 MW, and economically feasible - 250 MW. By 2010, due to hydro resources, it is possible to generate 40 million kWh and, accordingly, displace 16 thousand tons of fuel equivalent.
On the territory of the Republic of Belarus, 1,840 sites have been identified for the placement of wind turbines with a theoretical potential of 1,600 MW and an annual electricity generation of 16 thousand tons of fuel equivalent.
However, in the period up to 2015, the technical feasible and economically feasible use of the wind potential will not exceed 5% of the installed power and will amount to 720 - 840 million kWh.
World energy reserves.
The fundamentals of hydraulics, technical thermodynamics, and the theory of heat transfer are presented. The fundamentals of hydrostatics, the kinematics and dynamics of moving streams, thermal and energy characteristics of ideal and real gases, the main types of heat transfer, the theory of the similarity of hydrodynamic and heat exchange processes are considered.
The manual is intended for students studying in the specialties: 28020265 "Engineering protection environment". It can be used by students of other specialties studying the disciplines "Hydraulics" and "Heat engineering".
Liquid models.
In order to simplify the solution of many problems, instead of a real liquid, one or another model of a liquid is considered, which has only some of the properties of real liquids. These properties are decisive in the problem being solved, therefore, such simplifications do not give significant errors in determining the desired quantities.
Consider the main existing fluid models.
An ideal fluid is one that is devoid of viscosity.
An incompressible fluid is a fluid that does not change its density when pressure changes.
A perfect fluid is an incompressible fluid in which there are no adhesion forces between molecules, and the intrinsic volume of molecules is zero.
A perfect gas is a compressible liquid (gas) in which there are no adhesion forces between molecules, and the intrinsic volume of molecules is zero.
Ideal gas is perfect gas. devoid of viscosity.
A baroclinic liquid is a gas. whose density is a function of pressure and temperature.
A barotropic liquid is a gas. in which the density depends only on pressure.
TABLE OF CONTENTS
Foreword
Basic notation
Introduction
Part I. BASICS OF HYDRAULICS
1. PHYSICAL PROPERTIES OF LIQUIDS
1.1. Basic physical properties of liquids
1.2. Fluid Models
2. HYDROSTATICS
2.1. Differential Equations of Equilibrium of a Liquid
2.2. Hydrostatic law. Hydrostatic pressure
2.3. Equilibrium conditions for liquids in communicating vessels
2.4. The simplest hydraulic machines
2.5. Basic methods and instruments for measuring pressure
2.6. Archimedes' law
2.7. Balance and stability of bodies. immersed in liquid. Equilibrium of a body floating on a liquid surface
2.8. Equilibrium of the Earth's atmosphere
3. HYDRODYNAMICS
3.1. Basics of kinematics
3.1.1. Lines and tubes of current. Flow equation
3.1.2. The movement of a liquid particle of a continuous medium
3.1.3. Vortex and non-vortex flow
3.1.4. Circulation speed
3.2. Basics of dynamics
3.2.1. Forces acting on a particle of a continuous medium. The tense state of the elementary volume. Stokes' law of friction
3.2.2. Differential continuity equation
3.2.3. Differential equations for the transfer of momentum. Euler and Navier-Stokes equations
3.2.4. Differential Energy Equation
3.3. Viscous flow motion
3.3.1. Fluid flow modes
3.3.2. Features of turbulent flow
3.3.3. Equations of motion and energy for laminar and turbulent fluid flow
3.3.4. Turbulence models
3.4. Low viscosity fluid motion
3.4.1. Boundary layer
3.4.2. Non-viscous flow motion
4. HYDRAULIC RESISTANCE
4.1. Length resistance
4.2. Local hydraulic resistance
Part II. FUNDAMENTALS OF THERMODYNAMICS
5. THERMODYNAMIC SYSTEM AND ITS PARAMETERS
5.1. Thermodynamic system and its state
5.2. Thermal state parameters
6. PERFECT GAS
6.1. Ideal gas equation of state
6.2. Mixtures of ideal gases
7. ENERGY CHARACTERISTICS OF THERMODYNAMIC SYSTEMS
7.1. Internal energy. Enthalpy
7.2. Job. Heat
7.3. Heat capacity
8. FIRST START OF THERMODYNAMICS
8.1. Formulation of the first law of thermodynamics
8.2. The first law of thermodynamics for basic thermodynamic processes
9. SECOND BEGINNING OF THERMODYNAMICS
9.1. Formulation of the second law of thermodynamics
9.2. Carnot cycle
9.3. Clausius integral
9.4. Entropy and thermodynamic probability
10. REAL GAS
10.1. Equations of state for real gases
10.2. Couples. Vaporization at constant pressure
10.3. Equation of Cliperon-Clausius
