Fluid Statics

  • What is the main difference between a fluid and a solid?
  • Define, and give the symbol and units for:
  • Specific gravity
  1. Pressure
  • Write an equation that relates Pgauge, Patm, and Pabs.
  • When doing fluid statics problems,
  1. What do we know about the pressure in a continuous fluid?
  1. What happens to pressure as you go down through a fluid?
  1. What happens to pressure as you go up through a fluid?
  • What is the buoyant force? What is the equation? Which density, volume, etc. do we use?
  • Briefly describe the way we derived buoyant force.

Practice Problems:

1)All lecture and homework problems. If you know how to do them and understand them, you will likely do well on the exam.

2)Determine the elevation difference, delta h, between the water levels in the two open tanks shown below: (Dr. Olson’s first exam, Fall ’07)

3)A teapot with a brewer at the top is used to brew tea, as shown below. The brewer blocks the vapor from escaping the teapot, causing the pressure in the teapot to rise and the water to rise up the spout. If the volume of the water in the spout is negligible compared to the volume of water in the teapot, determine the maximum cold-water height (i.e., before any heat is added), H, that would not cause an overflow at the spout when enough heat is added to produce a gage pressure of 0.32 kPa for the vapor. (Dr. Olson’s first exam, Spring ’06)

4)Approximate a fishing boat as a box measuring 20 m long by 5 m wide by 5 m high with a mass of 100,000 kg.

a)What is the draft, d, of the boat? (the draft is the depth the boat sits in water).

b)The fishing net accidentally catches a 1m x 1m x 1m block of aluminum (SG = 2.7), and the fishermen slowly begin to reel the net in. What is the draft of the boat now (assume the block of aluminum is completely submerged in the water)?

Shear Stress, Newton’s Law of Viscosity

Define/give units/symbols/extra info/give examples as appropriate:

  • Shear stress – definition, units, symbol
  • Shear strain – definition, symbol, =U/H
  • Viscosity – define, symbol, units
  • Kinematic Viscosity – units, symbol
  • Newtonian fluid – define (what is the equation that describes it if it is Newtonian?), examples, make a graph of how it behaves
  • Non-Newtonian fluid – give examples, define, name two categories, making graphs for how they behave

Pipe Flow

  • Describe why dimensionless quantities are useful in describing situations like pipe flow.
  • Reynold’s number: symbol, equation (for pipe flow), what ratio of forces does it describe
  • friction factor: symbol, equation (for pipe flow), what ratio of forces does it describe
  • How do the Reynold’s number and friction factor relate for laminar flow? Turbulent flow?
  • Write the Hagen-Poiseuille equation. When can we use it (look back to the assumptions made when Dr. Hebert derived it in class)?
  • What is the equation that gives the power input required to pump an incompressible Newtonian fluid through a pipe?
  • What is relative roughness? What is the symbol for it? What dimensionless quantity does it affect?
  • How do you find the hydraulic diameter of a non-circular pipe?
  • Describe how to find solutions in pipe flow with the following unknowns, assuming all other quantities are known (some solutions may be iterative):
  • |ΔP|
  • Q or v
  • D

Particle Flow

  • What is the equation for Reynold’s number for flow past a sphere?
  • What is the equation for the drag coefficient for flow past a sphere?
  • What is the relationship between Re and CD in the Stokes flow region? What is the requirement to be in the Stokes region (both qualitative and quantitative)?
  • Where would you find Re and CD relationships for flow that is not Stokes?
  • Define, give equations, symbols and units for
  • Superficial velocity
  • Void fraction
  • Volume fraction
  • Hydraulic diameter
  • Packed bed friction factor
  • What is the Ergun equation? When does it apply? How can it be simplified, and when? (example 4.6 in Denn is good)

General Tips

  • Know how to do the homework and examples worked in class. These are your best predictors of what kinds of problems will be on the exam (of course, the problems on the exam will be shorter).
  • There are a lot of equations, especially relating Re and f in chapters 3 & 4. Know when each of them applies, so that in a given circumstance you have an idea of which one to use.