THERMODYNAMICS. Class times: Monday 9:15 12:00. Machine Laboratory Room 10

Transcription

1 THERMODYNAMICS dr hab. inż. Dariusz Mikielewicz, prof. PG Heat Technology Department Faculty of Mechanical Engineering Gdansk University of Technology Class times: Monday 9:15 12:00 Office No. 111 LM Contact hours: Monday 8:00 9:00 Tuesday 9:00 10:00 Machine Laboratory Room 10 Lecture 45 hours (15 lectures) Pierwsza strona

2 Objectives of the lecture Presentation of concepts of energy balance, laws of thermodynamics and types of thermodynamical cycles in engineering practice. Presentation of principal laws of heat transfer, namely conduction, convection, radiation. Introduction to heat exchangers. Acquired competencies: General view on thermodynamics and heat transfer from the point of view of a user operating on the borders of that topic. Simple calculations of thermodynamical cycles and heat transfer. A feeling of energy conversion. Examination Positively passed tutorials. Exam in June. Good attendance to lectures!!!

3 CLASSROOM RULES Common courtesy while in the classroom is a pre-requisite for learning. The following administrative guidelines and rules shall apply: Please turn off all cell-phones, pagers, beepers, etc. before entering the classroom. Do not read newspapers once the lecture has started. Refrain from socializing with fellow students during the lecture. Your cooperation in complying with these rules is appreciated by the instructor and your classmates. Acquired competencies: General view on thermodynamics and heat transfer from the point of view of a user operating on the borders of that topic. Simple calculations of thermodynamical cycles and heat transfer. A feeling of energy conversion. Examination Positively passed tutorials. Exam in June. Good attendance to lectures!!!

4 Co to jest wymiana ciepła?

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6 Introduction - Nature of thermodynamics Energy drives the human development. Everything which is available to humanity, i.e. goods, services, material production is directly proportional to the amount of energy used per person. deals with energy and its conversion. That would indicate that thermodynamics is a science most closely linked with the needs of a human. As we are aware there is a number of possible types of energy. All of them may become the topic of thermodynamical considerations.

7 Introduction - Nature of thermodynamics

8 Laws of restrict the amount of available energy to perform the useful work. That imposes the necessity for a more efficient use of energy resources and application only most efficient processes of energy conversion. Known types of energy: 1. Friction energy 2. Electrical energy 3. Magnetic energy 4. Nuclear energy 5. Chemical energy 6. Quantum energy Generally speaking thermodynamics deals with two types of energy: HEAT and WORK. At the beginning let s discuss briefly the wide scopeofproblemsofthermodynamics.

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14 Compressed air boundary surroundings Borders of the system can be real or imaginary.

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16 Systems and their behaviour

17 Systems and their behaviour

18 State of thermodynamical system is described by thermodynamical parameters parameters of state. Usually, at the beginning it is not possible to present all properties. Typical properties are temperature, pressure, volume, density, chemical energy, amount of substance. These coordinates are usually named the system properties.

19 TEMPERATURE = state of hotness Slowly moving atoms or particles have low temperature. Fast moving atoms or particles have a high temperature. High T v Low T

20 PRESSURE = force acting on a surface impact p = F A F A weight

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22 DENSITY = mass per unit volume Large density ρ = v = Continuum and pressure m V 1 ρ Small density Definition of pressure tacitly assumes that volume is large enough that the number of molecules inside is no susceptible to fluctuations in time. If that is the case then the system can be regarded as a continuum. Pressure is defined as a ratio of normal component of force exerted by the substance on the walls of the system to the surface. Considered volume is such that it can be regarded as continuum.

23 AMOUNT OF SUBSTANCE = how much of it dozen.... plenty Avogadro number

24 T P T K

25 p 1 2 T P V 1 V 2 V

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27 Temperature, heat and zeroeth Law of It is usually assumed that we understand meaning of words heat and temperature. The objective of thermodynamics are investigations into the precise comprehension of these terms. Typical intuitive perception of temperature when we contact something tells us about energy or heat transfer. Therefore it can be concluded that between two bodies of the same temperature there is no transfer of heat. Balance of temperature does not allow us to define an absolute temperature scale. Definition of teperature balance stems from so called zeroeth Law of. It says: If two bodies are in thermal balance with the third body then they are in thermal balance with each other.

28 The condition for a full balance of these bodies is also the balance of pressures, lack of chemical reactions during the contact of these bodies. Heat is the energy resulting from temperature difference

29 T 1 rod temperature T 2 T 1 > T 2 T 1 T 2 heat Two bodies connected with a rod Example of heat flow.

30 1.4 Temperature scales Most commonlyusedthesedaysisthecelsiusscale( 0 C). A corresponding absolute scale is the Kelvin scale(k). Another scale is the Fahrenheit scale ( 0 F), with corresponding Rankine scale( 0 R). Absolute zero for Kelvin and Rankine scales is the same!!!; C. 0 F = /5 0 C 0 R = 0 F K = 0 C R = 9/5 K

31 Normal pressure p 0 = N/m 2 1 Triple point of hydrogen Boiling point of hydrogen Boiling point of hydrogen at p Boiling point of neon at p Triple point of oxygen Boiling point of oxygen p Triple point of water Boiling point of water p Solidification point of zinc Solidification point of silver Solidification point of gold Some thermometric points.

32 STATES OF THE MATTER Phase is a quantity is of matter that is homogeneous throughout in both chemical composition and physical structure. Homogeneity in physical structure means that the matter is all solid, all liquid or all vapour. System can contain one or more phases. Solid Liquid Gas Plasma

33 State of the matter directly depends on a value of specific thermodynamical properties, such as pressure and temperature. p K p P Solid Triple point T P Liquid Vapour T K Critical point Gas Plasma T

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36 Substance that expands on freezing Substance that contracts on freezing

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