Thermal energy refers to the energy possessed by an object due to the movements of particles within the object. It’s the internal kinetic energy of the object, which comes from the random movements of the object’s molecules and atoms.
While molecules and atoms that make up matter move all the time, when an object heats up, the increase in temperature makes these particles move faster and collide with each other. The faster these particles move, the higher the thermal energy of the object.
It can be written mathematically as the product of Boltzmann’s constant () and the absolute temperature (T).
The term “thermal energy” can also be applied to the quantity of heat transferred or energy carried by heat flow.
Thermal energy (or heat energy) can be transferred from one body to another via three processes –
- Conduction: is the most common form of heat transfer, which occurs via physical contact: The internal energy transfers due to the microscopic collisions of particles and motion of electrons within a body.
- Convection: is the transfer of heat from one region to another by the movement of fluids, such as liquids and gases.
- Radiation: is the transmission of energy in the form of particles or waves through space or a medium. The hotter the object, the more it will radiate thermal energy.
To better explain this phenomenon, we have gathered some of the best examples of thermal energy that you see in everyday life.
Table of Contents
12. Solar Energy
Type of heat transfer: Radiation
The Sun is a nearly perfect sphere of hot plasma that converts hydrogen into helium through billions of chemical reactions, which eventually produce an intense amount of heat.
Instead of staying near the Sun, the heat radiates away from the star and into space. A small portion of this energy (heat) reaches the Earth in the form of light. It mostly contains infrared, visible, and ultraviolet light. The transfer of heat energy in this way is called thermal radiation.
While some of the heat energy gets through the Earth’s atmosphere and reaches the ground, some of it gets blocked by clouds or reflected off other objects. Sunlight that does reach the surface of the Earth warms it.
According to the University of Oregon, the entire Earth receives an average of 164 Watts per square meter over a 24 hour day. This means the whole planet receives 84 Terawatts of power.
11. Melting Ice
Type of heat transfer: Convection
Heat energy always flows from regions of higher temperature to regions of lower temperature. For instance, when you add ice cubes to your beverage, the heat moves from the liquid to the ice cubes.
The temperature of liquid drops as heat transfers from beverage to ice. The heat continues to move to the coldest area in the drink until it reaches an equilibrium. This loss of heat causes the temperature of the beverage to plummet.
10. Fuel Cells
A fuel cell that takes hydrogen and oxygen as input
Heat transfer: Depends on the type of fuel cell
Fuel cells are electrochemical devices that convert the chemical energy of a fuel and oxidant gas into electrical energy. When a fuel cell operates, a significant amount of input is used to generate electrical energy, but the remaining portion is transformed into thermal energy, depending on the type of fuel cell.
The heat produced throughout this process is harnessed to increase energy efficiency. Theoretically, fuel cells are far more energy-efficient than conventional processes: if waste heat is captured in a cogeneration scheme, efficiencies of up to 90% can be achieved.
9. Geothermal Energy
Type of heat transfer: Mantle Convection
Geothermal energy is the heat derived within the sub-surface of the Earth. It is contained in the fluids and rocks beneath the Earth’s crust and can be found deep down in the Earth’s hot molten rock, magma.
It is produced from the radioactive decay of materials and continual heat loss from the planet’s formation. The temperature and pressure at the core-mantle boundary could reach more than 4000°C and 139 GPa, causing some rocks to melt and solid mantle to behave plastically.
This results in portions of the mantle convecting upward (since the melted rock is lighter than the surrounding solid rock). Steam and/or water carry the geothermal energy to the planet’s surface, from where it can be utilized for cooling and heating purposes, or it could be harnessed to produce clean electricity.
8. Heat Energy In The Ocean
Type of heat transfer: Convection and Conduction
For decades, oceans have absorbed more than 9/10th of the atmosphere’s excess heat from greenhouse gas emissions. According to a study, the ocean has been heating at a rate of 0.5 to 1 watt of energy per square meter over the last ten years.
Oceans have incredible potential for storing thermal energy. Since their surfaces are exposed to direct sunlight for prolonged periods, there is a huge difference between the temperatures of the shallow and deep water marine regions.
