Energy, Processes and CyclesBasic Concepts of Thermodynamics Part 2Graciano Emmanuelito E. Dela Cruz IIISchool of Mechanical EngineeringMapua Institute of Technology

Some Commonly Used Conversions:Pressure:1 atm = 14.696 psia = 101.325 kPa1 atm = 29.921 in Hg = 760 mmHg 1 bar = 105 Pa = 105 N/m21 bar = 14.5 psi1 kgf/cm2 = 14.22 psi

Force:1 kgf = 1 kilopond, kp1 kgf = 9.80665 N1 lbf = 4.448 N1 kgf = 2.2046 lbf

Power:1 kW = 3413 Btu/hr1 kW = 3600 kJ/hr1 HP = 0.746 kW = 2545 Btu/hr1 PS (Metric HP) = 0.7355 kW1 HP = 33000 ft-lb/min

Mass:1 short ton (US) = 2000 lbs1 long ton (British) = 2240 lbs1 Metric ton(tonne) = 2204.6 lbs = 1000 kg1 kg = 2.2046 lbsEnergy:1 Btu = 1.055 kJ1 Btu = 778.16 ft-lb1 kCal = 4.186 kJ1 Btu/lb = 2.326 kJ/kg

Length:1 kilometer = 3280.8 ft1 mile = 5280 ft1 yard = 3 ft1 meter = 3.2808 ft

Volume:1 (US) gallon = 3.78543 liters1 ft3 = 7.481 gal (US)1 liter = 1000 cm31 m3 = 1000 liters15.85 gal/min = 1 liter/s15850 gal/min = 1 m3/s264.177 gal = 1 m31 petroleum barrel (unrefined) = 42 gal (barrel)1 petroleum barrel (refined) = 55 gal (drum)

Mechanical Work and PowerMechanical Work is defined as the product of a force F and a displacement D when both are measured in the same direction (collinear).W=F x DPower is the time rate at which work is done on or by a system.

Kinetic and Potential energiesKinetic energy is defined as the work in moving the system a distance.Acceleration work is the work done on the system to change its velocity.KE = mV2 = (m/gc)V2Where gc is the gravitational constant

The curse of gc

Potential energy of a system mass depends on its position in the gravitational field.Gravitational work is the work done against gravity to change the elevation of a systemPE =mgz, where z is the elevationKinetic and Potential energies

Shaft workShaft work, sometimes called rotational mechanical work, is evaluated in terms of the external torque transmitted by a rotating shaft.Torque is the turning moment exerted by a tangential force acting at a distance from the axis of rotation.

Electrical workElectrical work is the mechanical work required to move the charge in the electrostatic field (for example, an electric circuit).

Internal energyThe sum of the energies of all the molecules in a system, energies that appear several complex forms, is the internal energy, U.U = mcvT , where Cv is a the specific heat at constant volume.

Flow energyFlow energy is a special form of work that is significant for a moving stream.Often called flow work, it is work done in pushing a fluid across a boundary, usually into or out of a system.Wf = pV, where p is the pressure and V is the volume of the system.

Heat Heat, Q, is energy in transit (on the move) from one body or system to another solely because of a temperature difference between the systems.

Enthalpy, HThe sum of the internal energy and the flow work is known as the enthalpy.Also known as heat content.H = U + pVH = mcpT , where Cp is a the specific heat at constant pressure.

Entropy, SDegree of randomness or disorder.

Thermodynamics processesConstant pressure process or isobaric or isopiestic processConstant volume process or isometric or isochoric processConstant temperature process or isothermal processConstant entropy process or isentropic process or adiabatic process (heat is zero)Constant enthalpy process or isenthalpic processPolytropic process

Thermodynamic cyclesA combination of two or more processes which, when completed, returns the system to its initial state is known as a THERMODYNAMIC CYCLE. In other words, the system goes through a number of states and finally reaches the original state again.

Factors of a thermodynamic cycleWorking fluidHot body / hot reservoirHeat engine or heat pumpCold body / heat sink

Thermodynamic cyclesCarnot CycleInternal combustion enginesOtto cycleDiesel cycleStirling and Ericsson cyclesGas turbine cycle (Brayton cycle)Vapor power systemsRankine cycleReheat, regenerative, reheat-regen, cogenerationRefrigeration cycle Reversed Carnot cycle / vapor compression cycle

Carnot cycleCarnot cycle is the most efficient cycleSadi Carnot

Nicolas Leonard Sadi Carnot1796-1832French physicist and military engineer who, in his 1824 Reflections on the Motive Power of Fire, gave the first successful theoretical account of heat engines.

Internal combustion engines

Air Standard Otto cycleA theoretical cycle of interest in analyzing the behavior of reciprocating spark ignition enginesNicholas August Otto (1832-1891)

Air Standard Diesel CycleBasis for the Compression Ignition engine or the Diesel EngineRudolf Karl Christian Diesel (1858-1913)

The 1st Diesel engine

4 stroke and 2 stroke

Brayton cycleContinuous combustion processGas turbine cycleGeorge Brayton (1830-1892)

Vapor Power SystemsElectrical Power available in homes and industry is developed in an electrical generator at a steam power plant.This model for a steam power cycle is called the Rankine cycle.

William John Macquorn RankineScottish engineer and physicist.Professor of engineering at the Univ. of Glasgow.

You should know your cycle!