What is Conduction: Definition and 423 Discussions
Thermal conduction is the transfer of internal energy by microscopic collisions of particles and movement of electrons within a body. The colliding particles, which include molecules, atoms and electrons, transfer disorganized microscopic kinetic and potential energy, jointly known as internal energy. Conduction takes place in all phases: solid, liquid, and gas.
Heat spontaneously flows from a hotter to a colder body. For example, heat is conducted from the hotplate of an electric stove to the bottom of a saucepan in contact with it. In the absence of an opposing external driving energy source, within a body or between bodies, temperature differences decay over time, and thermal equilibrium is approached, temperature becoming more uniform.
In conduction, the heat flow is within and through the body itself. In contrast, in heat transfer by thermal radiation, the transfer is often between bodies, which may be separated spatially. Also possible is the transfer of heat by a combination of conduction and thermal radiation. In convection, the internal energy is carried between bodies by a moving material carrier. In solids, conduction is mediated by the combination of vibrations and collisions of molecules, of propagation and collisions of phonons, and of diffusion and collisions of free electrons. In gases and liquids, conduction is due to the collisions and diffusion of molecules during their random motion. Photons in this context do not collide with one another, and so heat transport by electromagnetic radiation is conceptually distinct from heat conduction by microscopic diffusion and collisions of material particles and phonons. But the distinction is often not easily observed unless the material is semi-transparent.
In the engineering sciences, heat transfer includes the processes of thermal radiation, convection, and sometimes mass transfer. Usually, more than one of these processes occurs in a given situation.
The conventional symbol for thermal conductivity is k.
Hello,
Can anybody explain to me how does this:
dQ=-X*dS*grad(T)*dt
t being time and T being TD temperature.
transforms into this:
Q=-X*S*(T2-T1)*delta(t)/d
delta(t) being time interval
d being thickness length of material
X being heat conductivity
Thanks
Homework Statement
Electrons present in the outermost orbit are valence electrons. If we supply sufficient energy to these electrons they make their transition from valence band to conduction band and electrons in conduction band are termed as conduction electrons. My question is, take for...
Homework Statement
For copper we find that J=\sigmaE , where \sigma has the value 5.8x10^7 mksc units. If an alternating electric field represented by E0ei\omegat exists within the copper. Find the ratio of the conduction to the displacement current density at a frequency of 1megacycle/sec...
In Bird, Stewart, Lightfoot "Transport Phenomena", they post the following equation for heat conduction with a nuclear heat source:
Sn=Sn0 [1+b(r/R)^2]
where Sn is volumetric thermal energy, r is radius and R is radius of the fuel pellet.
The text state that b is a dimensionless...
Homework Statement
A specimen (cuboid 30*15*10mm), material properties (known): density p, thermal conductivity k, heat capacity Cp, I have one surface temperature data Ts (this point is the same level as the body-centred point), and assumed that there is a heat source in the center of this...
1. The problem statement
I'd like to use Matlab to help me model and solve a simple 2D steady state heat conduction problem:
A square section duct is buried in the Earth some distance below the surface. This duct is at a steady temperature of 60 degrees C. I need to use the central divided...
1. A large block of steel [k=45 W/m°C, alpha=1.4x10^-5 m2/s] is initially at a uniform temperature of 35 C. The surface is suddenly exposed to a constant heat flux of 3.2x10^5 W/m2 Find the temperature at a depth of 2.5 cm after 30 seconds has elapsed.
I need to calculate the density of states for a dispersion relation which is like the free electron dispersion, but with one effective mass in the kx, ky directions, and a different effective mass in kz. So I need to integrate the inverse gradient of E(k) over a surface of constant energy, ie...
Warning: I'm not a practicing chemist. Answers in as-simple-as-possible language (but not oversimplified!) would be greatly appreciated!
I'd like to know if the chemical properties of a solid can be affected by conduction band electrons. I assume that, in the majority of cases (and perhaps...
Homework Statement
There's a slab of a material with temperature T1 on the left and the T2 on the right. The thickness of the material is l with area A. In the centre, there is heat generation Qvol in the centre, which is a thin rod.
Find the heat transfer Q through the material.
Homework...
Hi everyone, I recently started studying heat conduction using differential equations and this has been stumping me for a while.
I am having trouble understanding what type of heat conduction problem this is.
We are given a 100cm long copper rod with ends maintained at 0 C. The center of the...
Homework Statement
Let the ends of a copper rod 100 cm long be maintained at 0 degrees C. Suppose that the center of the bar is heated to 100 degrees C by an external heat source and that this situation is maintained until a steady state results. Find this steady-state temperature...
