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.

View More On Wikipedia.org
Recent contents Top users
  1. Somefantastik

    Equation of heat conduction, vague text book

    Hey all, This is the equation of heat conduction in my PDE textbook: \int ^{t_{2}}_{t_{1}} \int\int\int_{A} [c \rho \frac{\partial u}{\partial t} - \nabla \dot \left( k \nabla u \right)]dxdydzdt = 0. where c is specific heat, rho is density, A is the subregion bounded by a smooth...
  2. K

    Conduction through a spherical shell.

    How do I solve for the temperature at a certain time for conduction through a spherical shell? I have a shell 5 cm thick with a radius of 0.5m. I am starting with Q=KA(T2-T1)/L and I am completely lost as to where to go with it. Thanks!
  3. R

    Transient conduction with finite element analysis

    Homework Statement Hi, I've got a civ engineering problem relating to conductive heat flow using finite element analysis. I'm investigating the dissipation of heat from square and circular pile foundations. I'm applying a thermal load to the centre of the concrete pile which induces heat...
  4. U

    Steady state heat conduction problem

    I have to solve a problem regarding "2D steady state heat conduction problem with an internal heat generation source". For boundary value, dirichlet is applied at 3 sides and neumann is at one side. I can solve this problem when no internal heat source exists and only dirichlet is applied...
  5. A

    Diffusion Problem (Conduction)

    Homework Statement Since the problem involved formulas I have posted it as an attachment. Please check the attachment first. (I have not scanned this problem, just wrote it in word and posted it) The Attempt at a Solution My approach on this problem is to start with separation of variables...
  6. R

    Valence- and conduction band offset

    Homework Statement There has been created a heterojunction of two different semiconductors, Si and GaP. I am to determine the valence- and conduction band offset with Tershoff's model. Homework Equations The problem is that I can't find the relevant model. Therefore, I cannot find the...
  7. I

    Convection, Conduction, Or Radiation. You decide

    Hello everyone, new guy here. I'd like some other minds on an on-going debate i have with quite a few people. The subject is "Radiant Floor Heat". I'm not going to cover any formulas at this point as i need to convey the conceptual side of things first. We know that heat is transferred...
  8. S

    Concentration of conduction electrons

    This is part of a longer problem, and probably obvious, but if I calculate this wrong, the rest of the calculations will be wrong too!... Question: Given the mass density, molar mass, and electrical resistivity of a substance at room temperature, how do you calculate the concentration of the...
  9. R

    How Much Energy is Conducted Through a Copper Pipe?

    Homework Statement I have to find the energy removed through conduction from a copper pipe. Pipe Inner Diameter (Din): 8mm Pipe Wall Thickness (Dout): 1mm Thermal Conductivity (k): 401W/m.K Temp inside pipe -150C, Outside 30C Length (L)=1m Homework Equations The Equation I used was...
  10. J

    Magnetic fields and conduction

    Homework Statement 12.5A, 3.1x10^-5 Homework Equations How far from a long conductor passing a current of 12.5A is the magentic field of strength 3.1x10^-5T? The Attempt at a Solution B= uI/2(pi)r r=uI/2(pi)B =(4pi)(12.5A)/ 2(pi)(3.1x10^-5T) = 8.1x10^5m
  11. S

    Calculating Heat Energy in Conduction: A Mars Case Study

    Homework Statement the problem is one of understanding. if heat is incident on a surface raising the temperature to some number then conducts through the solid to the other side how much heat energy is actually at the other side?? i understand the temperatures will be different and that heat...
  12. A

    What Causes Metals to Conduct Heat?

