Convection is the heat transfer due to the bulk movement of molecules within fluids such as gases and liquids, including molten rock. Convection includes sub-mechanisms of advection, diffusion. Convection cannot take place in most solids because neither bulk current flows nor significant diffusion of matter can take place. Diffusion of heat takes place in rigid solids, but, called heat conduction. Convection, additionally may take place in soft solids or mixtures where solid particles can move past each other. Thermal convection can be demonstrated by placing a heat source at the side of a glass filled with a liquid, observing the changes in temperature in the glass caused by the warmer fluid circulating into cooler areas. Convective heat transfer is one of the major types of heat transfer, convection is a major mode of mass transfer in fluids. Convective heat and mass transfer takes place both by diffusion – the random Brownian motion of individual particles in the fluid – and by advection, in which matter or heat is transported by the larger-scale motion of currents in the fluid.
In the context of heat and mass transfer, the term "convection" is used to refer to the combined effects of advective and diffusive transfer. Sometimes the term "convection" is used to refer to "free heat convection" where bulk-flow in a fluid is due to temperature-induced differences in buoyancy, as opposed to "forced heat convection" where forces other than buoyancy move the fluid. However, in mechanics, the correct use of the word "convection" is the more general sense, different types of convection should be further qualified, for clarity. Convection can be qualified in terms of being natural, gravitational, granular, or thermomagnetic, it may be said to be due to combustion, capillary action, or Marangoni and Weissenberg effects. Heat transfer by natural convection plays a role in the structure of Earth's atmosphere, its oceans, its mantle. Discrete convective cells in the atmosphere can be seen as clouds, with stronger convection resulting in thunderstorms. Natural convection plays a role in stellar physics.
The convection mechanism is used in cooking, when using a convection oven, which uses fans to circulate hot air around food in order to cook the food faster than a conventional oven. The word convection may have different but related usages in different scientific or engineering contexts or applications; the broader sense is in fluid mechanics, where convection refers to the motion of fluid regardless of cause. However, in thermodynamics "convection" refers to heat transfer by convection. Convection occurs on a large scale in atmospheres, planetary mantles, it provides the mechanism of heat transfer for a large fraction of the outermost interiors of our sun and all stars. Fluid movement during convection may be invisibly slow, or it may be obvious and rapid, as in a hurricane. On astronomical scales, convection of gas and dust is thought to occur in the accretion disks of black holes, at speeds which may approach that of light. Convective heat transfer is a mechanism of heat transfer occurring because of bulk motion of fluids.
Heat is the entity of interest being advected, diffused. This can be contrasted with conductive heat transfer, the transfer of energy by vibrations at a molecular level through a solid or fluid, radiative heat transfer, the transfer of energy through electromagnetic waves. Heat is transferred by convection in numerous examples of occurring fluid flow, such as wind, oceanic currents, movements within the Earth's mantle. Convection is used in engineering practices of homes, industrial processes, cooling of equipment, etc; the rate of convective heat transfer may be improved by the use of a heat sink in conjunction with a fan. For instance, a typical computer CPU will have a purpose-made fan to ensure its operating temperature is kept within tolerable limits. A convection cell known as a Bénard cell is a characteristic fluid flow pattern in many convection systems. A rising body of fluid loses heat because it encounters a colder surface. In liquid, this occurs. In the example of the Earth's atmosphere, this occurs.
Because of this heat loss the fluid becomes denser than the fluid underneath it, still rising. Since it cannot descend through the rising fluid, it moves to one side. At some distance, its downward force overcomes the rising force beneath it, the fluid begins to descend; as it descends, it warms again and the cycle repeats itself. Atmospheric circulation is the large-scale movement of air, is a means by which thermal energy is distributed on the surface of the Earth, together with the much slower ocean circulation system; the large-scale structure of the atmospheric circulation varies from year to year, but the basic climatological structure remains constant. Latitudinal circulation occurs because incident solar radiation per unit area is highest at the heat equator, decreases as the latitude increases, reaching minima at the poles, it consists of two primary convection cells, the Hadley cell and the polar vortex, with the Hadley cell experiencing stronger convection due to the release of latent heat energy by condensation of water vapor at higher altitudes during cloud formation.
