ENGR 320: Thermodynamics &

Heat Transfer

Lecture 1

Spring 2015

Dr. AT Weakley

McClure 209

Class Agenda

• Syllabus Day! Kind of…

– Course description, briefly

– Course Requirements

– Grading

• Lecture topics:

– Chapter 1: Motivation for Thermodynamics, real applications

– Current research example: Liu 2015 Paper

– Chapter 2.1: The Control volume approaches

Syllabus Breakdown

• See syllabus

Chapter 1:Process Equipment, Applications of

Thermodynamic Principles

• ENGR Thermodynamics is motivated by real world applications:

– Steam Power Plant [Chapter 1.1]

• Purpose:

– Fuel in (coal, air, oil) power out (kWh)

• System (partial): – Σ (Steam power plant operations) :

» Reactor (1)

» Boiler (2)

» Turbine (3)

» Heat exchanger (4)

– Possible (and rational) to analyze each unit operation individually

Chapter 1.1: Steam Plant, example

• Question: Which unit operation is doing work to produce power?

• Answer: Turbine (aka, expanders)

• Specific course goal: – Use thermodynamic principles to size a turbine (and other

operations) for a knowledge of fluid, process constraints • First law (ideal) How much energy (per unit time) in our working fluid

(steam) do we need to produce X amount of mechanical power (Chapter 2-6)?

• Second law Why do we do worse than we expect? (Chapter 7-9)

Chapter 1.1: Steam Plant, example • This analysis is a crude (but useful) idealization

– What do we ignore for our turbine analysis in ENGR 320?

• Friction losses to-and-from turbine (pipe friction, mechanical friction, etc. need fluid mechanics)

• Internal workings of turbine (turbine mechanics, heat losses through turbine wall, wear-and-tear, etc.)

• Transients (i.e., d/dt; time-dependent phenomena, transport phenomena)

• Heat transfer through turbine walls (Chapter 13 covers heat transfer)

Classical thermodynamics assumes processes are intransient, independent of spatial consideration (x, y ,z)

(equilibrium approximation)

Chapter 1.1-1.2: Nuclear Propulsion,

Fuel Cells

• Nuclear Propulsion: Analogous to steam power plant, from a classical thermo point-of-view

– Uses steam as working fluid to drive a turbine(s)

• A fuel cell is less obvious:

– First approximation: uses principles of chemical reaction equilibrium (Chapter 12)

• At thermal and mechanical equilibrium, how much electrical energy can we expect to extract from this reaction?

• Energy is this class usually concerns only heat-energy or mechanical energy (work)

Chapter 1.2: Fuel Cell

• What are we ignoring (e.g.)?

– Chemical kinetics (activation energy, catalyst properties, reaction rate; advanced)

• Will the reaction even proceed? How fast?

– Chemical potential explicitly (“activity” of solution, intermolecular interactions; advanced)

• What if the mixture isn’t an ideal gas? What if solution doesn’t want to mix?

Classical thermodynamics = Tells us the best we can do!

Chapter 1.3: Vapor-Compression

Refrigeration Cycle

• Questions: What does work on our fluid of interest?

• Answer: Compressor!

– Exact opposite of turbine

– Compressor does work on fluid

– Turbine produces work from fluid

• Thermodynamics let’s us analyze each operation in the step-by-step (Cycle; Chapter 11)

Chapter 1.3: Thermodynamic Cycles

• Thermodynamics let’s us characterize a cycle

WRT to a working fluid (or fluid mixture)

– P-V and T-S diagrams

– Tip for future: Always have a diagram in mind!

• Simple example: one refrigerant (“Freon”)

PV Diagram of Refrigeration Cycle

Fluid: “Freon”

2 = Condenser

1=Compressor

3 = Valve

4 = Evaporator

•

•

•

•

Superheated vapor Two-phase region

(Liq/Vap)

Subcooled

Liquid

Can energetically characterize each point in process!

• Using either equations of state (ideal gas law)

• Tabulated data (back of book)

P (Mpa)

ν (m3/kg)

Chapter 1.4: Thermoelectric

Refrigerator

• Can we refrigerate a space in a more direct manner?

• Yes: Thermoelectric Refrigeration

– Simple version: Temperature difference = voltage difference

– Usually more expensive

– Used in sensitive electronic equipment

– Figure 1.8a

Why you need this class:

Cutting-Edge ENGR Research!

• Liu (2015!) presents a reasonable design for

thermoelectric power generation (Figure 1.8b)

– Courses needed to understand ~80% of article:

• Fluid mechanics (ENGR 335)

• Thermodynamics (ENGR 320)

– Let’s take a look

Liu (2015): Oceanic Thermoelectric

Power Plant • Intriguing!

Liu (2014), N J. Phys. 16, 123019

Chapter 2.1: Thermodynamic Systems

• Where do we start? Definitions.

• System: “Comprises a device of combination of

devices containing a quantity of matter under study.”

(p. 15)

– Open system: Mass flows in and/or out of system

– Closed system: Mass is fixed

Systems Control Volume

• For ENGR problems, useful to introduce concept of control volume (CV)

– If system = a device/operation then CV is an abstraction of such a device

– Illustrates rudimentary mass and energy flows in and out of system (across control surfaces)

– Figure 2.2: Air Compressor

Chapter 2.1: Control Volume,

Attributes 1. Control surface (CS): constrains all matter, energy, or

devices inside the CV (aka, defines system boundaries)

2. Surroundings define everything outside CV/CSs

3. CV contains mass and energy generated and/or consumed + flowing in and/or out

4. Control surfaces are stationary or movable

5. Control mass = mass within CV is constant

6. Isolated system = not influenced at all by surroundings

Control Volumes!!!!

Moral to the story

Always start a problems in ENGR 320 by drawing

a control volume

Even if problem is trivial or complex!

HW1: Tips

• Problem 2.1:

– Use Figure 2.2 and definitions to draw a CV

around steam power plant in Figure 1.1

• I nclude both mass and energy (heat) flows

• Use arrows to denote direction

• Label clearly!

• Problem 2.2:

– Read question carefully. Only consider the main

turbine loop (etc.) and NOT the entire submarine!