CHAPTER 1_ INTRODUCTION AND OVERVIEW

The main subcategories of thermal-fluid sciences are thermodynamics, heat transfer, and fluid mechanics.

The purpose of developing an intuitive systematic problem-solving technique is to provide a model for effectively solving engineering problems.

Understanding accuracy and significant digits in engineering measurements is crucial for ensuring the reliability and precision of calculations and results.

The objectives include:

1. Acquaintance with thermodynamics, heat transfer, and fluid mechanics.
2. Comfort with metric SI and English units.
3. Development of a systematic problem-solving technique.
4. Learning the proper use of software packages in engineering.
5. Understanding accuracy and significant digits in calculations.

Thermal-fluid sciences, derived from the Greek word 'therme' meaning heat, encompass the study of energy, its transfer, transport, and conversion. They are crucial in engineering as they apply to the design and analysis of systems like power plants, automotive engines, and refrigerators, integrating principles from thermodynamics, heat transfer, and fluid mechanics.

Thermodynamics is defined as the science of energy, encompassing all aspects of energy and energy transformations, including power generation and refrigeration.

Use software to determine the values of x, y, and z that satisfy the given equations. The solutions will vary based on the computational method used.

The conservation of energy principle states that 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 term 'thermodynamics' originates from the Greek words therme (heat) and dynamis (power), reflecting early efforts to convert heat into power.

The first law of thermodynamics states that energy cannot be created or destroyed; it can only change forms, asserting that energy is a thermodynamic property.

The second law of thermodynamics asserts that energy has quality as well as quantity, indicating that actual processes occur in the direction of decreasing quality of energy.

A person who has a greater energy input (food) than energy output (exercise) will gain weight, while a person with a smaller energy input than output will lose weight. This relationship is expressed as ΔE = E_in - E_out.

Classical thermodynamics is a macroscopic approach to the study of thermodynamics that does not require knowledge of the behavior of individual particles, allowing for direct solutions to engineering problems.

Heat transfer is significant in thermodynamics as it deals with the transfer of energy from one system to another due to temperature differences, which is essential for understanding energy exchanges in various systems.

Thermodynamics is concerned with the amount of heat transfer as a system undergoes a process from one equilibrium state to another, but it does not provide information on the rate or duration of the process.

Heat transfer deals with systems that lack thermal equilibrium, meaning it focuses on the rates of heat transfer and the variation of temperature, which cannot be analyzed solely through thermodynamic principles that focus on equilibrium states.

The basic requirement for heat transfer is the presence of a temperature difference. There can be no net heat transfer between two bodies that are at the same temperature.

The rate of heat transfer in a certain direction depends on the magnitude of the temperature gradient (the temperature difference per unit length). A larger temperature gradient results in a higher rate of heat transfer.

The two main branches of mechanics are statics, which deals with bodies at rest, and dynamics, which deals with bodies in motion under the action of forces.

When a shear force is applied to a rubber block between two plates, the block deforms, and the angle of deformation (shear strain) increases in proportion to the applied force. The upper surface of the rubber moves with the upper plate, while the lower surface remains stationary, demonstrating the continuous deformation characteristic of fluids.

Asphalt behaves as a solid and resists shear stress for short periods, but when subjected to shear stress over extended periods, it deforms slowly and behaves like a fluid. This illustrates the borderline cases between solids and fluids.

The primary dimensions in physical quantities are mass (m), length (L), time (t), and temperature (T).

Secondary dimensions, also known as derived dimensions, are expressed in terms of primary dimensions. Examples include velocity (V), energy (E), and volume (V).

The two main unit systems in use today are the English system (also known as the United States Customary System, USCS) and the metric SI (International System of Units).

The Metric Convention Treaty of 1875 established the meter and gram as the metric units for length and mass, respectively, and created the General Conference of Weights and Measures (CGPM) to oversee the metric system.

