Trans_Energéticas

Transformaciones Energéticas

In physics, energy (from the Greek ἐνέργεια - energeia, "activity, operation", from ἐνεργός - energos, "active, working"[1]) is a quantity that can be assigned to any particle, object, or system of objects as a consequence of its physical state. Different forms of energy include kinetic, potential, thermal, gravitational, sound, elastic and electromagnetic energy. The forms of energy are often named after a related force. German physicist Hermann von Helmholtz established that all forms of energy are equivalent - energy in one form can disappear but the same amount of energy will appear in another form.[2] Energy is subject to a conservation law. Energy is a scalar physical quantity. In the International System of Units (SI), energy is measured in joules, but in some fields other units such as kilowatt-hours and kilocalories are also used.

Any form of energy can be transformed into another form. When energy is in a form other than thermal energy, it may be transformed with good or even perfect efficiency, to any other type of energy. With thermal energy, however, there are often limits to the efficiency of the conversion to other forms of energy, due to the second law of thermodynamics. As an example, oil is reacted with oxygen, potential energy is released, since new chemical bonds are formed in the products which are more powerful than those in the oil and oxygen. The released energy resulting from this process may be converted directly to electricity (as in a fuel cell) with good efficiency. Alternately it may be converted into thermal energy, if the oil is simply burned in order to heat the combustion gases to a certain temperature. In the latter case, however, some of the thermal energy can no longer be used to perform work at that temperature, and is said to be "degraded." As such, it exists in a form unavailable for further transformation. The remainder of the thermal energy may be used to produce any other type of energy, such as electricity.

¿Qué vas a aprender?:

Introducción a las energías. Fotocopia de Energías Página 1. Apartado 4.2 (pág. 68) del libro.
Unidades de energía. Conceptos Físicos de las fotocopias y página 66-67 libro.
Formas de manifetación de la energía (relaciones matemáticas y físicas). Apartado 4.3 del libro ( esquema de página 70). Explicaciones según las fotocopias de Energías. Señalar las fórmulas que han ser conocidas. Ver tabla Pág. 72
Transformaciones energéticas: máquinas, procesos y rendimientos obtenidos.
Principio de la conservación de la energía. Apartado 4.4 del libro. Esquema página 76.
Uso racional de la energía. Apartado 4.5 del libro.

Problemas obligatorios

Fotocopia de ejercicios de energía. Ejemplos del tema:.7,8,17,19. Ejercicios del tema: 22,23,31.

Nota sobre los calores de combustión de los combustibles Fósiles (Wikipedia) (Tabla de Datos para problemas)

Resumen:

The heat of combustion (ΔHc0) is the energy released as heat when a compound undergoes complete combustion with oxygen under standard conditions. The chemical reaction is typically a hydrocarbon reacting with oxygen to form carbon dioxide, water and heat. It may be expressed with the quantities:

energy/mole of fuel (J/mol)
energy/mass of fuel
energy/volume of fuel

The heating value or calorific value of a substance, usually a fuel or food (see food energy), is the amount of heat released during the combustion of a specified amount of it. The calorific value is a characteristic for each substance. It is measured in units of energy per unit of the substance, usually mass, such as: kcal/kg, kJ/kg, J/mol, Btu/m³. Heating value is commonly determined by use of a bomb calorimeter.

The heat of combustion for fuels is expressed as the HHV, LHV, or GHV:

The quantity known as higher heating value (HHV) (or gross calorific value or gross energy or upper heating value) is determined by bringing all the products of combustion back to the original pre-combustion temperature, and in particular condensing any vapor produced. This is the same as the thermodynamic heat of combustion since the enthalpy change for the reaction assumes a common temperature of the compounds before and after combustion, in which case the water produced by combustion is liquid.
The quantity known as lower heating value (LHV) (or net calorific value) is determined by subtracting the heat of vaporization of the water vapor from the higher heating value. This treats any H2O formed as a vapor. The energy required to vaporize the water therefore is not realized as heat.
Gross heating value (see AR) accounts for water in the exhaust leaving as vapor, and includes liquid water in the fuel prior to combustion. This value is important for fuels like wood or coal, which will usually contain some amount of water prior to burning.

A common method of relating HHV to LHV is:

HHV = LHV + hv x (nH2O,out/nfuel,in)

where hv is the heat of vaporization of water, nH2O,out is the moles of water vaporized and nfuel,in is the number of moles of fuel combusted.[1]

Most applications which burn fuel produce water vapor which is not used and thus wasting its heat content. In such applications, the lower heating value is the applicable measure. This is particularly relevant for natural gas, whose high hydrogen content produces much water. The gross calorific value is relevant for gas burnt in condensing boilers and power plants with flue gas condensation which condense the water vapor produced by combustion, recovering heat which would otherwise be wasted.

Transformaciones Energéticas

Problemas obligatorios

Diferencias entre la liberación de energía Química y Núclear