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Questions tagged [thermal-conductivity]

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Thermal radiations

everything having temperature above 0 k emits radiation. But those radiations depend upon temperature of the body and not on nature of the body. Why thermal radiations are not material dependent?
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How much conduction, radiation and convection influence in a thermos flask?

It has been thoroughly repeated that thermos flasks prevent heat loss by minimizing heat conduction, radiation and convection from the bottle to its ambient. This has been answered in this SE. However,...
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1answer
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Copper conductor thermal limitation [on hold]

"The maximum permissible current density of copper in open air is approximately 3.1×106 A/m2 of cross-sectional area, above which it begins to heat excessively." I came across the above statement ...
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Why do low concentrations of H2 in He gas exhibit lower thermal conductivity than either?

Thermal conductivity of He+H2 mixtures, as a function of molar concentration of H2, exhibit a minimum at around 14% H2. See Fig. 2 below from "Thermal conductivity of the hydrogen-helium mixture". ...
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1answer
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How is the 1D transient heat conduction equation derived? [closed]

From my book: $$\frac{\partial T}{\partial t}=\alpha\frac{\partial^2 T}{\partial^2 t}$$ with an initial condition and boundary conditions $$T(x,0)=T_0$$ $$T(L,t)=T_0$$ $$-k\left.\frac{\...
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Semiconductors with low thermal conductivity (lattice matched to GaAs)

What are the semiconductors with lowest thermal conductivity that can be grown on GaAs with the least possible incorporated strain (i.e. lattice-matched or close to it)? GaAs has thermal conductivity ...
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0answers
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Will forcing a gas through an aluminum foam cool or heat it up

Metal foams are known to be porous and interconnected when in open cell form, will forcing a gas stream through the network heat it up due to restrictions and friction or cool it down due to large ...
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How do I relate phase shift to heat capacity or thermal conductivity for frequency domain thermoreflectance?

I'm trying to measure either thermal conductivity or heat capacity of Silicon devices using frequency domain thermoreflectance (FDTR). I can get phase shift between the incoming signal from pump laser ...
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4answers
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Why don't you get burned by the wood benches in a sauna?

When you go to the sauna you may sit in a room with 90°C+. If it is a "commercial" sauna it will be on for the whole day. How does it come that when you sit on the wood you don't get burned? I ...
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1answer
31 views

Infrared pass material thermal camera

I have a situation in which I need to use a thermal camera in a rain enviroment, the camera is mounted on a gymbal and can rotate 360 degrees, so I tought it may be an option to build a dome in order ...
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2answers
55 views

Doubt in definition of linear thermal expansion

It's stated in my textbook that upon heating a rod , the linear change in its length is directly proportional to its original length and the change in temperature , therefore the equations should look ...
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0answers
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Doubt in the Peierls's paper on thermal conduction

I was reading Peierls's 1929 paper On the Kinetic Theory of Thermal Conduction in Crystals, where I encountered a notational discrepancy. There, the author considers a linear $1-D$ chain of ...
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2answers
62 views

Compression of gas [closed]

What happens when a gas kept in a metallic container is suddenly compressed via a piston and left for some time? Does the pressure increase or decrease?
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1answer
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Relationship between CO2 concentration and thermal conductivity of the air in a volume?

How much would the percentage of CO2 in a room need to change in order to make a measurable change (using transient hot wire method) to the thermal conductivity of the air inside room? Are there other ...
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0answers
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What formulas do I need to calculate the time it takes for a room with opened window to become the same temperature as outside?

I want to calculate how long I have to open my window to become the same temperature as outside. To make things more easy let’s assume there’s almost no wind helping the exchange of temperature.
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1answer
49 views

Thermal resistance of a rod

I have a confusion about how to calculate the thermal resistance of a solid rod ( not hollow). The general formula is $$R=\ln(r2/r1)/(2\pi Lk)$$ In my case, $r1=0$ Any hint would be highly ...
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Fluid dynamics - boundary later equation $f'''+ff''-f'^2+\theta = 0$ and $\theta''+Prf\theta' = 0$

Our lecturer gave us a system of boundary layer equations: $$\begin{align}f'''+ff''-f'^2+\theta &= 0 \\ \theta''+Prf\theta'&=0 \end{align}$$ subject to boundary conditions: $$f=f'=0, \...
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2answers
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which give higher cooling rate , strong circulated water or thick copper plate? [duplicate]

imagine if I have hot metal piece I want to cool it as fast as possiple, should I put it in strong circulated water bath or just stick it between 2 thick copper plates ? the calculated heat ...
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1answer
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which is more effective chilling for metal casting, thick copper die or water-cooled thin copper mold? [closed]

It is will known that increasing cooling of a metal casting will lead to finer micro-structure which mean higher mechanical properties. If I have 2 molds one is thick copper die ,& second is just ...
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2answers
76 views

What is temperature as a function of time in Fourier's Law?

