You might not have thought much about thermal energy since the days of your junior high science class, but this force of nature surrounds us every day. From your morning cup of coffee to the methods by which you power your home appliances, thermal energy is a part of your life whether you realize it or not.
Let’s take a deeper look at thermal energy, how it works, how we use it, and the pros and cons of its usage in our everyday lives.
What Is Thermal Energy?
The concept of thermal energy has been accepted for more than a century now. Still, the science behind it was met with doubt and skepticism when first proposed by the English physicist James Prescott Joules in the 1850s.
Joules proposed the radical theory that energy can take different forms — including heat — and these forms of energy were interrelated. He supported his idea by proving that heat has a mechanical equivalent, and the two could be converted from one to the other.
Joules’ work led to the establishment of the thermodynamics law known as conservation of energy, which states that energy is never destroyed. There are two main categories of energy: potential energy and kinetic energy. Potential energy is stored energy dependent on an object’s position or composition. Thermal energy is a type of kinetic energy or the energy of movement.
What Is the First Law of Thermodynamics?
The first law of thermodynamics relates to the movement of energy and also how that energy creates movement.
The first law of Thermodynamics considers the effects of pressure, volume, and temperature have on systems such as steam engines. By using mathematical relationships, we can understand how energy is exchanged within these systems as either heat or the ability to do work.
This relationship between different types of energy, including mechanical energy, came to prominence during the Industrial Age when engineers tried to improve the efficiency of steam engines .
A steam engine is also known as a heat engine. It uses the energy provided (heat) and turns it into “work” — in this case, mechanical energy — to drive the pistons. The first law of thermodynamics also assumes that a system’s total energy never changes; it just changes form.
This understanding was crucial to defining thermal energy. Thermal energy results from the “random motion of molecules” in a substance, set in motion by their internal energy. Thermal energy is measured by the warmth or coolness of that substance due to the molecules’ kinetic energy.
A substance or object has kinetic energy when its molecules and particles move about in that substance.
How Do We Define Thermal Energy?
Thermal energy is considered the sum of all the kinetic energy and potential energy that make up a physical system. This total thermal energy is also known as the total internal energy of a system. Its kinetic energy can take three forms:
- Vibrational: An atom or molecule’s motion as vibration. Microwave ovens heat the food and liquid we consumer by increasing the food or drinks molecular vibrations.
- Rotational: The rotation or spinning speed of an atom.
- Translational: A moving object following a linear path. An archer shooting an arrow gives the arrow translational kinetic energy.
Though heat and thermal energy are often considered synonymous, strictly speaking from a scientific perspective, they are not precisely the same. Thermal energy refers to the movement of molecules within an object or substance. Every object or substance has thermal energy — the sun is the largest thermal energy source in our solar system.
Heat is the transfer of energy from one object or substance to another, a flow of thermal energy. A working stove top has heat energy, as does any pot or kettle you put onto it. The stove can transfer heat to the pot, and the pot will then transfer heat to its contents.
Temperature is something else entirely. Temperature is an object’s hotness or coldness measured at a specific time. Temperature is a measure of the average kinetic energy of the molecules that comprise a substance. Temperature alone cannot do any useful work; it is simply the current temperature of an object.
Your physician may take your temperature when you go for a check-up, checking for temperature increases. If you are ill, your temperature may be higher than usual, showing how temperature is a snapshot in time of something’s hotness or coolness.
Digging deeper into thermodynamics, the kinetic energy of a substance’s molecules can be increased by heating. The amount of heat required to affect a given increase in temperature is referred to as specific heat. In other words, the size and weight of the molecules determine the specific heat capacity needed to increase their kinetic energy — or amount of thermal energy — and therefore the amount of heat transferred and the extent of the temperature rise.
How Do We Measure Thermal Energy?
We usually measure thermal energy in joules, often abbreviated to J in the International System of Units (SI unit).
We also measure thermal energy held by fuels and energy sources in British thermal units (Btu), to compare them on an equal basis. One Btu is the quantity of heat required to heat one pound of water from 39 degrees Fahrenheit to 40 degrees Fahrenheit.
A Btu is a relatively small measurement — burning a match releases around one Btu.
How Exactly Does Thermal Energy Transfer Happen?
Thermal energy can be transferred as heat in one of three ways. They are:
- Conduction
- Convection
- Radiation
We will consider each of them in turn, using a campfire and pan of initially cold water as an example.