Longitudinal circulation, on the other hand, comes about because the ocean has a higher specific heat capacity than land (and thermal condu
The Men's junior time trial of the 2014 UCI Road World Championships took place in and around Ponferrada, Spain on 23 September 2014. The course of the race was 29.50 km with the finish in Ponferrada. Lennard Kämna became the first German rider to win the world title since Marcel Kittel in 2006, with a winning margin of 45 seconds over his nearest competitor; the silver medal went to American rider Adrien Costa, with the bronze medal going to Australia's Michael Storer. All National Federations were allowed to enter four riders for the race, with a maximum of two riders to start. In addition to this number, the outgoing World Champion and the current continental champions were able to take part. For the event, competing riders used numbers 2 to 70. Number 1 was scheduled to be worn by the defending World Champion, Igor Decraene, but three weeks prior to the championships – on 30 August 2014 – Decraene was killed in Zulte, while returning from a house party; the course of the men's junior time trial was 29.50 km.
The time trial started in the centre of Ponferrada and passed through La Martina, Posada del Bierzo and Carracedelo before returning to Ponferrada. The total incline of the course was 172 m. A few kilometres before the finish there was a climb, with an incline of over 100 m and a maximum inclination of 7%. A short stretch before riding into Ponferrada was made for the championships. All times are in Central European Time. 69 cyclists from 40 nations took part in the men's junior time trial. The number of cyclists per nation is shown in parentheses; the UCI assigned premiums for the top 3 finishers with a total prize money of €1,380
Stacey Dales is a Canadian former basketball player and a current reporter on the NFL Network. Dales was born in Collingwood and raised in Brockville, Ontario. Before attending the University of Oklahoma, she attended Thousand Islands Secondary School and Dales was a star for the TISS Pirates ladies basketball team during her high school years, Dales was a major reason why TISS captured three consecutive Ontario ‘AA’ high school senior girls basketball championships 1994, 1995 & 1996. After graduating in 1997 she attended the University of Oklahoma, Dales made an Olympic appearance for Canada in 2000 and was a first team All-American in 2001 and 2002, she was named the 2001 and 2002 Big 12 Conference Player of the Year and is the Big 12 all-time career assist leader. In 2002, she was the all-sports Academic All-American of the Year, she was the first Oklahoma player to record 600 rebounds and 700 assists. During her senior year she led the Sooners to the NCAA Championship game where they lost to Connecticut.
Dales was drafted third overall in 2002 by the Washington Mystics, the highest pick for a Canadian. That year she was named to the All-Star team as a replacement; when she was with Washington, she was diagnosed with Raynaud's phenomenon in her hands. In 2004, she announced her retirement from the league for the first time. After a one-year retirement, Dales joined the Chicago Sky, who picked her in the expansion draft of 2006 after Washington left her unprotected. On April 5, 2008, Dales announced her retirement from the WNBA for the second time. Dales was inducted into Brockville's Hall of Fame alongside her brother Burke. Source A 6'0" guard-forward, Dales played for the Washington Mystics and Chicago Sky, she ranked 4th in the WNBA for 3-pointers made and 2nd in 3-point attempts in 2007. From 2002 - 2008 Dales served as a men's and women's college basketball analyst, as well as a sideline reporter for college football and the NBA, on ESPN. Dales was the first female at ESPN to work as an in-studio men's basketball analyst.
In August 2009 the NFL Network announced that it hired Dales to serve as host and national reporter/correspondent for NFL Media Programming. Dales is in her tenth year, entering her eleventh NFL season, with the NFL Network. For the 2010 Winter Olympics in Vancouver, Dales was hired by NBC Universal Sports to work as a correspondent. Dales has served as a sideline reporter for TNT covering primetime NBA games as well as for CBS covering primetime NFL games. In 2018 and 2019 Dales was hired as a brand ambassador and spokesperson for Phillips 66 in connection with its long running partnership with the Big 12 Basketball Tournament. In 2018, Fox Sports announced that it hired Dales to serve as color analyst for women's college basketball coverage for the 2018-2019 season. Dales' brother Burke played 10 seasons in the Canadian Football League, retiring in 2014, her cousin, Jason Arnott, played 18 seasons in the NHL, retiring in 2013. Player Profile Interview with The Oklahoman Interview with New York Times Involvement in animal welfare Dales retires from the WNBA