Introduction

Basic Thermodynamics Concepts

Heat.System.State.Path.Process.Cycle.Property.

Contd..Process - Any change that a system undergoes from one equilibrium state to another is called a process. Path - The series of state through which a system passes during a process is called a pathCycle - A process with identical end states is called a cycle.

A review of basic thermodynamics: A refresherThe ball representsmass exchange

The arrow representsenergy exchange

Zeroth Law of thermodynamicsThe Zeroth Law deals with thermal equilibrium and provides a means for measuring temperatures. Difference between thermal equilibrium and Thermodynamic equilibrium.

Zeroth Law of thermodynamics

First Law of thermodynamicsThe first law is the law of conservation of energy. The algebric sum of the work transfers is proportional to the algebric sum of heat transfer.

Limitations of First Law It does not place any distinction on the direction of the process under consideration. It will not help to predict, whether the system would undergo a change or no. It simply states that in a certain process heat and work are mutually convertible.

Second Law of thermodynamicsThe Second law of clausis states thatIt is impossible to construct a device that operates in a cycle and produces no effect other than the removal of heat from a body at one temperature and the absorption of an equal quantity of heat by a body at a higher temperature.

Second Law of thermodynamics contd..The Second law of Max Plancks states thatIt is impossible to construct an engine working on a cyclic process whose sole purpose is to convert all the heat supplied to it into equivalent amount of work.

Few ExamplesSome common examples.All processes in nature occur unaided or spontaneously in one direction. But to make the same process go in the opposite direction one needs to spend energy.

Third Law of ThermodynamicsIt is impossible by any procedure no matter how idealized, to reduce any system to the absolute zero temperature in a finite number of operations.

Summation of three laws

You cant get something for nothing To get work output you must give some thermal energyYou cant get something for very little To get some work output there is a minimum amount of thermal energy that needs to be givenYou cant get every thingHowever much work you are willing to give 0 K cant be reached.

Definitions of Reversible Process

A process is reversible if after it, means can be found to restore the system and surroundings to their initial states.

Some reversible processes:

Constant volume and constant pressure heating and cooling -the heat given to change the state can be rejected back to regain the state

Reversible Process (contd)

Isothermal and adiabatic processes -the work derived can be used to compress it back to the original state.Elastic expansion/compression (springs, rubber bands)

Some Irreversible Process

Thermodynamic ProcessesA process in which the volume remains constant constant volume process. Also called isochoric process / isometric process A process in which the pressure of the system remains constant. constant pressure process. Also called isobaric process A process in which the temperature of the system is constant. constant temperature process. Also called isothermal process A process in which the system is enclosed by adiabatic wall. Adiabatic process

Rankine Vapor power cycle

T-s diagram Rankine power cycle

P-V diagram Rankine power cycle

Rankine Cycle contd Process 1-2: Water from the condenser at low pressure is pumped into the boiler athigh pressure. This process is reversible adiabatic.Process 2-3: Water is converted into steam at constant pressure by the addition of heatin the boiler.Process 3-4: Reversible adiabatic expansion of steam in the steam turbine.Process 4-1: Constant pressure heat rejection in the condenser to convert condensateinto water.The steam leaving the boiler may be dry and saturated, wet or superheated. Thecorresponding T-s diagrams are 1-2-3-4-1; 1-2-3-4-1 or 1-2-3-4-1.

Thermal efficiency of rankine cycleConsider one kg of working fluid, and applying first law to flow system to various processes with the assumption of neglecting changes in potential and kinetic energy, we can write,q - w = dhFor process 2-3, w = 0 (heat addition Process), we can write,(q )boiler= (dh )boiler =(h3-h2)