What is Conduction: Definition and 421 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.
If aluminum foil were used to help conduct heat with pine and sheet rock (0.14 W▪m/m2▪°C and 0.43 W▪m/m2▪°C respectively) would it also help conductivity for glass and plexiglass (0.86 W▪m/m2▪°C and 0.19 W▪m/m2▪°C respectively)? When does the transition of insulator and conductor happen for...
Two ideas:
1) Negative charged object get close to A then we close K1 key. So -10SI charge from sphere A moves to sphere B and 30SI charge moves from sphere B to sphere A. At this moment sphere A has 30SI charge and sphere B has -10SI charge.
2) We close K1 key so system of 2 spheres should have...
good morning gentlemen, while wandering around the internet I came across bone conduction. most devices use a piezoelectric near the ear. Long story short, is it possible to place the piezo on your shoulder or hand instead to hear the sound? the distance is better, can the sound be heard in the...
Hello,
I've seen in a few books on solid state physics that one can deduce an expression for average K.E.:
$$<\:K.E.>\:=E_c+3/2\:k_B\:T$$
from the following:
$$<\:K.E.>\:=\:\frac{\int \:\left(E-E_c\right)g\left(E\right)f\left(E\right)dE}{\int \:g\left(E\right)f\left(E\right)dE}$$
I can't...
I had an idea thinking about heat transfer and how placing water over a hot surface will transfer the heat to the water. It got me thinking, in a case where water could not be an option for a medium could I use metal, which would still have a higher heat transfer to absorb more of the heat...
Hi guys, I'm a 2nd year mechanical student currently taking heat and mass transfer. A question came up in my mind when I was looking into the conduction heat transfer.
If I put block B on block A where block A is 573K and block B is 303K. Is there any way that I can calculate the time required...
I understand that electrical conductivity is a measure of how easily charges are able to move in an object.
During charging by conduction (for conductors), it seems that we simply have to add the charges of both object together and divide by two to obtain the resultant charge of either object...
Hi,
I am doing e-field simulations and have came across two types; electrostatic and dc conduction. I know that electrostatic means there is no changing field so I'm just hoping for discussion on when one is more appropriate than the other and when one definitely should or should not be used.
Suppose I have a perfect crystal(e.g.TiO2-Rutile, band gap=3ev), under UV light, there should photoconductivity, according to the condensed matter theory, some of these excited conduction band electrons would form small polarons, I am wondering how many percent of the free conduction band...
Hello,
I have this band structure plot for five band Hamiltonian model. I want to know which bands are valence and which one is conduction bands. Also if they have any special name I like to know that.
Thank you.
(A) incorrect, because opposite signs attract, and the sphere would've been drawn to the charged rod.
(B) correct, according to the answer key, but if the charge of the sphere and the charge of the rod are the same, then wouldn't they repel each other? I'm confused as to why this is the correct...
I am a new to this and I try to understand the basics.
So initially once the atoms of silicon come together to form a solid, due to Pauli law no electrons can exist in the same energy state,thus many energy states are formed which together make the bands.
My problem starts at this stage where I...
On the surface of a semi-infinite solid, a point heat source releases a power ##q##; apart from this, the surface of the solid is adiabatic. The heat melts the solid so that a molten pool forms and grows. Let's hypothesize that the pool temperature is homogeneously equal to the melting...
Please could someone point me in the direction of an equation/ book I can use to obtain the convection coefficient for steam in a heating jacket. Steam is at 1 bar pressure. I think I need to use a dimensionless number. Thanks
I have solved the first 2 parts.
For the 3rd part, I have obtained the equation:
T(x) - T0 = (T1 - T0)e^(-Φx/fc), where f = fm in the question.
How do I obtain that expression for H?
Thank you!
Good afternoon everyone!
I've learned that thermal conductivity has a form of second-rank tensor. As you know, diagonal components of stress tensor mean normal stress and other components mean shear stress and like that do off-diagonal components of thermal conductivity tensor have some special...
The current density is given by the formula
##J_e = (n\mu_n + p\mu_p)qE = \sigma E; \sigma \text{=conductivity}## ->eq1
The resistivity of intrinsic germanium is 60 Ohm-cm, the equation 1 becomes
##J_i=n_i(\mu_n + \mu_p)qE## ->eq2
##J_i=60 \text{ ohm-cm} ##
Applying the standard equations...
I've written a calculator that computes the number of conduction electrons in a segment of wire with a specific gauge. For a 1 ft segment of 24awg copper wire, this is what it prints out.
AWG [0 - 36]? 24
Wire length (mm) (0 - inf)? 304.8
AWG 24
radius: 0.255 mm dia: 0.511 mm area...
Are there any known instances of heat transfer via conduction or convection happening at relativistic speeds? Is this even possible or is there a non-relativistic limit to how fast heat can transfer in these ways, like how sound can only move so fast?
When we measure 'the rate of conduction heat transfer'=Q , we assume that the hot side and the cold side's area are same. But if the both side's area is different to each other, how can i know the rate of conduction heat transfer?
like below figure.
Would you like to help me?? Thanks.
I am open to ideas of a way to test a bus bar for insulation flaws that has a 3D shape that varies in a production environment.
I have a DC bus bar that when it was just straight we would run a high potential test on a metal table that is the reference plane, and then flip it over to test the...
I'm having trouble to understand why it's said that electrons in the conductor band are free while electrons in the valence band are not.
I know by the Schrodinger equations that the trajectory of an electron inside a specific band and with a specific energy level is a probability. From what I...
Recently, I have been studying some solid-state physics and I came across this ##E-k## diagram online. Here's an image for reference to what I am referring to...
