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) 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 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 –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 –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 –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 –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