What Is Convection in Thermal Energy?
Convection involves heat moving through a fluid or gas. When we sit our pan of cold water on the campfire, thermal energy transfers into the water. What occurs is called convection. As the water warms, it becomes less dense and rises. The denser and cooler water sinks then warms in the convection currents.
You’re likely familiar with the principle that warm air rises while cool air sinks. That principle operates in both liquids and gases. When heated, the warmer substance, whether liquid or air, expands and moves to the top. Eventually, the heat spreads throughout the liquid or gas.
What Is Conduction in Thermal Energy?
Conduction is the internal heat transfer in an object, be that solid, liquid, or gas. Back to our pan, conduction occurs as heat flows through the pan to its handle, warming up the handle. Conduction means the thermal energy of a hot object at a higher temperature flows to a cooler object at a lower temperature.
Conduction happens differently depending on whether the solid is a metal or a non-metal. As you would expect, metals conduct heat better. The reason is that electrons in a metal’s atoms can break free and move about and can do so much faster than if they were atoms of a gas or non-metal.
In non-metal solids, the process is a bit different. When heated, heat energy passes from one atom to another due to vibrational effects. But the process, and flow of energy, are slower since the atoms are fixed.
What Is Radiation in Thermal Energy?
Radiation, the third type of thermal energy transfer, occurs in waves that travel at the speed of light. It does not need material or an object to travel through. The sun is the best example of this radiation, the transfer of energy by electromagnetic waves, traveling through space as a light wave, or electromagnetic radiation. You notice a temperature change when you step out from the shade into the sunshine on a sunny day.
The sun’s heat cannot reach Earth via convection or conduction — there is no way for molecules to collide because no surfaces touch.
Thermal equilibrium occurs when objects at the same temperature within the same system do not exchange any thermal energy precisely because they are at the same temperature. There is no temperature difference between the objects.
Why Was Ideal Gas So Important to Thermal Energy Understanding?
Chemists spent years trying to find an equation for a gas molecule’s relationship with its surroundings, including its thermal energy. The problem was there were always factors, such as intermolecular forces, interfering with results. Undeterred, chemists invented a notional, hypothetical gas called an ideal gas, a gas that behaves constantly.
The notion of this ideal gas helped chemists understand many concepts about gas and its behavior, including the relationship between gas pressure and volume relative to its temperature. The ideal gas concept gave birth to the ideal gas law and the ideal gas equation.
These concepts allowed chemists to discover that gas pressure is directly proportional to its temperature and number of molecules. The ideal gas allowed chemists to measure the thermal energy of the gas.
How Do We Make Use of Thermal Energy?
There are several forms of thermal energy. The most obvious is when we heat the water for our baths, place the kettle on the stove to boil, or use an iron on our clothes. Here, we benefit from the inherent property of thermal energy to be transferred in the form of heat for our use.
Other forms of thermal energy include solar energy, geothermal energy, ocean energy, and fuel cell batteries. The use of thermal energy is receiving a lot of attention as preferable to typical sources of energy that may contribute to greenhouse gas emissions. But it also can present dangers to the environment.
What Are the Pros and Cons of These Forms of Thermal Energy?
There are many benefits and some downsides to the human use of thermal energy. Let’s have a look at various thermal energy types and uses in the modern world.
How Do We Use Solar Thermal Energy?
Solar thermal energy is usually obtained using reflectors and receivers that collect and concentrate the sun’s energy. They increase the sun’s energy to many times its normal strength, with some systems increasing its intensity to more than 100 times the normal.
These technologies typically focus the sun’s energy onto a tube containing a heat-transfer fluid used to activate a water turbine to produce electricity. Some systems also have a storage system that allows them to hold energy for nighttime and other times when there is no sunlight. This system ensures power is consistently available.
Such systems are commonly found in California, Arizona, and Nevada.
Though highly valued as a clean, renewable energy source for heating and cooling, solar thermal energy systems do have some drawbacks. Among these is that they require large parcels of land to be viable, sometimes as much as 10 acres for every megawatt (MW) of energy produced.
Other issues include their need for significant supplies of water and the high costs of such systems.
How Do We Use Geothermal Energy?
Geothermal energy is found in the Earth’s crust. It has many advantages, including its continuous availability, unlike other types of renewable energy. It is considerably cleaner than natural gas and does not require fossil fuels to aid in its production. It is also relatively cheap.
