ENGI-3015: Engineering Thermodynamics & Heat Transfer - Chapter 1 Notes

Chapter 1: Introduction

Overview

• This course covers Engineering Thermodynamics and Heat Transfer.
• The required textbook is "Fundamentals of Thermal-Fluid Sciences," 6th Edition, by Yunus A. Çengel, John M. Cimbala, and A. Ghajar (McGraw-Hill, 2022).
• Course materials are copyrighted and for use only by registered students. Reproduction, posting, sharing, or redistribution are prohibited.

Objectives

• Become acquainted with thermodynamics and heat transfer and understand their basic concepts.
• Become comfortable with metric SI and English units.
• Develop a systematic problem-solving technique.
• Understand accuracy and significant digits in calculations.

Application Areas of Thermodynamics & Heat Transfer

• Refrigerators, boats, aircraft, spacecraft, power plants, human body, cars, wind turbines, food processing, and industrial piping networks are all application areas.

1-1 Introduction to Thermal Sciences

• Thermal-fluid sciences deal with energy and its transfer, transport, and conversion.
• Thermal-fluid sciences include thermodynamics, heat transfer, and fluid mechanics.
• Many engineering systems, like solar hot-water systems, rely on thermal-fluid sciences.

1-2 Thermodynamics

• Thermodynamics is the science of energy.
• It deals with the amount of heat transfer during a process as a system changes from one equilibrium state to another.
• It does not indicate how long the process will take.
• Energy is the ability to cause changes.
• The name thermodynamics comes from the Greek words therme (heat) and dynamis (power).

Energy

• Energy cannot be created or destroyed; it can only change forms (the first law).
• Energy Storage (Time-Dependent)
• Energy Conversion
• Energy Relationships
• Energy Transfer

The Laws of Thermodynamics

(1) The First Law of Thermodynamics

• An expression of the conservation of energy principle.
• Also known as the conservation of energy principle.
• Conservation of energy principle: During an interaction, energy can change from one form to another, but the total amount of energy remains constant.
• Energy cannot be created or destroyed.
• The first law asserts that energy is a thermodynamic property.
• $Energy<em>{in} = Energy</em>{out} + Energy_{storage}$

(2) The Second Law of Thermodynamics

• It asserts that energy has quality as well as quantity, and actual processes occur in the direction of decreasing quality of energy.
• Classical thermodynamics: A macroscopic approach that does not require knowledge of individual particle behavior.
• Statistical thermodynamics: A microscopic approach based on the average behavior of large groups of individual particles.

1-3 Heat Transfer

• Heat is the form of energy transferred due to a temperature difference.
• Heat Transfer is the science that determines the rates of energy transfers and temperature variation.
• Engineering often focuses on the rate of heat transfer.
• Thermodynamic analysis alone cannot determine how long it takes for hot coffee in a thermos to cool to a certain temperature.

Laws Governing Heat Transfer

• The First Law requires that the rate of energy transfer into a system equals the rate of increase of the system's energy.
• The Second Law requires that heat be transferred in the direction of decreasing temperature.

1-4 Fluid Mechanics

• Not included in ENGI-3015 course.

1-5 Importance of Dimensions and Units

• Dimensions: Any physical quantity.
• Units: Magnitudes assigned to dimensions.

Types of Dimensions

• Primary/Fundamental dimensions: mass $m$, length $L$, time $t$, and temperature $T$.
• Secondary/Derived dimensions: velocity $V$, energy $E$, and volume $V$, expressed in terms of primary dimensions.

Types of Units

• Metric SI system: A simple, logical system based on decimal relationships.
• English system: No systematic numerical base; units are related arbitrarily.

Examples of SI and English Units

• $1 \text{ lbm} = 0.45359 \text{ kg}$
• $1 \text{ ft} = 0.3048 \text{ m}$
• $Force = (Mass)(Acceleration)$
• $F = ma$
• $1 \text{ N} = 1 \text{ kg} \cdot \frac{\text{m}}{\text{s}^2}$
• $1 \text{ lbf} = 32.174 \text{ lbm} \cdot \frac{\text{ft}}{\text{s}^2}$
• $Work = Force \times Distance$
• $1 \text{ J} = 1 \text{ N} \cdot \text{m}$
• $1 \text{ cal} = 4.1868 \text{ J}$
• $1 \text{ Btu} = 1.0551 \text{ kJ}$

Weight Calculation

• $W = mg$
• Where:
  • $W$ = weight (N)
  • $m$ = mass (kg)
  • $g$ = gravitational acceleration
• $g = 9.807 \frac{\text{m}}{\text{s}^2}$
• $g = 32.174 \frac{\text{ft}}{\text{s}^2}$
• $W = 9.807 \text{ kg} \cdot \frac{\text{m}}{\text{s}^2} = 9.807 \text{ N}$
• $W = 32.174 \text{ lbm} \cdot \frac{\text{ft}}{\text{s}^2} = 1 \text{ lbf}$

Tables of Dimensions and Units

• Table 1-1: Seven fundamental dimensions and their SI units (length, mass, time, temperature, electric current, amount of light, amount of matter).
• Table 1-2: Standard prefixes in SI units (yotta, zetta, exa, peta, tera, giga, mega, kilo, hecto, deka, deci, centi, milli, micro, nano, pico, femto, atto, zepto, yocto).

Dimensional Homogeneity

• All equations must be dimensionally homogeneous.
• All non-primary units can be formed by combinations of primary units.
• Force units:
  • $N = kg \cdot \frac{m}{s^2}$
  • $lbf = 32.174 \cdot lbm \cdot \frac{ft}{s^2}$
• Every term in an equation must have the same units.

1-6 Problem-Solving Technique

1. Problem Statement
2. Schematic
3. Assumptions
4. Thermodynamic Properties
5. Physical Laws - Fundamental Equations
6. Analysis & Calculations
7. Reasoning, Verification, and Discussion

Importance of Assumptions

• Assumptions must be reasonable and justifiable.
• Example: Estimating air density in Denver requires considering atmospheric pressure.

Significant Digits in Calculations

• Information in engineering calculations is known to a limited number of significant digits (usually three).
• Results should not be reported with more significant digits than the given data.
• Reporting more significant digits implies greater accuracy than exists.
  *Example:
• Volume $V = 3.75 L$
• Density $p = 0.845 \frac{kg}{L}$
• Mass $m = pV = 3.75 \times 0.845 = 3.16875 kg$
• Rounding to 3 significant digits: $m = 3.17 kg$

Chapter 1 Summary

• Introduction to Thermal Sciences
• Application areas of thermal sciences
• Thermodynamics
• Heat Transfer
• Importance of Dimensions and Units
• Some SI and English units
• Dimensional homogeneity
• Unity conversion ratios
• Problem-Solving Technique
• A Remark on Significant Digits
• Read and study Chap 1 – Textbook