Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Summary of Energy Topics Chapter 1: Thermodynamics / Energy Introduction Chapter 2: Systems & Processes Chapter 3: Work, Energy, Temperature & Heat Chapter 4: Work Processes of Closed Systems Chapter 5: Thermodynamic Properties Chapter 6: Steam Tables Chapter 7: Ideal Gases Chapter 8: Conservation of Mass & Energy Chapter 9: 1 st Law of Thermodynamics Chapter 10: Steady Flow Energy Equation Chapter 11: Heat Engines and Reversibility Chapter 12: 2 nd Law of Thermodynamics Chapter 13: Entropy Chapter 14: General Energy

Chapter 3: Work, Energy, Temperature & Heat WORK A force is that which can cause a mass to accelerate. The S.I. unit of force is the Newton (N) Mechanical work is the phenomenon of a force acting while its point of action moves through a distance.  W =F  s (scalar product) The S.I. unit of work is the joule (1 J = 1 Nm)

Chapter 3: Work, Energy, Temperature & Heat Work = Force × Distance  Work = C × Δs = C × (b-a) Static Friction When the force is constant over a distance: When the force varies over a distance: f(x) Work Work = Force × Distance

Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 3: Work, Energy, Temperature & Heat Work done on a system is normally positive (+J) Work done by a system is normally negative. (- J) Shear work or shaft work is work that involves only a displacement in the plane of the boundary of a system (= +J) W=  F  ds W=  T  d  = T   = rotation (radians) T = Torque τ = r.F.sin

Normal work or displacement work is work that involves only a displacement normal to the boundary of a system. W=  F  ds However, F=p.A …(N/m 2 )  W =  p.A ds since dV = -Ads… change in Vol = area × distance moved W= -  pdV irrespective of the shape of the boundary. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 3: Work, Energy, Temperature & Heat Area ds

Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 3: Work, Energy, Temperature & Heat Electric power Power is a rate of work. The S.I. unit = Watt (1 W = 1J/s) Energy is generally supplied to a system as electric power rather than mechanical power

ENERGY Energy is the capacity to do work S.I. unit = joule (J). Kinetic energy is the energy possessed by a mass (m) due to its velocity (v) E k = mv 2 /2 OR E k /m = v 2 /2 Potential energy is the energy possessed by a mass (m) due to its position in the gravitational (g) field measured from a reference datum point (z) E p = mgz OR E p /m = gz E p = mgh Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 3: Work, Energy, Temperature & Heat Conservation of energy

Chapter 3: Work, Energy, Temperature & Heat Internal energy is the molecular energy possessed by a substance. It includes the kinetic energy of translation, rotation, and vibration of molecules, as well as potential energy associated with static electric energy of atoms within a molecule of crystal Total Energy The total energy of a system is the sum of all the types of energy it possesses E = E k + E p + U e = e k + e p + u

Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering 1 st Law Thermodynamics: Energy can neither be created or destroyed but only transformed from one form to another.

TEMPERATURE Property that explains if something is hot or cold Measured with thermometers or electronic devices Remember: Two systems are said to have the same temperature if when they are brought into contact with each other, no change occurs to any of their properties. The Zeroth law of thermodynamics states; that if two systems each have the same temperature as a third system then they have the same temperature as each other. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 3: Work, Energy, Temperature & Heat

Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 3: Work, Energy, Temperature & Heat The temperature of a system that contains the solid (e.g. ice), liquid (e.g. water), and vapour (e.g. steam) phases of a pure substance in equilibrium is called the triple point temperature of that substance This can occur at a certain pressure! Triple point: 0.01˚C at atm

Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 3: Work, Energy, Temperature & Heat The Kelvin scale is the S.I. unit for temperature: Typical scales used: Celsius ( o C), Fahrenheit ( o F) and less known Rankine ( o R) exist!

Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 3: Work, Energy, Temperature & Heat

HEAT (which can also be described as heat transfer) is energy transfer across a boundary due to temperature difference. S.I. = joule (J) An adiabatic process is one in which there is no heat transfer between a system and its surroundings. An adiabatic boundary does not permit heat transfer, e.g. insulating materials (poor heat conductors). The sign convention for heat (+) Heat transfer to a system is normally taken to be positive with respect to the system. (-) Heat transfer from a system is normally taken to be negative. Dr. Owen Clarkin School of Mechanical & Manufacturing Engineering Chapter 3: Work, Energy, Temperature & Heat