Transcript ES 202 Lecture 1 - Rose

ES 202
Fluid and Thermal Systems
Lecture 2
(12/03/2002)
Assignments
• Reading:
– Cengel & Turner Section 10-1 and 10-3
– Review Statics (concept of static equilibrium)
• Homework:
– 2-41, 2-46, 2-62 in Cengel & Turner
Road Map of Lecture 2
• Announcements
• Finish review section of Lecture 1
• What is a fluid?
• Hydrostatics
– Forces in a fluid
– Concept and properties of pressure
– Hydrostatic pressure distribution
• Active learning exercises: manometer
Announcements
• Lab 1 this week in this classroom
• Do the pre-lab before lab session
• Check on textbook availability
• Instructor’s web page (contains lecture presentations)
http://www.rose-hulman.edu/~luic
• Corrections on extension: 6998
• Thanks for filling out the questionnaire
– Some advice from Rose grads: the different engineering
disciplines are not disjoint
Announcements (cont’d)
– Example of thermal fluid application in other fields
– Learn to work with others
– Don’t be tunnel vision in viewing your education; expose
yourself to different disciplines (widen your thinking)
– Is this course easy or difficult?
– Propose to hold review session on major concepts from ES
201 (need your input)
Tips for Success
• Keep up with homework daily (best) or weekly
(minimum)
• See me when you need any help
• Give me feedback at anytime (the earlier the
better)!
Familiar Terminology
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Close system/open system
Control mass/control volume
Storage
Production
Net influx
Conservation of mass
Conservation of linear momentum
Zeroth law of thermodynamics – concept of temperature
First law of thermodynamics – concept of energy
Second law of thermodynamics – concept of entropy
What is entropy, enthalpy and energy? What are they good
for?
What is a Fluid?
• Give me some descriptions about a fluid
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Examples: gas, liquid
Something that flows
Something that fits the shape of its container
It continuously deforms under the application of a force
• What is the main difference between a solid
and a fluid?
Forces in a Fluid
• Start from a control volume analysis
– Body force (acts on the contents within the control volume)
– Surface force (acts on control surface)
• Shear stress
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Parallel to a control surface
A new fluid property: viscosity (thin vs thick)
Interpretation of viscosity from microscopic view
Effects of viscosity on fluid flows
• Notion of no-slip conditions at solid boundaries
• Development of velocity gradient (only when there is fluid motion)
• Give rise to viscous stress
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Temperature dependency of viscosity
Examples (flow over an airfoil, automobile, flow inside a pipe)
Applications (lubrication in ball bearing, protect engine block)
A small research project (meaning of 10W30, 10W40)
Forces in a Fluid (cont’d)
• Normal stress
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Normal to a control surface
Pressure is the major component to normal stress
Interpretation of pressure from microscopic view
Pressure is a scalar
Pressure as a point property
Isotropic property of pressure (Pressure at a point is the same in all
directions)
– How does pressure change in a fluid?
– Pressure does not change in the horizontal direction for a fluid at rest
(what will happen if pressure varies in the horizontal direction?)
– Gage vs absolute pressure
Hydrostatic Pressure Distribution
• In horizontal direction:
P = constant
• In vertical direction:
Active Learning Exercise