Homework Statement
I am trying to find the temperature profile through a cylinder wall. It is a one dimensional, steady state conduction problem without internal heat generation
Homework Equations
d/dr(r*dT/dr)=0 where r is radius and T is temperature
The Attempt at a Solution
I...
When stimulated in the middle of axon, nerve conduction is bidirectioal. Now I know the andromic conduction stops at the first synapse. Is the reason for this, that there are no neurotransmitters in the body of a neuron, and more importantly no calcium channels there to activte them. Thanks :smile:
Homework Statement
The following cylinder has a temperature inside Ti and temperature outside To. Using the general equation for heat conduction in a cylinder, write the temperature distribution equation as a function of the radius T(r). What is the temperature midway at r=a? (Take the heat...
Homework Statement
The door of an oven has a piece of glass of dimensions 20cm X 30 cm and thickness 0.50cm.when the interior of the oven is at temperature 200°C,determine the quantity of heat that flow through the glass in one hour.(for glass,K=0.80 Wm^-1K^-1)
Homework Equations...
So, when I was learning about static electricity and induction and conduction, there were several labs done where a pith ball or electroscope could be manipulated through induction when a charged object was placed near it.
In the case of the little pith ball, a negatively charged piece of PVC...
Hello All,
I have been trying to figure this out for quite some time now.
Obviously, from a mechanical point of view, it is best to keep to keep the Playstation on a hard surface to ensure unrestricted air flow into the cooling intake vents.
But, still remains, is a deeper question...
Homework Statement
Hello! I am supposed to explain the behaviour of the thermal conductivity of tungsten. I have plotted the relation
http://img340.imageshack.us/img340/9776/heatcond.jpg is also experimental data
Temp[0 10 50 100 300 500 1000 2000 3400]
and thermal conductivity...
Hello everyone,
I don't understand how depolarisation jumps when axons are myelinated. Ok myelin is an insulator so in that section no current passes through. But how does that make the current jump, when current reached myelin wouldn't it be inhibited, why does it still travel. Also what do...
for metals the conduction and valence bands overlap. So how do you distinguish between the conduction and valence bands? How do you find out the lower limit of the conduction band and the higher limit of the valence band?
Or is it the case that the highest conduction band in a metal goes from...
Homework Statement
a) A slab of thickness L and constant thermal conductivity \lambda generates heat at a constant rate throughout of g W m–3. The heat is dissipated from both sides of the slab by convection into the ambient air at a temperature Tf with a heat transfer coefficient h. The...
Hello friends
Fourier law of heat conduction states that:
Q ~ A.(Dt/Dx) where A= area normal to direction of heat flow.
Dt/Dx= temp gradient in same direction.
Now, obviously rate of heat flow will depend upon temp gradient but my doubt is how/why...
As I understand it, thermodynamics indicates that heat will dissipate from hotter parts of a system to cooler parts. This is why, for example, it is impossible to harness latent heat to create energy if there is no heat-sink to move the heat from relative warmth to cold.
What has me puzzled is...
Hi, I have a very basic question on formation of valance and conduction band. It is said that conduction band is above the valance band.
So In a hypothetical lithium molecule formation(for example purpose) : If 100 Lithium atoms combine together, then 1S shell is split into 100 1S shells (one...
Homework Statement
The base of the room in a house consists of wooden board which is 15 mm thick and of area 200 m^2. The thermal conductivity of the board is 0.15 W/m/K. The temperature of the room is maintained at 0 degree celcius and the base is at 20 degree celcius. If the owner now...
Hey guys,
I was wondering about problem 12C.1 in Transport phenomena by Bird, Stewart and lightfoot.
The problem states that a block of material initially at uniform T0 is suddenely exposed to T1 at all surfaces.
Assume a solution of T=X(x,t)Y(y,t)Z(z,t)
any help with...
Homework Statement
An animal has a core body temperature of 37oC and a skin temperature of 34oC while in surrounding of an air temperature of 25oC. If the skin temperature fell, what would happen to:
(i) the rate of heat transfer via conduction through body tissue?
(ii) the rate of heat loss...
Homework Statement
A mountain climber has a body surface of 1.80 m2 and wears fibrous clothing 1.00 X 10-2 m thick. He has a skin temperature of 33.1 ºC while the outer surface of his clothing is at 273.15 K. Calculate the total rate of conduction of heat through his clothing in Watts,
(a)...
Homework Statement
An aluminum wire with a diameter of 0.100 mm has a uniform electric field of 0.200 V/m imposed along its entire length. The temperature of the wire is 50.0 C.
a) Determine resistivity
b) Current density
c) Total current
d) Drift speed of the conduction electrons...
