Thermodynamics_ chapter 1 introduction ppt

This presentation briefly describes about thermo dynamics introduction

1. Thermodynamics Sidra Zahid Lecturer Department of Engineering Sciences National University of Sciences and Technology PN Engineering College, PNS Jauhar , Karachi

2. Books Text Book: Thermodynamics by Yunus A Cengel and M A Boles, 5 th Edition Reference: There are many other books of thermodynamics are available, however, the text book is very detailed and other reference books are generally not required.

3. Assessment (Approximately) Assignments & Quizzes 20 % Midterm 30% Final 50%

4. Open Book or Closed Book Final exam will be closed books and closed notes Final exam will have some charts available if required Tests and Quizzes may or may not be open book.

5. DEFINITION (Chapter 1) THERMODYNAMICS can be defined as the Science of Energy Therm e (heat) Dynamis (power) Thermodynamics is (Now) broadly interpreted to include all aspects of energy and energy transformations

6. Applications of Thermodynamics It is hard to imagine a scenario where Thermodynamics is not involved Our Own body consists of many applications of Thermodynamics: Heart Cells Brain Blood vessels Lungs etc

7. Applications of Thermodynamics Our home has many examples of thermodynamics

8. Applications of Thermodynamics Power Plant Heat Exchanger Jet engine Refrigeration system

9. Problem Solving Technique Step 1: Problem Statement In your own words, briefly state the problem, the key information given, and the quantities to be found. Step 2: Schematic Draw a realistic sketch of the physical system involved, and list the relevant information on the figure. Step 3: Assumptions State any appropriate assumptions made to simplify the problem to make it possible to obtain a solution. Assume reasonable values for missing quantities that are necessary.

10. Problem Solving Technique Step 4: Physical Laws Apply all the relevant basic physical laws and principles (such as the conservation of energy), and reduce them to their simplest form by utilizing the assumptions made. Step 5: Properties Determine the unknown properties at known states necessary to solve the problem from property relations or tables. List the properties separately, and indicate their source, if applicable.

11. Problem Solving Technique Step 6: Calculations Substitute the known quantities into the simplified relations and perform the calculations to determine the unknowns. Pay particular attention to the units and unit cancellations, and remember that a dimensional quantity without a unit is meaningless. Step 7: Reasoning, Verification, and Discussion Check to make sure that the results obtained are reasonable and intuitive, and verify the validity of the questionable assumptions.

12. Dimensions and Units Any physical Quantity can be characterized by Dimensions The Magnitudes assigned to the Dimensions are called Units

13. Dimensions and Units Some Dimensions are Fundamental/primary dimensions while others are secondary/derived dimensions Mass, Length, Time, Temperatures are the examples of primary dimensions Velocity, Force and Power are the examples of secondary dimensions and are expressed in terms of primary dimensions. V= Length/Time F= Mass x Length / (Time x Time)

14. Unit Systems English system: Pound, foot etc Conversion are arbitrary SI system: Single universal system (in progress) Gram, meter etc Conversion are simple, multiples of ten.

15. SI Units

16. Dimensional Homogeneity We all know apples and oranges can not add All equation terms should have same dimensions!!!

17. System, Surrounding and Boundary System : Region in space chosen for study. The mass or region outside the system is its surrounding . Boundary : System is separated by a real or imaginary boundary from surroundings. Boundary can be fixed or movable. It is shared by both system and the surrounding It has zero thickness.

18. Types of System There are three types of System: Close System or Control Mass Open System or Control Volume Isolated System

19. Close system A close system (control mass) has a fix mass . No mass can cross the boundary, so no change in mass. Volume can change, so the boundary can move. Energy can move the boundary.

20. Open System An open system (control volume) has fixed volume. It may have fixed or moving boundary. It may have Real or Imaginary boundary. It usually has a mass flow. Its volume is usually fixed. Energy can flow from it.

21. Isolated system An isolated system is a system in which no mass or energy can cross the boundary of the system. Ideally there are no perfect isolated system in the universe, but in many engineering problems it is a convenient option to consider a system an isolated system for the finite amount of time. Isolated System can be considered an special case of Close System with an additional constraint of no energy crossing the boundary of the system. Any example?

22. Properties of a system Property is a characteristic of a system. Pressure, temperature, volume are properties. Electric resistivity and velocity are also properties. The properties that are independent of the size/mass of the system are intensive properties. The properties that are dependent on the size or extent or mass of the system are extensive properties. Extensive properties per unit mass are called Specific Properties.

23. Continuum “Matter is a continuous and homogeneous with no holes or voids.” This is true for most cases of gases even though the gas molecules are widely spaced. This theory is not good for high vacuum conditions, but for our course in this class it will stay valid.

24. Density and Specific Volume Density is defined as mass per unit volume Specific volume is reciprocal of density, i.e., volume per unit mass The Density of substance in general depends on the Temperature and Pressure. The effect of Temperature and Pressure is different for different state of matters.

