Thermal energy is the energy possessed by a substance due to the movement of its atoms or molecules. Heat is energy that is transferred from one place to another through radiation, conduction, or convection. Thermal energy has been used for cooking, heating, producing energy, and in industry. Geothermal and solar energy are being explored as alternatives to fossil fuels.
The atoms and molecules that make up a substance are in constant motion. This motion is what gives a material its temperature: the more the molecules move, the hotter the temperature. Thermal energy is simply the energy possessed by a substance due to the movement of its atoms or molecules. It’s important not to confuse it with heat, which is energy that is transferred from one place to another. Thermal energy has long been exploited by man for cooking, heating, producing energy and in industry.
Radiation, conduction and convection
Heat is defined as energy that is transferred from one region to another, always flowing from an area of higher temperature to an area of lower temperature. It can be transferred via infrared radiation, a form of electromagnetic radiation with a wavelength range that lies between radio waves and visible light. This interacts with matter to cause molecules to move at higher speeds, which is seen as an increase in temperature: the material becomes warm or hot, because energy has been transferred from the source of the radiation to the absorbing material . For example, if an object is held near a flame, it becomes hot due to the flame’s infrared radiation.
The transfer can also take place in two other ways. In conduction, the motion of molecules in a warm region causes an increase in motion in cooler areas as the molecules collide with each other. For example, if a metal spoon is held in a flame, the other end of the spoon will eventually become hot.
Convection involves the movement of a region of gas or liquid that is hotter than its surroundings. For example, the sun warms the ground, which in turn warms the air, which then moves upwards, as warm air is less dense than the cooler air above. It’s convection that drives the world’s weather systems, as warm air from the tropics rises and flows outward.
Thermal Energy and Matter
Thermal energy can cause a change in the state of matter. If the molecules in a solid increase their motion sufficiently, it will melt to become a liquid. Further increase will cause the liquid to boil and become a gas, although liquids also tend to evaporate at temperatures well below their boiling points, as some molecules will be moving fast enough to escape the liquid. Because the molecules in a gas move faster than those in a liquid, a gas has more energy. This is why sweating makes people cold: when sweat evaporates, it takes heat away from the body.
Exploiting thermal energy
The use of thermal energy, either directly or to generate electricity, drove the industrial revolution. It enabled the large-scale production of iron and steel and produced the steam to drive turbines used to generate electricity. Humanity has long been heavily dependent on the burning of fossil fuels, such as oil, coal and natural gas, as sources of thermal energy. Concerns about pollution, climate change and non-renewability, however, have generated much interest in alternatives.
One of the sources exploited is geothermal energy. Earth has a molten core, which is thought to have a temperature of 5,432-9,032°F (3,000-5,000°C). This high temperature results in part from residual heat from the Earth’s formation, trapped under insulating layers of rock in the crust, and in part from the decay of radioactive elements. Between the core and the crust is the mantle, a hot, semi-liquid region that drives plate tectonics and volcanic eruptions. There are many “hot spots” on the earth’s crust where this heat is close to the surface and can be harnessed in various ways.
Geothermal heat can be used directly, to heat homes or to generate electricity. Geysers are a ready source of hot water, but most geothermal projects involve drilling holes and pumping water into them. The water is heated below the surface and pumped back to provide energy. Geothermal energy is not, strictly speaking, a renewable energy source, but there is a huge amount of heat from the core that will not be depleted in the foreseeable future.
Although solar energy can be harnessed to produce electricity directly through solar panels, another area being explored is that of solar thermal. This involves capturing heat from the sun to provide energy or hot water. This can be used for central heating in homes, where water, or another fluid, is pumped through a container that receives sunlight, raising its temperature. Alternatively, the sun’s heat can be used to drive mechanical devices that generate electricity or it can be focused by convex mirrors to provide heat for cooking or other purposes. This idea can also be adopted on a large scale to boil water that drives a turbine or to build a “solar oven” capable of reaching the extreme temperatures required for some industrial processes.
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