Thermodynamics I: Energy

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Thermodynamics I Energy Heat Transfer
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Objectives

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

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Introduction

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

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Thermodynamics

• Defn science concerned with the
  interrelationship between thermal energy and
  mechanical energy
• 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

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Classifications of Energy
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Thermal Energy

• Defn Energy associated primarily with systems
  of molecules (vice particles)
• Internal Energy (stored)
• PE associated w/ forces of attraction between
  molecules (bonding)
• KE associated with motion/activity of molecules
  (vibration, rotation, translation)

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Thermal Energy - Heat

• Heat thermal energy in transition (parallel of
  work) - must have DT
• Temperature the measure of an objects internal
  kinetic energy
• Units for heat BTU

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Mechanical Energy

• Energy associated with large bodies or objects
• Potential relative position between particles
• PE mgh
• Kinetic relative velocities between particles
• KE 1/2mv2

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Mechanical Energy - Work

• Work mechanical energy in transition (affect of
  an object using force over a distance)
• Units same as energy (ft-lbf or J)
• Ex Is a bullet moving through air at high speed
  producing work?

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Power

• Defn measure of the rate at which work is done
• Units Hp or J/s
• Ex Who was done more work?
• 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?

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Mechanisms of Heat Transfer

• Energy moves from higher temp -gt lower temp
• Types conduction, radiation, and convection
• Convention
• Higher temp source
• Lower temp sink or receiver

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Conduction

• Defn transfer of thermal energy when source and
  sink are in physical contact
• Energy transfer occurs layer to layer
• General Conduction Equation QkA/LDT

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Radiation

• Defn electromagnetic wave phenomenon (like
  radio or light)
• No physical contact
• All objects radiate some energy
• Transparent substances are poor absorbers of
  radiant energy -gt radiation passes through (i.e.
  tinted glass)

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Convection

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

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Effects of Heat Transfer

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

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Effects of Heat Transfer
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Effects of Heat Transfer

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

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Effects of Heat Transfer
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Questions?