BASIC THERMODYNAMICS

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BASIC THERMODYNAMICS

• 60B-101

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INTRODUCTION
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Enabling Objectives

• Explain 1st 2nd Laws Thermodynamics
• Define
• Thermal and mechanical energy
• Potential, kinetic, internal, and chemical energy
• Flow and mechanical work
• Heat, conduction, convection, radiation
• Sensible heat, saturation point, saturated liquid
• State, property, latent heat, subcooled liquid
• Saturated, superheated, and desuperheated stm

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OVERVIEW

• Forms of Energy.
• Laws of Thermodynamics.
• Methods of Heat Transfer.
• Properties of Water and Steam.
• Thermodynamic Cycles.

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Forms of Energy

• Chemical Energy energy stored within chemical
  bonds of a substance (FUEL).
• Thermal Energy energy arising from a chemical
  reaction or friction (HEAT).
• Kinetic Energy energy of a substance or object
  in motion.
• Mechanical Energy work produced by a mechanical
  device.

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First Law of Thermodynamics

• Energy can neither be created nor destroyed but
  rather transformed from one form to another.

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First Law of Thermodynamics

• Fuel is burned to heat working substance.
  (Chemical Energy to Thermal Energy)
• The work done by heat becomes kinetic energy in
  the working substance. (Thermal Energy to
  Kinetic Energy)
• Working substance is passed across turbine to do
  work, i.e. rotate shaft. (Kinetic Energy to
  Mechanical Energy)
• Work done by engine produces non-useable heat
  which must be lost, i.e. friction.
  (Mechanical Energy to Thermal Energy)

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Thermal vs. Mechanical

• Stored (Internal)
• Internal KE (Temp)
• Internal PE (Chemical)
• Transitional (Heat)
• All systems share thermal and mechanical energy!

• Stored
• (Mechanical) KE
• (Mechanical) PE
• Transitional (Work)

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Describe the Energy

• Stored Energy
• Transitional Energy?

• Nitroglycerin
• Glass beaker

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Describe the Energy

• KE (mechanical)

• PE (mechanical)
• What about thermal and transitional energy?

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Energy in Transition

• Kinetic Energy
• Initiated Chemical Reaction
• Chemical energy
• heat
• work
• Energy in Transition

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Second Law of Thermodynamics

• No thermodynamic process can have a thermal
  efficiency of 100.

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Second Law of Thermodynamics

• No engine can convert all energy supplied to it
  into work. It is not 100 efficient.
• Some energy is LOST.
• Heat of combustion is transferred to equipment.
• Heat of friction is produced by equipment.
• Both of these are unusable and will ultimately be
  lost to the environment. (i.e. carried
  away by a cooling system/medium)

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Types of Heat Transfer

• Conduction
• Convection
• Radiation

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Conduction

• The transfer of energy by direct physical
  contact.
• Must have temperature differential.
• Factors affecting rate
• Magnitude of delta T.
• Area of contact.
• Type and thickness of material.

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Convection

• The transfer of energy from one point to another
  by the use of a moving fluid.
• Example Seawater flow through a condenser.

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Radiation

• The release/absorption of electromagnetic
  radiation.
• Example Heat from burning fuel radiates to
  generating tubes in boiler firebox.

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WHAT IS A HEAT EXCHANGER?

• WHERE TWO FLUIDS MEET TO TRANSFER HEAT.
• SHELL AND TUBE TYPE IS MOST COMMON

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Heat Exchangers

• Found in many systems throughout plant.
• Classified by
• Construction
• Plate
• Shell and tube
• Tube-in-tube
• Flow Path

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THREE TYPES OF SHELL AND TUBE HEAT EXCHANGERS

• PARALLEL FLOW
• COUNTER FLOW
• CROSS FLOW

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PARALLEL FLOW

• BOTH FLUIDS TRAVEL IN THE SAME DIRECTION.
• RAPID DROP IN HEAT TRANSFER EFFICIENCY.
• UNEVEN STRUCTURAL STRESS.