    Hi, I understand what make metal a conductor of electricity, but what allows it to conduct heat? Is it that it does not absorb heat because it's electrons are easily liberated?
  13. O

    Calculation of Conduction Electron Population for Semi Conductor

    Hi everyone, From this website (link: http://hyperphysics.phy-astr.gsu.edu/HBASE/solids/fermi3.html#c1 ), we get the following expression: Population Density of Conduction Electron = \int ^{\infty}_{Egap}N(E)d(E) = \frac{2^{5/2}(m \pi k T)^{3/2} exp (-E gap/2kT)}{h^3} My questions are based...
  14. C

    Potential Inside a Hollow Conduction Sphere

    Here is a question I have been pondering on for a while and got rather stuck, could anyone help out? 'A charge is diestributed uniformley with density \sigma over the surface of a hollow conducting sphere of radius a. Show by direct integration that the potential at any point inside it is...
  15. P

    Calculating Heat Conduction Time for a Wooden Cylinder on a Hot Plate

    If a wooden cylinder at 298K with perfectly insulated sides (other than the one in contact with the hot plate) where placed with one end on a hot plate until any point on the cylinder reached a temperature of 523K and the power of the hot plate is known and it all goes into the wood. How long...
  16. P

    Heat Conduction in a Cube: Calculating Temperature Over Time

    If heat is applied to one side of a cube, how can the temperature at different distances into the cube be calculated after different amounts of time have elapsed?
  17. P

    Calculating Entropy Change of a Wire Conduction

    Homework Statement Each end of a metal wire is in thermal contact with a different heat reservoir. Reservoir 1 is at a temperature of 752 K, and reservoir 2 is at a temperature of 345 K. Compute the total change in entropy that occurs from the condustion of 1096 J of heat through the wire...
  18. M

    1D/2D Transient Heat Conduction (Diff. Eqs)

    Homework Statement My problem is not necessarily the 2D problem, it's getting the answer in one dimension (I have the y-direction). The problem is the boundary conditions...anyways. Solve for the temperature of a 1D transient metal bar, with the following boundary conditions. Imposed...
  19. T

    Magnetisation due to conduction electrons

    Homework Statement Due to its spin, the electron possesses a magnetic moment μB. Treating the conduction electrons in a metal as a free electron gas, obtain an expression for the magnetization due to the magnetic moments of the conduction electrons, when placed in a magnetic field. Evaluate...
  20. B

    Thermal Conduction Through a Sphere

    I have come across a problem where I must find the rate of heat flow to the surface of a sphere from the center. The sphere has a constant coefficient of thermal conduction. The problem also supplies the temperature difference between the center/surface and the radius of the sphere. My...
  21. L

    How Can Heat Conduction Be Modeled in a Cylindrical CanSat?

    Hey everyone! I am currently on a project building a small CanSat. This is a small satellite of the size of a coke can which will be launched together with a balloon and then descend from an altitude of 35 000 m. My problem now is to work out the heat conduction to see if our insulation is...
  22. S

    How Long Will It Take for Ice to Melt in a Styrofoam Cooler?

    Homework Statement A large styrofoam cooler has a surface area of 1.0m^2 and a thickness of 2.5cm. If 5.0kg of ice at 0C is stored inside and the outside temperature is a constant 35C, how long does it take for all the ice to melt? (Consider conduction only) Homework Equations...
  23. J

    Heat Transfer: Conduction vs. Convection vs. Radiation

    As I remember learning in school, heat cannot flow from cold to hot. But isn't that true only for conduction and convection? Radiation heat is purely Infrared waves, and there should not be any issue with that. Please correct if I am wrong.
  24. B

    Conduction electron ferromagnetism

    Homework Statement We approximate the effect f exchange interactions among the conduction electrons if we assume that electrons with parallel spins interacti with each other with energy -V, and V is positive, while electrons with antiparallel spins do not interact with each other. (a) Show...
  25. S

    MATLAB Solving 2D Conduction Problem with Matlab

    Hi. Everyone I have stuck in the problem of 2D conduction problem by using matlab, here is the following question: Consider a long bar of square cross section (1.0 m to the side) and of thermal conductivity 2 W/m.K. Three of these sides are maintained at a uniform temperature of 300°C. The...
  26. A

    Cylindrical general differential equation of conduction

    Homework Statement Desperate help needed on the derivation of the differential equation on conduction on a clyinder, i have come close to the answer and working with the co-ordinates scale of T(r,0,z). I am sure that i have made a simple mistake but am blind to it right now, i have...
  27. E

    Conduction vs. Induction: What's the Difference?