The CGPM adopted the following fundamental quantities and their units in 1960:

1. Meter (m) for length
2. Kilogram (kg) for mass
3. Second (s) for time
4. Ampere (A) for electric current
5. Degree Kelvin (°K) for temperature
6. Candela (cd) for luminous intensity.

Before the new definition adopted in 2018, the kilogram was defined as the mass of a shiny metal cylinder, known as Le Grand K, which has been stored in Paris since 1889.

In 2018, a resolution was adopted to define the kilogram in terms of the Planck constant (h), which has a fixed value of 6.62607015 x 10^-34 m² kg/s.

The standard kilogram is defined using fixed universal constants as follows:

1 kg = (299,792,458)² h. AVcs / (6.62607015 x 10⁻³⁴)(9,192,631,770) c²

The original definition of the meter was 1/10,000,000 of the distance between the north pole and the equator. In 1983, it was redefined as the distance traveled by light in a vacuum in 1/299,792,458 of a second.

The SI unit prefixes are significant in engineering as they provide a standardized way to express multiples and submultiples of units, facilitating communication and understanding across different fields and industries.

Force is defined as the product of mass and acceleration:

F = ma

where F is the force, m is the mass, and a is the acceleration.

Weight (W) is defined as the gravitational force applied to a body, calculated using the formula:

W = mg

where m is the mass of the body and g is the local gravitational acceleration.

Mass is a measure of the amount of matter in a body and remains constant regardless of location, while weight is the gravitational force acting on that mass and varies with changes in gravitational acceleration.

SI: newton (N) — defined as 1 kg·m/s².

English: pound-force (lbf) — defined as the force required to accelerate a mass of 1 slug at 1 ft/s² (1 lbf = 1 slug·ft/s²).

Gravitational acceleration (g) varies with location due to factors such as latitude and altitude. For example, g is approximately 9.807 m/s² at sea level, but it decreases with altitude and varies from 9.832 m/s² at the poles to 9.789 m/s² at the equator.

The approximate constant value of gravitational acceleration (g) at sea level is 9.81 m/s².

Work is defined as force times distance, and its unit is newton-meter (N·m), which is called a joule (J).

In the metric system, energy is defined as the amount needed to raise the temperature of 1 g of water by 1°C, which is 1 calorie (cal). The equivalent of 1 calorie is 4.1868 joules (J).

kW (kilowatt) is a unit of power (energy per time), while kWh (kilowatt-hour) is a unit of energy (total energy consumed).

Dimensional homogeneity means that every term in an equation must have the same unit. If different units are added, it indicates an error in the analysis.

A wind turbine rated at 30 kW operating for 2200 hours per year generates 66,000 kWh of electricity (30 kW × 2200 hours).

The total electric energy generated per year is 66,000 kWh (30 kW × 2200 h).

The money saved per year is $7,920 (66,000 kWh ×$0.12/kWh).

Units can be used to verify that calculations yield the correct dimensions, ensuring that a formula is dimensionally homogeneous, which indicates it may be correct.

The formula is m = ρV, where m is mass, ρ is density, and V is volume.

The mass of the oil is 1,700 kg (m = ρV = 850 kg/m³ × 2 m³).

Unity conversion ratios are ratios that are equal to 1 and are unitless. They can be used to convert units conveniently in calculations without altering the value. For example, 1 N / (1 kg·m/s²) = 1 and 1 lbf / (32.174 lbm·ft/s²) = 1. Using these ratios helps avoid confusion that may arise from using the gravitational constant in equations.

To calculate the weight of 1 lbm on Earth, use the formula W = mg, where m is the mass and g is the gravitational acceleration. For 1.00 lbm: W = (1.00 lbm)(32.174 ft/s²) × (1 lbf / 32.174 lbm·ft/s²) = 1.00 lbf. This shows that 1 lbm weighs 1 lbf on Earth.

The gravitational constant, such as gc = 32.174 lbm·ft/lbf·s², is often used in equations to match units. However, its use can lead to confusion. Instead, it is recommended to use unity conversion ratios for clarity and simplicity in unit conversions.

