Heat Transfer - Free Educational videos for Students in K-12

Heat Transfer - By MITK12Videos

Transcript


00:05	Hello . My name is James White and today will
00:08	be investigating heat transfer . Heat transfer effects are everyday
00:11	life . For example . It allows our computers to
00:14	run without burning up . It helps us to design
00:17	houses . They use less energy . It makes cooking
00:19	food possible and very importantly it helps keep us warm
00:23	or cool . Like this radiator . We will look
00:25	at three different types of heat transfer , conduction ,
00:28	convection and radiation and find examples where they occur around
00:32	us to do this , we'll use a thermal camera
00:35	. A thermal camera can see the radiation given off
00:37	by all objects and use it to measure their temperatures
00:41	. For example , cold objects normally give off less
00:43	radiation than hot objects which give off more radiation .
00:47	The camera records this radiation and creates a picture .
00:51	The colours in the picture represent temperatures hotter temperatures are
00:55	lighter colors and colder temperatures are darker colors . In
00:58	this picture , my hand is warm but the copper
01:00	wire below it is cold . However , the camera
01:05	isn't always correct . Let's look at a video of
01:07	a lighter flame , although the flame appears to be
01:10	the same temperature as my hand , It's actually about
01:14	2,000°C. This is too hot for the video to show
01:18	us the real temperature . Using the lighter and copper
01:22	wire , we will observe the first type of heat
01:24	transfer conduction . I'll show you are a simple experiment
01:29	, conductive heat transfer occurs when there is a temperature
01:32	difference between two materials in contact with each other .
01:36	In this case , the right side of the wire
01:38	is heated by the lighter . At this point ,
01:40	temperature in the material is very high in one area
01:43	and cold in other areas , heat transfers from the
01:46	high temperature side to the low temperature side . Let's
01:49	watch as this happens over time , the temperature of
01:59	the material becomes more and more uniform as heat transfer
02:03	moves energy from hot to cold areas of the wire
02:07	. When engineering a building , we often care about
02:10	keeping warm or cold air inside . How well a
02:14	wall can retain heat in the building depends on two
02:17	things . Its thickness and its thermal conductivity , materials
02:22	that are thicker will let less heat through materials with
02:26	higher thermal conductivity will let more heat through . How
02:30	do you think this metal door compares to this foam
02:33	panel , which lets through more heat . What about
02:37	traditional materials like these adobe blocks ? When the temperature
02:42	of a wall or door is different than the surrounding
02:44	air , a different type of heat transfer begins to
02:47	occur . Named conviction . A lighter , a copper
02:51	wire and a cardboard backdrop make up . Are a
02:53	simple experiment . When a material is hotter or cooler
02:57	than a fluid surrounding it , it causes the fluid
03:00	to rise or sink . In the case of a
03:02	hot wire , heated air rises as cold air fills
03:05	its place . This cools down the wire faster than
03:07	conduction . If we push the wire towards the cardboard
03:11	, we see that the hot air rising off the
03:13	wire heats the cardboard . This hot stream of air
03:16	is called the convection current and is part of natural
03:19	convection . Sometimes natural convection isn't fast enough . So
03:24	engineers will use force conviction . Your computer uses forced
03:28	convection to keep itself from overheating . That's what your
03:31	fans do . Using the thermal camera . We can
03:35	see that this laptop has several hot components here ,
03:38	here , here and here . When these components get
03:42	too hot , fans in the laptop will start to
03:44	pull cool air across the parts . This results enforced
03:49	conviction . The hot air is then blown out the
03:52	side or back of the computer . Earlier , I
03:56	mentioned that all objects give off radiation when radiation from
03:59	a hot object hits another object , it warms it
04:02	up . This process is called thermal radiation too .
04:07	Bright lights a piece of aluminum foil and a cardboard
04:10	backdrop . Make our simple experiment when the lights are
04:13	turned on , let's see what happens . We can
04:17	see the radiation from the lights is absorbed by the
04:20	cardboard . However , the radiation is reflected by the
04:24	aluminum foil . When the lights are turned off ,
04:30	we can see that the cardboard under the aluminum foil
04:32	was not heated because radiation never reached it . The
04:37	sun is an extremely hot object and its thermal radiation
04:41	warms our entire planet . This means that when designing
04:45	a building window placement is a very important part of
04:48	the thermal engineering . When the sun's radiation comes through
04:52	windows , it will heat up the exposed cooler indoor
04:56	materials , conduction and convection . Then transfer this heat
05:00	around the building by considering thermal radiation and design a
05:04	building will be warmer during the winter and cooler during
05:07	the summer . Radiators are a common way to heat
05:11	buildings in cold environments . Although named a radiator ,
05:15	this device actually uses radiation and convection transfer its heat
05:18	to the room . Thermal radiation is sent out in
05:21	all directions from the radiator and makes you very warm
05:24	when you stand next to it . Natural convection then
05:27	circulates the hot air from the radiator around the building
05:32	. There are so many examples of heat transfer around
05:35	us every day , and , as engineers , we
05:37	have to think about using them to make the world
05:39	a better place .

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