Thermodynamic System. A thermodynamic system is a volume in space containing a quantity of matter that is being studied for thermodynamic analysis.

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2 Thermodynamic System A thermodynamic system is a volume in space containing a quantity of matter that is being studied for thermodynamic analysis. The system is bounded by an arbitrary surface called the boundary. It separates the system from the surroundings. The boundary may be real or imaginary, may be at rest or in motion, and may change its size and shape. Mathematically speaking, the boundary has zero thickness, and thus it can neither contain any mass nor occupy any volume in space. The mass or region outside the system is called the surroundings or the environment. The surrounding interacts in some fashion with the system and hence has a detectable influence on the system.

3 Classification of System Basically, there are three types of systems: open system closed system and isolated system

4 Closed System A closed system (also known as a control mass) consists of a fixed amount of mass, and no mass can cross its boundary. That is, no mass can enter or leave a closed system. Examp: a piston-cylinder assembly filled with gas. But energy, in the form of heat or work, can cross the boundary; the matter may also change in chemical composition within the boundaries. The volume of a closed system does need to be fixed.

5 Open System An open system, or a control volume, is a properly selected region in space for which both mass and energy (heat and work) may cross the boundary. Examp: Flow through nozzle, compressor, turbine. The boundaries of a control volume are called a control surface. ** In an engineering analysis, the system under study must be defined carefully. In most cases, the system investigated is quite simple and obvious, and defining the system may seem like a tedious and unnecessary task. In other cases, however, the system under study may be rather involved, and a proper choice of the system may greatly simplify the analysis.

6 Isolated System An isolated system is one that is not influenced in any way by the surroundings. This means that no mass, heat, or work cross the boundary of the system. An Isolated system is a special case of closed system that does not interact in any way with its surroundings. Figure: Three types of thermodynamic System

7 Describing Systems and Their Behavior Thermodynamic systems can be studied by the two approaches : Microscopic approach: statistically averaging the behavior of the individual particles which make up the substance. Macroscopic approach (sometimes called Classical approach): large scale behavior of a substance.

8 State and Property The condition of a system at any instant of time is called its state. State at a given instant is determined by the properties 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. Examp: Different phase of a given mass of water.

9 A thermodynamic property is any characteristic of a system by which its physical condition may be described. Its numerical value depends only on the (local) thermodynamic equilibrium state of the system and is independent of the path (that is, the prior history how that state was attained). Examp: Some familiar properties: pressure P, temperature T, volume V, mass m. less familiar ones : viscosity, modulus of elasticity, electric resistivity. ** The state of a system frequently may be completely identified from a knowledge of only a few of its properties. The values of all remaining properties can be determined from the values of the few that are used to specify the state. The ideal gas formula, pv = RT, is an example of such an equation of state for a simple system.

10 Intensive property Intensive properties are those that are independent of the extent or mass of a system, Example: Temperature T, pressure P, density ρ, velocity v, chemical concentration etc. If a single phase system is divided arbitrarily into n parts, then the value of a given intensive property will be the same for each of the n subsystems. Thus intensive properties have the same value throughout a system in equilibrium. If the system is not in equilibrium, the property vary from place to place within the system at any moment [may be functions of both position & time].

11 Extensive Property Extensive properties are those whose values depend on the size or extent of the homogeneous system.. Example: Total mass m, total volume V, total momentum, Energy E and the quantity of electric charge etc. May change with time. A property is extensive if its value for the whole system is the sum of its values for the various subsystems or parts. If a system is divided into n(possibly unequal) parts, then the extensive property Y for the whole system is Y sys = i = 1 to n Yi ** Generally, uppercase letters are used to denote extensive properties (with mass m being a major exception), and lowercase letters are used for intensive properties (with pressure P and temperature T being the obvious exceptions).

12 Specific Property Extensive properties per unit mass or mole are called specific properties. Example: specific volume (v = V/m) and specific total energy (e = E/m).

13 Process and Cycle Any change or transformation that a system undergoes from one equilibrium state to another is called a Process. Or, A thermodynamic process is the succession of thermodynamic states that a system passes through as it goes from an initial state to a final state. A system subjected to a thermodynamic process normally experiences a change in its thermodynamic state. A system passes through a completely specified path from an initial state to a final state is called a process. The series of states through which a system passes during a process is called the path of the process.

14 Figure: Three process paths that change the Figure: A process between states 1 and 2 state of the system from A to B. and the process path. Process for which a particular property remains constant is designated by the prefix iso- is often used to designate a process.

15 Figure: A thermodynamic cycle A system is said to have undergone a cycle if it returns to its initial state at the end of the process through a series of state changes. That is, for a cycle the initial and final states are identical. The change in the value of any property for a cyclic process is zero.