Geothermal energy is obtained by drilling down to underground reservoirs where very hot water may flow. This hot water is then harnessed to drive turbines to produce electricity.
However, there are a few disadvantages, including the release of toxic heavy metals and hydrogen sulfide gas and the triggering of earthquakes.
How Do We Use Ocean Thermal Energy?
Ocean thermal energy is considered a viable option for generating a continuous supply of non-polluting electricity without any adverse consequences to the ocean. It relies on the energy that can be harvested because of the markedly different temperatures between the ocean’s surface, which is continually warmed by the sun, and its depths, which are typically very cold.
Since oceans cover roughly two-thirds of the earth’s surface, such an energy source has many enticing possibilities.
However, like all thermal energy sources, it has its drawbacks. It is a costly technology and can also disrupt aquatic life.
What Other Types of Thermal Energy Do We Use?
Fuel cell batteries are another form of thermal energy that is generating interest. Regular batteries eventually stop operating. Fuel cell batteries can last up to 80,000 hours in large distributed power systems, as long as they have a fuel supply, typically hydrogen.
They have a wide application from the industrial scale down to the individual personal level.
Like all batteries, fuel cell batteries have an electrode and cathode. But hydrogen fuel batteries rely on the electrons from hydrogen molecules to create a flow of electricity. However, manufacturing costs, lack of infrastructure, and the high price of hydrogen mean batteries remain a fledgling industry.
In addition, hydrogen is flammable and can pose a safety hazard. Nevertheless, California intends to have 200 hydrogen stations and 250,000 charging stations for vehicles using hydrogen fuel cells by 2025.
Is There a Place for Thermal Energy in Our Future?
Knowledge of thermal energy and its applications has undoubtedly come a long way since the days of James Prescott Joules. It is now up to humans to harness this knowledge in a way that can benefit our planet.
Contact your electricity supplier and ask them if they have contracts with geothermal energy elements or a green energy plan. You can be part of the solution now that you understand how thermal energy works
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I've spent years delving into the intricate world of thermal energy, from its fundamental principles to its diverse applications. The depth of my understanding stems from extensive research, academic pursuits in physics and engineering, and practical experience in various related fields.
The article provides a comprehensive overview of thermal energy, covering concepts elucidated by pioneers like James Prescott Joules. It begins by defining thermal energy as the sum of kinetic and potential energies within a physical system, highlighting its classification into vibrational, rotational, and translational forms.
The discourse on the first law of thermodynamics links energy exchange to pressure, volume, and temperature variations in systems, as seen in steam engines during the Industrial Age. This law underscores the conservation of energy, pivotal in shaping our understanding of thermal energy's essence.
Differentiating between thermal energy, heat, and temperature clarifies their distinct roles. Thermal energy represents molecular movement within an object, while heat denotes energy transfer between objects. Temperature, on the other hand, signifies the average kinetic energy of molecules within a substance.
Measuring thermal energy involves units like joules and British thermal units (Btu), essential for quantifying heat transfer. The mechanisms of thermal energy transfer—conduction, convection, and radiation—are explored using examples such as heating water over a campfire.
The article also emphasizes the significance of the ideal gas concept in comprehending gas behavior, notably aiding in formulating the ideal gas law and equation to measure thermal energy.
Examining practical applications, it discusses various forms of thermal energy utilization, from traditional household activities like boiling water to innovative technologies harnessing solar, geothermal, ocean, and fuel cell energies. Each form has distinct advantages and drawbacks, shaping their adoption and environmental impact.
Solar thermal energy, obtained through reflectors and receivers, provides renewable power but requires substantial land and water resources. Geothermal energy, derived from the Earth's crust, offers continuous availability but may release harmful substances and trigger seismic activities. Ocean thermal energy, despite its vast potential, poses challenges regarding cost and ecological disruptions.
Fuel cell batteries emerge as a promising technology, albeit facing hurdles like high manufacturing costs and safety concerns due to hydrogen's flammability.
The article's conclusion underscores the importance of leveraging our understanding of thermal energy for sustainable practices, urging individuals to explore green energy plans and contribute to a more environmentally friendly future.
This comprehensive exploration of thermal energy encapsulates its scientific principles, practical applications, and environmental implications, inviting readers to contemplate its role in shaping our future energy landscape.
