Thermodynamics, Fluid Dynamics, and Heat Transfer ( Chapter 2) 2 - - PowerPoint PPT Presentation

Thermodynamics, Fluid Dynamics, and Heat Transfer (Chapter 2)

Faculty of Engineering and Applied Science

Memorial University of Newfoundland

• St. John’s, Newfoundland, Canada

2

Learning Outcomes (Chapter 2)

• Review of Thermodynamics

– First law, Second law, Exergy

• Review of Fluid Dynamics

– Conservation of mass, momentum, and Mechanical energy

• Review of Heat Transfer

– Conduction, Convection, Radiation

• Important Dimensionless Groups

Faculty of Engineering and Applied Science

Memorial University of Newfoundland

• St. John’s, Newfoundland, Canada

3

Thermal-Fluid Fundamentals

• First Law of Thermodynamics

– Classic sign convention

• (+) for work done by the system, and (-) for work done on the system

– Heat Engine convention

• (+) for work done on the system, and (-) for work done by the system
• This is the “Heat Engine” convention. It is opposite to what you learned.

Faculty of Engineering and Applied Science

Memorial University of Newfoundland

• St. John’s, Newfoundland, Canada

4

Thermal-Fluid Fundamentals

• First Law of Thermodynamics

– The Work Term:

• (+) for work done on the system, and (-) for work done by the system
• This is the “Heat Engine” convention. It is opposite to what you learned.

Faculty of Engineering and Applied Science

Memorial University of Newfoundland

• St. John’s, Newfoundland, Canada

5

Thermal-Fluid Fundamentals

• Second Law of Thermodynamics

Faculty of Engineering and Applied Science

Memorial University of Newfoundland

• St. John’s, Newfoundland, Canada

6

Thermal-Fluid Fundamentals

• Exergy

– Reference (dead state) – Increasing exergy – Maximum

Faculty of Engineering and Applied Science

Memorial University of Newfoundland

• St. John’s, Newfoundland, Canada

7

Thermal-Fluid Fundamentals

• Conservation of Mass and Momentum

– Conservation of Mass – Conservation of Momentum – Bernoulli’s Equation

Faculty of Engineering and Applied Science

Memorial University of Newfoundland

• St. John’s, Newfoundland, Canada

8

Thermal-Fluid Fundamentals

• The Extended Bernoulli Equation:

– It is differences in total pressure that drive flow, not static pressure alone. – If flow speed changes, then there may be static pressure recovery.

Faculty of Engineering and Applied Science

Memorial University of Newfoundland

• St. John’s, Newfoundland, Canada

9

Thermal-Fluid Fundamentals

• Conservation of Mechanical Energy

– Convention:

• Pumps add energy to fluid.
• Turbines extract energy from the fluid.

– In words:

• Energy at point 1 + Energy added =

Energy at point 2 + Energy converted + Losses

Faculty of Engineering and Applied Science

Memorial University of Newfoundland

• St. John’s, Newfoundland, Canada

10

Thermal-Fluid Fundamentals

• Conservation of Mechanical Energy

Faculty of Engineering and Applied Science

Memorial University of Newfoundland

• St. John’s, Newfoundland, Canada

11

Thermal-Fluid Fundamentals

• Understanding Mechanical Energy

Faculty of Engineering and Applied Science

Memorial University of Newfoundland

• St. John’s, Newfoundland, Canada

12

Thermal-Fluid Fundamentals

• How to wisely choose a CV?

Faculty of Engineering and Applied Science

Memorial University of Newfoundland

• St. John’s, Newfoundland, Canada

13

Thermal-Fluid Fundamentals

• Example 1: Find the force on the T-section, Fx and Fy.

Neglect viscous effects. Assume ρ=1000 (kg/m3).

Faculty of Engineering and Applied Science

Memorial University of Newfoundland

• St. John’s, Newfoundland, Canada

14

Thermal-Fluid Fundamentals

• Example

2: Analyse flow through the sudden expansion shown in the figure.

Faculty of Engineering and Applied Science

Memorial University of Newfoundland

• St. John’s, Newfoundland, Canada

15

Thermal-Fluid Fundamentals

• Example 3: If the headloss between points 1 and 2

was calculated

• f

20 (m), how much power is transferred to the turbine? How much power is ideally derived assuming no losses?

Faculty of Engineering and Applied Science

Memorial University of Newfoundland

• St. John’s, Newfoundland, Canada

16

Thermal-Fluid Fundamentals

• Example 4: Water flows at a rate of 70 (l/s) Through a flanged faucet with

a partially closed gate valve spigot. The inner diameter of the pipe at the location of the flange is 2 (cm), and the pressure at that location is measured to be 90 (kPa). The total weight of the faucet assembly plus the water within it is 60 (N). Calculate the net force on the flange.

Faculty of Engineering and Applied Science

Memorial University of Newfoundland

• St. John’s, Newfoundland, Canada

17

Thermal-Fluid Fundamentals

• Important Dimensionless Groups

Faculty of Engineering and Applied Science

Memorial University of Newfoundland

• St. John’s, Newfoundland, Canada

18

Thermal-Fluid Fundamentals

• Conduction Heat Transfer

– General heat conduction equation (Cartesian) – Fourier’s Law

• k: Conductivity
• ρ: Density
• c: Heat capacity

Faculty of Engineering and Applied Science

Memorial University of Newfoundland

• St. John’s, Newfoundland, Canada

19

Thermal-Fluid Fundamentals

• Convection Heat Transfer

– Newton’s cooling law – Nusselt number

• h: Convection coefficient
• L: Characteristic length
• kf: Fluid’s conductivity

Faculty of Engineering and Applied Science

Memorial University of Newfoundland

• St. John’s, Newfoundland, Canada

20

Thermal-Fluid Fundamentals

• Radiation Heat Transfer

– Stefan-Boltzmann Law:

• ε: Surface emmisivity
• F1-2: View factor
• σ: Stefan-Boltzmann constant