Basic concepts in Thermodynamics for GATE exam preparation

This article deals with basic concepts in engineering thermodynamics. The study of thermodynamics is very much important in thermal engineering specialization in M. Tech or M. E level. So, the GATE exam offers more importance to this subject and its related topics. Follow the below mentioned basic concepts that will help you in GATE 2013 Exam.

New GATE examination Pattern: GATE 2014

What is Thermodynamics? Why study Thermodynamics? 

• Thermodynamics deals with relations between heat and work. It predicts many relationships between properties of matter.
• Thermodynamics systems and surroundings: thermodynamics systems: it is defined as any prescribed and identifiable collection of matter upon which attention is focused for investigation.

Basic Concepts in Engineering  Thermodynamics - Mechanical Engineering 

•  In the polytropic process, we have pV^n = constant, if the value of n is infinitely large, the process is called a constant volume process.
• The molecular volume of any perfect gas at 600 +103 N/m2 and 270c will be 4.17 m3/kg mol.
• The thermodynamic cycle used in a thermal power plant is Rankine.
• The same heat input and the same compression ratio efficiency depend mainly on the working substance.
• The change in enthalpy for small temperature change ∆T for an ideal gas is given by the relation ∆H = Cp ∆T.
• Entropy, for reversible flow, is given by the relation dS = dqh/T.
• The S.I. unit of pressure is Pascal.
• Superheated vapor behaves approximately as a gas.
• A sterling cycle has two isothermal and two constant volume processes.
• Brayton cycle has two isentropic and two constant pressure processes.
• Otto cycle consists of two isentropic and two constant volume processes.
• The diesel cycle consists of two isotropic, one constant volume one constant pressure process.
• Ericsson cycle has two isothermals and two constants pressure processes.
• Brayton cycle cannot be used in reciprocating engines even for the same adiabatic compression ratio and work output because a large volume of low-pressure air cannot be efficiently handled in rotation engines.
• Brayton cycle is generally used for gas turbines.
• Antifreeze chemicals are those that lower down the freezing points of liquids.
• The clog point of oil refers to the temperature at which paraffin and waxes in oil start precipitating.
• If the value of n is defiantly large in a polytropic pV^n = C. Then the process is called constant volume process.
• A heat exchange process where the product of pressure and volume remains constant is called a hyperbolic process.
• Zeroth law of thermodynamics provides the basis for measuring the thermodynamic property of temperature.
• 1 watt = 1 Nm/s.
• For a six compression of air set, with the minimum work condition the temperature rise in the cylinders will be the same.
• In the case of a steam engine, the cut-off ratio is the ratio of piston stroke which the piston has traveled when cut off occurs.
• The reason for insulating the pipe is to minimize the heat loss from the surface.
• Under ideal conditions, isothermal, isobaric, isochoric, and adiabatic processes are quasi-static processes.
• Isentropic flow is reversible adiabatic flow.
• Exhaust gases from an engine possess kinetic energy
• The extension and compression of a helical spring is an example of a reversible process.
• At a critical point, the latent enthalpy of vaporization is zero.
• Change in temperature = zero relation is not applicable in a free expansion process.
• An ideal engine absorbs heat at a temperature of 1270c and exhausts heat at a temperature of 770c. Its efficiency will be 13%.
• The triple point of a substance is the temperature and pressure at which the solid does not melt, the liquid does not boil and the gas does not condense.