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Conduction is caused by the random motion of atoms and molecules. As such, it is an ineffective mechanism for heat transport over macroscopic distances and short time distances. Take, for example, the temperature on the Earth, which would be unbearably cold during the night and extremely hot during the day if heat transport in the atmosphere was to be only through conduction. In another example, car engines would overheat unless there was a more efficient way to remove excess heat from the pistons.

How does the rate of heat transfer by conduction change when all spatial dimensions are doubled?

Because area is the product of two spatial dimensions, it increases by a factor of four when each dimension is doubled A final = ( 2 d ) 2 = 4 d 2 = 4 A initial size 12{A rSub { size 8{"final"} } = \( 2d \) rSup { size 8{2} } =4d rSup { size 8{2} } =4A rSub { size 8{i"nitial"} } } {} . The distance, however, simply doubles. Because the temperature difference and the coefficient of thermal conductivity are independent of the spatial dimensions, the rate of heat transfer by conduction increases by a factor of four divided by two, or two:

Q t final = kA final T 2 T 1 d final = k 4A initial T 2 T 1 2d initial = 2 kA initial T 2 T 1 d initial = 2 Q t initial . size 12{ left ( { {Q} over {t} } right ) rSub { size 8{"final"} } = { { ital "kA" rSub { size 8{"final"} } left (T rSub { size 8{2} } - T rSub { size 8{1} } right )} over {d rSub { size 8{"final"} } } } = { {k left (4A rSub { size 8{"initial"} } right ) left (T rSub { size 8{2} } - T rSub { size 8{1} } right )} over {2d rSub { size 8{"initial"} } } } =2 { { ital "kA" rSub { size 8{"initial"} } left (T rSub { size 8{2} } - T rSub { size 8{1} } right )} over {d rSub { size 8{"initial"} } } } =2 left ( { {Q} over {t} } right ) rSub { size 8{"initial"} } } {}


  • Heat conduction is the transfer of heat between two objects in direct contact with each other.
  • The rate of heat transfer Q / t size 12{Q/t} {} (energy per unit time) is proportional to the temperature difference T 2 T 1 size 12{T rSub { size 8{2} } - T rSub { size 8{1} } } {} and the contact area A size 12{A} {} and inversely proportional to the distance d size 12{d} {} between the objects:
    Q t = kA T 2 T 1 d . size 12{ { {Q} over {t} } = { { ital "kA"` left (T rSub { size 8{2} } - T rSub { size 8{1} } right )} over {d} } } {}

Conceptual questions

Some electric stoves have a flat ceramic surface with heating elements hidden beneath. A pot placed over a heating element will be heated, while it is safe to touch the surface only a few centimeters away. Why is ceramic, with a conductivity less than that of a metal but greater than that of a good insulator, an ideal choice for the stove top?

Loose-fitting white clothing covering most of the body is ideal for desert dwellers, both in the hot Sun and during cold evenings. Explain how such clothing is advantageous during both day and night.

The figure shows a group of musicians wearing long, loose-fitting lightly colored robes that go down to their feet.
A jellabiya is worn by many men in Egypt. (credit: Zerida)


(a) Calculate the rate of heat conduction through house walls that are 13.0 cm thick and that have an average thermal conductivity twice that of glass wool. Assume there are no windows or doors. The surface area of the walls is 120 m 2 and their inside surface is at 18. C , while their outside surface is at 5 .00º C . (b) How many 1-kW room heaters would be needed to balance the heat transfer due to conduction?

(a) 1.01 × 10 3 W

(b) One

The rate of heat conduction out of a window on a winter day is rapid enough to chill the air next to it. To see just how rapidly the windows transfer heat by conduction, calculate the rate of conduction in watts through a 3 . 00-m 2 window that is 0 .635 cm size 12{0 "." "635"`"cm"} {} thick (1/4 in) if the temperatures of the inner and outer surfaces are 5 .00ºC and 10 . C , respectively. This rapid rate will not be maintained—the inner surface will cool, and even result in frost formation.

Calculate the rate of heat conduction out of the human body, assuming that the core internal temperature is 37 . C , the skin temperature is 34 . C , the thickness of the tissues between averages 1 .00 cm , and the surface area is 1 . 40 m 2 .

84.0 W

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, College physics ii. OpenStax CNX. Nov 29, 2012 Download for free at http://legacy.cnx.org/content/col11458/1.2
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