Which three are the most predominant in the refrigerator (convection, conduction, or radiation)?
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Convection and conduction are both important.  Radiation is negligible.  Heat is transported from the inside air to the refrigerant, and from the refrigerant to the outside air, through two heat exchangers.  In each exchanger, heat is transferred by a mixture of convection and conduction* between refrigerant and heat exchanger tubing, conduction through the walls of the tubing, and convection* (which may be forced by a fan) between the tubing and the air.  \n*Some may disagree with my interpretation of which kinds of heat transfer dominate each of these phases; it's a judgment call.  If most of the heat transfer is due to motion of the fluid (refrigerant or air) it's convection; if not it's conduction.
406070
these are different zones in stars one of which is the sun.  the radiation zone and the convection zone transfer heat in two different ways.  heat passes thru the radiation zone as electromagnetic radiation.  heat passes thru the convection zone as hot matter rising, cooling, falling, heating.  the radiation zone is transparant to electromagnetic radiation.\n\nhttp://en.wikipedia.org/wiki/Sun#Structure
12026
Good luck with your exam, this should help:\n\nConvection  is the transfer of heat by the actual movement of the warmed matter. Heat leaves the coffee cup as the currents of steam and air rise. Convection is the transfer of heat energy in a gas or liquid by movement of currents. (It can also happen is some solids, like sand.) The heat moves with the fluid. Consider this: convection is responsible for making macaroni rise and fall in a pot of heated water. The warmer portions of the water are less dense and therefore, they rise. Meanwhile, the cooler portions of the water fall because they are denser.\n\nConduction is the transfer of energy through matter from particle to particle. It is the transfer and distribution of heat energy from atom to atom within a substance. For example, a spoon in a cup of hot soup becomes warmer because the heat from the soup is conducted along the spoon. Conduction is most effective in solids-but it can happen in fluids. Fun fact: Have you ever noticed that metals tend to feel cold? Believe it or not, they are not colder! They only feel colder because they conduct heat away from your hand. You perceive the heat that is leaving your hand as cold.\n\nRadiation: Electromagnetic waves that directly transport ENERGY through space. Sunlight is a form of radiation that is radiated through space to our planet without the aid of fluids or solids. The energy travels through nothingness! Just think of it! The sun transfers heat through 93 million miles of space. Because there are no solids (like a huge spoon) touching the sun and our planet, conduction is not responsible for bringing heat to Earth. Since there are no fluids (like air and water) in space, convection is not responsible for transferring the heat. Thus, radiation brings heat to our planet.
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It could potentially be both depending how the substance is heated [and let is not forget about radiation].\n\nIf the heating element is at the bottom, some of the heat is obviously transfered to the gas/liquid through conduction, but afterward, convection currents form to transfer heat more effectively.\nIf the heating element is at the top on the other hand, convection currents wont form quite as much and you must rely much more heavily on conduction to transfer the heat.  A similar situation occurs if you have the heating element on the side, in the middle of the gas/liquid.\n\nhttp://hyperphysics.phy-astr.gsu.edu/hbase/thermo/heatra.html
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Heat is actually a microscale form of kinetic energy. The molecules of a hot object are in rapid motion; the hotter, the higher the average speed. If the object is gaseous the motion consists of free-path travel and collisions with other molecules. If it is liquid the paths between collisions are shorter, and if solid the motion is vibrational with no secular movement. \nIn conduction, heat is transferred by collisions between molecule populations with different average speeds. The transfer continues until both populations have the same average speed. \nIn convection, heat is transferred by mixing fluids of differing temperature. The mixing can be forced or driven by density differences caused by temperature difference. It is not necessary that molecular collisions occur in convection, since mixing alone changes the average molecular speeds.\nIn radiation, the molecular motion is converted to microwave or infrared energy by rigid motion of molecules or flexing of molecular bonds (ref.). Shorter wavelengths (light, UV, X-rays, gamma rays) are produced at higher temperatures where atomic electrons and nuclei may become involved. Radiative energy is not considered heat, but is converted to heat by absorption.