This temperature difference can be used to run a heat engine and generate electricity. This type of energy conversion, known as ocean thermal energy conversion, can operate continuously and can support various spin-off industries.
7. Solar Cooker
Type of heat transfer: Radiation and Conduction
A solar cooker is a low-tech, inexpensive device that uses the energy of direct sunlight to heat, cook or pasteurized drink and other food materials. On a sunny day, it can achieve a temperature of up to 400°C.
All solar cookers work on three basic principles:
- Concentrate sunlight: The device contains a mirrored surface to concentrate light from the Sun into a small cooking area.
- Convert light energy into heat energy: When light falls on a receiver material (cooking pan), it converts light to heat, and this is what we call conduction.
- Trap heat energy: A glass lid isolates the air inside the cooker from the outside air, minimizing convection (heat loss).
6. Rubbing Your Hand Together
Type of heat transfer: Conduction
When you rub your hands together, friction turns mechanical energy into thermal energy. The mechanical energy refers to the motion of your hands.
Since friction occurs due to the electromagnetic attraction between charged particles in two touching surfaces, rubbing hands together results in the exchange of electromagnetic energy between the molecules of our hands. This leads to the thermal excitation of molecules of our hands, which ultimately produces energy in the form of heat.
5. Heat Engine
Type of heat transfer: Convection
A heat engine converts thermal energy to mechanical energy, which can then be used to do mechanical work. The engine takes the energy from being warm (compared to the surroundings) and turns that into motion.
Depending on the type of engine, different processes are applied, such as using energy from nuclear processes to generate heat (uranium) or igniting fuel through combustion (coal or gasoline). In all processes, the objective is the same: convert heat into work.
Everyday examples of heat engines include a steam locomotive, internal combustion engine, and thermal power station. They all are powered by the expansion of heated gases.
4. Burning Candle
Type of heat transfer: Conduction, Convection, Radiation
Candles make light by producing heat. They convert chemical energy into heat. The chemical reaction is called combustion, where candle wax reacts with oxygen in the air and makes a colorless gas named carbon dioxide along with a small amount of steam.
The steam is produced in the blue part of the flame, where the wax burns cleanly with lots of oxygen. But since no wax burns perfectly, they also produce a little smoke (aerosol) in the bright, yellow part of the flame.
Throughout the process, the wick absorbs the wax and burns to produce light and heat energy.
3. Electric Toasters
Type of heat transfer: Thermal radiation
An electric toaster takes in electrical energy and converts it into heat very efficiently. It consists of rows of thin wires (filaments) that are spaced widely enough apart to toast the whole bread surface.
When electricity flows through the wire, energy is transferred from one end to another. This energy is carried by electrons. Throughout the process, electrons collide with one another and with the atoms in the metal wire, giving off heat. The greater the electric current and the thinner the wire, the more collisions happen and the more heat is produced.
2. Modern Home Heating Systems
Type of heat transfer: Convection
Two common types of heating systems installed in buildings are warm-air and hot-water heating systems. The first one uses thermal energy to heat air and then circulates it through a system of ducts and registers. The warm air blows out of ducts and circulates throughout the rooms, pushing cold air out of the way.
Whereas, the second one uses thermal energy to heat water and then pump it throughout the building in a system of pipes and radiators. The hot radiator radiates thermal energy to the surrounding air. The warm air then moves across the rooms in convection currents.
Read: 10 Best Examples Of Kinetic Energy
1. CPUs and Other Electric Components
A fan-cooled heat sink on the processor
Type of heat transfer: Convection and Conduction
CPU, GPU, and system on a chip dissipate energy in the form of heat due to the resistance in electronic circuits. GPUs in laptops/desktops consume and dissipate significantly more power than mobile processors due to their higher complexity and speed.
Read: 14 Best Examples Of Convection With Simple Explanation
Various types of cooling systems are used to keep microprocessors at optimal temperatures. A conventional desktop CPU cooling system, for example, is designed to dissipate up to 90 watts of heat without exceeding the maximum junction temperature for the desktop’s CPU.
You write: “Thermal energy (or heat energy) can be transferred from one body to another via three processes.”
Actually only two of those processes transfer thermal energy from one body to another. Contact me for details.