10.4. pT-diagram of phase transitions
Part III. FUNDAMENTALS OF THE THEORY OF HEAT AND MASS EXCHANGE
11. BASIC CONCEPTS AND LAWS OF THE THEORY OF HEAT AND MASS EXCHANGE
11.1. Types of heat transfer
11.2. Basic concepts and laws of molecular and convective heat transfer
12. FOUNDATIONS OF THE THEORY OF SIMILARITY OF PHYSICAL PHENOMENA
12.1. Mathematical formulation of problems of fluid dynamics and heat transfer
12.2. Foundations of the theory of the similarity of physical processes
12.3. Defining size and defining temperature
12.4. Revealing Generalized Variables from the Mathematical Formulation of the Problem
12.5. Obtaining Similarity Numbers Based on Dimension Analysis
13. THERMAL CONDUCTIVITY AND HEAT TRANSFER IN STATIONARY MODE
13.1. Thermal conductivity of substances
13.2. Thermal conductivity and heat transfer through a flat wall
13.3. Thermal conductivity and heat transfer through a cylindrical wall
13.4. Thermal conductivity and heat transfer through the ball wall
14. THERMAL CONDUCTIVITY DURING NON-STATIONARY MODE
14.1. Conditions for the similarity of unsteady temperature fields
14.2. Non-stationary thermal conductivity of a flat wall
15. HEAT DISCHARGE
15.1. Factors affecting the intensity of heat transfer
15.2. The relationship between heat transfer and friction
15.3. Friction and heat transfer laws for a turbulent boundary layer
15.4. Heat transfer during forced convection of a flat plate
15.4.1. Heat transfer from a plate with a laminar boundary layer
15.4.2. Heat transfer from a plate with a turbulent boundary layer
15.5. Heat transfer with external flow around a single pipe and tube bundles
15.6. Heat transfer during fluid flow in pipes and channels
15.7. Heat transfer with free convection
15.8. Heat transfer during phase transformations
15.8.1. Condensation heat transfer
15.8.2. Boiling heat transfer
15.8.3. Heat transfer during boiling in conditions of fluid movement through pipes
15.9. Heat transfer enhancement
16. RADIATION HEAT EXCHANGE
16.1. Basic concepts and definitions
16.2. Basic laws of radiation heat transfer
16.3. Radiative heat transfer between solids separated by a transparent medium
16.4. Protective screens
16.5. Radiative heat transfer between gas and shell
17. HEAT EXCHANGERS
17.1. The main types of heat exchangers
17.2. Thermal design of a recuperative heat exchanger
17.3. About the hydraulic calculation of a recuperative heat exchanger
17.4. Ways to improve the efficiency of heat exchangers
Bibliography.
The theoretical foundations of refrigeration and machine processes and air conditioning concepts are mainly based on two fundamental sciences: thermodynamics and hydraulics.
Definition 1
Thermodynamics is a science that studies the laws governing the transformation of internal energy into various chemical, physical and other processes considered by scientists at the macro level.
Thermodynamic provisions are based on the first and second principles of thermodynamics, which were first formulated in early XIX centuries and became the development of the foundations of the mechanical hypothesis of heat, as well as the law of transformation and conservation of energy, formulated by the great Russian researcher M.V. Lomonosov.
The main direction of thermodynamics is technical thermodynamics, which studies the processes of mutual transformation of heat into work and the conditions under which these phenomena occur most effectively.
Definition 2
Hydraulics is a science that studies the laws of equilibrium and motion of fluids, as well as develops methods of using them to solve complex engineering problems.
The principles of hydraulics are often applied in solving many issues related to the design, engineering, operation and construction of various hydraulic pipelines, structures and machines.
The outstanding founder of hydraulics is considered the ancient Greek thinker Archimedes, who wrote scientific work"On floating bodies". Hydraulics as a science arose much earlier than thermodynamics, which is directly related to the social intellectual activity of a person.
Development of hydraulics and thermodynamics
Figure 1. Hydraulic flow measurement. Author24 - online exchange of student papers
Hydraulics is a complex theoretical discipline that carefully examines issues related to mechanical movement various liquids in natural and man-made conditions. Since all elements are considered as indivisible and continuous physical bodies, then hydraulics can be considered one of the sections of continuum mechanics, to which it is customary to include a special substance - liquid.
