ENTC 489: Announcements

1
ENTC 489 Announcements

• Yes, lab this week
• Homework assignments
• Assigned Problems from Introduction to Thermal
  and Fluids Engineering (Kaminski and Jensen)
• 2.12, 4.39, 4.40, 4.44, plus the handout
  problems.
• Due next Tuesday, September 15th before 1050 am
• For more information, go to
• http//etidweb.tamu.edu/classes/entc489/502/Index.
  htm

2
Thermal Systems

• Review of Fluids
• Energy Equation
• Class I problems
• Pumps (more in depth than in ENTC 303)

3
Conservation of Energy
4
Example

• Water flows from a reservoir at 1.2 ft3/sec.
  Calculate the energy lost from the system due to
  valves, elbows, pipe entrance and fluid friction.

12 ft
Valve
Elbow
13 ft
3 inches
Elbow
5
Fluid Power

• PA hAW
• W gQ
• Power added to a fluid by a pump or removed by
  friction or a motor
• PA hAgQ
• Previous example
• Calculate the amount of power lost in Btu

6
Power

• Power Energy/Unit Time
• Units 1 hp 550 lb-ft/sec
• 1 hp 745.7 W

7
Mechanical Efficiency of Pumps
Pumps cannot be 100 efficient because of
energy losses due mechanical friction within the
pump Pump efficiency is usually within 50 to
90 Manufacturers provide eM values for each
pump and should be part of the performance data
8
Fluid Losses (hL)

• Frictional Losses (due to fluid friction in
  pipes)
• Minor Losses (due to valves, fittings, etc.)
• How to calculate fluid losses?
• Need to identify type of flow
• Laminar or Turbulent?
• Must know flow conditions and piping system
  specifications (size, length, etc.)

9
Fluid Losses
Laminar
Turbulent
Fluid Characteristic
Need to know Velocity Pipe Diameter Viscosity Den
sity Roughness
Need to know Velocity Pipe Diameter Viscosity Den
sity
10
Reynolds Number
Re lt 2000 Laminar Flow Re gt 4000 Turbulent 2000
lt Re lt 4000 Critical Region or Transitional
11
Energy loss due to friction
hL?

• Due to flowing fluid
• Proportional to velocity head
• Proportional to the ratio Length of Pipe/Diameter
  of Pipe (L/D)
• Darcy equation
• hL Energy loss due to friction, N-m/N
• or lb-ft/lb
• L length of flow stream or pipe, m D
  pipe diameter, m
• v average fluid velocity, m/sec
• f friction factor (dimensionless)

12
Friction Loss in Laminar Flow

• Fluid friction is independent of surface
  roughness for laminar flow
• Hagen-Poiseuille Equation

Laminar Flow
13
Example

• Determine the energy loss if water at 25 C flows
  30 m through a 8 mm diameter pipe with an average
  velocity of 0.15 m/sec.

14
Friction Loss in Turbulent Flow

• Does depend on surface roughness!
• Surface roughness is expressed as e

e
Part of Table 9.2
15
Friction Loss in Turbulent Flow

• f f(Re, e, D)
• Moody chart shows f as a funtion of Re and e

16
Moody Chart
D/e
f
Re
17
Equations for Friction Factor

• Laminar flow gt
• Turbulent Flow gt
• (Equation 8-7)

18
Frictional Pressure Drop

• For Laminar or Turbulent Flow, Pressure Drop (DP)
  is as follows

19
Example

• Water at 25 C (SG 1.0) is pumped from A to B
  where the pressure is 550 kPa. A pump is located
  21 m below point B, and the two points (A B)
  are connected by a 240 m plastic pipe with an
  inside diameter of 50 mm. Q 110 L/min.
  Calculate PA.

20
Pipe Friction Losses
21
Non-Circular Cross Section
What is the Reynolds Number for configurations
like these?
ALL SIDES ARE CLOSED
22
Flow in Noncircular Sections

• Q Av
• v Q/A
• A1v1 A2v2, where A1 and A2 are
  cross-sectional areas

23
Hydraulic Radius
Wetted Perimeter
Wetted perimeter is defined as the sum of the
length of the boundaries of the section actually
in contact with the fluid (wetted parts)
24
Example

• Determine the hydraulic radius of the following
  non-circular section

100 mm
Bars diameter 25 mm
200 mm