D3Difference between conduction, convection and radiation:Conduction and convection:Conduction and convection both transfer heat but in theirown unique way firstly conduction requires a direct contact with the moleculesto allow heat transfer and conduction occurs not only in metals but also inliquids as well. In comparison with convection this method of transferring heatwhich takes place in all fluids which include the heat passing through theliquids and gases.
Another difference between conduction and convection is theway the process differ from each other in conduction molecular collisions aredone in the substance which actually transfers the heat from one the heatsource throughout the whole material on the other hand convection relies on theactual flow of the matter. This is a clear differentiation in the way theactually how each methods carries out the transfer of heat in their own uniqueway. And finally on of the major difference in conduction and convection arethe process and the way it is carried out in each of them and the examples ofobjects they are carried out in. Firstly in conduction the process involvestransferring heat by heat the material at one end of a metal which will givethe particles energy which pass on the energy by direct contact with each othereventually successfully passing the kinetic energy from one end to the otherhowever this can also take place in liquids because Liquids are also tightlypacked materials and so the particles are not really free to move about. Thisputs them in the category of being in the process of conduction. Howeverconduction works best with metals which have a different molecular motion toliquids.
Solids have a vibrational motion which they are in a fixed position. Incomparison with conduction, convection relies on fluid currents to transferenergy. In convection the material itself moves from one place to the otherhowever in conduction energy moves through the material. In comparison withconduction convection relies on rotational motion which the molecules rotate inand around the axis. This clearly shows the way their molecules behave duringthe process.
Unlike conduction convection relies heavily on bulk motion of afluid. For example, the flow of liquid water transports molecules or ions thatare dissolved in the water. the flow of air carries molecules presents in air,including both concentrated species and dilute species. Convection does nothave surface properties because it does not have a surface.Convection and radiation:Radiation and convection transfer heat through differentmethods. So one of the main differences between them is the way they transferheat. So firstly the difference is that convection relies on a medium to carrythe thermal energy from point a to point b. on the other hand radiation doesnot require a medium to transfer its energy by.
Another difference is thatradiation transfer heats using electromagnetic waves on the other hand.Convection is a mechanism of heat transfer which involves a mass flow ofmaterial. And one of the most interesting differences between the two is theirorigin. Convection takes place because of thermal expansion of matter.Radiation is a result of the motion of charges in materials due to kineticenergy of the molecules. Temperature Dependence Convection results in a heatflow rate that is approximately directly proportional to the temperaturedifference. Radiation is effected in a heat flow level that is reliant on onthe difference between fourth powers of temperatures of the object and thesurroundings. Convection is the transfer of heat energy through the movement offluid particles.
Hence, convection cannot take place in solids, since the solidparticles are not fluid. Therefore, convection only takes place in liquids andgases. because of convective heat transfer between water molecules. Incomparison, radiation does not require any medium for heat transfer. Solarradiation is an example of radiation or radiative heat transfer.
Furthermorethe difference between the molecular motions of convection is rotational motionmolecule can rotate in and around the axis. and transitional motion in such kind of motion, molecules can move fromone place to another in same or different direction but always remains in sameaxis. These type of molecular motions occur in convection however because radiationdoes not have a medium it travels through. So the molecular motion is not knownunlike convection which totally depends on it. And also the bulk flow likemolecular motion of radiation because it does not depend on a state so mostlyconvection mostly relies on it. Surface propertiesthermal radiation the surfacehas many properties which include matte black surface which are good absorbersand emitters of heat and the shiny silver surfaces are poor absorbers of heatand good reflectors of heat.
And convection does not have surface propertiesbecause it does not have a surface.Conduction and radiation:Conduction and radiation are quite different from each otherfrom their surface of objects to the molecular motion. Each individual methodtransfers heat in their own unique way.
So firstly, let’s discuss the majordifferentiation in their process and what it involves. Conduction is a process,which involves the transfer of heat between objects through direct contact. Onthe other hand, the process of radiation involves heat beingtransmitted/transfer without any physical contact between objects. Anotherdifference between the two is in the process but two do with it at themolecular form.
Conduction can transfer heat in two states that is solids andliquids but it does this more effectively in the state of solid. Therefore, theprocess involves heat energy being transferred from one end of a material tothe other in this case the material that will be used is a metal. A metalcontains metal ions and free electrons.
Ions are charged particles that aremade when metal atoms lose their electrons, which then become free electrons.These ions are held closely together and they vibrate continually. The more theheat an object receives the more kinetic energy these vibrations have.
This kinetic energy is transferred from hot parts ofthe metal to cooler parts by the free electrons. These move through thestructure of the metal, colliding with ions as they go. On the other hand the radiationstates that it does not require particles for heat transfer. Because radiationdoes not require a medium to travel through such as a solid, liquid or gas. Radiationuses electromagnetic waves to transfer heat.