    Hello, Can someone please explain the difference between conduction and induction? Thank you, ~English10
  28. M

    Conduction - Steady State Triangular Element

    Homework Statement Obtain the temperature distribution T(x,y) of the triangular cross section, assuming constant thermal conductivity, k. The triangle is a right-isosceles triangle with the right angle at (0,0). The triangle goes "up" to a, and to the right to a, then diagonally across...
  29. O

    Calculate Energy & Cost for 7 Hour Oven Use

    The temperature in an electric oven is 165°C. The temperature at the outer surface in the kitchen is 55°C. The oven (surface area = 1.6 m2) is insulated with material that has a thickness of 0.023 m and a thermal conductivity of 0.045 J/(sm°C). a) How much energy is used to operate the oven...
  30. L

    Energy transfer in electricity conduction

    Hi, I was wondering something. What is the mechanism of energy transport when electricity is conducted through a conductor? The continuity equation requires current to be constant in a circuit, which means the expectation velocity of the electrons in the conduction bands must be constant...
  31. C

    How Does Steady State Heat Conduction Impact Home Heating System Design?

    In the steady state heat conduction through a solid rod the theoretical derivation tells that heat in-heat out-heat accumulated =0. What is a practical steady state heat conduction problem? what is transient heat conduction
  32. G

    Valance band to Conduction Band (Valance Electron), Energy Band Gap Levels

    I am looking to calculate the energy gap of for starters periodic elements and were wondering how we could get the list and calculation. Is there a table somewhere based on certain temperatures and constants of energy gap level? We would like to get a list of the energy gap energy for valance...
  33. D

    Question about heat conduction equation.

    I know how to solve a 1-D heat conduction equation when both ends are kept at 0 temperature(using separation of variables and Fourier series.). In the notes, the prof asked us to solve for one end kept at zero and the other insulated (at x=L) and referred to a non-existent chapter in our...
  34. T

    Heat Transfer (Conduction) problem

    Homework Statement Find the amount of thermal energy that flows per day through a solid oak wall 10.0 cm thick, 3.00 m long, and 2.44 m high, if the temp of the inside wall is 21.1 C while the temp of the outside wall is -6.67 C. Homework Equations Q= k(A)(T2-T1)t/d coefficient of...
  35. J

    Conduction of Heat through a Material

    Homework Statement .005 m of Ice is in contact with .0015 m of Aluminum. The temp of the Ice is -10.0 degrees C, and the temp of the Aluminum is -25.0 degrees C. I need to calculate the heat per second per square meter that is conducted through the Ice - Aluminum combination Homework...
  36. A

    Solving Two Identical Conduction Spheres Problem

    Homework Statement Two identical conduction spheres are placed with their centers 0.30m apart. One is given a charge of 12 x 10 ^-9 C, the other a charge of -18 x 10 ^-9 C a) Find the electrostatic force exerted on one sphere by the other. b) The spheres are connected by a conducting wire...
  37. R

    Number of conduction electrons question

    Homework Statement Calculate how many conduction electrons pass through a given area per second when a current of 1A flows. Homework Equations Current density, j = i/A (i=current, A=cross sectional area) Current desntiy, j = nevD (n=no of electrons per unit volume, e=charge on...
  38. A

    Heat conduction in nuclear reactor (introductory question)

    Homework Statement The elements of a boiling water nuclear reactor consist of long cylindrical rods of uranium dioxide (U02) of diameter 8mm surrounded by a thin layer of aluminium cladding. In the reactor core the elements are cooled by boiling water at 285°C with a heat transfer...
  39. M

