thermal energy

Examples of thermal energy in the following topics:

• Humans: Work, Energy, and Power

  • The human body converts energy stored in food into work, thermal energy, and/or chemical energy that is stored in fatty tissue.
  • Conservation of energy implies that the chemical energy stored in food is converted into work, thermal energy, or stored as chemical energy in fatty tissue, as shown in .
  • Energy consumed by humans is converted to work, thermal energy, and stored fat.
  • By far the largest fraction goes to thermal energy, although the fraction varies depending on the type of physical activity.
  • Energy consumed by humans is converted to work, thermal energy, and stored fat.

• Heat and Work

  • When energy is exchanged between thermodynamic systems by thermal interaction, the transfer of energy is called heat.
  • Heat is transfer by conduction occurs when an object with high thermal energy comes into contact with an object with low thermal energy.
  • The high temperature body loses thermal energy, and the low temperature body acquires this same amount of thermal energy.
  • The system is then said to be at thermal equilibrium.
  • This means that the total energy within a system is affected by the sum of two possible energy transfers: heat and work.

• Other Forms of Energy

  • Thermal, chemical, electric, radiant, nuclear, magnetic, elastic, sound, mechanical, luminous, and mass are forms that energy can exist in.
  • Thermal Energy: This is energy associated with the microscopic random motion of particles in the media under consideration.
  • An example of something that stores thermal energy is warm bath water.
  • Electric Energy: This is energy that is from electrical potential energy, a result of Coulombic forces.
  • For example, luminous energy is radiant energy.

• Elastic Potential Energy

  • If a force results in only deformation, with no thermal, sound, or kinetic energy, the work done is stored as elastic potential energy.
  • If the only result is deformation and no work goes into thermal, sound, or kinetic energy, then all the work is initially stored in the deformed object as some form of potential energy.
  • Elastic energy of or within a substance is static energy of configuration.
  • Thermal energy is the randomized distribution of kinetic energy within the material, resulting in statistical fluctuations of the material about the equilibrium configuration.
  • For example, for some solid objects, twisting, bending, and other distortions may generate thermal energy, causing the material's temperature to rise.

• Transforming Chemical Energy

  • An electrical energy plant converts energy from one form to another form that can be more easily used .
  • For example, geothermal energy plants start with underground thermal energy (heat) and transform it into electrical energy that will be transported to homes and factories.
  • ATP is the principle form of stored energy used for cellular functions and is frequently referred to as the energy currency of the cell.
  • The energy released during cellular respiration is then used in other biological processes.
  • This geothermal energy plant transforms thermal energy from deep in the ground into electrical energy, which can be easily used.

• Reactions of Alkanes

  • Alkanes can be burned in the presence of oxygen to produce carbon dioxide, water, and energy; in situations with limited oxygen, the products are carbon monoxide, water, and energy.
  • With the addition of a halogen gas and energy, alkanes can be halogenated with the reactivity of the halogens proceeding in the following order: Cl2>Br2>I2.
  • The complex alkanes with high molecular weights that are found in crude oil are frequently broken into smaller, more useful alkanes by thermal cracking; alkenes and hydrogen gas are also produced by using this method.
  • Thermal cracking is typically performed at high temperatures, and often in the presence of a catalyst.

• Thermal Stresses

  • Solids also undergo thermal expansion.
  • What are the basic properties of thermal expansion?
  • An increase in temperature implies an increase in the kinetic energy of the individual atoms.
  • In a solid, unlike in a gas, the atoms or molecules are closely packed together, but their kinetic energy (in the form of small, rapid vibrations) pushes neighboring atoms or molecules apart from each other.
  • Thermal stress is created by thermal expansion or contraction.

• Thermal Radiation

  • If it didn't, we could set up an adjacent blackbody enclosure at the same temperature and energy would flow between them.
  • $\displaystyle \text{Another Kirchoff's Law: }S_\nu = B_\nu(T) \text{ for a thermal emitter}$
  • Because $I_\nu=B_\nu(T)$ outside of the thermal emitting material and $S_\nu=B_\nu(T)$ within the material, we find that $I_\nu=B_\nu(T)$ through out the enclosure.
  • If we remove the thermal emitter from the blackbody enclosure we can see the difference between thermal radiation and blackbody radiation.
  • A thermal emitter has $S_\nu = B_\nu(T)$,$B_\nu(T)$ so the radiation field approaches $B_\nu(T)$ (blackbody radiation) only at large optical depth.

• Thermal Bremsstrahlung Emission

  • The most important case astrophysically is thermal bremsstrahlung where the electrons have a thermal distribution so the probablility of a particle having a particular velocity is
  • We know that radiation comes in bunches of energy $\hbar \omega$ so for a particular frequency $mv^2/2 > h\nu$ for the electron to have enough energy to emit a photon.
  • ${\bar g}_{ff}$ is the thermally averaged Gaunt factor.
  • Thermal bremsstrahlung spectra for two temperatures that differ by a factor of ten

• Thermal Bremsstrahlung Absorption

  • If we assume that the photon field is in thermal equilibrium with the electrons and ion we can obtain an expression for the corresponding absorption,
  • We can also integrate $\alpha_\nu^{ff}$ over all photon energies to get the Rosseland mean absorption coefficient which is