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A refrigerator (often called a "fridge" for short) is an appliance for the storage and preservation of perishable food; food kept in a refrigerator lasts longer than that left at room temperature as the cold inhibits bacterial growth. A refrigerator maintains a cold temperature above the freezing point of water; commonly refrigerators are used in conjunction with freezers, which maintain temperatures below freezing, or a refrigerator may have an integrated freezer compartment. The refrigerator is a relatively modern invention amongst kitchen appliances. It replaced the common icebox which had been a household item for almost a century and a half prior, and is sometimes still called by the name "icebox".\n\nCommercial units, which go by many other names, were in use for almost 40 years prior to the common home models. The fact that they operated with toxic ammonia gas systems made them unsafe for home use. Practical household refrigerators were introduced in the 1920s and gained wider acceptance in the 1930s as prices fell and non-toxic, nonflammable synthetic refrigerants, such as Freon or R-12 refrigerants were introduced.\n\nthe advantages and disadvantages u can look straight to my source... it has many information... i hope this helps... good luck ^^
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It is one of the ways heat is transported.  The other two are conduction and convection.
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The heat transfer coefficient is usually represented by the variable h and is used in problems involving natural convection.  It can vary depending on the type and speed of the fluid.  Typical values can be found in a heat transfer book for different fluids with forced or natural convection.
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Food can be heated at least four different ways in an "oven" and some use more than one way.  The oven may be named for the principle method of heating because of any advantages.\n\nMicrowave ovens use microwaves to agitate the electrons of molecules in the food, especially water.  Conduction is the direct flow of heat from one body to another by contact.  Although an oven may not heat food directly by conduction, the food container (bake pan?) may heat up first then conduct heat into the food.  Food may also be heated in an oven by convection.  Hot gas rises and cool gas falls due to differences in density when the hot gas expands and the gases circulate through the oven by natural or forced convection (perhaps using a fan).  Lastly food may be heated in an oven by radiation of heat similar to the warmth you feel when holding your hand up towards the sun.  Radiation heating occurs because the electrons in the metal oof the heating elements are raised to higher orbits and when they return to rest positions they re-emit the energy (supplied by electricity passing through resistance) as infrared radiation which is electromegnatic like light but of much longer wavelengths.  Food is broiled by close exposure to the hot heating element.\n\nRadiation heating may also be produced using banks of specialy light bulbs (which may grow red) that emit infrared radiation.  When the radiation strikes the object to be heated (paint, etc.) it enters the molecules and agitates the electrons of the materrial increasing vibrations heats the material.\n\nSome colors are more easily heated by infrared radiation than others.  At the extremes, black absorbs almost all radiation and heats up while pure white reflects most radiation and stays cool.  That is why you may stay "cool" in the summer heat wearing light or white clothes (like the desert dwellers).
38522
1. flow of electrons\n2. mechanical energy\n3. motor, lightbulb\n4. the rate of flow of electrons
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convection, advection and radiation
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Basic four different types of chillers: \nReciprocating, centrifugal, or screw-driven chillers are mechanical machines that can be powered by electric motors, steam, or gas turbines. \nAbsorption chillers are powered by a heat source (such as steam or hot water).\n\nCheck out the following links:\nBasic knowledge on a Chiller\nA Manufacturer of Chillers, different types. Trane
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Heat is transferred by conduction, convection and radiation. In medium-temperature applications radiation would only be a small part of the total, and an opaque material will prevent radiative escape of heat in any case. Conduction and convection are minimized by the structure of a typical insulator in addition to the material properties mentioned in the first answer. Styrofoam, for instance, consists of very thin partitions of styrene plastic which enclose gas-filled bubbles. This means each convection cell or mixing space is small and essentially a small proportion of the total insulation thickness, so you don't have the coldest internal gas mixing with the hottest gas. Conduction is low because gas conducts heat more slowly than a solid. The conduction path through the solid styrene is convoluted and of small thickness, both of which minimize conduction. In houses, fiberglass insulation uses similar principles except that the air spaces are connected. This means a larger convection cell potentially exists, but it is baffled by all the glass strands, so circulation and mixing are much slower and smaller-scale.