25. Specific Gravity The ratio of the density of a substance to the density of some standard substance at a specified temperature (usually water at 4°C = 1000 kg/m3) is called specific gravity or relative density It is a dimensionless quantity Substances with SG less than 1 are lighter than water and will float on water.

26. Specific Weight The weight of a unit volume of a substance is called specific weight

27. State of the system The state of the system at any particular time is defined or “fixed” by specifying the properties associated with the system at that moment. Consider a system not going any change, at this point, all the properties can be measured or calculated throughout the entire system, which gives us a set of properties that completely describes the condition, or the State , of the system.

28. State of the system At a given state, all the properties of a system have fixed values. If the value of even one property changes, the state will change to a different one.

29. Equilibrium State Thermodynamics deals with equilibrium states. The word equilibrium implies a state of balance. In an equilibrium state there are no unbalanced potentials (or driving forces) within the system. There are different types of Equilibrium for eg . Thermal, Mechanical, Chemical and Phase equilibrium etc Example of Thermal Equilibrium

30. State Postulate “The state of a simple compressible system is completely specified by two independent, intensive properties.” Independent Properties Intensive Properties

31. A system is called a simple compressible system in the absence of electrical, magnetic, gravitational, motion, and surface tension effects . These effects are due to external force fields and are negligible for most engineering problems. Otherwise, an additional property needs to be specified for each effect that is significant. If the gravitational effects are to be considered, for example, the elevation z needs to be specified in addition to the two properties necessary to fix the state. The state of nitrogen is fixed by two independent, intensive properties.

32. Processes To describe a process completely, one should specify the initial and final states of the process, as well as the path it follows, and the interactions with the surroundings. Any change that a system undergoes from one equilibrium state to another is called a process. The series of states through which a system passes during a process is called the path of the process

33. Quasi-Equilibrium Process When a process proceeds in such a manner that the system remains infinitesimally close to an equilibrium state at all times, it is called a quasi-static, or quasi-equilibrium process. A quasi-equilibrium process can be viewed as a sufficiently slow process that allows the system to adjust itself internally so that properties in one part of the system do not change any faster than those at other parts.

34. An example of pressure shown here. How the temperature /heat will effect?

35. Quasi-Equilibrium Processes Quasi-equilibrium process is an idealized process and is not a true representation of an actual process. But many actual processes closely approximate it, and they can be modeled as quasi-equilibrium with negligible error. Engineers are interested in quasi-equilibrium processes for two reasons. First, they are easy to analyze. Second, work-producing devices deliver the most work when they operate on quasi-equilibrium processes. Therefore, quasi-equilibrium processes serve as standards to which actual processes can be compared.

36. Process Diagram Process diagrams plotted by employing thermodynamic properties as coordinates are very useful in visualizing the processes. Some common properties that are used as coordinates are temperature T, pressure P, and volume V.

37. Processes - Keeping a property constant Process Property held constant isobaric pressure isothermal temperature isochoric volume isentropic entropy (see Chapter 7)

38. Cycle A system is said to have undergone a cycle if it returns to its initial state at the end of the process. That is, for a cycle the initial and final states are identical.

39. Difference Between Steady and Uniform The term steady implies no change with time. The opposite of steady is unsteady, or transient. The term uniform implies no change with location over a specified region.

40. Steady Flow Process A large number of engineering devices operate for long periods of time under the same conditions, and they are classified as steady-flow devices. Processes involving steady-flow devices devices can be represented reasonably well by a somewhat idealized process, called the steady-flow process, which can be defined as: A process during which a fluid flows through a control volume Steadily. Steady-flow conditions can be closely approximated by devices that are intended for continuous operation such as turbines, pumps, boilers, condensers, and heat exchangers or power plants or refrigeration systems

41. Temperature We can say, temperature is a measure of ‘hotness’ or ‘coldness’ of a substance. Based on our physiological sensation we can tell the temperature qualitatively as very hot, hot, cold or very cold. But two persons can have different opinion for the same temperature based on their sensation and understandings of qualitative description. Our sensation can also be misleading (different feeling for metal and wood which are at the same temperature). So we need some quantitative basis for telling the exact temperature.

42. Temperature Temperature is a thermodynamic property that measures the energy content of a mass. When heat energy is transferred to a body, the body's energy content increases and so does its temperature. In fact it is the difference in temperature that causes energy (heat) to flow from a hot body to a cold body.

43. Zeroth Law of Thermodynamics The zeroth law of thermodynamics states that if two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other. This simple statement is the basis of temperature measurement. By replacing the third body with a thermometer, the zeroth law can be restated as two bodies are in thermal equilibrium if both have the same temperature reading even if they are not in contact.

