Thermodynamics I: Energy & Heat Transfer

Objectives Comprehend the various forms of energy including potential/kinetic, thermal, and mechanical Comprehend the various forms of energy including potential/kinetic, thermal, and mechanical Understand the process of energy conversion Understand the process of energy conversion Comprehend the heat transfer process of conduction, convection, and radiation Comprehend the heat transfer process of conduction, convection, and radiation

Introduction Naval ships use either fossil fuel or nuclear fuel as energy for operation Naval ships use either fossil fuel or nuclear fuel as energy for operation Definition of energy? Definition of energy? Types of energy/sources Types of energy/sources Important for ALL officers to have basic understanding of engineering behind naval vessels Important for ALL officers to have basic understanding of engineering behind naval vessels

Thermodynamics Def’n: science concerned with the interrelationship between thermal energy and mechanical energy Def’n: science concerned with the interrelationship between thermal energy and mechanical energy Energy conversion of greatest significance on ship is thermal mechanical Energy conversion of greatest significance on ship is thermal mechanical Heat transfer: science that deals with methods by which thermal energy is able to translate Heat transfer: science that deals with methods by which thermal energy is able to translate

Classifications of Energy

Thermal Energy Def’n: Energy associated primarily with systems of molecules (vice particles) Def’n: Energy associated primarily with systems of molecules (vice particles) Internal Energy (stored): Internal Energy (stored): PE: associated w/ forces of attraction between molecules (bonding) PE: associated w/ forces of attraction between molecules (bonding) KE: associated with motion/activity of molecules (vibration, rotation, translation) KE: associated with motion/activity of molecules (vibration, rotation, translation)

Thermal Energy - Heat Heat: thermal energy in transition (parallel of work) - must have  T Heat: thermal energy in transition (parallel of work) - must have  T Temperature: the measure of an object’s internal kinetic energy Temperature: the measure of an object’s internal kinetic energy Units for heat: BTU Units for heat: BTU

Mechanical Energy Energy associated with large bodies or objects Energy associated with large bodies or objects Potential: relative position between particles Potential: relative position between particles PE = mgh PE = mgh Kinetic: relative velocities between particles Kinetic: relative velocities between particles KE = 1/2mv 2 KE = 1/2mv 2

Mechanical Energy - Work Work: mechanical energy in transition (affect of an object using force over a distance) Work: mechanical energy in transition (affect of an object 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 at high speed producing work? Ex: Is a bullet moving through air at high speed producing work?

Power Def’n: measure of the rate at which work is done Def’n: measure of the rate at which work is done Units: Hp or J/s Units: 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 stairs in one minute, or Man who carries 55 lb box up 10ft of stairs in one minute, or Woman who carries 55 lb box up 10ft of stairs in 30 seconds? Woman who carries 55 lb box up 10ft of stairs in 30 seconds?

Mechanisms of Heat Transfer Energy moves from higher temp -> lower temp Energy moves from higher temp -> lower temp Types: conduction, radiation, and convection Types: conduction, radiation, and convection Convention: Convention: Higher temp: source Higher temp: source Lower temp: sink or receiver Lower temp: sink or receiver

Conduction Def’n: transfer of thermal energy when source and sink are in physical contact Def’n: transfer of thermal energy when source and sink are in physical contact Energy transfer occurs layer to layer Energy transfer occurs layer to layer General Conduction Equation: Q=kA/L*  T General Conduction Equation: Q=kA/L*  T

Radiation Def’n: electromagnetic wave phenomenon (like radio or light) Def’n: electromagnetic wave phenomenon (like radio or light) No physical contact No physical contact All objects radiate some energy All objects radiate some energy Transparent substances are poor absorbers of radiant energy -> radiation passes through (i.e. tinted glass) Transparent substances are poor absorbers of radiant energy -> radiation passes through (i.e. tinted glass)

Convection Not really a transfer, but a transport Not really a transfer, but a transport Def’n: transportation or movement of some portions of a fluid within a mass of fluid Def’n: transportation or movement of some portions of a fluid within a mass of fluid Due to density differences caused by temperature differences Due to density differences caused by temperature differences Natural circulation: due to density only Natural circulation: due to density only Forced circulation: mechanical device Forced circulation: mechanical device

Effects of Heat Transfer Sensible vs Latent Heat Sensible vs Latent Heat Sensible Heat: Sensible Heat: Heat absorbed or rejected with a corresponding change of temp, but no change in phase Heat absorbed or rejected with a corresponding change of temp, but no change in phase Latent Heat: Latent Heat: Heat absorbed or lost w/ a change in phase Heat absorbed or lost w/ a change in phase

Effects of Heat Transfer

Latent Heat of Vaporization/Condensation: Latent Heat of Vaporization/Condensation: Liquid Vapor (no change in temp) Liquid Vapor (no change in temp) Latent Heat of Fusion: Latent Heat of Fusion: Liquid Solid Liquid Solid Saturated liquid/saturated vapor Saturated liquid/saturated vapor Subcooled liquid Subcooled liquid Superheated vapor Superheated vapor

Effects of Heat Transfer

Questions?