We know that,
Conduction Heat Transfer Q = KA(t2-t1)/thickness
K is the coefficient of thermal conductivity. If T2 = 1020°C and T1= 22°C also consider we know A and thickness value.
K depends on temperature. K varies with temperature. For all the materials we have a tabular data of K for...
Hi all,
This question asks me to calculate the number of quantum states, as well as electrons per cm^3 of the crystal in the room temperature.
The problem is I only dealt with a single element before without any calculation for 1cm^3 whatsoever. For example for a Silicon semiconductor, I can...
In this case with a presence of the airgap, what should I do with the equation that is provided to be? Must the temperature gradient be caculated spearately (glass+air+glass) ? My tutor provided the hint that the heat flux should be constant for the windows, so in this case should I just omit...
For the first part, since this is a intrisinc semiconductor, n=p= intrisinc carrier concentration. Hence free electrons and hole = ##(1.5*10^{10})## per cubic centimeter.
As for part 2, here are my steps. But I'm not sure if it's correct.
I first find the number of atoms of one cubic...
I am trying to determine the size of a single cartridge heater or 2 cartridge heaters to heat a large mass of aluminum to 400F. The aluminum block will be sitting inside an insulated (all sides) enclosure. The following are the specs for this problem.
- Max surface temp of aluminum block is...
At T = 0K, the valance band of a semiconductor is completely filled, and no current can flow, acting as an insulator. Is there every a situation where the opposite can occur, such that the conduction band is filled (and the valance band is completely empty) forcing the semiconductor to be an...
Hi everybody
I follow climate denier pages and every now and then come across a claim that doesn't seem to have been debunked yet. One such claim is made here:
<link to uacceptable source deleted>
The gist of the article is that scientists experimented with using different gases in double...
Saltatory nerve conduction occurs because of myelination of nerve fibers. This is done by Schwann cells in the peripheral nervous system and oligodendrocytes in the central nervous system. From what I understand, it happens because depolarization of the membrane at an unmyelinated area of the...
Hi, just thinking about a possible project and it may involve bolting aluminium plates together and putting a very small voltage across them.
If I take two plates of aluminium, leave them to oxidise in air (we all know Al forms a surface layer) then is there a minimum voltage that will flow...
I'm having trouble verifying an experiment I ran to determine the power dissipation of a heating element. 13.15W of power was applied to 3ft nichrome wire. Temperature readings were collected until they stabilized at 128.5F (room temp was 70F). I want to create a mathematical model of the system...
It is easy to understand heat conduction in a gas as the nucleus of atoms may collide with transfer of kinetic energy. But the space within a solid is vastly empty space and the nucleus of the atoms cannot collide. So if the surface of a solid is in contact with a hot gas, how is kinetic energy...
Hi,
Could you please help me with the queries below?
Question 1:
Please have a look on the attachment, conduction_band2, or check the following link for better resolution http://imagizer.imageshack.us/a/img921/4356/vODcjh.jpg
It says, "Figure 1–7 shows energy diagrams for insulators...
Homework Statement
Homework Equations
Finite difference method
The Attempt at a Solution
I have tried two different approaches, but still i am wrong in the question. Can anyone guide me how to attempt this question?
Thank you
Homework Statement
I am wrong in my attempt, yet I can't figure out the reason why...
Homework Equations
(solution with h=250 W/m^2*K instead of 350 W/m^2*K)
The Attempt at a Solution
This is how I obtain the answers, which I checked all the calculations and I don't think there is...
Consider two solid objects in the vacuum (of different materials, if you will) at different temperatures approaching each other until they make "perfect contact" through flat surfaces (no gaps or defects, so that thermal contact conductance effects are absent, even though interfacial thermal...
Homework Statement
descibe the operational principle of a thermocouple
Homework EquationsThe Attempt at a Solution
A thermocouple works using the seebeck affect. Two dissimilar metals joined together at one end forming a "hot" junction this is where the temperature is measured. At the other end...
Homework Statement
One end of a solid cylindrical copper rod 0.200 m long and 0.0250 m in radius is inserted into a large block of solid hydrogen at its melting temperature, 13.84 K. The other end is blackened and exposed to thermal radiation from surrounding walls at 500.0 K. (Some telescopes...
Homework Statement
I don't understand the derivation of the right side of the last equation.
Homework EquationsThe Attempt at a Solution
I got to this point, I also don't understand why it did not include C_2 for the variation of temp. along the fin.
I am guessing the right side is the...
Apologies upfront, I have a backlog of PF threads I have created not replied to...I will endeavour to do so when I can.
So I've read that IGBTs are more efficient than MOSFETs for lower than 20kHz frequencies (and are capable of use for high voltage rating and better performance than ordinary...
Homework Statement
A 1.75m long PVC pipe with a thermal conductivity of 0.19 W/mK has an internal diameter of 3mm and an external diameter of 5.5mm. Inner temperature is 298K and outer temperature is 273K. Calculate the heat transfer rate through the pipe and thus the decrease in the inner...
When does an N-ch Mosfet conduct when drain voltage varies from 0V to Vdd(like 5V).
In case of Source voltage changing between 0V to 5V, all you do is check if VGS > Vth, with Vdrain fixed at 5V.
But in case of Drain Voltage changing between 0V to 5V, how does it work?
Students seeking “deeper” understanding of basic electricity, frequently come with one of the following misconceptions.
1. Electrons are like balls, they start with potential energy and gain kinetic energy. They deliver their energy to the far end of the wire by filling a bucket.
2...
Okay...Is it possible to charge a metal, by conduction, using only a single terminal of a battery?...Like it we touch only the negative terminal with the metal, is it going to get a negative charge??...If not, then why?