**Unit 3: Convection**
*In this unit, we will study the second mode of heat transfer:
convection. While conduction is the major mode of heat transfer in
solids (as you learned in Unit 2), convection is the major mode of heat
transfer in fluids. Convection occurs because of movements of fluids.
Heat is carried away and dispersed thorough the fluid. Convective heat
transfer occurs in nature (e.g. cooling down effects of wind) and in
engineering systems (e.g. heating of homes, cooling of equipment).

We will examine two major types of convective heat transfer: forced convection and natural convection. In forced convection, movement of fluid is due to external forces such as a pump, while in natural convection, it is due to density differences driven by non-uniformity of temperature. *

**Unit 3 Time Advisory**

This unit will take you approximately 32 hours to complete.

☐ Subunit 3.1: 3 hours

☐ Subunit 3.2: 3 hours

☐ Subunit 3.3: 4 hours

☐ Reading: 3 hours

☐ Assignment: 1 hour

☐ Subunit 3.4: 2 hours

☐ Subunit 3.5: 2 hours

☐ Subunit 3.6: 2 hours

☐ Subunit 3.7: 8 hours

☐ Video Lectures: 4 hours

☐ Reading: 4 hours

☐ Subunit 3.8: 8 hours

☐ Video Lectures: 4 hours

☐ Reading: 4 hours

☐ Subunit 3.9: 8 hours

☐ Video Lectures: 4 hours

☐ Reading: 4 hours

**Unit3 Learning Outcomes**

Upon successful completion of this unit, the student will be able to:

- Define Nusselt and Sherwood numbers.
- Calculate heat transfer in convective boundary layers.
- Calculate heat transfer of flows over plane wall, sphere, and cylinder.
- Calculate heat transfer of pipe flows.
Calculate heat transfer of free convection.

**Web Media: YouTube: Julius Summer Miller’a “Heat Energy Transfer by Convection – Part 1” and “Heat Energy Transfer by Convection – Part 2”**Link: YouTube: Julius Summer Miller: “Heat Energy Transfer by Convection – Part 1” and “Heat Energy Transfer by Convection – Part 2” (YouTube)

Instructions: Please watch these two science demonstration video, in which Dr. Julius Summer Miller performed several simple experiments to illustrate heat convection. You may want to repeat some of these experiments at home.

Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.**Reading: MIT: Professors John Lienhard IV and John Lienhard V’s A Heat Transfer Textbook: “Chapter 6”**Link: MIT: Professors John Lienhard IV and John Lienhard V’s A Heat Transfer Textbook: “Chapter 6” (PDF)

Instructions: Please click on the link “Download A Heat Transfer Textbook,” which will take you to a download request form. After you fill in relevant information about you, you will be able to download the book. Note that the only information required on the form is your city, country, and occupation. The book is in PDF format (17.2 MB). Save a copy of the book for future use in this course. This is one of the best books on heat transfer. Please read section 6.1 in “Chapter 6: Laminar and Turbulent Boundary Layers” (pp 271-278). Note that the reading will cover the material that you need to know for subunits 3.1 and 3.2.

Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

**3.1 Introduction to Boundary Layers**
**Note: This topic is covered by the reading below the Unit 3
introduction.**

**3.2 Local/Average Convection Coefficients for Heat and Mass Transfer**
*Note: This topic is covered by the reading below the Unit 3
introduction.*

**3.3 Laminar and Turbulent Flow**
- **Reading: MIT: Professors John Lienhard IV and John Lienhard V’s A
Heat Transfer Textbook: “Chapter 6”**
Link: MIT: Professors John Lienhard IV and John Lienhard V’s *A
Heat Transfer Textbook: “Chapter
6”* (PDF)

```
Instructions: For this unit, please read sections 6.2-6.8 in
“Chapter 6: Laminar and Turbulent Boundary Layers (pp 278-323).”
Note that the reading will cover the material that you need to know
for subunits 3.3-3.6, and any inclusive sub-subunits. In Section
6.2, you may want to skim through page 288 and focus on equation
6.24 on page 289. Make sure that you understand figure 6.11. Pay
attention to sections 6.4 and 6.6, which provide detailed
discussions on the Prandtl number, boundary layer thicknesses, and
the Reynolds analogy. Browse through section 6.5, because we are
going to revisit this section in subunit 3.7.
Terms of Use: Please respect the copyright and terms of use
displayed on the webpage above.
```