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COUNTER FLOW

• FLUIDS TRAVEL IN OPPOSITE DIRECTIONS.
• MARGINAL DROP IN HEAT TRANSFER EFFICIENCY.
• EVEN STRUCTURAL STRESS.
• EX SSTG Lube oil cooler

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CROSS FLOW

• FLUIDS TRAVEL AT ANGLES TO EACH OTHER.
• UNEQUAL VOLUMETRIC RATES.
• OFTEN USED TO CHANGE THE PHASE OF ONE OF THE
  FLUIDS.
• Ex Condenser

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Factors Affecting Heat Exchangers

• Marine Growth
• Scaling
• Reduces Heat Transfer
• Insulates and increases tube thickness
• Reduces area of physical contact
• Reduces Flow Rate
• Reduces rate of heat transfer

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Properties of Water and Steam

• Sensible Heat
• Heat added to a substance which produces a
  temperature increase.
• Latent Heat
• Heat added to a substance which causes a phase
  change.

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TERMS

• SATURATION TEMPERATURE- TEMPERATURE, OR POINT AT
  WHICH WATER CHANGES PHASE TO STEAM (PRESSURE
  DEPENDENT).
• SUPERHEATED STEAM- STEAM AT TEMP ABOVE SATURATION
  POINT.
• DESUPERHEATED STEAM- SUPERHEATED STEAM THAT HAS
  BEEN COOLED TO A TEMP JUST ABOVE SAT POINT.

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FIVE COMPONENTS OF A THERMODYNAMIC CYCLE

• WORKING SUBSTANCE- MEDIUM BY WHICH ENERGY IS
  CARRIED THROUGH A CYCLE.
• ENGINE- DEVICE THAT CONVERTS THE ENERGY OF A
  WORKING SUBSTANCE INTO USEFUL MECHANICAL ENERGY
  TO PERFORM WORK.

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• HEAT SINK- ABSORBS HEAT FROM WORKING SUBSTANCE
  AFTER IT HAS PERFORMED WORK IN THE ENGINE.
• HEAT SOURCE- SUPPLIES HEAT TO THE WORKING
  SUBSTANCE.
• PUMP- MOVES THE WORKING SUBSTANCE FROM THE LOW
  PRESSURE SIDE TO THE HIGH PRESSURE SIDE OF THE
  CYCLE.

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Thermodynamic Cycles

• Heat Source
• Engine
• Heat Receiver
• Pump
• Working Substance

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Thermodynamic Cycles

• Closed Cycle
• Steam Propulsion

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Thermodynamic Cycles

• Open Cycle
• Gas Turbine Engine (Brayton Cycle)

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Thermodynamic Cycles

• Open Cycle
• Diesel

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Summary

• Forms of Energy.
• Laws of Thermodynamics.
• Methods of Heat Transfer.
• Properties of Water and Steam.
• Thermodynamic Cycles.

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QUESTIONS?
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STUDY SCENARIOS

• What does the Second Law of Thermodynamics imply
  about the efficiency of naval propulsion plants?
• There will always be losses associated with the
  thermodynamic process (friction and heat). We
  can convert all work to heat but not all
  energy(heat) can be converted into usable work.

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STUDY SCENARIOS

• What type of steam is produced if saturated steam
  is heated past the saturation temperature at a
  constant pressure? What type of heat are you
  adding, latent or sensible?
• Superheated steam is created by adding sensible
  heat to saturated steam.

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STUDY SCENARIOS

• The next morning, you observe shipyard workers
  conducting an open and inspect of a
  shell-and-tube heat exchanger. What types of
  heat transfer occur in this type of heat
  exchanger?
• Conduction and Convection.

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STUDY SCENARIOS

• The inspection reveals a large amount of scale on
  the tubes of the heat exchanger. The shipyard
  workers tell you that this will not affect the
  efficiency of the heat exchanger, and that the
  tubes do not require cleaning. Do you agree with
  the shipyard workers? Why or why not?
• Flow rate decreases, tube thickness increase, and
  material quality decreases. All lower efficiency.