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Thermal Transpiration
Thermal transpiration (or thermal diffusion) refers to the thermal force on a gas due to a temperature difference. Thermal transpiration causes a flow of gas in the absence of any other pressure difference, and is able to maintain a certain pressure difference called thermomolecular pressure difference in a steady state. The effect is strongest when the mean free path of the gas molecules is comparable to the dimensions of the gas container. Thermal transpiration appears as an important correction in the readings of vapor pressure thermometers, and the effect is historically famous as being an explanation for the rotation of the Crookes radiometer. See also * Knudsen pump — a gas pump with no moving parts which functions via thermal transpiration. *Thermophoresis Thermophoresis (also thermomigration, thermodiffusion, the Soret effect, or the Ludwig–Soret effect) is a phenomenon observed in mixtures of mobile particles where the different particle types exhibit different re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Crookes Radiometer Thermal Creep
Crookes is a suburb of the City of Sheffield, England, about west of the city centre. It borders Broomhill to the south, Walkley and Crookesmoor to the east and open countryside around the River Rivelin to the north. The population of the ward of the same name was 17,700 at the 2011 Census. Etymology The suburb is said to derive its name from the Old Norse "Krkor" which means a nook or corner of land. History Crookes lies near the course of a Roman road from Templeborough to Brough-on-Noe (now Lydgate Lane) and the main road is itself over 1,000 years old.Crookes' long and colourful history as a Sheffield village Sheffield Star. 6 February 20 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mean Free Path
In physics, mean free path is the average distance over which a moving particle (such as an atom, a molecule, or a photon) travels before substantially changing its direction or energy (or, in a specific context, other properties), typically as a result of one or more successive collisions with other particles. Scattering theory Imagine a beam of particles being shot through a target, and consider an infinitesimally thin slab of the target (see the figure). The atoms (or particles) that might stop a beam particle are shown in red. The magnitude of the mean free path depends on the characteristics of the system. Assuming that all the target particles are at rest but only the beam particle is moving, that gives an expression for the mean free path: :\ell = (\sigma n)^, where is the mean free path, is the number of target particles per unit volume, and is the effective cross-sectional area for collision. The area of the slab is , and its volume is . The typical number of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vapor Pressure Thermometer
A vapour pressure thermometer is a thermometer that uses a pressure gauge to measure the vapour pressure Vapor pressure (or vapour pressure in English-speaking countries other than the US; see spelling differences) or equilibrium vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phase ... of a liquid. References Thermometers {{thermodynamics-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Crookes Radiometer
The Crookes radiometer (also known as a light mill) consists of an airtight glass bulb containing a partial vacuum, with a set of vanes which are mounted on a spindle inside. The vanes rotate when exposed to light, with faster rotation for more intense light, providing a quantitative measurement of electromagnetic radiation intensity. The reason for the rotation was a cause of much scientific debate in the ten years following the invention of the device, but in 1879 the currently accepted explanation for the rotation was published. Today the device is mainly used in physics education as a demonstration of a heat engine run by light energy. It was invented in 1873 by the chemist Sir William Crookes as the by-product of some chemical research. In the course of very accurate quantitative chemical work, he was weighing samples in a partially evacuated chamber to reduce the effect of air currents, and noticed the weighings were disturbed when sunlight shone on the balance. Investigat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Knudsen Pump
The Knudsen pump also referred to as "thermal transpiration pump" or "Knudsen compressor" is a gas pump that utilizes no moving parts. Instead it uses thermal transpiration, the phenomenon that gas molecules drift from the hot end to the cold end of a narrow channel. Thus a hot vacuum chamber "transpires" into the cold chamber. This thermal transpiration Thermal transpiration (or thermal diffusion) refers to the thermal force on a gas due to a temperature difference. Thermal transpiration causes a flow of gas in the absence of any other pressure difference, and is able to maintain a certain pressu ... flow is induced when the boundary walls of the pump have a temperature gradient. Because the pump is based simply on temperature differences and has no moving parts, it could provide reliable and precise control of gas flow for a variety of applications, such as gas-sensing breath analyzers, chemical weapons detectors, and in satellite control. It is named after Martin Knudsen, a D ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thermophoresis
Thermophoresis (also thermomigration, thermodiffusion, the Soret effect, or the Ludwig–Soret effect) is a phenomenon observed in mixtures of mobile particles where the different particle types exhibit different responses to the force of a temperature gradient. This phenomenon tends to move light molecules to hot regions and heavy molecules to cold regions. The term ''thermophoresis'' most often applies to aerosol mixtures whose mean free path \lambda is comparable to its characteristic length scale L, but may also commonly refer to the phenomenon in all phases of matter. The term ''Soret effect'' normally applies to liquid mixtures, which behave according to different, less well-understood mechanisms than gaseous mixtures. Thermophoresis may not apply to thermomigration in solids, especially multi-phase alloys. Thermophoretic force The phenomenon is observed at the scale of one millimeter or less. An example that may be observed by the naked eye with good lighting is when the ho ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