**3.3.1 Velocity Boundary Layers**
*Note: This topic is covered by the reading below subunit 3.3.*

**3.3.2 Thermal Boundary Layers**
*Note: This topic is covered by the reading below subunit 3.3.*

**3.4 Boundary Layer Equations**
*Note: This topic is covered by the reading below subunit 3.3.*

**3.5 Discussion over Dimensionless Parameters**
*Note: This topic is covered by the reading below subunit 3.3.*

**3.6 Reynold's Analogy**
*Note: This topic is covered by the reading below subunit 3.3.*

**3.7 External Flow**
- **Reading: MIT: Professors John Lienhard IV and John Lienhard V’s A
Heat Transfer Textbook: “Chapter 7”**

```
Link: MIT: Professors John Lienhard IV and John Lienhard V’s A Heat
Transfer Textbook: “[Chapter
7](http://web.mit.edu/lienhard/www/ahtt.html)” (PDF)
Instructions: Please click on the link “Download A Heat Transfer
Textbook,” which will take you to a download request form. After
you fill in relevant information about you, you will be able to
download the book. Note that the only information required on the
form is your city, country, and occupation. The book is in PDF
format (17.2 MB). Save a copy of the book for future use in this
course. This is one of the best books on heat transfer. For this
unit, please read “Chapter 7: Forced Convections in a Variety of
Configurations” (pp. 342-388). Note that the reading will cover the
material that you need to know for subunits 3.7 and 3.8. This
reading will introduce you to heat transfer for external flows, such
as flows over a cylinder, a sphere, and across tube fields and
forced convection heat transfer.
Terms of Use: Please respect the copyright and terms of use
displayed on the webpage above.
```

**Lecture: YouTube: Indian Institute of Technology (IIT) Bombay: Professor S.P.Sukhatme and Professor U.N.Gaitonde’s “Lecture 18: Forced Convection,” “Lecture 19: Forced Convection-2,” “Lecture 20: Forced Convection-3,” and “Lecture 21: Forced Convection-4”**Link: YouTube: Indian Institute of Technology (IIT) Bombay: Professor S.P.Sukhatme and Professor U.N.Gaitonde’s “Lecture 18: Forced Convection”, “Lecture 19: Forced Convection-2”, “Lecture 20: Forced Convection-3”, and “Lecture 21: Forced Convection - 4” (YouTube) .

Instructions: Please watch these videos (ranging from approximately 45-50 minutes for each video), which will introduce you to the basic concepts of forced convection. These videos cover the material that you need to know for subunits 3.7 and 3.8. In Lecture 18, pay attention to definitions of local heat transfer coefficient and average heat transfer coefficient. Also, make sure that you remember the definitions of Nusselt number, Reynolds number, and Prandtl number. In Lecture 19, Professor U.N. Gaitonde works through an example of convective heat transfer with constant heat flux at wall.

Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

**3.7.1 Introduction to External Flow**
*Note: This topic is covered by the resources below subunit 3.7.*

**3.7.2 Flow over a Flat Plate**
- **Reading: MIT: Professors John Lienhard IV and John Lienhard V’s A
Heat Transfer Textbook: “Chapter 6”**

```
MIT: Professors John Lienhard IV and John Lienhard V’s A Heat
Transfer Textbook: “[Chapter
6](http://web.mit.edu/lienhard/www/ahtt.html)” (PDF)
Instructions: Please click on the link “Download A Heat Transfer
Textbook,” which will take you to a download request form. After
you fill in relevant information about you, you will be able to
download the book. Note that the only information required on the
form is your city, country, and occupation. The book is in PDF
format (17.2 MB). Save a copy of the book for future use in this
course. This is one of the best books on heat transfer. For this
sub-subunit, please read sections 6.5 in “Chapter 6: Laminar and
Turbulent Boundary Layers” (pp. 278-323) carefully. The reading
introduces you to equations that can be used to calculated heat
transfer coefficient of forced convection over a flat plate.
Terms of Use: Please respect the copyright and terms of use
displayed on the webpage above.
```

