ENGINEERING THERMODYNAMICS Dr. M.R.SWAMINATHAN Assistant Professor Internal Combustion Engineering Division Department of Mechanical Engineering ANNA UNIVERSITY CHENNAI-25.

THERMODYNAMICS It is the Science of Energy Interactions It deals about the relations between heat, work and the properties of the system. Thermodynamics is derived from the Greek words Thermo (Heat) and Dynamis (Power)

Thermodynamics is a science that is based in experimental findings These findings have been formalised into certain laws A famous saying is that Thermodynamics is the study of Three Laws (or) Study of 3E’s namely – Energy, Entropy & Equilibrium

If we like to Rise the temperature of water in the pressure cooker for boiling rice Burn some fuel in the combustion chamber of an aero engine to propel an aircraft. Cool our room on a hot humid day. Heat up our room on a cold winter night. What is the minimum amount of electricity or fuel we need to use?

On the other hand if we burn, Some coal / gas in a power plant to generate electricity. Petrol in a car engine. What is the maximum energy we can get out of these process? Thermodynamics allows us to answer some of these questions

THERMODYNAMICS - APPROACH There are two points of view from which the behaviour of matter can be studied  Microscopic (Statistical)  Macroscopic (Classical)

MACROSCOPIC APPROACH In macroscopic approach certain quantity of matter is considered, without a concern on the events occurring at the molecular level. These effects can be perceived by human senses or measured by instruments. eg: pressure, temperature

MICROSCOPIC APPROACH In microscopic approach the effect of molecular motion is considered.  At microscopic level the pressure of a gas is not constant. The temperature of a gas is a function of the velocity of molecules.  Most microscopic properties cannot be measured with common instruments nor can be perceived by human senses

CONCEPT OF CONTINUUM Matter is made up of atoms that are placed at distance An assumption that a continuous homogeneous matter with no recess is known as CONTINUUM It allows us to treat properties of the matter as continuous functions of space variables.

CONCEPT OF CONTINUUM  The concept of continuum is valid only when the characteristic length (like diameter) is much larger than the mean free path of the gas  The mean free path of atmospheric air is nm

Knudsen number A dimensionless parameter known as Knudsen number ( Kn = λ / L ) describes the degree of departure from continuum. where λ – molecular mean free path & L – characteristic length Usually when Kn > 0.01, the concept of Continuum does not hold good.

Consider a container filled with oxygen at atmospheric conditions. The diameter of the oxygen molecule is about 3x10-10 m and its mass is 5.3x10-26 kg. The mean free path of oxygen at 1 atm pressure and 20°C is 6.3x10-8 m.That is, an oxygen molecule travels, on average, a distance of 6.3x10-8 m (about 200 times of its diameter) before it collides with another molecule

THERMODYNAMIC SYSTEM System is the one upon which we focus our attention. System is that about which we are interested in analysing It may be a Boiler or Compressor or Nozzle