Homework Statement
Estimate the mean drift velocity of a conduction electron in copper, assuming that there is one conduction electron per atom. Consider No. 14 wire (diamter 0.16 cm), common in houses, carrying 5A. The result should be very small. Why then does an electric light turn on...
Homework Statement
If I have a cup filled with boiling water, where will heat loss by conduction and heat loss by convection occur?
Homework Equations
The Attempt at a Solution
I think that heat loss out of the top of the cup (water in contact with air) will be convection, and...
Hi All,
I'm trying to understand heat so I'm going to say what I understand and ask you to please tell me if I am correct. Thank you.
Radiative Heat - This is heat transferred in the form of electromagnetic radiation and does not need a medium. If in a vacuum, the radiation will travel...
Homework Statement
a thermometer wall mounted through the wall of a steam pipe is a steel tube with 0.1 in wall thickness, 0.5 in outer diameter, 2 in length and k=26W/(mK). The flow produces an h value of 100W/(m^2K) on the outside surface of the well. If the thermometer reads 149 deg C...
Homework Statement
Find the the T(x). See attachment. The top, bottom as well as the left side are adiabatic. The fluid temperature on the side of convective heat transfer is a function of x. The dimension for the width is W.
Homework Equations
How to find T(x)
The Attempt at a...
Dear all, I have difficulty in solving this problem (see the figure in attached thumbnails)
I have a rectangular shape with length/height of L and the thickness/width of \delta
Within the rectangular area, a heat conduction occurred. I would like to determine the temperature profile within the...
Homework Statement
I need to set up the mathematical formulation of the following heat conduction scenarios:
a) A slab in 0\le x \le L is initially at a temperature f(x). For times t>0 the boundary at x=o is kept insulated and the boundary at x=L dissipates heat by convection into the...
I'm trying to build a simple model to determine the temperature of a solution in a refrigerator assuming that the temperature in the refrigerator is constant. I'm also assuming that the solution in the fridge is the same temperature as it's vessel and that the vessel is solid and made only of...
Homework Statement
a bushwalker wears clothing that is 2.0cm thick with a surface area of 1.9m^2. The material has k = 0.042 WM^-1K^-1. Her skin temperature is 33 degrees C and the ambient temp. is 0 degrees C.
Calculate rate of heat loss through her clothing while she is sitting...
Help! Heat Conduction into a gas!
Hello All, I have a problem I've been trying to solve for some time and can't quite seem to figure it out. I need the help of some experts out there. I am no physics expert but I do have a basic understanding of math, algebra, and geometry. I am a beginner...
Hi all, I am working on the problem below, and I wrote the code, but it's not working. Can anyone help me out? And even any ideas on how to improve the code to make it more succinct?
http://i25.tinypic.com/2v0zi8m.jpg
Basically, it is a 2D conduction problem with convection heat...
Homework Statement
conductivity=1/100 siemens/meter
epsilon=3*epsilon[0]
at which frequency displacement current is equal to conduction current?
Homework Equations
The conduction current is LaTeX Code: I =C * \\frac {dV}{dt}
The displacement current D can be calculated from...
Homework Statement
I need to go into this test with great aplomb.
In each of Problems 1 through 8 find the steady-state solution of the heat conduction equation a2uxx=ut that satisfies the given boundary conditions.
1. u(0,t)=10, u(50,t)=40
...
3. ux(0,t)=0, u(L,t)=0...
Homework Statement
In each of Problems 1 through 8 find the steady-state solution of the heat conduction equation ∂2uxx=ut that satisfieds that given set of boundary problems.
...
3. ux(0,t)=0, u(L,t)=0
Homework Equations
Assume u(x,t)=X(x)T(t)
The Attempt at a...
Hello,
I am trying to understand one-dimensional unsteady state heat conduction for a program I am writing. The program will eventually be coded for two and three dimensional structures. Can anyone provide some basic background info./tutorial to understand the governing equation and...
Homework Statement
A conduction heat wave is caused to pass through a metal bar of average temperature Tmean = 35.0 °C, altering its temperature sinusoidally with an amplitude of Ti = 2.0 °C. The equation which gives the temperature, T(x,t), of the metal bar at any place x (in meters) inside...
Homework Statement
The question - A small sphere (emissivity = 0.90, radius r1) is located at the center of a spherical asbestos shell (thickness=1.0cm, outer radius r2). The thickness of the shell is small compared to the inner and outer radii of the shell. The temperature of the small sphere...
Homework Statement
a conduction coil with 2 resistors are connected, according to the drawing. write the expression for the potential difference Vac over the coil after t seconds after the switch is closed.
Homework Equations
The current at any time: (a) i=I(1-e-Rt/L)
The electro motive...