**3.7.3 Flow across a Cylinder**
*Note: This topic is covered by the resources below subunit 3.7*

**3.7.4 Flow over a Sphere**
*Note: This topic is covered by the resources below subunit 3.7*

**3.7.5 Flow across Tube Fields**
*Note: This topic is covered by the resources below subunit 3.7*

**3.8 Forced Convection Heat Transfer**
*Note: This topic is covered by the resources below subunit 3.7.*

**3.9 Free Convection**
- **Web Media: Infrared Imaging Experiments’s “Natural Convection - A
Vertical View” and “Natural Convection-A Horizontal View”**
Link: Infrared Imaging Experiments’s “Natural Convection - A
Vertical View” and “Natural Convection-A Horizontal
View” (YouTube)

Instructions: Please click on the above link, which will take you
to a webpage of heat transfer experiments captured by Infrared
video. Browse to the sections titled “Natural Convection - A
Vertical View” and “Natural Convection - A Horizontal View.” Read
the descriptions and watch the videos. Click on the link “Read
more” if you are interested in a more detailed description of the
experiments. The videos will provide you some insights into the
dynamics of natural convection.

Terms of Use: Please respect the copyright and terms of use
displayed on the webpage above.

**Reading: MIT: Professors John Lienhard IV and John Lienhard V’s A Heat Transfer Textbook: “Chapter 8”**Link: MIT: Professors John Lienhard IV and John Lienhard V’s*A Heat Transfer Textbook: “Chapter 8”*(PDF)Instructions: For this subunit, please read sections 8.1-8.4 (pages 399-416), which will introduce you to natural convection and dimensionless numbers characterizing natural convective heat transfer. Make sure that you know how to define the Raleigh number for different geometrical configuration of the heating surface (section 8.3).

Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

**Lecture: YouTube: Indian Institute of Technology (IIT) Bombay: Prof. S.P.Sukhatme and Prof. U.N.Gaitonde’s “Lecture 22: Natural Convection-1,” “Lecture 23: Natural Convection-2,” and “Lecture 24: Natural Convection-3”**Link: YouTube: Indian Institute of Technology (IIT) Bombay: Professor S.P.Sukhatme and Professor U.N.Gaitonde’s “Lecture 22: Natural Convection-1,”, “Lecture 23: Natural Convection-2,” and “Lecture 24: Natural Convection-3” (YouTube)

Instructions: Please watch these videos in their entity (about 50-53 minutes for each video), which will introduce you to the basic equations and dimensionless numbers for free convection.

Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

**Unit 3 Assessment**
- **Assessment: California State University Northridge: Larry
Caretto's "April 11 Homework"**
Link: California State University Northridge: Larry Caretto's
"April 11
Homework"
(HTML).

```
Instructions: Open the link above that will take you to the
homepage of ME 375 – Heat Transfer taught by Professor Larry
Caretto. Click on "April 11": to download the Word file hw09.doc.
Solve all the problems listed in the homework. For each problem,
read the problem statement in bold and attempt to solve it. After
you complete your solutions, check with the answers below each
problem statement.
Terms of Use: Please respect the copyright and terms of use
displayed on the webpage above.
```

**Assessment: The Saylor Foundation's "Unit 3 Assessment"**Link: The Saylor Foundation's "Unit 3 Assessment" (PDF)Instructions: Please complete the linked quiz. When you are done, check your work against The Saylor Foundation's "Unit 3 Assessment Answer Key" (PDF).