Basic Concepts Of Engineering Thermodynamics SARDAR VALLABHBHAI PATEL INSTITUTE OF TECHNOLOGY,VASAD Basic Concepts Of Engineering Thermodynamics Made By:- Kanthan Patel (120410119107) Ketan Patel (120410119089)

Introduction Thermodynamic can be defined as the scince of energy.It deals with the most basic processes occuring in nature. Thermodynamics is made up from two greek words:- 1)Thermo:- Hot or Heat 2)Dynamics:- study of matter in motion

Basic laws Zeroth Law:-If two systems are both in thermal equilibrium with a third then they are in thermal equilibrium with each other. First Law:-The increase in internal energy of a closed system is equal to the heat supplied to the system minus work done by it. Second Law:-The second law of thermodynamics says that the entropy of any isolated system not in thermal equilibrium almost always increases. Isolated systems spontaneously evolve towards thermal equilibrium—the state of maximum entropy of the system. More simply put: the entropy of the world only increases and never decreases. Third Law:-The third law of thermodynamics states that the entropy of a system approaches a constant value as the temperature approaches absolute zero. 

System, surroundings and boundary System: A quantity of matter or a region in space chosen for study. Surroundings: The mass or region outside the system Boundary: The real or imaginary surface that separates the system from its surroundings.

Type of system (isolated system) Isolated system – neither mass nor energy can cross the selected boundary Example (approximate): coffee in a closed, well-insulated thermos bottle

Type of system (Closed system) Closed system – only energy can cross the selected boundary Examples: a tightly capped cup of coffee

Type of system (Open system) Open system – both mass and energy can cross the selected boundary Example: an open cup of coffee

Properties of a system Properties of a system is a measurable characteristic of a system that is in equilibrium. Properties may be intensive or extensive. Intensive – Are independent of the amount of mass: e.g: Temperature, Pressure, and Density, Extensive – varies directly with the mass e.g: mass, volume, energy, enthalpy

Properties of a system Specific properties – The ratio of any extensive property of a system to that of the mass of the system is called an average specific value of that property (also known as intensives property)

State, Equilibrium and Process State – a set of properties that describes the conditions of a system. Eg. Mass m, Temperature T, volume V Thermodynamic equilibrium - system that maintains thermal, mechanical, phase and chemical equilibriums.

Types of Thermodynamics Processes Cyclic process - when a system in a given initial state goes through various processes and finally return to its initial state, the system has undergone a cyclic process or cycle. Reversible process - it is defined as a process that, once having take place it can be reversed. In doing so, it leaves no change in the system or boundary. Irreversible process - a process that cannot return both the system and surrounding to their original conditions

Types of Thermodynamics Processes Adiabatic process - a process that has no heat transfer into or out of the system. It can be considered to be perfectly insulated. Isentropic process - a process where the entropy of the fluid remains constant. Polytropic process - when a gas undergoes a reversible process in which there is heat transfer, it is represented with a straight line, PVn = constant. Throttling process - a process in which there is no change in enthalpy, no work is done and the process is adiabatic.

Thermodynemic Equilibrium Thermal equilibrium- Temperature should be same throughout the system. Mechanical equilibrium-Unbalanced forces should be absent, eg, change in pressure Chemical equilibrium –No chemical reaction and mass transfer

Quasi-static Process Any change that a system undergoes from one equilibrium state to another is called a process, and the series of states through which a system passes during a process is called the path of the process. 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. 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 quasistatic, 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.

Quasi-static Process

Quasi-static Process The prefix iso- is often used to designate a process for which a particular property remains constant. An isothermal process, for example, is a process during which the temperature T remains constant. An isobaric process is a process during which the pressure P remains constant. An isochoric (or isometric) process is a process during which the specific volume v remains constant.

Thermodynamic Functions There are two types of functions defined in thermodynamics, path function and point function. Path function depends on history of the system (or path by which system arrived at a given state). Examples for path functions are work and heat. Point function does not depend on the history (or path) of the system. It only depends on the state of the system. Examples of point functions are: temperature, pressure, density, mass, volume, enthalpy, entropy, internal energy etc. Path functions are not properties of the system, while point functions are properties of the

Thermodynamic Functions system. Change in point function can be obtained by from the initial and final values of the function, whereas path has to defined in order to evaluate path functions. Figure 4.1 shows the difference between point and path functions. Processes A and B have same initial and final states, hence, the change in volume (DVA and DVB) for both these processes is same (3 m3 ), as volume is a point function, whereas the work transferred (WA and WB) for the processes is different since work is a path function. It should also be noted that the cyclic integrals of all point functions is zero, while the cyclic integrals of path functions may be or may not be zero.

Zeroth Law If two thermodynamic systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other. When two systems are put in contact with each other, there will be a net exchange of energy between them unless or until they are in thermal equilibrium. That is the state of having equal temperature. Although this concept of thermodynamics is fundamental, the need to state it explicitly was not widely perceived until the first third of the 20th century, long after the first three principles were already widely in use. Hence it was numbered zero -- before the subsequent three.

Zeroth Law