thermal conductivity Definition and Topics - 40 Discussions
The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by
k
{\displaystyle k}
,
λ
{\displaystyle \lambda }
, or
κ
{\displaystyle \kappa }
.
Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal conductivity. For instance, metals typically have high thermal conductivity and are very efficient at conducting heat, while the opposite is true for insulating materials like Styrofoam. Correspondingly, materials of high thermal conductivity are widely used in heat sink applications, and materials of low thermal conductivity are used as thermal insulation. The reciprocal of thermal conductivity is called thermal resistivity.
The defining equation for thermal conductivity is
q
=
−
k
∇
T
{\displaystyle \mathbf {q} =-k\nabla T}
, where
q
{\displaystyle \mathbf {q} }
is the heat flux,
k
{\displaystyle k}
is the thermal conductivity, and
∇
T
{\displaystyle \nabla T}
is the temperature gradient. This is known as Fourier's Law for heat conduction. Although commonly expressed as a scalar, the most general form of thermal conductivity is a second-rank tensor. However, the tensorial description only becomes necessary in materials which are anisotropic.
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'm trying to find a heat transfer equation that includes time. Metal tank, partially filled with liquid. I need to find the time it would take for the temperature on the outside of the tank to drop from θ2 to θ1, given thickness, metal and liquid's properties, and tank dimensions
I worked on a lab experiment that was meant to measure heat capacity but left me with some other questions. The students measured the mass of a cup of liquid nitrogen as it boiled off, recording mass vs time. Then they drop a solid object into the bath, one experiment with a small bit iron...
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Hello! I am a materials engineering BSc student currently writing my bachelor thesis. The topic of my thesis is regarding the PV/T system and the best material choice for the interface between the glass/glass PV module and the heat mat. I would appreciate any ideas for material with best thermal...
Homework Statement
Hello,
As part of my engineering orientation class, my team and I have to make a device that can keep a beaker of water warm. We have a list of materials we can and cannot use, but my team and I have decided on aluminum foil and maybe wood. We don't actually have to build...
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Hello, my name is Stephen Lanford and I am currently working on a Physics II lab.
I am solving for the thermal conductivity of four materials (glass, plexiglass, pine, and sheetrock) using data from thermal conductivity experiments. The experiments consist of a steam chamber at 100 C, a block...
Phonons on their own lead to the common heat equation. One sees that for example in insulators or non doped semiconductors.
However in metals (or conductors), the electrons are the ones that are mostly responsible for the heat transfer, which extremely surprisingly to me, is also of the form of...
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...
HI,
I have application where i need to lift metal plate, 3kg weight, ( 3mmX 15mm), 250degree.C hot, for the period of 1min and put it back. For lifting purpose i am using actuators. As i have no opportunity to make hole in plate i have to use magnet for lifting purpose. I got Electromagnet...
rajaryan
Thread
magnet electromagnet
metal
temperature
thermalthermalconductivity
Homework Statement
I must calculate chemical potential using the Boltzmann equation in relaxation time approximation $$f=f^0-\tau v_z^2 \partial f^0/\partial z,$$ where ##f^0## is given as
$$f^0 = 2(\frac{m}{2\pi\hbar})^3 \frac{1}{\exp{\beta(z)(\frac{mv^2}{2}-\mu(z))}+1}$$
I have to consider...
Does the phonon thermal conductivity account for a large part of the total thermal conductivity in thermoelectric materials like Bismuth Telluride?
As far as I know, the phonon conductivity is the largest contributor to the total thermal conductivity in semiconductors. Is this still true for...
Hi!
I am using a Zn-Mg alloy (52% and 48% respectively) as a phase change material in a thermal energy storage system, but I have been unable to track down important properties, such as specific heats and thermal conductivity.
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Homework Statement
Homework Equations
P = k A \frac{dT}{dx}
The Attempt at a Solution
a)
Assuming steady state transfer, energy transfers through rods at the same rate everywhere.
Letting T be the temperature at the point of welding.
P_1 = k_1 A \frac{T_h-T}{L} \\ P_2 = k_2 A \frac{T -...
Hello Physics Forums!
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1. Homework Statement
I've been failing to find examples dealing with "longitudinal" thermal conductivity and how two objects in contact with each other would affect the heat flow compared to not being in contact at all.
Problem: Given the following information, determine the thermal energy...
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Homework Statement
Case 1: Which will boiling faster the container having steel ball dipped in it or container having only water?
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every condition of each the cases have same volume...
Homework Statement
In each of the following, state and explain which container will have the hotter liquid after thirty seconds:
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I'm designing an oven and want to ensure that the insulation I specify has a low enough Thermal Conductivity (k) to resist excessive heat loss. I determine heat loss (Hout)with the following equation: Hout=A*U*(T1-T0). U is dependent on k (U=k/L). I omitted the heat transfer coefficient in...
Homework Statement
I would like to derive an equation that relates the thermal conductivity to the pressure using the kinetic theory of gases. However, I assumed that thermal conductivity was independent of pressure.
Homework Equations
I know that P = 2N/3V (1/2mv^2)
Also:
I believe that...
How does insulator's density affect its thermal conductivity?
For example, considering such insulators as rock wool, It seems that the thermal conductivity should increase with an increase in density (due to elimination of 'air pockets'). However, experimental results, in many cases, look more...
It is a thought I just thought of with all the wonderful attention that climate change has been getting recently. The thought goes as follows:
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Wood and Copper are heated upto a steady state condition which will have a higher average of temperature at points ?
Please state your mathematical approach
1. Homework Statement
Dimensions remain same for both the materials as well as the temperatures both are heated to is the same
Homework...
First off, for my EE100 class I chose to replicate the industrial electrical blankets that are out there.
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Two metal rods, one silver and the other gold, are attached to each other. The free end of the silver rod is connected to a steam chamber, with a temperature of 100oC, and the free end of gold rod to a ice water bath, with a temp of 00 C. The rods are 5.0 cm long and have a square cross-section...