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It was hard to obtain even this information (ref. 1) on the web. Apparently lithium absorption technology is quite similar to that using ammonia which has several useful web descriptions (e.g., ref. 2). Both types use a heat source to operate, and have a complicated means of condensing and circulating refrigerant. Following is an earlier answer I gave to a question on absorption refrigerators which deals with the ammonia type:\nThere are two types of these refrigerators.  One operates in a "batch" like cycle having a generation phase and a refrigeration phase, with a check valve to ensure unidirectional flow.  The other system operates in a continuous cycle, has no moving parts and still achieves unidirectional flow in an intriguing way. \nBoth types use heat to drive the ammonia gas out of its water solution at one point in the loop, pass the gas through a condenser and an evaporator, and redissolve it at another point.\nIn the two-phase system the generation phase drives the ammonia out of solution, and the ammonia cools, condenses and flows through the check valve into a receiver.  The refrigeration phase removes the heat which reduces system pressure, allowing the liquid ammonia to evaporate, cool the refrigerator, and be reabsorbed by the water.\nThe continuous cycle performs the same operations concurrently in a similar loop without a check valve and with constant pressure throughout the loop.  What enables the refrigerant to circulate is the addition of hydrogen gas into the ammonia gas in the evaporator and the gaseous space of the absorber which follows the evaporator.  In the words of ref. 2, each of the two gases in the evaporator, according to Dalton's law, "behaves as if it occupies the space alone. [...] Total pressure in the system is the sum of the vapor pressure of the ammonia plus the hydrogen pressure.  When the pressure of the ammonia vapor is below the pressure corresponding to the vapor pressure for ammonia alone, the ammonia continues to evaporate. It tries to reach a vapor pressure corresponding to the temperature in the absorber."\nNote that the flow of the ammonia keeps the hydrogen in the evaporator and absorber and out of the condenser.  What the quote above means is that flow occurs because both the condensation and the subsequent evaporation of the ammonia occur at nearly the same temperature and at just the same total pressure.  How is this possible?  Because the ammonia pressure is 100% of the pressure in the condenser but a smaller percentage of that same pressure when in the evaporator due to the added hydrogen.  This creates a continuous movement of the ammonia around the loop!  The diagram in the ref. 2 page clarifies this and provides many practical details omitted from this description.\nEDIT: Found another page with good comparison between ammonia and lithium bromide systems with diagrams, ref. 3.
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fluids - convection is due to the movement of molecules
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Besides the typical methods such as refrigeration which uses expanding freon or amonia gas to transfer heat or standard evaporation, two other electro-mechanical methods come to mind.\n\nOne method is a thermoelectric cooler which can heat or cool based on the direction of DC electric current flow. It is built from a junction of two metals which are different and when DC current passes through the junction, heating or cooling can occur depending on the direction of the flow of the DC current. This is known as the Peltier effect.\n\nThe second totally mechanical method is known as a Vortex seperator. Air is introduced at high speed into a tube with a curving vane inside. As the air spins up through the tube, the colder air, which is heavier is forced outside due to centrifical force while the air moving up the center is warmer and lighter than the cold air. The difference in the weights of the cold and warm air cause them to seperate from each other with the cold air unable to make the tight turns and is forced to the outside of the tube as it spins to the top. These units typically have a cold air output connection on the outside of the tube at the end and a warm air connection in the center of the tube at the end.
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convection microwaves have the capacity to brown food while cooking. eg:- the crust you see in baked dishes.\ngeneral microwaves may have most of the other features except browning. also convection feature means the oven will cost more. many don't use the convection feature inspite of it existing in the microwave so unless you are into major baking and roasting and hoping to get that perfect brown covering you can simply go in for a regular microwave its cheaper n has all the other features we require on a daily basis.