Already in ancient China and Egypt, people knew how to build dams and water mills on rivers, irrigation systems in huge rice fields, in which powerful water-lifting machines were used. In Rome, six centuries BC. e. a water supply system was built, which speaks of the ultra-high technical culture of that time. The first treatise on hydraulics should be considered the teachings of Archimedes, who was the first to invent a machine for lifting water, which was named as a result of the "Archimedean screw". It is this device that is the prototype of modern hydraulic pumps.
The first pneumatic concepts appeared much later than hydraulic ones. Only in the 18th century. n. e. on the territory of Germany, a machine for the "movement of gas and air" was presented. With the development of technology, hydraulic systems have been modernized and the area of their practical application has rapidly expanded.
In the development of thermodynamics in the 19th century, scientists distinguish three main periods, each of which had its own distinctive properties:
- the first was characterized by the formation of the first and second thermodynamic principles;
- the second period lasted until the middle of the 19th century and was distinguished by the scientific works of prominent European physicists such as the Englishman J. Joule, the German explorer Gottlieb, and W. Thomson;
- the third generation of thermodynamics was discovered by the famous Austrian scientist and member of the St. Petersburg Academy of Sciences Ludwig Boltzmann, who, through numerous experiments, established the relationship between the mechanical and thermal forms of motion.
Further, the development of thermodynamics did not stand still, but advanced at an accelerated pace. Thus, the American Gibbs developed chemical thermodynamics in 1897, that is, made physical chemistry an absolutely deductive science.
Basic concepts and methods of two scientific directions
Figure 2. Hydraulic resistance. Author24 - online exchange of student papers
Remark 1
The subject of research in hydraulics is the basic laws of equilibrium and chaotic movement of fluids, as well as methods of activating hydraulic systems for water supply and irrigation.
All these postulates were known to man long before our era. The term "liquid" in fluid mechanics has a broader meaning than is commonly believed in thermodynamics. The concept of "liquid" includes absolutely all physical bodies capable of changing their shape under the influence of arbitrarily small forces.
Therefore, this definition means not only ordinary (droplet) liquids, as in thermodynamics, but also gases. Despite the difference between the studied branches of physics, the laws of motion of droplet gases and liquids at certain conditions it is possible to consider the same. The main of these conditions is the speed indicator in comparison with the same sound parameter.
Hydraulics studies primarily the flow of fluids in various channels, that is, flows bounded by dense walls. The concept of "channel" includes all devices that limit the flow itself, including flow paths of pumps, pipelines, clearances and other elements of hydraulic concepts. Thus, in hydraulics, mainly internal flows are studied, and in thermodynamics, external ones.
Remark 2
The subject of thermodynamic analysis is a system that can be separated from the external environment by some control surface.
The research method in thermodynamics is a macroscopic method.
To accurately characterize the macrostructural properties of the system, the values of the macroscopic concept are used:
- nature:
- temperature;
- pressure;
- specific volume.
The peculiarity of the thermodynamic method is that it is based on the only fundamental law of nature - the law of transformation and conservation of energy. This means that all the key relationships that make up the basis of the mathematical apparatus are derived only from this position.
Fundamentals of hydraulics and thermodynamics
When studying the basics of hydraulics and thermodynamics, it is necessary to rely on the concepts of those branches of physics that will help you better master and understand the principle of the functionality of hydraulic machines.
All physical bodies are composed of atoms in constant motion. Such elements attract at a relatively short distance and repel at a fairly close distance. In the center of the smallest particle there is a positively charged nucleus, around which electrons move randomly, forming electron shells.
Definition 3
A physical quantity is a quantitative description of the properties of a material body, which has its own unit of measurement.
Almost a century and a half ago, the German physicist K. Gauss proved that if you choose independent units of measurement for several parameters, then on their basis, through physical laws, it is possible to establish the units of quantities that are included in absolutely any branch of physics.
The unit of measure for speed in hydraulics is a derived unit of a concept derived from the units of the system in the form of meter and second. The considered physical quantities (acceleration, speed, weight) are determined in thermodynamics using the basic units of measurement and have dimensions. Despite the presence of molecular forces, water molecules are always in constant motion. The higher the temperature of a liquid substance, the faster its constituent parts move.
Let's dwell on some physical properties liquids and gases. Fluids and gases in a hydraulic system can easily deform to maintain their original volume. V thermodynamic system everything looks completely different. For such a deformation in thermodynamics, you do not need to perform any mechanical work. This means that the elements acting in a certain concept are weakly resistant to a possible shift.
