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Thermal Energy
From CopperWiki
Thermal Energy is the kind of energy that is related to and/or caused by heat. When thermal energy is applied to a substance, the average velocity of the particles or molecules which make up the substance increases -- and it gets warmer! The thermal energy of an object consists of the total kinetic energy of all its atoms and molecules. It is a form of energy related to heat and temperature.
Over 2000 years ago, the Greeks built their houses in such a way that the sun's rays entered during the winter, but not during the summer. The Romans put glasses in windows which allowed the sun's light to pass through but trapped its heat.
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Landscaping for Energy EfficiencyThe energy crisis and eyes destined to be dim like their owners
The sun gives off more energy in one second than people have used since the beginning of time. It is the ultimate source of energy available to man. It produces thermal energy (heat energy) in the form of radiation. Thermal energy is created by the movement of atoms and molecules in matter. The way rubbing our hands together produces heat, so is heat produced with atoms and molecules rubbing against each other. This is known as heat thermal energy.
Temperature and heat are related to thermal energy. Temperature is the average kinetic energy of all the atoms or molecules in an object. When thermal energy flows from an object of one temperature to another of different temperature, heat is created. Like the flow of heat is felt when warm air from a furnace reaches you.
Thermal energy from the sun can be transferred into water and stored in insulated containers and kept heated constantly by the sun’s radiation, and retain energy overnight. This energy is also used to heat water and heat homes, and find various applications. This is unlike photovoltaics which convert solar energy into electricity.
[edit] All about thermal energy
Thermal energy can be created both internally and externally. It can be created internally with chemical, nuclear and electrical reactions and from external effects, such as mechanical motion, radiation and thermal conduction.
Mechanical motion, radiation and thermal conduction, which are external sources of energy, can also increase the thermal energy of an object. Heat is caused by friction of objects rubbed together, like the pounding on a metal makes it warm.
When sunlight radiates on an object its energy is transferred to the object's molecules and makes them move faster. In other words, the object heats up.
[edit] Energy of the sun
The energy of the sun can be directly collected to create both high temperature steam (greater than 100oC) and low temperature heat (less than 100oC) for use in a variety of heat and power applications.
Solar thermal energy offers a cheap way of harnessing the sun's power to generate electricity. While solar panels, or photovoltaics, also use silicon to turn the sun's rays directly into electric current, solar thermal technology uses infrastructure similar to traditional power plants.
In its basic form parabolic mirrors focus the sun's rays to a single point to produce temperatures in excess of 1000oC. The high temperatures create steam to drive electric turbine generators. As it is a cheap technology it can be deployed on a large scale.
[edit] Cheap way of harnessing the sun's power
Chemical and nuclear reactions, along with electrical effects create or increase thermal energy. The energy transferred by these actions cause an object's internal particles to increase their motion and thus their kinetic energy. For example, some chemical reactions cause nearby molecules to accelerate, thus increasing the total thermal energy of the object.
Similarly the thermal energy of a material increases as nuclear fission or nuclear decay give off high-speed particles
In electrical applications the kinetic motion in the wire’s molecules increases with the resistance of electrons in an electrical circuit. This increases the thermal energy of the wire.
[edit] Low temperature solar thermal dystems
In the low temperature solar thermal systems solar radiation is collected to heat air and water mainly for
- space heating for homes, offices and greenhouses
- domestic and industrial hot water
- pool heating
- desalination
- solar cooking, and
- crop drying
These technologies include passive and active systems.
Passive systems
This system does not use pumps or motors to collect energy. It is employed mostly in buildings where the building itself acts as the collector. There is very low additional cost in the case of new buildings as the orientation of the building is used to capture and use solar radiation.
The passive system reduces heating cost by 40 percent in cold climates. In hotter climates this system can reduce the absorption of solar radiation and thus bring down cooling costs.
Active systems
In the active system, pumps circulate water or another heat absorbing fluid through a solar collector made of copper tubes bonded to a metal plate. The collector is painted black and positioned in an insulated box with glass panel covering.
[edit] Solar hot water system
The solar hot water system (SHS) is a mature technology for meeting the hot water needs of buildings. In Europe, a SHS can generally meet between 50–65 percent of domestic hot water requirements, while in subtropical climates, such as Asia and northern Australia, the percentage can be 80–100 percent of the needs.
The same energy collectors can be used for home heating too. Large district heating systems are used in Sweden and some other countries to heat water during the summer for use during winter.
[edit] Thermal energy storage
Thermal energy is stored as a battery stores heating or cooling capacity for later use. Cooling capacity is stored by removing heat from a storage medium. Storage can be latent (involving freezing and melting) or sensible (involving change in temperature). Water is the preferred medium for cool thermal storage. Heat storage media include water, paraffin phase-change materials, and solid sensible media such as bricks.
[edit] Latent storage
A typical latent cool storage module is a closed container of water in which a heat exchanger made from coils of plastic tubing is immersed. Capacity is stored by circulating antifreeze solution that is cooled by refrigeration equipment through the tubing to freeze the water. Stored capacity is used when fluid warmed by cooling loads flows through the tubing and is cooled by melting the ice. System controls determine when storage is made and used.
[edit] Sensible storage
This uses a stratified storage tank, employing the temperature dependence of water density, which is greatest at approximately 4°C (39°F), to separate warmer water from cooler water. Water enters and leaves the tank at equal flow rates through diffusers: warm at the top and cool at the bottom. A thin thermal transition layer (thermocline) forms at the interface between the warm and cool water and is displaced as water flows through the tank. The direction of flow is from bottom to top while capacity is being stored, and it reverses when capacity is extracted. Newer sources of thermal energy storages as well as usages are being developed.
