Chemical Engineering Thermodynamics (CHPE208) Summer 2014-15 Chapter 1 Introduction & Definitions Chapter 1 – Introduction & Definitions

Chapter - 1 Introduction & Definitions What is Thermodynamics? System and surroundings Thermodynamic System Properties Intensive and extensive properties Mass, Force, Temperature & Zeroth law of thermodynamics, Pressure, Work & System work, Heat Dimensions & Units Chapter 1 – Introduction & Definitions

What is Thermodynamics? Thermodynamics is the branch of physical science which deals with the relations between heat and other forms of energy (such as mechanical, electrical, or chemical energy), and by extension, of the relationships between all forms of energy. Laws of thermodynamics Zeroth law (thermodynamic equilibrium and temperature) First law (conservation of energy [work, and heat]) Second law (Entropy) Third law (Absolute zero temperature) Thermodynamics deals with equilibrium states. Thermodynamic considerations do not establish the rate of chemical or physical processes. Rates depend on driving forces and resistances. Driving forces are thermodynamic variables, but resistances are not. Thermodynamics does not deal with rate of energy transfer. Chapter 1 – Introduction & Definitions

Chapter 1 – Introduction & Definitions System & Surroundings System is defined as a quantity of matter or a region in space chosen for study and application of thermodynamics. Surroundings: The mass or region outside the system is called its surroundings Boundary: The real or imaginary surface that separates the system from its surroundings is known as boundary Types of system: Based on the mass and energy interactions between a system and its surroundings, a systems cane be classified as open, closed or isolated system Closed system (control mass) consists of fixed mass, and there can be no mass transfer between system and surroundings, but energy can be exchanged between system and surroundings. Open system (control volume): both energy and mass can be exchanged between a system and its surroundings. Isolated system: In an isolated system, there can be neither mass nor energy exchange between the system and surroundings Chapter 1 – Introduction & Definitions

Closed System Closed system (also known as a control mass) Consists of a fixed amount of mass, and no mass can cross the boundary, i.e. no mass can enter or leave the closed system Energy can cross the boundary The volume of a closed system does not have to be fixed 5

Closed System

Isolated System In an isolated system, even energy is not allowed to cross the boundary NO 7

Open System In an Open system (also called control volume) Both mass and energy can cross the boundary of a control volume. Boundaries of a control volume are called a control surface Control surface can be real or imaginary A control volume can be fixed in size and shape or it may involve a moving boundary This involves mass flow such as a compressor, turbine, or nozzle. 8

Open System

Chapter 1 – Introduction & Definitions System Properties Any characteristic of a system is called a property. Some familiar properties are Pressure (P), Temperature (T), Volume (V), Mass (m) Density (ρ) is defined as mass per unit volume of substance. SI units: kg/m3, kg/l, g/cc or g/cm3 Specific volume (ν) is defined as the volume per unit mass ν=V/m = 1/ ρ; SI Units: m3/kg, l/kg, cc/g or cm3/g Specific gravity (SG) is defined as the ratio of density of a substance to density of some standard substance at specified temperature and pressure Chapter 1 – Introduction & Definitions 10

Chapter 1 – Introduction & Definitions Types of Properties Intensive properties are the properties that do not depend on the size (mass) of a system. Examples: temperature, pressure, and density. Extensive properties are properties that depend on the size (mass) of a system. Examples: Mass m, Volume V, and total Energy E. Specific properties. Some examples of specific properties are specific volume (v = V/m) and specific total energy (e = E/m). Note: Ratio of any two extensive properties is an intensive property. Example:  = m/V, v = V/m Chapter 1 – Introduction & Definitions

Chapter 1 – Introduction & Definitions How to differentiate between intensive and extensive properties? Divide the system into two equal parts with a partition If each part has the same property value as the original system, the property is intensive If each part has only half the property value of the original system, the property is extensive Chapter 1 – Introduction & Definitions

Chapter 1 – Introduction & Definitions Mass Chapter 1 – Introduction & Definitions

Chapter 1 – Introduction & Definitions Force Exercise: An astronaut weighs 730 N in Houston, Texas, where the local acceleration of gravity is g = 9.81 m/s2. What are the astronaut’s mass and weight on the moon, where g = 1.67 m/s2? Chapter 1 – Introduction & Definitions

State and Equilibrium1/2 For a system not undergoing any change, a set of properties which can completely describe the system is called as the state of the system. At a given state, all the properties of a system have fixed values If the value of one property changes, the state will change Thermodynamics deals with equilibrium states. • In an equilibrium state, there are no unbalanced potentials (or driving forces) within the system

State and Equilibrium2/2 Thermodynamic Equilibrium: A system is said to be in thermodynamic equilibrium if it maintains thermal, mechanical, phase, and chemical equilibrium. Thermal Equilibrium: The temperature throughout the entire system is uniform Mechanical Equilibrium: The pressure throughout the Phase Equilibrium: The mass of each phase is in equilibrium Chemical Equilibrium: Chemical composition does not change with time, i.e.no chemical reactions take place 16

The State Postulate

Processes and Cycles Process: Any change that a system undergoes from one equilibrium state to another is called as a process. Path: Path is the series of states through which a system passes during a process. How to describe a process completely? 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 interaction with surroundings Cycle: A system is said to have undergone a cycle if it returns to its initial state at the end of the process, and so the initial and final states are identical for a cyclic process.