16 Equilibrium Properties are truly defined when a system is in equilibrium. The word equilibrium implies a state of balance. In an equilibrium state there are no unbalanced potentials (or driving forces) within the system. A system in equilibrium experiences no changes with time when it is isolated from its surroundings. Hence a system in equilibrium cannot change in state without an interaction with its surroundings.

17 Classification of Equilibrium There are many types of equilibrium, and a system is not in thermodynamic equilibrium unless the conditions of all the relevant types of equilibrium are satisfied. Thermal equilibrium if the temperature is the same throughout the entire system. That is, the system involves no temperature differential, which is the driving force for heat flow. Figure: A closed system reaching thermal equilibrium.

18 Mechanical equilibrium is related to pressure, and a system is in mechanical equilibrium if there is no change in pressure or force at any point of the system with time. (the study of mechanical equilibrium is called statics). Phase equilibrium A phase equilibrium exists within a system when no phase transformations (such as vaporization or melting) occur within the system. Chemical equilibrium A system is said to be in chemical equilibrium when no chemical reactions or no change in chemical composition occur within the system. Phase equilibrium is also chemical equilibrium. Since the subject matter of thermodynamics contains all these types of phenomena, we lump all these definitions together to define thermodynamic equilibrium.

19 Zero th Law of Thermodynamics It states that if two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other. Consider three thermodynamic systems, A, B, and C. If system B is in thermal equilibrium with (i.e., is the same temperature as) system C and system B is in thermal equilibrium with system A, then system A is in thermal equilibrium with system C.

20 Figure: The zeroth law of thermodynamics applied to a mercury in a glass thermometer. The zeroth law tells us that if the glass is at the same temperature as (i.e., is in thermal equilibrium with) the surrounding fluid, and if the mercury is at the same temperature as the glass, then the mercury is at the same temperature as the surrounding fluid. Thus, the thermometer can be graduated to show the mercury temperature, and this temperature is automatically (via the zeroth law) equal to the temperature of its surroundings.

21 Pressure It is the average rate of change of momentum due to all the colliding molecules on a unit area. Pressure is defined as a normal force exerted by a fluid per unit area. When dealing with liquids and gases, it is ordinarily spoken of pressure; for solids it is known as of stresses. The pressure in a fluid at rest at a given point is the same in all directions.

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23 The actual pressure at a given position is called the absolute pressure, and it is measured relative to absolute vacuum (i.e., absolute zero pressure). Most pressure measuring devices, however, are calibrated to read zero in the atmospheric, and so they indicate the difference between the absolute pressure and the local atmospheric pressure. This difference is called the gage pressure. Pressures below atmospheric pressure are called vacuum pressures. + ; for P gage above the atmospheric pressure - ; for P gage below the atmospheric prresure

24 Temperature The temperature is a thermal state of a body which distinguishes a hot body from a cold body. The temperature of a body is proportional to the stored molecular energy i.e. the average molecular kinetic energy of the molecules in a system. A particular molecule does not have a temperature, it has energy. The gas as a system has temperature.

25 Energy Transport Mechanism There are three energy transport mechanisms, any or all of which may be operating in any given system: 1. heat, 2. Work and 3. mass flow. The sign conventions for heat and work are not the same. Heat transfer into a system is taken as positive, whereas work must be produced by or come out of a system to be positive..

26 Work Work is a transient quantity which appears at the boundary when a system changes its state due to the movement of a part of the boundary under the action of a force. If a system changes its state from state 1 to state 2, then the associated work can be written as Where state. is elementary work between two successive equilibrium In mechanics, work is defined as the integral of a force over a displacement. In mathematical form, work (W) is a scalar quantity defined according to: Unit:: Joule or N-m

27 Work can take on a number of forms (e.g., electrical, mechanical, or magnetic) since it can result from a variety of potential differences. pdv work or Displacement work: Let, initially the gas in the cylinder be a system having initially the pressure p 1 and volume V 1. The system is in thermodynamic equilibrium. Let the piston moves out to a new final equilibrium state 2, having the properties p 2 and V 2. At any intermediate point in the travel of the piston let the pressure be p and volume V.

28 When the piston moves an infinitesimal distance dl, the infinitesimal amount of work done by the gas on the piston Where, dv = a dl = infinitesimal displacement volume When the piston moves from state 1 to state 2 the total amount of work

29 Heat Heat is also a transient quantity, which transfer across the boundary when a system changes its state due to difference in temperature between the system and surroundings. Similarly, Unit: Joule

30 Path function and Point function Path functions are functions whose value depends on the path followed by the process. These are not the function of end state of the process. Path functions have inexact differential designated by δ.

31 Point Function Point functions are the functions whose have definite value for a given state. Thermodynamic properties are point functions. Point functions have exact or perfect differential. The change in value thus depends on the end states of the system irrespective of the path the system follows. W=f(P,V) => / V( W/ P) / P( W/ V)