The systematic approach involves: 1. Grasping the fundamentals of the subject. 2. Mastering these fundamentals by testing knowledge through problem-solving. This method is essential for tackling complicated real-world problems effectively.

The first step is to clearly state the problem in your own words, including the key information given and the quantities to be found.

Drawing a schematic helps visualize the physical system, shows key features, and indicates energy and mass interactions with the surroundings, aiding in understanding the entire problem at once.

This step should include stating appropriate assumptions and approximations made to simplify the problem, justifying questionable assumptions, and assuming reasonable values for missing quantities.

Relevant basic physical laws and principles should be applied and reduced to their simplest form, clearly identifying the region to which each law is applied.

Checking the reasonableness of results ensures that the outcomes are intuitive and valid, helping to verify questionable assumptions and avoid unrealistic conclusions.

Key factors include neatness, organization, completeness, and visual appearance. These elements help in effective communication and make it easier to spot errors and inconsistencies.

Understanding the fundamentals is crucial because software packages are tools that require proper training to use effectively. Without a solid foundation, users may misuse these tools, leading to misinformation and errors in engineering practice.

Carelessness can lead to skipping steps, which often results in increased time spent on corrections and unnecessary anxiety. A logical and orderly approach is essential to avoid these pitfalls and ensure effective problem-solving.

The analogy compares using engineering software without proper training to a person using a wrench thinking they can work as a car mechanic. It highlights that tools alone do not equate to expertise; fundamental knowledge is necessary for effective application.

When presenting results, it is important to discuss the significance of the results, their implications, and any limitations. Additionally, recommendations should be made, and caution should be taken against misunderstandings regarding the applicability of the results.

Engineering software packages have shifted the emphasis in courses from mathematics to physics, allowing more time to discuss the physical aspects of problems in detail while spending less time on solution mechanics.

Engineers must have a thorough understanding of fundamentals to develop a 'feel' for physical phenomena, put data into perspective, and make sound engineering judgments, especially since misunderstandings can lead to significant damage.

EES can solve systems of linear or nonlinear algebraic or differential equations numerically, has a large library of thermodynamic property functions, and allows users to supply additional property data, but it requires users to understand and formulate the problem using relevant physical laws.

1. Start the EES program and open a new file.
2. Input the equations: 'x - y = 4' and 'x^2 + y^2 = x + y + 20'.
3. Click on the 'calculator' icon to obtain the solution.
4. The solution will show x = 5 and y = 1.

In engineering calculations, results should not be reported with more significant digits than the least precise measurement. This avoids falsely implying greater accuracy. For example, if volume and density are both known to three significant digits, the mass calculated from them should also be reported to three significant digits, not more.

Results should be rounded to the same number of significant digits as the least precise measurement involved in the calculation. For instance, if the volume is 3.75 L and density is 0.845 kg/L, the mass calculated as 3.16875 kg should be rounded to 3.17 kg to reflect the precision of the input data.

1. Start Excel and enable the Solver Add-In.
2. Choose cells for variables (e.g., x and y) and enter initial guesses.
3. Rewrite equations so no variables are on the RHS.
4. Set the objective cell and constraints in the Solver.
5. Solve the equations to find the values of x and y.

Retaining all digits during intermediate calculations ensures accuracy and prevents rounding errors. The final result should be rounded to the appropriate number of significant digits based on the precision of the input data, which reflects the true accuracy of the measurements used.

A common error is reporting calculated results with more significant digits than the input data allows, which can mislead about the precision of the result. For example, calculating mass from volume and density known to three significant digits should not yield a result reported to six significant digits.

Thermal-fluid sciences deal with energy and its transfer, transport, and conversion. They are studied under three subcategories: thermodynamics, heat transfer, and fluid mechanics.

The first law of thermodynamics expresses the conservation of energy principle, asserting that energy is a thermodynamic property.