Types of Processes In most of the processes we study, one property of thermodynamic is held constant, also, the prefix iso- is often used to designate a process for which a particular property remains constant. isothermal process, is a process during which the temperature T remains constant; isobaric process is a process during which the pressure P remains constant; and isochoric (or isometric) process is a process during which the specific volume v remains constant. Isentropic process: Entropy held constant 19

Steady and Unsteady States Steady state implies no change with time. The term uniform, however, implies no change with location over a specified region. Unsteady state or transient, the opposite of steady The steady-flow process: a process during which a fluid flows through a control volume steadily. That is, the fluid properties can change from point to point within the control volume, but at any fixed point they remain the same during the entire process (V, m & E), ie not change with time. Steady-flow Process Here CV – Control volume 20

Temperature and the Zeroth Law of Thermodynamics A measurement of the overall microscopic kinetic energy of a body or a system, fast-moving molecules have high kinetic energy → they have high temperature. when an object is in contact with another object that is at a different temperature, heat is transferred from the object at higher temperature to the one at lower temperature until both objects attain the same temperature (ie Thermal Equilibrium). The equality in Temperature is the only requirement for thermal equilibrium Chapter 1 – Introduction & Definitions

Temperature and the Zeroth Law of Thermodynamics If two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other If the third body is a thermometer and it is in thermal equilibrium with two different bodies, then the two bodies must also be in equilibrium and at the same temperature Chapter 1 – Introduction & Definitions 22

Chapter 1 – Introduction & Definitions

Chapter 1 – Introduction & Definitions Pressure Example: At 300.15 K (27C) the reading on a manometer filled with mercury is 60.5 cm. The local acceleration of gravity is 9.784 m/s2. To what pressure does this height of mercury correspond? Chapter 1 – Introduction & Definitions

Chapter 1 – Introduction & Definitions Work Chapter 1 – Introduction & Definitions

Chapter 1 – Introduction & Definitions System work When work is done by a thermodynamic system, it is usually a gas that is doing the work. The work done by a gas at constant pressure is: For non-constant pressure, the work can be visualized as the area under the pressure-volume curve which represents the process taking place. The more general expression for work done is: System work is a major focus in the discussion of heat engines. Chapter 1 – Introduction & Definitions

Chapter 1 – Introduction & Definitions Energy - 1 Since the definition of velocity is u = dl/dt, the expression for work becomes,: This equation may now be integrated for a finite change in velocity from u1 to u2: Chapter 1 – Introduction & Definitions

Kinetic Energy - Exercise Problem: An automobile having a mass of 1250 kg is travelling at 40 m/s. What is its kinetic energy? How much work must be done to ring it to a stop? Answer: Given data: m = 1250 kg; velocity, v = 40 m/s A work equivalent to the kinetic energy must be done to stop the automobile, Work = 1 MJ Chapter 1 – Introduction & Definitions

Chapter 1 – Introduction & Definitions Energy - 2 Exercise: Verify that the SI unit of kinetic and potential energy is the joule Chapter 1 – Introduction & Definitions

Chapter 1 – Introduction & Definitions Heat A hot object brought in contact with a cold object becomes cooler, whereas the cold object becomes warmer because heat (Q) is transferred from the hot object to the cold one. Heat always flows from higher temperature to a lower one, and when there is no temperature difference there is no net transfer of heat. Temperature difference is called as the driving force for the heat transfer. The rate of heat transfer from one body to another is proportional to the temperature difference between the two bodies. In thermodynamic sense, heat is never regarded being stored within a body. Heat exists only as energy in transit from one body to another. When heat is added to system, it is stored not as heat but as kinetic and potential energy of the atoms and molecules making up the system. Chapter 1 – Introduction & Definitions

Dimensions and Units - 1 Primary Dimension Symbol SI unit mass m (sometimes M) kg (kilogram) length L (sometimes l) m (meter) time t (sometimes T) s (second) temperature T (sometimes q ) K (Kelvin) electric current I (sometimes i) A (ampere) amount of light  (luminous intensity) C (sometimes I) c (candela) amount of matter n or N (sometimes ) mol (mole) Secondary Dimension SI Unit Force F N (Newton) Acceleration a m/s2 Pressure P or P N/m2, Pa Energy E J, N.m Power P W (J/s) Chapter 1 – Introduction & Definitions

Chapter 1 – Introduction & Definitions Dimensions and Units - 2 Chapter 1 – Introduction & Definitions