44. Development of Temperature Scale Several properties of matter change with temperature in ‘repeatable’ or ‘predictable’ way. Expansion properties, Electric resistance etc Water freezes and boils at the same temperature all the time (at constant pressure) A mixture of ice and water that is in equilibrium with air saturated with vapor at 1 atm pressure is said to be at the ice point . A mixture of liquid water and water vapor (with no air) in equilibrium at 1 atm pressure is said to be at the steam point .

45. Temperature Scales READ THE TOPIC FROM BOOK The temperature scale used in the SI system today is the Celsius scale (formerly called the centigrade scale; in 1948 it was renamed after the Swedish astronomer A. Celsius, 1702–1744, who devised it) . The temperature scale in the English system the Fahrenheit scale (named after the German instrument maker G. Fahrenheit, 1686–1736). On the Celsius scale, the ice and steam points were originally assigned the values of 0 and 100°C, respectively. The corresponding values on the Fahrenheit scale are 32 and 212°F. These are often referred to as two-point scales since temperature values are assigned at two different points.

46. Temperature Scales In thermodynamics, it is very desirable to have a temperature scale that is independent of the properties of any substance or substances. Such a temperature scale is called a thermodynamic temperature scale. This is developed later in conjunction with the second law of thermodynamics. The thermodynamic temperature scale in the SI is the Kelvin scale, named after Lord Kelvin (1824–1907). The temperature unit on this scale is the kelvin , which is designated by K (not °K). The lowest temperature on the Kelvin scale is absolute zero, or 0 K. The thermodynamic temperature scale in the English system is the Rankine scale, named after William Rankine (1820–1872). The temperature unit on this scale is the rankine , which is designated by R.

47. Temperature Relationship When temperatures of C are used and when K??

48. The International Temperature Scale of 1990 (ITS-90) The International Temperature Scale of 1990, which supersedes the International Practical Temperature Scale of 1968 (IPTS-68), 1948 (ITPS-48), and 1927 (ITS-27), was adopted by the International Committee of Weights and Measures at its meeting in 1989 at the request of the Eighteenth General Conference on Weights and Measures. The ITS-90 is similar to its predecessors except that it is more refined with updated values of fixed temperatures, has an extended range, and conforms more closely to the thermodynamic temperature scale. On this scale, the unit of thermodynamic temperature T is again the kelvin (K), defined as the fraction 1/273.16 of the thermodynamic temperature of the triple point of water, which is sole defining fixed point of both the ITS-90 and the Kelvin scale and is the most important thermometric fixed point used in the calibration of thermometers to ITS-90.

49. Pressure Pressure is the normal force exerted by a fluid per unit area. Pressure is the compressive force per unit area. The term pressure is used generally for gases and liquids. In solids we use Normal Stress.

50. Pressure Force per unit area in SI system is (Pascal) N/m 2 There are many other pressure units for eg , atmosphere ( atm ) , bar, kgf /sq.cm, (In English system pound/sq.in (psi)) Absolute Pressure : the actual pressure at a given point, measured relative to absolute vacuum. Gage Pressure : Most pressure gages are made to show pressure relative to atmosphere. Pressure below the atmospheric pressure is called the vacuum pressure. In thermodynamics we generally use Absolute Pressure in calculations.

51. NOTE: Pressure is the compressive force per unit area, and it gives the impression of being a vector. However, pressure at any point in a fluid is the same in all directions. That is, it has magnitude but not a specific direction, and thus it is a scalar quantity.

52. Variation of Pressure with Depth It will come as no surprise to you that pressure in a fluid at rest does not change in the horizontal direction. However, this is not the case in the vertical direction in a gravity field. Pressure in a fluid increases with depth because more fluid rests on deeper layers, and the effect of this “extra weight” on a deeper layer is balanced by an increase in pressure

53. consider a rectangular fluid element of height ∆z, length ∆x, and unit depth (into the page) in equilibrium. Assuming the density of the fluid ρ to be constant, a force balance in the vertical z-direction gives: where is the weight of the fluid element. Dividing by and rearranging gives: Variation of density is negligible with depth for liquids (not valid for oceans) and for gasses when the elevation is not much. The variation of density of liquids or gases with temperature can be significant and may need to be considered when high accuracy is desired. Assumptions:

54. For fluids whose density changes significantly with elevation:

55. Pressure Measuring Devices We noticed that an elevation change of ∆ z in a fluid at rest corresponds to , which suggests that a fluid column can be used to measure pressure differences. A device based on this principle is called a manometer , and it is commonly used to measure small and moderate pressure differences. A manometer mainly consists of a glass or plastic U-tube containing one or more fluids such as mercury, water, alcohol, or oil.

56. Other Pressure Measuring Devices Modern Electronic Transducers Change in Pressure is converted to change some electric system Thereby changing electric properties, voltage, capacitance or resistance Generate some current/voltage to record the pressure Bourdon Tube

57. Assignment #1 CHAPTER 1 Q- 14 TO Q- 73 Omit : 24, 51, 55, 57