16 effects found

Endothermic Reactions

An Endothermic Reaction is one that needs to absorb some form of energy (normally heat) from its environment or surroundings to carry out the process, causing a depletion of energy capacity of the surroundings.
A chemical reaction where the energy content of the products is more than that of the reactants; heat is taken in by the system.

Example: Solid Barium Hydroxide Octahydrate and Ammonium Thiocyanate are mixed in a beaker and the beaker is placed inside another beaker containing water. The mixture is stirred and the two solids react resulting in absorption of heat from the surrounding, i.e water in another beaker, resulting in decreasing in temperature of water kept in outer beaker.

Capillary-porous materials

Capillary-Porous Materials are porous structures made of materials like Steel, Aluminum, Nickel or Copper in various ranges of pore sizes. Fibrous materials, like ceramics, have also been used widely.
The main disadvantage of ceramic fibres is that, they have little stiffness and usually require a continuous support by a metal mesh. More recently, interest has turned to carbon fibres as a wick material. Carbon fibre filaments have many fine longitudinal grooves on their surface, high capillary pressures, and are chemically stable. A number of heat pipes that have been successfully constructed using carbon fibre wicks seem to show a greater heat transport capability. The prime purpose of the wick is to generate capillary pressure to transport the working fluid from the condenser to the evaporator. It must also be able to distribute the liquid around the evaporator section, to any area, where heat is likely to be received by the heat pipe.

Example: Working of the capillary-porous material inside the Heat-Pipe - Inside the container is a liquid under its own pressure, that enters the pores of the capillary material, wetting all internal surfaces. Applying heat at any point along the surface of the heat pipe causes the liquid at that point to boil and enter a vapor state. When that happens, the liquid picks up the latent heat of vaporization. The gas, which then has a higher pressure, moves inside the sealed container to a colder location where it condenses. Thus, the gas gives up the latent heat of vaporization and moves heat from the input to the output end of the heat pipe. Animation depicts the concept.

Corona Discharge

Corona Discharge is an electrical discharge around a conductor in a gas, that occurs, when the electric field around the conductor exceeds the value required to ionize the gas, but is insufficient to cause a spark.

Example: A phenomenon called 'glow or corona discharge' maybe sometimes observed in high-tension power lines in damp weather.

Stirling Effect

Stirling Effect is the expansion of a gas when heated, followed by the compression of the gas when cooled.
In 1816, a Scottish Reverend, Robert Stirling won a patent on a hot air engine that converted heat to work (or vice versa) through repeated compression and expansion of the working fluid at different temperature levels. The concept was not used as for cooling until 1834, when John Hershel used a closed cycle Stirling engine for making ice.

Example: In Stirling refrigeration cycle, the piston compresses and expands the working fluid (Helium) and it is driven by an AC linear motor. The displacer shuttles this gas back and forth from the cold side to the warm side of the cooler. During expansion, heat is absorbed at the cold side; and during compression, heat is rejected at the hot side.

Nernst-Ettinghausen Effect

No description available