THERMODYNAMICS

THERMODYNAMICS
Thermodynamics is the branch of science which deals with the interconversion of heat energy and mechanical energy. All those problems that are related to the interconversion of heat energy and work done are studied in thermodynamics. In thermodynamics we discuss different cycles such as Carnot cycle, Rankine cycle, Otto cycle, diesel cycle, refrigerator, IC engines, EC engines, Compressors, turbines and air conditioners.
FIRST LAW OF THERMODYNAMICS
	STATEMENT:                                                                                                                          "During any process total energy of a system and its surroundings is constant." OR "It is impossible to construct a machine which performs work continuously with taking energy from an external source." OR "Energy can neither be created nor destroyed but it can be converted from one form of energy to another form of energy."
	MATHEMATICAL REPRESENTATION
	Let a system absorbs DQ amount of heat energy. Addition of heat energy increases the internal energy of system from U1 to U2 and some useful work is also performed by the system. Increase in internal energy is given by: DU = U1 – U2 and work done is DW According to the first law of thermodynamics:                                                                                                     DQ = DU+ DW SIGN CONVENTION: DQ = positive if heat is added to a system DQ = negative if heat is released from a system DW = positive if work is done by the system DW = negative if work is done on the system
	APPLICATIONS OF THE FIRST LAW OF THERMODYNAMICS
	Heat can be supplied to a thermodynamic system under the following conditions: ISOBARIC     PROCESS ISOCHORIC   PROCESS ISOTHERMAL PROCESS ADIABATIC    PROCESS
	ISOBARIC     PROCESS
	A thermodynamic process in which pressure of the system remains constant during the supply of heat is called an ISOBARIC PROCESS.
	EXPLANATION
	Consider a cylinder fitted with a frictionless piston. The piston is free to move in the cylinder. An ideal gas is enclosed in the cylinder.
	Let the initial volume of the	system is V1 and initial internal energy is U1. Let DQP the gas is heated from
	T1 K to T2 K. Addition of heat causes the following changes in the system:
	Internal energy increases from U1 to U2. Volume of the system increases from V1 to V2. Temperature increases from T1 K to T2 K. Work (DW) is done by the gas on the piston.
	According to the first law of	thermodynamics:
	DQ = DU+ DW But DW = PDV Thus                                                                                           DQP = DU+ PDV As DV = (V2 - V1)                                                                                           DQP = DU+ P (V2 - V1)
	GRAPHICAL REPRESENTATION
	Graph between P & V for an isobaric process is a straight line which is parallel to V-axis.
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