1. Cost-effectiveness: An Engineers's Real Job Problem 3.138* Created By: Patrick Thomas

2. Problem A pitot-static probe to measure the velocity distribution in a water tunnel at 20 o C. U-tube manometer that uses a liquid of specific gravity 1.7. Maximum velocity= V max = 2.3 m/s. U-tube manometers to choose from are 8, 12, 16, 24, and 36 inches, with increasing cost (respectively). Which U-tube manometer should be purchased?

3. Assumptions Incompressible flow One-dimensional flow Steady flow

4. Important Formulae The Pitot Formula: Hydrostatic Relationship for Manometer Specific gravity  Specific Weight 

5. Calculations Using the rearranged Pitot Equation, we can solve for the pressure difference: With the pressure difference and specific weight, we can solve for the displaced liquid using the hydrostatic equation:

6. Discussion Although an 8 inch manometer would suffice, I suggest purchasing a 12 inch manometer (for a factor of safety of 2).

7. Relation to Biofluids The pitot-static probe measures slow moving fluids well. Thus, the pitot-static probe would make a great blood pressure measurement device. The pitot-static probe runs into problems when the flow is not laminar, however.