**Subject Code/Name:** MAE2402 - Thermodynamics and Heat Transfer **Workload:** 3x1 hr lectures per week, 3 hr tute (not marked), 3 Labs throughout the semester with 2 small lab reports on the first 2 and a long group lab report on the last one

**Assessment:** 3x5% topic tests, 2x3% short lab reports, 9% long lab report, 70% exam

**Recorded Lectures:** Yes, with screen capture.

**Past exams available:** 7 past exams, no solutions or answers.

**Textbook Recommendation:** Prescribed Text: Y.A. Çengel, Introduction to Thermodynamics and Heat Transfer, 2nd ed, McGraw-Hill, 2008.

The textbook is quite useful, you'll need to read up on extra material for this unit.

**Lecturer(s):** Dr. Meng Wai Woo

**Year & Semester of completion:** Sem 2 2013

**Rating:** 3.5 Out of 5

**Your Mark/Grade:** 60 - C

**Comments: ** Going to get this out the way right away, this unit isn't easy. It'll require a lot of work, things aren't straight forward and you'll need to do a lot of extra work to just be baseline. The first half of the course is on Thermodynamics, as the unit title suggests, which at first is a little tricky and takes a bit of getting used to. There is one or two main formulas that you will use for Thermodynamics that you'll need to get manipulating for each problem (there are a whole heap of other smaller formulas for thermo, but that's the main one. Know how to use the first law and everything goes from there). Heat Transfer is quite different to Thermo, in the sense Thermo had a few main formulas, while Heat Transfer has a

**whole heap** (and I meant a large amount) of formulas. Once you work out which formula to apply though, it's not too bad, it's just a matter of working out what fits the situation. I found Thermo harder than Heat Transfer, but most people were the other way around (could have something to do with being sick and missing a week of unit when we were covering the guts of the Thermo component though).

The labs aren't too bad, in our year we had a Steam Boiler efficiency lab where you look at efficiencies throughout certain stages of the steam boiler, a finned surfaces lab where you look at the heat transfer rate of different types of fins and compare them to a flat plate and finally an IC (Internal Combustion) Engine + Propeller lab where you try to work out a power band for the propeller and explain why it's the shape it is, and why the efficiency is so low or high. They take a bit of outside research to write them up properly, the last lab you write up as a group report and is worth three times as much as the other labs and you get 2 weeks to write it up. You get to choose which lab you want to do as the big write up, as you add yourself to a lab group at the start of semester corresponding to certain lab timetables. But there are only a limited number of slots for each, so I suggest you decide which one you want to do, form a group and get in early.

Now for tutes, they're aren't compulsory (and we're given solutions to them beforehand), and because of that not many people go, unless it is the tute which has the test in the same week (which for us was the 3 hr block before the actual test). Now this means in a tute you can get lots of help if you want to. I got slack a little bit after I got sick, and so wasn't always up to date with tutes.

**I suggest you go to the tutes and get worth out of them, I know they're not compulsory but don't get slack, don't put them off. The tests jump up on you quickly.**There are three tests, for us the first two were on the thermodynamics component and the last on one part of the Heat Transfer component. Not many people did well on theses tests, with the distribution of test 1 being multi-modal with one group centered at 25% and one group centered at around 75%. That is

**you either get it or you don't**. It improved for the latter tests, but again, you don't want to be learning the content and questions the night before.

**Thermo and Heat Transfer takes a lot of situation and thinking about properties of the material or substance, rather than just using formuals.** You need to be able to plug in the correct values into those formuals, which is the tricky part. It's not always clear cut, be prepared to have every question having something new in it.

The exam itself, I found it quite hard, even if you think that you're prepared, odds are you're not.

**Do not underestimate this unit**. I did at the start of the semester, and then when I missed a week of uni was forever fighting to catch back up.

**Don't let yourself fall behind**. You have a scientific calc, but at some points you will have to do fairly complicated methods with it.

**Unit Topics and Breakdown:**Thermodynamics

- Thermodynamic Concepts

- Energy and Enegry Transfer

- First Law and Energy Analysis

- Properties of Pure Substances

- Property Tables and Ideal Gases

- Energy analysis of closed systems

- Internal energy and specific heats

- Energy transport by mass

- Energy analysis of steay flow open systems

- Second law of thermodynamics

- Refrigerators and heat pump

- The Carnot Cycle

Heat Transfer

- Mechanisms of Heat Transfer

- Steady Heat Conduction

- Steady Heat Conduction in Cylinders and Spheres

- Heat Transfer from Finned Surfaces

- Transient Heat Conduction

- Transient heat conduction in multidimensional geometries

- Convection heat transfer

- External forced convection

- Internal forced convection

- Laminar and Turbulent Flow

- Natural convection

- Internal natural convection

- Radiation heat transfer

- Radiation Properties

- Radiation view factors

- Radiation heat transfer between surfaces

I've also included two sample questions from the Heat Transfer part of the course, with what you'd have to do to approach it and go through it. Just to give you a feel for the unit.

Heat Transfer Sample Question 1

Engine oil at

flows over a

-m-long flat plate whose temperature is

with a velocity of

. Determine the total drag force and rate of heat transfer over the entire plate per unit width.

Solution:

Firstly we find the film temperature, which is the average of the temperature of the surface and the temperature of the free stream medium.

.

The fluid properties of oil are then evaluated at this temperature. For this we turn to our data tables, and since they normally have intervals of

, we would linearly interpolate between the values to get our constants. That is we would use

, which since we're going to need four constants means we have to do this four times (this is the annoying part -.-).

So we're given this for the properties of Engine Oil from the data table.

Interpolating gives

Now to find out the behavior of the flow (that is whether it is Laminar, Transitional or Turbulent), we need to find the Reynolds number, which is a dimensionless constant given by

.

We are told that the critical Reynolds number is

, since this is less than that we have a Laminar Flow.

Now to find the rate of heat transfer, we need the heat transfer coefficient,

, but to find this we need to find another dimensionless constant, the Nusselt Number, Nu. The relationship between Nu and Re, Pr will change depending on the flow. We look at the formula sheet which has three relationships for Laminar, Transitional and Turbulent flows, which as we know the flow is turbulent comes out to be

given that

, which is true.

Now we can find the rate of heat transfer, using

.

Heat Transfer Sample Question 2

A long

-cm-diamter steam pipe whose external temperature is

oasses through some open area that is not protected against the winds. Determine the rate of heat loss from the pipe per unit of its length when the air is at

atm pressure and

and the wind is blowing across the pipe at a velocity of

.

Solution:

We'll use the same method as above, except that our relationship for flow around a sphere will be different, and the characteristic length,

is the diameter of the cylinder, rather than the length of the plate. Since we have a sphere we will assume the flow is turbulent around the back end of the sphere, and so turbulent throughout.

Properties of air at

atm.

Finding the Reynolds number.

Finding the Nu number. We have a correlation for flow around a cylinder.

The heat transfer rate then becomes