THERMODYNAMICS Basic Units and Pressure Concepts in 11 Minutes!

Introduction

This tutorial provides a comprehensive overview of thermodynamics, focusing on key concepts such as fundamental laws, units of measurement, heat capacity, pressure basics, and practical examples. Understanding these topics is essential for anyone studying physics or engineering, as they form the foundation for analyzing energy systems.

Chapter 1: Thermodynamics Definition

• Thermodynamics is a branch of physics that examines the relationship between heat transfer and mechanical work within a system.
• Key variables include:
  • Temperature
  • Pressure
  • Volume
  • Specific volume
  • Internal energy
  • Enthalpy
  • Entropy
• The field is governed by four fundamental principles, known as the laws of thermodynamics.

Chapter 2: Thermodynamics Laws

• The four laws of thermodynamics are:
  • Zeroth Law: Establishes a basic definition of temperature and thermal equilibrium.
  • First Law: Focuses on energy conservation and its transformations.
  • Second Law: Deals with entropy and the direction of energy transfers.
  • Third Law: Discusses absolute zero temperature and the behavior of systems at this limit.
• Most calculations in thermodynamics involve:
  • Joules (energy)
  • Watts (power)
  • Pascals (pressure)

Chapter 3: Units Used in Thermodynamics

• The International System of Units (SI) includes:
  • Length: Meters (m)
  • Time: Seconds (s)
  • Amount of substance: Moles (mol)
  • Electric current: Amperes (A)
  • Temperature: Kelvin (K)
  • Luminous intensity: Candela (cd)
  • Mass: Kilograms (kg)
• In thermodynamics, focus primarily on:
  • Energy (Joules)
  • Power (Watts)
  • Pressure (Pascals)
• English units (e.g., BTUs) may be encountered but are less common.

Chapter 4: Heat Capacity and Specific Heat

• Specific heat is defined as the energy required to raise the temperature of one kilogram of a substance by one degree Celsius.
• Example for water:
  • Specific heat ≈ 4184 J/kg°C
  • To raise the temperature of 1 kg of water from 20°C to 21°C, approximately 4.184 kJ of energy is needed.

Chapter 5: Specific Heat Example

• Consider heating 200 mL of water (0.2 kg) with a 20 W electric pot:
  • Energy supplied in 5 minutes = Power × Time = 20 W × 300 s = 6000 J (or 6 kJ).
  • Using the specific heat formula:
    • Change in temperature = Energy / (Mass × Specific heat)
    • Change in temperature = 6000 J / (0.2 kg × 4184 J/kg°C) ≈ 7.17°C.
  • Final temperature = Initial temperature + Change = 4°C + 7.17°C ≈ 11.17°C.

Chapter 6: Pressure Basics and Hydrostatic Pressure

• Pressure is defined as force per unit area.
• Hydrostatic pressure can be derived from the equilibrium of fluid elements.
• The formula is:
  • Change in pressure (dp) in the z-direction = -ρg dz, where:
    • ρ is the fluid density,
    • g is gravitational acceleration,
    • dz is the change in height.

Chapter 7: Piston Pressure Example

• Consider a piston with a diameter of 4 cm and height of 1.2 cm over a cylinder connected to a U-shaped duct filled with oil (density = 0.9 g/cm³).
• Given that the fluid columns have a vertical difference of 10 cm:
  • Calculate the pressure inside the cylinder:
    • Pressure due to the fluid column = ρgz.
    • Substitute values to find pressure in Pascals.
• The equilibrium condition leads to the calculation of the piston density:
  • Use the relationship between pressure, area, and weight to derive the density of the piston.

Conclusion

In this tutorial, we covered essential thermodynamic concepts, including laws, units, heat capacity, and pressure basics, reinforced by practical examples. Understanding these principles is vital for further exploration of thermodynamics in engineering and physics. For deeper knowledge, consider exploring more advanced topics through the provided lecture links and resources.