In addition, radiation is a resultof the motion of charges in materials due to kinetic energy of the molecules.Like heat is transferred in metals by conduction. On the other hand, Solarradiation is an example of radiation or radiative heat transfer.
Anotherdifference between the two is the rate at which they transfer the heat. Radiationis fastest way yet in transferring heat in comparison with conduction which isa much slower process. But the rate of process of conduction can be manipulatedin the sense the more heat is given the faster the particles gain kineticenergy and transfer heat. In heat radiation the law of refraction and reflectiondoes flow which can have its own advantages like transfer heat to places itisn’t possible to do so in other methods this can reach every where throughreflection and refraction. For examples using giant/ small mirrors to reflect heatonto another object. This is perfect example of transferring of heat byradiation.
Another difference betweenthe two methods is their molecular motion. Conduction uses mostly the molecularmotion that is known as vibrational motion this type of motion In thistype of motion, molecules can vibrate at their mean position. These motions arevery common in solid state. This is very well suited to the function of theheat transfer that is by vibrations of particles and producing kinetic energy.On the other hand unlike conduction the molecular motion of radiation is notknown. Because radiation does not require a medium to travel through. And sodoes not involve particles but involves electromagnetic waves. And one final differencebetween the two is surface properties: for e.
g. thermal radiation the surface has many properties which includematte black surface which are good absorbers and emitters of heat and the shinysilver surfaces are poor absorbers of heat and good reflectors of heat. On theother hand conduction has rough and smooth surface which effects the rate ofconduction.Heat wastage in buildings can be minimised:There are different and several ways in which heat loss canbe reduced. Fitting carpets and curtains is a simple way to reduce heat lossalso if possible to fit reflective foil in the walls and to fit a draughtexcluder. Another way that heat loss can be reduced through thewindows is by installing double glazed windows. They have air or vacuum betweenthem and therefore there will not be conduction or convection, this mean thatif the double glazing is made with air between the glass and convection will bereduced and will leave little room for the air to move around as air is a verypoor conductor.
Without double glazed windows there is a chance of bulk flow ofheat escaping through the glass as well as this the cold glass can turn theheat to water vapour. The trapped air in the gap is an insulator, it does notstop heat being conducted from the inner pane to the outer pane but it doesslow heat transfer by conduction down a lot. The air gap is too narrow to allowthe air to circulate easily. This therefore reduces the rate of heat transferby convection.
The trapped air reduces the rate of heat loss through the windowby conduction and convection. The room in the house therefore stays warmer forlonger reducing heating costs. Heat radiates through air and glass, which itdoes so some of it is reflected and some of it is absorbed. This percentage increasesas there is more glass but overall heat transfer by radiation is hardly changedby double glazing a window, it is conduction and convection that change themost. Molecular motion states that the double glazed widow will do a good jobto minimise heat loss. The reduction of conduction and convection due to thefact that there are no molecules present in the double glazing which are the carrierof heat energy from one end to another end. This prevents molecular motionbecause there is not any molecules present at all in a vacuum so there for nomolecular motion takes place.
Heat loss in walls can be condensed by installing cavitywall insulation. “This involves blowing insulation materials into the gaps thatare left between the brick and the inside wall.” Due to insulating materialsbeing bad conductors they will reduce heat loss by conduction and it alsoprevents air circulating inside the cavity and therefore reduces heat loss byconvection. Without cavity insulation there is a risk of bulk flow of heatescaping through gaps and holes in the walls. With double glazing and cavitywall instillations the molecular motion of the heat convection around your hometherefore resulting to less waste of heat, keeping your home warmer and moreefficient.Cavity wall insulation slows down the rate at which it escapes,keeping as much of it as possible inside your home for as long as possible.
Cavitywall insulation makes it much more difficult for heat to pass through yourwalls by filling up the cavity with a material with lots of small air pocketsin it. These compartments are more efficient at dropping heat transfer byconvection than the big air cavity was. They make it impossible for largeconvection currents to be set up. “They reduce what is known as your walls’ Uvalue – which is a measure of how quickly they lose heat.” The lower the Uvalue, the slower heat transfer – and the less energy you need to keep yourhome warm. Another way to prevent heat loss in houses is by installinghot water tank jacket. This helps keep the tank which your hot water getsstored after being heated by the boiler because if it’s poorly insulated thenthe heat will get lost very quickly. This causes the boiler to use more energywhen reheating the water for any use.
Is an insulator that covers the hot watercylinder to prevent it from heat loss when it heats and boils up the water. Itmay be a reason; it will cost a lot of money by boiling the water every time itcools down because it is losing heat fast since it is not insulated. By puttinga jacket around the tank, the heat energy stays trapped inside longer before itis lost. This reduces the processes of conduction, convection and radiation.Byadding these three important parts into a building we’re reducing the occurringof these three processes. In addition, by reducing these processes we havereduced the waste of heat in these buildings.
The shiny surface of the jacketreflects the radiation so the transfer of heat does not take place. Andprevents heat transfer by radiation.