Chapter 1 - Intro to Thermo

Chapter 1: Getting Started

• This chapter introduces introductory concepts and definitions.
• Learning outcomes include explaining fundamental concepts (closed system, control volume, boundary, surroundings, property, state, process, extensive and intensive properties, and equilibrium).

Learning Outcomes

• Identify SI and English Engineering units, including specific volume, pressure, and temperature.
• Describe relationships among Kelvin, Rankine, Celsius, and Fahrenheit temperature scales; and apply appropriate unit conversion factors.
• Apply problem-solving methodology.

Defining Systems

• System: The part of the universe being studied.
• Surroundings: Everything external to the system.
• Boundary: Separates the system from its surroundings.

Control Mass or Closed System

• A system that always contains the same matter.
• No mass transfer across the boundary.
• Energy transfer across the boundary is permitted.
• An isolated system is a special type of closed system that does not interact with its surroundings in any way—no mass or energy interaction.

Control Volume or Open System

• A region of space where mass flows.
• Mass and energy cross the boundary of a control volume.

Macroscopic and Microscopic Views

• Macroscopic view: Describes system behavior in terms of gross effects such as pressure and temperature that can be measured by instruments (e.g., pressure gauges, thermometers).
• Microscopic view: Characterizes a system by statistical means using the average behavior of particles.

Property

• A macroscopic characteristic of a system that can be assigned a numerical value without knowing the previous behavior of the system.
• Examples include volume, energy, pressure, and temperature.

State

• The condition of a system described by its properties.
• The state can often be specified by providing the values of a subset of its properties.
• Example: State of a gas is often described by p, V, and T.

Process

• A transformation from one state to another.
• When any of the properties of a system changes, the state changes, and the system undergoes a process.
• Example: If the volume of a system changes from V₁ to V₂, there is the process from State 1 to State 2. Property value changes.

Extensive Property

• A property that depends on the size or extent of a system.
• Examples include mass, volume, and energy.
• The value for an extensive property of an overall system is the sum of the values for the parts it's divided into.

Intensive Property

• A property that is independent of the size or extent of a system.
• Examples include pressure and temperature.
• Its value is not additive as for extensive properties.

Equilibrium

• A state where a system does not interact with its surroundings but its state may change via internal spontaneous events.
• Intensive properties such as temperature and pressure tend towards uniform values.
• All such changes cease, the system is at an equilibrium state.
• Equilibrium states and processes play an important role in thermodynamic analysis.

Units (1 of 2)

• A unit is a specified amount of a quantity used for comparison.
• Examples include meters, feet, and miles for length.
• Two systems of units: SI (Système International d'Unités) and English Engineering units.

Units (2 of 2)

• Table 1.3 shows units for mass, length, time, and force in SI and English units.
• Base units for mass, length, and time and force has a unit derived from them using F=ma (Eq.1.1)

Density (p) and Specific Volume (v)

• From a macroscopic perspective, matter is treated as continuously distributed.
• Density is mass per unit volume (p = m/V).
• Density is an intensive property that can vary from point to point.
• Specific volume is the reciprocal of density (v = 1/p).
• Specific volume is an intensive property.
• SI: (kg/m³), English:(lb/ft³).

Pressure (p)

• Pressure in a fluid at rest is defined as the limit, where F_normal is the force normal to the area, and A is the area (p = lim F_normal/A_{→ A'} as A→A').
• The force that the fluid exerts on one side of the area has an equal but oppositely directed force exerted by the fluid on the other side.

Pressure Units

• SI unit of pressure is the pascal (Pa).
• 1 Pa = 1 N/m².
• Other units include kPa, bar, and MPa.
• English units include lbf/ft² and lbf/in².

Absolute Pressure

• Pressure measured with respect to a complete vacuum.
• Absolute pressure must be used in thermodynamic relations.

Gage and Vacuum Pressure

• Gage pressure is the difference between the absolute pressure of a system and atmospheric pressure.
• Vacuum pressure is the difference between atmospheric pressure and the absolute pressure of a system.

Temperature (T)

• Temperature is the property that determines if two objects are in thermal equilibrium.
• If two objects are in contact and isolated, they will interact thermally until they are in thermal equilibrium.

Thermometers (1 of 2)

• Any object with a measurable property that changes with temperature can be used as a thermometer.
• A thermometric property is a property that changes with temperature.
• The substance that exhibits changes in the thermometric property is called a thermometric substance.

Thermometers (2 of 2)

• Example: Liquid-in-glass thermometer.
• Other types include thermocouples, thermistors, and radiation thermometers.

Temperature Scales

• Kelvin, Rankine, Celsius, and Fahrenheit scales.
• Kelvin is the SI base unit for temperature.
• Rankine is an English base unit.
• Formulas for conversions between these scales.

Design

• Engineering design is a decision-making process.
• Fundamental elements include establishing objectives, synthesis, analysis, construction, testing, and evaluation.
• Design is constrained by factors including economics, safety and environmental impact.

Problem-Solving Methodology

• Known: Identify what is known.
• Find: State what is to be determined.
• Schematic and Given Data: Sketch and label relevant data.
• Engineering Model: List assumptions and idealizations.
• Analysis: Reduce equations to produce desired results.