ES 202 Fluid and Thermal Systems Lecture 14: Phase Change (1/14/2003)

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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 &amp; Turner Reading assignment Section 3-1 to 3-4, 3-6 in Cengel &amp; Turner. Announcements. A note on Lab 2 write-up due date

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### ES 202Fluid and Thermal SystemsLecture 14:Phase Change(1/14/2003)

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

ES 202 Fluid & Thermal Systems

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
• 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

• 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

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

Background Quiz (Cont’d)

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

ES 202 Fluid & Thermal Systems

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

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
• 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
• 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
• 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