    Why Are Some Materials Better Conductors/Insulators than Others?

    why are some materials better conductors/insulators than others? it'll helped if explained at the atomic level thanks
  40. W

    Heat Transfer in Elephant Ears: Convection and Radiation

    Homework Statement elephants have large ears because they need additional skin to balance the large amount of mass (to balance the heat eleminated from their skin with the heat generated by their body mass) by which methods of heat transfer do the ears eliminate excess body heat...
  41. S

    Solve Heat Conduction Problem: Oven Energy Use & Cost

    The temperature in an electric oven is 160 °C. The temperature at the outer surface in the kitchen is 38.6 °C. The oven (surface area = 1.44 m2) is insulated with material that has a thickness of 0.0249 m and a thermal conductivity of 0.0405 J/(s m C°). (a) How much energy is used to operate the...
  42. C

    What factors affect the electric field around a charged conduction sphere?

    Ok for example, if a solid conduction sphere was charged to 500volts and had radius of 1cm. Then charge, Q = VR = 5? So the E field just outside the sphere would be E = (1/4pi epsilon) x charge/R^2 = 4.5 x 10^14? Or am i getting confused?
  43. K

    Completely filled conduction band

    Hi all, From Pauli's principles, electrons cannot move into an already filled state. If i assume that somehow I fill in all the energy states in the conduction band (Population inversion :confused: )and then apply an electric field what happens?? Thanks...
  44. G

    Heat conduction problem: sphere

    A solid sphere of radius a is immersed in a vat of fluid at a temperature T_0. Heat is conducted into the sphere according to dT/dt = D(d^2T/dr^2) (d-> partial derivative btw) If the temperature at the boundary is fixed at T_0 and the initial temperature of the sphere is T_1, find the...
  45. D

    Degeneracy conduction electrons

    I'm supposed to show that the degeneracy of the energy levels of conduction electrons at fixed k_z[/tex] in zero magnetic field is given by \frac{2L_x L_y}{\pi \hbar ^2} m \mu _B B Where the energy levels of the electrons are of the form (approximation): E_{n,n_z} = E_n(k_z)=...
  46. J

    How Do You Calculate Heat Transfer in a Truncated Cone Using Fourier's Law?

    A truncated cone 30cm high is made of Aluminum. The dia at the top is 7.5cm, and 12.5cm at the bottom. The lower surface is maintained at 93 deg C, the upper surface at 540 deg C. the other surface is insulated. Assuming 1 dimensional heat flow, calculate the rate of heat transfer in watts...
  47. B

    Human Conduction: Exploring Electric Shock

    Hi folks, I was just looking into conduction as part of an electric shock, as in, the flow mechanism, when I ran across an article about such things, which states: "However, NO ELECTRONS FLOWED THROUGH YOUR BODY AT ALL. The electric charges in a human body are entirely composed of positive...
  48. Amith2006

    Heat conduction through spheres

    Sir, 1) Two spheres of different materials, one with double the radius and 1/4th wall thickness of the other are filled with ice. If the time taken for complete melting of ice in the large sphere is 25 minutes and that in smaller sphere is 16 minutes, what is the ratio of the thermal...
  49. E

    Electrical Conduction: Exploring Drift Speed and Force Requirements

    Hi all, If we state that low (drift) speed free electrons are responsible for the transport of power than it follows we need big forces. Regardless the explanation of what happens inside a wire i.e. classical / semi / qm etc. as far as I’m concerned this wire is a box in which I push small...
  50. M

    Heat Conduction: Steel vs. Concrete - Can You Help Tinus?

    Help with Heat Conduction Question My question is: These days they reinforce concrete walls with steel bars. Would the steel bars enhance or degrade the insulating value of the concrete wall? Explain? Metal is a good conductor and concrete is a good insulator. My answer so far is that it...
Back
Top