es 202 fluid and thermal systems lecture 14 phase change 1 14 2003 l.
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ES 202 Fluid and Thermal Systems Lecture 14: Phase Change (1/14/2003). Assignments. Homework: 3-2, 3-4, 3-6, 3-9 in Cengel & Turner Reading assignment Section 3-1 to 3-4, 3-6 in Cengel & Turner. Announcements. A note on Lab 2 write-up due date

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assignments
Assignments
  • Homework:
    • 3-2, 3-4, 3-6, 3-9 in Cengel & Turner
  • Reading assignment
    • Section 3-1 to 3-4, 3-6 in Cengel & Turner

ES 202 Fluid & Thermal Systems

announcements
Announcements
  • A note on Lab 2 write-up
    • due date
    • one write-up per lab group (higher expectation)
    • Contents: water wall, Torricelli experiment, pipe friction
    • Advice: start early, discuss with me if you need advice
  • Homework policy for Problem 11-105
    • not an easy problem
    • contains many concepts in a complete solution
    • Goal of homework: facilitate your learning
  • Feedback on Exam 1 from you

ES 202 Fluid & Thermal Systems

road map of lecture 14
Road Map of Lecture 14
  • Background quiz
  • Phase change
    • example: the boiling process
    • difference in molecular structure
    • State Principle
    • representation of P-v-T surface
    • two dimensional projection of P-v-T surface
    • terminology and definition
    • models:
      • ideal gas
      • incompressible substance

ES 202 Fluid & Thermal Systems

slide5

Background Quiz

  • How many phases does a substance have?
    • solid
    • liquid
    • gas
  • Zeroth law of thermodynamics
    • Statement: If two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other.
    • Significance: Introduce the concept of temperature
  • First law of thermodynamics
    • Significance: Conservation of energy
  • Second law of thermodynamics
    • Significance: Entropycannot be destroyed

ES 202 Fluid & Thermal Systems

slide6

Background Quiz (Cont’d)

  • Energy balance for an open system:
  • Entropy balance for an open system:

ES 202 Fluid & Thermal Systems

slide7

Background Quiz (Cont’d)

  • Simple substance:
    • there is only one reversible work mode which can change the energy of the system
      • think of work mode as an independent control knob (apart from heat transfer) which can change the energy of a system
  • State Principle:
    • Two independent, intensive thermodynamic properties are sufficient to fully determine the thermodynamic state of a simple substance.
    • For example:
    • Example from ideal gas model:

ES 202 Fluid & Thermal Systems

slide8

The Boiling Process

  • Exercise: Sketch the temperature variation of a pot of water from the moment that you turn on the stove
  • Question: The temperature does not change even though you keep adding heat to the system. Where does the energy go?
  • Question: What happens to the water during the boiling process, i.e. its internal structure?
  • Question: What is the surrounding pressure on the water?

ES 202 Fluid & Thermal Systems

p v t surface
P-v-T Surface
  • State Principle:
    • Two independent, intensive thermodynamic properties are sufficient to fully determine the thermodynamic state of a simple substance.
  • One can visualize the thermodynamic state of a simple substance on a 3D surface
  • Show the P-v-T surface
    • identify the solid, liquid, vapor regions
    • identify the two-phase dome

ES 202 Fluid & Thermal Systems

two dimensional representation
Two-Dimensional Representation
  • The 3D surface can be represented by multiple contour lines on a 2D plane, for example:
    • P-v plane (direction of increasing temperature)
    • T-v plane (direction of increasing pressure)
    • P-T plane
  • Sketch these above planes for:
    • an ideal gas
    • an incompressible substance
  • Where are the ideal gas model and incompressible substance state located on the P-v-T surface relative to the two-phase dome?

ES 202 Fluid & Thermal Systems

terminology and definition
Terminology and Definition
  • Pure substance
  • Compressed liquid
  • Saturated liquid
  • Saturated vapor
  • Superheated vapor
  • The two-phase (vapor) dome
  • Saturated liquid line
  • Saturated vapor line
  • Critical point
  • Triple point
  • Quality
  • Trace the boiling process on the T-v plane
    • effect of imposed pressure on boiling point

ES 202 Fluid & Thermal Systems