Thermal energy is produced by the heat that is given off from specific sources. It is a kind of kinetic energy that is produced when the molecules of a heat-emitting body or object, experience an acceleration in their velocity, or an increase in their molecular activities. This causes the molecules to collide against each other with a great force, resulting in a lot of molecular friction, thus producing heat. There are many examples of the use of thermal energy in our day-to-day life.
Thermal energy can exist in the form of radiation, latent absorption, or be generated by the application of direct heat. Radiation occurs when heat is transmitted as waves from its source to other objects in the vicinity. Latent heat energy is the energy that an object absorbs or releases, and is associated with changes in phase and difference in temperature. Chemical reactions are a common example of this type. The application of direct heat is the simplest one, where an object is either hot by itself (like fire), or is heated by direct exposure to a naturally hot object (live coals).
This is perhaps the most commonly harnessed form of thermal energy. It is being used on a large scale for industrial as well as domestic heating purposes. Nowadays, environmentally conscious people are using solar power heaters more than the conventional electricity-powered ones. The best applications of thermal energy that use the Sun as their heat source are:
- This device is used for cooking food in a large box-shaped structure which is coated with a black color for maximum heat absorption.
- It directly uses the heat from the Sun's rays for the cooking process. An upper panel that consists of a polished mirror attached to the inner surface reflects the light rays, and concentrates them on the interior surface of the device.
- The dark-colored walls of the cooker convert the light rays into heat energy, which is ultimately used for the cooking process. Also, this heat must be trapped inside, and hence, the utensils are covered with a transparent glass surface or a plastic bag, by which the heat convection effect is reduced.
- Essentially, a kind of "greenhouse gas effect" is induced inside this device. The cooker must be thermally insulated so that minimum heat is lost during the cooking process.
- Cooking time depends on the local and atmospheric conditions, intensity of the Sun's rays, type of device, quantity and kind of food, etc. Also, ensure that the cooker is not kept near a structure that may cast a shadow on it. Try to place it in an open area. This will certainly improve the cooking time.
- Solar cookers are quite less expensive, and are used for cooking outdoors during hiking, camping, on picnics, etc. When used on a domestic scale, they significantly help reduce our dependence on fossil fuels for the production of heat energy, thereby helping in the conservation of Earth's limited natural resources.
Solar Water Heater
- This device is a cheaper and environment-friendly way of using hot water for different purposes. Solar heaters for water are recorded as being used since the beginning of the last century.
- They mainly consist of one or multiple insulated panels or collectors, which are placed in the Sun's direction, and are covered with a glass top or a similar transparent material. They use heat-absorbing materials like glass sheets, metal sheets, or even photovoltaic cells (solar cells made up of silicon wafers).
- Heat-exchanging pipes or tubes are connected to the absorbent material. In some cases, parabolic mirrors are also used to focus the sun's rays on the panels. The tubes lead to the storage tanks, where potable water is separated from the "heat transfer fluid", which circulates through the collector panels.
- The hot water travels through different outlets, and is used for the required purposes. In some cases, especially when the storage tank is placed above the collectors, controller and pumping devices are used to regulate the water flow.
- Solar water heaters are basically of two types: Direct and Indirect. Both these types are further divided into active and passive systems. The working mechanism of each type differs, but the technological framework remains the same.
Heat Energy from the Oceans
This energy is harnessed by utilizing the difference between the temperatures of the deep- and shallow-water oceanic areas. Oceans and sea water surfaces have huge thermal energy storage potential, as they are exposed directly to the Sun's rays for very long durations. With the right technology, thermal energy can be harvested to power a lot of industries, applications, and machinery for the benefit of human civilization, without imposing a heavy cost on nature. This technology is universally known as ocean thermal energy conversion (OTEC).
Ocean Thermal Energy Conversion (OTEC)
- The temperature difference between cold and warm oceanic waters (both shallow and deep) is used to operate specific system engines.
- The theoretical blueprint of this technology was devised in the early 20th century, and a French physicist called Georges Claude developed the first OTEC plant in Cuba in 1930.
- The system engines are either of closed-cycle type or open-cycle type. The former uses fluids like ammonia that has a low boiling point, for making the generators produce electricity, while the latter directly uses ocean water vapor for electricity generation.
- Cold freshwater is a byproduct of this technology, which is used for refrigeration and in air conditioners. Another byproduct is the desalinated water that is used for drinking and irrigation purposes, apart from electricity generation.
- Aquaculture is a field where this technology can be utilized to a large extent. The generated electricity can be used to power heavy industrial machinery, and also be used for domestic purposes.
- OTEC technology is still in its infant stage. A lot of issues like the lack of optimum natural conditions, high expenses, and insufficient technology, make it difficult for the smooth functioning of its power plants. Currently, the only operating OTEC plant in the world is in Japan. It is controlled by the Saga University.
- It is generated from the radioactive decay of various elements, and from magmatic activities that occur beneath the Earth's crust. This energy is produced as well as stored inside the crust. Also, the Earth absorbs a lot of solar energy, which gets stored in the form of geothermal energy. Instances of its existence can be seen in the form of natural hot springs and warm ocean currents. Geothermal energy is being used to generate electricity in many countries, since long. Geothermal reservoirs and hot water springs are among the best examples of this.
Geothermal Energy Plants and Stations
- Currently, about 24 countries operate geothermal plants. They include the United States, Iceland, New Zealand, Indonesia, etc. These stations are mainly set up in locations which are directly affected by the convergent and divergent plate boundaries. They mainly harness energy from the geothermal reservoirs that are formed below the Earth's surface.
- About 93% homes in Iceland are powered by these electricity-generating plants. The most favorable location of this country which sits directly on the Mid-Atlantic oceanic ridge, enables it to harness vast amounts of thermal power.
- Enhanced geothermal systems (EGS) are the power stations which pump water into natural wells to harness the heat energy, as well as to utilize the hot water for various purposes including heating and electricity generation for industries and homes. Another type is known as liquid-dominated plant or reservoir (LDR). They convert the hot water into steam and use it to power the turbines. They are mainly set up near rift zones and volcanoes that are associated with hot-spots.
- Other types are: Dry steam power plant, Binary geothermal stations,Kalina system power stations, etc. Other than heating and electricity production, geothermal power plants are also used for purposes like sludge digestion, pasteurization, agricultural drying, and in mining processes to a certain extent. Geothermal energy is definitely environment-friendly and less expensive if utilized properly. It can help decrease the problem of global warming and greenhouse gases, as it is one of the most sustainable sources of thermal energy.
Hot Water Springs and Geysers
- Groundwater gets heated below the Earth's crust due to the geothermal gradient that is formed by various magmatic activities.
- Due to increase in the pressure caused by steam generation, the water is ejected out onto the Earth's surface from certain openings, resulting in the formation of hot water springs and geysers.
- Though these sources have not been harnessed as much as the thermal reservoirs, they do find a place among examples of thermal energy.
- The springs have a lot of mineral content including sulfur and phosphorus, and hence, are used as mineral sources for medicinal purposes. The heat generated from these springs is also used for cooking, fish breeding, domestic heating, public baths (in cold countries), etc.
Thermal energy forms the basis of the study of thermodynamics and heat energy. It is one of the oldest forms of energy employed by mankind, and was in use even before the discovery of petroleum and nuclear power sources.