The second law of thermodynamics states that energy has both quality and quantity, and actual processes occur in the direction of decreasing energy quality.

The basic requirement for heat transfer is the presence of a temperature difference between two bodies.

Fluid mechanics studies the behavior of fluids at rest (fluid statics) and in motion (fluid dynamics), as well as the interaction of fluids with solids or other fluids at boundaries.

It is crucial to pay attention to units to avoid errors caused by inconsistent units and to ensure accurate results in engineering calculations.

A systematic step-by-step approach is recommended, which includes:

1. Stating the problem
2. Drawing a schematic
3. Making appropriate assumptions
4. Applying physical laws
5. Listing relevant properties
6. Making necessary calculations
7. Ensuring results are reasonable.

Heat transfer focuses on the rates of heat transfer and temperature variations, while thermodynamics deals with energy conservation and quality. Heat transfer is concerned with the dynamics of energy transfer, whereas thermodynamics is about the static properties of energy.

The driving force for heat transfer is the temperature difference between two bodies.

Heat transfer is a nonequilibrium phenomenon because it occurs due to a temperature gradient, which means that energy is transferred until thermal equilibrium is reached.

Weight (W) can be calculated using the formula: W = mass × g. Therefore, W = 200 kg × 9.6 m/s² = 1920 N.

Weight (W) can be calculated using the formula: W = mass × g. Therefore, W = 10 lbm × 32.0 ft/s² = 320 Ibf.

The upward force can be calculated using the formula: F = mass × acceleration. Here, acceleration = 6 g = 6 × 9.81 m/s² = 58.86 m/s². Thus, F = 90 kg × 58.86 m/s² = 5297.4 N.

The weight reduction can be calculated as: Percent reduction = [(Weight at sea level - Weight at 13,000 m) / Weight at sea level] × 100. Weight at sea level = mass × g (9.807 m/s²), Weight at 13,000 m = mass × g (9.767 m/s²). Calculate the weights and then find the percent reduction.

First, calculate the weight of the water: Volume = 0.2 m³, Weight of water = Volume × Density = 0.2 m³ × 1000 kg/m³ = 200 kg. Total weight = weight of tank + weight of water = (3 kg + 200 kg) × 9.81 m/s² = 1994.4 N.

Net force = applied force - weight of the rock. Weight = mass × g = 2 kg × 9.79 m/s² = 19.58 N. Net force = 200 N - 19.58 N = 180.42 N. Acceleration = Net force / mass = 180.42 N / 2 kg = 90.21 m/s².

Energy (in kWh) = Power (in kW) × Time (in hours) = 4 kW × 3 h = 12 kWh. To convert to kJ, use the conversion: 1 kWh = 3600 kJ. Therefore, 12 kWh = 12 × 3600 kJ = 43200 kJ.

Weight on spring scale = mass × g = 150 lbm × 5.48 ft/s² = 822 lbf. Weight on beam scale remains the same as it measures mass, so it will be 150 lbf.

Filling time (t) can be expressed as: t = Volume (V) / Discharge rate (V). Therefore, t = V (in L) / V (in L/s).

(a) In engineering education, software packages enhance learning through simulations and modeling, allowing students to visualize complex concepts. (b) In engineering practice, they improve efficiency, accuracy, and productivity by automating calculations and providing advanced analysis tools.

Use numerical methods or software tools to find the positive real root of the equation. The specific root will depend on the software used for computation.

Use software to solve the system of equations. The solution will provide the values of x and y that satisfy both equations.

Use software to find the values of x, y, and z that satisfy all three equations. The specific solutions will depend on the software used.

Mass flow rate (ṁ) can be expressed as: ṁ = ρ × A × V, where ρ = air density, A = swept area = π(D/2)², and V = wind velocity. Thus, ṁ ∝ ρ × V × D².

The drag force (FD) can be expressed as: FD ∝ Cdrag × ρ × V² × A, where Cdrag = drag coefficient, ρ = air density, V = car velocity, and A = frontal area of the car.