ThermodynamicThermodynamics I: Energy &s I: Energy &Heat TransferHeat Transfer

ObjectivesObjectives

• Comprehend the various forms of Comprehend the various forms of energy including potential/kinetic, energy including potential/kinetic, thermal, and mechanicalthermal, and mechanical

• Understand the process of energy Understand the process of energy conversionconversion

• Comprehend the heat transfer Comprehend the heat transfer process of conduction, convection, process of conduction, convection, and radiationand radiation

IntroductionIntroduction

• Naval ships use either fossil fuel or Naval ships use either fossil fuel or nuclear fuel as energy for nuclear fuel as energy for operationoperation

• Definition of energy?Definition of energy?• Types of energy/sourcesTypes of energy/sources• Important for ALL officers to have Important for ALL officers to have

basic understanding of engineering basic understanding of engineering behind naval vesselsbehind naval vessels

ThermodynamicsThermodynamics

• Def’n: science concerned with the Def’n: science concerned with the interrelationship between thermal interrelationship between thermal energy and mechanical energyenergy and mechanical energy

• Energy conversion of greatest Energy conversion of greatest significance on ship is thermal significance on ship is thermal mechanical mechanical

• Heat transfer: science that deals Heat transfer: science that deals with methods by which thermal with methods by which thermal energy is able to translateenergy is able to translate

Classifications of Classifications of EnergyEnergy

Stored

Transitional

Thermal

Internal - Kinetic - Potential

Heat

Mechanical

- Kinetic - Potential

Work

Thermal EnergyThermal Energy

• Def’n: Energy associated primarily Def’n: Energy associated primarily with systems of molecules (vice with systems of molecules (vice particles)particles)

• Internal Energy (stored):Internal Energy (stored):• PE: associated w/ forces of attraction PE: associated w/ forces of attraction

between molecules (bonding)between molecules (bonding)• KE: associated with motion/activity of KE: associated with motion/activity of

molecules (vibration, rotation, molecules (vibration, rotation, translation)translation)

Thermal Energy - HeatThermal Energy - Heat

• Heat: thermal energy in transition Heat: thermal energy in transition (parallel of work) - must have (parallel of work) - must have TT

• Temperature: the measure of an Temperature: the measure of an object’s object’s internal kinetic energyinternal kinetic energy

• Units for heat: BTUUnits for heat: BTU

Mechanical EnergyMechanical Energy

• Energy associated with large Energy associated with large bodies or objectsbodies or objects

• Potential: relative position Potential: relative position between particlesbetween particles• PE = mghPE = mgh

• Kinetic: relative velocities Kinetic: relative velocities between particlesbetween particles• KE = 1/2mvKE = 1/2mv22

Mechanical Energy - Mechanical Energy - WorkWork

• Work: mechanical energy in Work: mechanical energy in transition (affect of an object transition (affect of an object using force over a distance)using force over a distance)

• Units: same as energy (ft-lbf or J)Units: same as energy (ft-lbf or J)• Ex: Is a bullet moving through air Ex: Is a bullet moving through air

at high speed producing work?at high speed producing work?

PowerPower

• Def’n: measure of the rate at Def’n: measure of the rate at which work is donewhich work is done

• Units: Hp or J/sUnits: Hp or J/s• Ex: Who was done more work?Ex: Who was done more work?

• Man who carries 55 lb box up 10ft of Man who carries 55 lb box up 10ft of stairs in one minute, orstairs in one minute, or

• Woman who carries 55 lb box up 10ft Woman who carries 55 lb box up 10ft of stairs in 30 seconds? of stairs in 30 seconds?

Mechanisms of Heat Mechanisms of Heat TransferTransfer

• Energy moves from higher temp -Energy moves from higher temp -> lower temp> lower temp

• Types: conduction, radiation, and Types: conduction, radiation, and convectionconvection

• Convention:Convention:• Higher temp: sourceHigher temp: source• Lower temp: sink or receiverLower temp: sink or receiver

ConductionConduction• Def’n: transfer of thermal energy Def’n: transfer of thermal energy

when source and sink are in when source and sink are in physical contactphysical contact

• Energy transfer occurs layer to Energy transfer occurs layer to layerlayer

• General Conduction Equation: General Conduction Equation: Q=kA/L*Q=kA/L*TT

RadiationRadiation

• Def’n: electromagnetic wave Def’n: electromagnetic wave phenomenon (like radio or light)phenomenon (like radio or light)

• No physical contactNo physical contact• All objects radiate some energyAll objects radiate some energy• Transparent substances are poor Transparent substances are poor

absorbers of radiant energy -> absorbers of radiant energy -> radiation passes through (i.e. radiation passes through (i.e. tinted glass)tinted glass)

ConvectionConvection

• Not really a transfer, but a transportNot really a transfer, but a transport• Def’n: transportation or movement of Def’n: transportation or movement of

some portions of a fluid within a mass some portions of a fluid within a mass of fluidof fluid• Due to density differences caused by Due to density differences caused by

temperature differencestemperature differences• Natural circulation: due to density onlyNatural circulation: due to density only• Forced circulation: mechanical deviceForced circulation: mechanical device

Effects of Heat Effects of Heat TransferTransfer

• Sensible vs Latent HeatSensible vs Latent Heat• Sensible Heat:Sensible Heat:

• Heat absorbed or rejected with a Heat absorbed or rejected with a corresponding change of temp, but corresponding change of temp, but no change in phaseno change in phase

• Latent Heat:Latent Heat:• Heat absorbed or lost w/ a change in Heat absorbed or lost w/ a change in

phasephase

Effects of Heat Effects of Heat TransferTransfer

Effects of Heat Effects of Heat TransferTransfer

• Latent Heat of Latent Heat of Vaporization/Condensation:Vaporization/Condensation:• Liquid Vapor (no change in Liquid Vapor (no change in

temp)temp)• Latent Heat of Fusion:Latent Heat of Fusion:

• Liquid SolidLiquid Solid• Saturated liquid/saturated vaporSaturated liquid/saturated vapor• Subcooled liquidSubcooled liquid• Superheated vaporSuperheated vapor

Effects of Heat Effects of Heat TransferTransfer

Questions?Questions?