Thermal Energy: Sources, Storage, Working & Applications

Thermal energy refers to the energy contained in a system that is responsible for the temperature of the system. Thermal energy is the energy retained by an object or system as a result of particle movement inside the object or system.

• Thermal energy can be described as an object's ability to perform work.
• It is the energy contained within a system that causes it to heat up.
• Therefore, we can say that the kinetic and thermal energy of the particles is the same.

Key Terms: Energy, Temperature, Heat, Thermal energy,  Kinetic energy, Atoms, Molecules, Natural gas, Thermodynamics

Checkout Important Question: What are the five types of energy?

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What Is Thermal Energy?

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Thermal energy or heat energy is the energy that is produced when a rise in temperature causes atoms and molecules to move faster and collide with each other.

• The temperature of a substance has a direct relationship with its thermal energy.
• It's also known as the measure of the average kinetic energy of a substance's constituent particles, which is responsible for their movement.
• Thermodynamics is a discipline of physics that studies how heat is transmitted across systems and how work is done in the process.

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Sources of Thermal Energy

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The various sources of thermal energy are:

Mechanical energy 

Mechanical energy is the energy stored in objects due to stress. Compressed springs and stretched rubber bands store mechanical energy, which can be converted to thermal energy. A good example of thermal energy is the energy released as a result of friction.

Mechanical energy

Chemical Energy

Chemical energy is the amount of energy held in the bonds between atoms and molecules. Chemical energy can be found in batteries, biofuels, petroleum, natural gas, and coal. When people burn wood in a fireplace or gasoline in a car's engine then chemical energy is transformed to thermal energy.

Chemical Energy

Solar Energy

 It is one of the most efficient producers of thermal energy. It is the most environmentally friendly and widely available source of thermal energy.

Solar Energy

Fossil Fuels

Fossil fuels are combustible substances formed from the dead remains of animals and plants that have been buried deep beneath the earth's surface for millions of years. Some examples of fossil fuels are coal, petroleum, natural gas, etc.

Fossil Fuels

Geothermal Energy

Geothermal energy is the energy derived from the earth. The energy emitted by volcanoes, hot springs, and geysers is a good example of geothermal energy.

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How Mass is Linked with the Thermal Energy

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Imagine the following circumstance where you have a glass of water and a beaker of water of the same temperature. The volume of water in the beaker is twice as much as in the glass.

• Due to the same temperature, the average kinetic energy of the water molecule is the same in both. 
• However, due to the increase in the volume, the total kinetic energy of water molecules in the beaker is twice that of water molecules in the glass.
• Therefore the thermal energy of the water in the beaker is twice that of the water in the glass.
• Thus thermal energy in an object increases when the mass of the object increases.

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Thermal Energy Application

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A stove's heated element holds thermal energy, and the higher the temperature, the more internal energy the stove has.

• The molecules are moving even though you can't see them.
• The faster the molecules move, the more internal heat energy they have.
• Immediately place a container of water on top of the hot element.
• So, what happens next? The stove's heat energy accelerates the movement of the particles in the pot and finally, the water.

It's critical to know the difference between these terminologies. Heat is used in this context to refer to the movement of thermal energy from one item or system to another, with the transfer being the crucial word.

• Thermal energy is the energy stored within an object or system as a result of particle movement.
• If you hold your palm above the stove, you can feel the heat.
• You can watch the temperature rise if you put a thermometer in the water as it heats up.
• A rise in internal energy will result in a rise in temperature.

Application of Thermal Energy

Thermal Energy from friction

Consider the case of a man pushing a box at a consistent speed across a rough floor.

• The work done is not stored as potential energy because the friction force is non-conservative.
• All of the friction force's work results in a transfer of energy into the box-floor system's thermal energy.
• This thermal energy is transferred as heat to the box and the floor, raising their respective temperatures.

Thermal Energy from Drag

When an object moves through a fluid, it transfers momentum and causes the fluid to flow. There would still be some leftover fluid motion if the object stopped moving. After a while, this would fade away.

• The large-scale motions of the fluid are eventually re-distributed into a vast number of smaller random motions of the molecules in the fluid.
• The increased thermal energy in the system is represented by these motions.

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Thermal Energy Storage

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Thermal energy storage is described as a system that permits heat energy to be transferred and stored. This strategy is embedded into modern technologies that work in tandem with renewable energy sources such as solar and hydropower systems.

• They can be stored so that when the demand for power rises, a steady supply can be maintained.
• The term "thermal energy storage" refers to a technique for storing heat.
• It is obtained by heating and cooling the storage system on a continuous basis.
• The thermal energy (chilled or hot water) is created during periods of low electrical demand or use, then stored in a thermal energy storage tank before being extracted and sent to the facility during peak hours.
• Diffusers at the top and bottom of the tank allow heated or cooled water to enter and exit the tank.
• Diffusers are used to reduce turbulence and allow the water in the tank to stratify, with cooler water at the bottom and hotter water at the top.
• A narrow and abrupt transition layer of water forms between the warm and cold water zones.

Thermal energy storage system

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Working Of Thermal Energy Storage System

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An example of a chiller system to understand how the thermal energy storage system works is given below: 

• A chiller cools the water, which contains 25% ethylene glycol.
• The solution circulates through the ice bank's heat exchanger, freezing 95% of the water that surrounds the heat exchanger.
• Using counterflow heat exchanging tubes, ice is created consistently in the ice bank tank.
• While ice is being created, the water continues to flow freely, preventing harm to the tank. The ice bank tank takes six to twelve hours to fully charge.

• The glycol solution cycles through the ice storage tank during peak daytime hours, supplying stored energy to the target.

• The cold glycol is transported to the cooling coil in the air at the right temperature.

Thermal energy storage systems can be of two types:

• Sensible heat storage: Heat energy is stored in either liquid or solid in this form. 
• Latent heat storage: Heat energy is preserved in Solid-Solid materials, Solid-Liquid materials, or Liquid-Gas state. 

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Thermal Energy Storage Applications

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• Thermal Energy used in solar power facilities is used to provide dispatchable power even at night.
• To run more and faster load changes in thermal power plants.
• Provide heat supply security and temporally separate heat and power generation in combined heat and power plants.
• In process industries, to recover and utilise heat that would otherwise be lost.
• Cooking, baking, water heating, and heating all consume thermal energy.

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Things to remember 

• The temperature of a substance has a direct relationship with its thermal energy.
• When higher the thermal energy, the more the molecules vibrate and thus hotter the substance.
• The energy contained within a system that is accountable for its temperature is referred to as thermal energy.
• Energy is measured in Joules.
• When heat is in or out of the object then the thermal energy changes.
• The thermal energy absorbed by water is equal to the thermal energy released by an object.