ENTC 303: Announcements

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ENTC 303 Announcements

• Homework assignment No.2 due today
• Homework assignment No.3
• From Mott
• 4.1, 4.4, forces due to gas pressure
• 4.12, forces on horizontal flat surfaces under
  liquids
• 4.16, 4.17, forces on rectangular walls (vertical
  inclined)
• 4.28, 4.29, forces on submerged plane areas
• 4.46, piezometric head (added to 4.28)
• 4.48, 4.49, forces on curved surfaces
• 4.56, piezometric head (added to 4.48)
• 5.4, 5.8, 5.16, 5.24, 5.25, buoyancy
• Due next Thursday, Sept 18th before class
• For more information, go to
• http//etidweb.tamu.edu/classes/entc303/

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Chapter 6 Flow of Fluids

• Example of fluid flow systems
• Fire sprinkler system
• Water distribution system in the house, city etc.
• Cooling systems (refrigerants, brines, chilled
  water, etc.)
• Fluid Power System
• Hydraulics
• Pneumatics
• Irrigation system in agriculture

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Definitions

• Volume (Volumetric) Flow Rate
• Q Cross Sectional AreaAverage Velocity of the
  fluid
• Q Av
• Weight Flow Rate
• W gQ
• Mass Flow Rate
• M rQ

v
Q Volume/Unit time Q AreaDistance/Unit Time
Volume
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Units and Conversion Factors

• Q m3/sec, ft3/sec
• W N/sec, lb/sec
• M kg/sec, slugs/sec
• Volume Flow Rate
• 1 L/min 0.06 m3/h
• 1 m3/sec 60,000 L/min
• 1 gal/min 3.785 L/min
• 1 ft3/sec 449 gal/min

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Typical Volume Flow Rates
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Key Principles in Fluid Flow

• Continuity for any fluid (gas or liquid)
• Mass flow rate In Mass Flow Rate out
• M1 M2
• r1A1v1 r2A2v2
• Continuity for liquids
• Q1 Q2
• A1v1 A2v2

M1
M2
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Example

• If d1 and d2 are 50 mm and 100 mm, respectively,
  and water at 70 C is flowing at 8 m/sec in
  section 1, determine v2, Q, W, M.

v1
v2
d2
1
2
d1
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Pipe and Tubing

• Steel Pipes General Purpose and come in standard
  sizes (specific thickness and diameter)
• Steel Tubing Fluid power systems, condensers,
  heat exchangers. Sizes designated by outside
  diameter and thickness. Typical sizes 1/8 2
  inches.
• Copper Tubing Plumbing, compressed and
  refrigeration lines. Types K and L. Type K is
  thicker than type L.

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Pipe and Tubing

• Ductile Iron Pipe Water, gas, sewage.
• Other types PVC, brass, concrete, nylon, etc.
  Used in corrosive environments or in special
  applications (labs, manufacturing plants, etc.)

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Recommended Velocity of Flow in Pipe or Tubing

• To minimize internal erosion, Figure 6-2 and
  Table in page 164 in Mott
• For same flow rate (Q) smaller diameter means
  higher velocity and vice versa

For same Flow Rate, Q
Recommended Range of Velocity
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Example

• Determine the maximum allowable volume flow rate
  in L/min that can be carried through a standard
  steel tube with an outside diameter of 1-1/4 and
  0.065 in wall thickness if the maximum velocity
  is to be 3.0 m/sec.

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Example

• Determine the required size standard Schedule 40
  steel pipe to carry 192 m3/hr with a maximum
  velocity of 6.0 m/sec.

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Conservation of EnergyBernoullis Equation

• Energy cannot be created or destroyed, just
  transformed
• Three forms of energy in fluid system
• Potential
• Kinetic
• Flow energy

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Potential Energy

• Due to the elevation of the fluid element
• Where,
• w weight of fluid element
• z elevation with respect to a reference level

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Kinetic Energy

• Due to the velocity of the fluid element
• Where,
• v average velocity of the fluid element

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Flow Energy

• Flow work or pressure energy
• Amount of energy necessary to move a fluid
  element across a certain section against pressure
• Where,
• p pressure on the fluid element

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Total Energy and Conservation of Energy Principle

• E FE PE KE
• Two points along the same pipe
• E1 E2
• Bernoullis Equation

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Heads
Assumption No energy is added or lost
Assumption Energy level remains constant
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Restrictions on Bernoullis Equation

• Valid only for incompressible fluids
• No energy is added or removed by pumps, brakes,
  valves, etc.
• No heat transfer from or to liquid
• No energy lost due to friction
• Note No system satisfies this condition, but
• Bernoullis equation can still be used
  to
• estimate changes in heads values