Can we find temperature as a function of time using Fourier's Law of thermal conduction? For example: If we have two square parallel plates of a given length, width, and distance apart with one ...
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1answer
55 views

Can a semiconductor become more conductive than a conductor with heat?

I am looking for a good idea for a science fair project for PA Junior Academy of Science (PJAS). An interesting idea that I have stumbled across is making semiconductors more conductive with heat. I ...
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1answer
30 views

Air gap in a radiant barrier insulation system: why?

It's generally accepted that a reflective surface, when used to insulate a system by reflecting radiant energy back to it, must have an air gap in front of it. Why exactly is this, and what determines ...
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1answer
37 views

Is placing a fire safe inside a larger fire safe helpful?

If I put a small fire safe (say, one rated for 1 hour at 1700°F) inside a larger, equivalently-rated fire safe, to what degree is the fire/heat protection improved?
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2answers
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Does the order in which I layer blankets matter? [closed]

It’s getting cold where I live and I sleep with multiple blankets. I am wondering whether it generally matters how I might use blankets to keep something warm; if I put blanket $A$ on top of blanket $...
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2answers
206 views

Is thermal conductivity correlated with speed of sound in metals?

Right off the bat I should say: thermal conductivity and electrical conductivity are definitely correlated in metals. image source: https://www.doitpoms.ac.uk/tlplib/thermal_electrical/printall.php ...
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1answer
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Thermal Efficiency

For a thermally efficient house, is it better for the windows to be framed with something like aluminium, or steel? I am considering the thermal conductivities, aluminium has a value of 200, while ...
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3answers
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Why does a steel rod keep increasing its temperature after removing the source of heat?

I watched an experiment and I'm not sure why this happened. A metal rod was heated by a flame like this: sensor ======== -> metal bar flame The metal sensor ...
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1answer
33 views

Vapor pressure of sublimating ice in vacuum

I am trying to find a vapor pressure of sublimating ice as a function of thermal energy being absorbed by ice. Basically, I am starting with a sample of ice (t=200K) in a vacuum. From there, I am ...
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0answers
25 views

Heat loss due to thermal penetration [closed]

I am doing an experiment on a regenerator (Period 120 s). I found the thermal penetration depth through the insulation as 13 mm. I'm not sure how to estimate this heat loss?. I tried to estimate by ...
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0answers
20 views

Pressure and temperature conditions for discarding the ideal gas model for air

I'm trying to calculate the heat conductivity of a mold-polymer interface. I'm assuming that there's a thin layer of air between the polymer and the mold (gap conductance). According to some ...
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2answers
25 views

Heating a stock water tank

I am building an insulated cover to go around a plastic stock watering tank for the winter. I have no electricity in the pasture and don't want to axe ice in the tank all winter. I am building 3 sides ...
0
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1answer
133 views

When/How does thermal radiation stop (if it stops) and conduction starts?

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 ...
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1answer
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Why does a salt water solution have a higher coefficient of thermal expansion (i.e. expands more) than distilled water?

I have found several different sources of data which show that a solution with a higher concentration of salt has a higher coefficient of volumetric thermal expansion than a lower concentration salt ...
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0answers
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modeling heat transfer in a non-hollow cylinder starting at r=0

I have 2 questions about the heat equation in a cylinder that involve the behaviour at $r=0$ and the boundary conditions. But first a little more context: I want to model a reaction in a cylindrical ...
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1answer
105 views

Derivation of thermal conductivity of a solid body

I am reading a german physics book called "Festkörperphysik" written by Gross/Marx. And I came to following situation: $$\frac{d\langle n\rangle}{dt}=\frac{\partial\langle n \rangle}{\partial t}\...
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3answers
66 views

How do phonons impact the way heat is transferred between two solids?

If we assume that in a system heat is only transferred by conduction (between two different solid of different materials), what role do phonons play in this phenomenon?
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1answer
57 views

Viscosity Vs Conduction

Viscosity of a moving fluid (e.g. a gas) is commonly related to the exchange of momentum between layers of such fluid moving at different velocities. Intuitively, one could think that in a gas such ...
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1answer
177 views

Understanding boundary conditions in heat transfer

In the context of heat transfer, how does one physically interpret the following boundary conditions: $$ u \cdot \mathbf{n} = 0, \qquad \frac{\partial u}{\partial \mathbf{n}} \cdot \tau = 0 $$ where $...
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1answer
39 views

Are there any thermal insulation equation that uses change over time and temperature?

I'm currently working on a science experiment to find out whether the thickness of a material affects the insulator's ability to insulate, and if so, to what extent. I've set up an experiment where ...
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0answers
160 views

Convert `w/m K` to Tog?

Im trying to work out some calculations for an underfloor heating system (UFH). Basicly i need to have a floor finish over the UFH with a a Tog <2.5. The floorings thermal resistance is ...
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1answer
106 views

Combined radiation with conductive and convective heat transfer

I have a tube(only the cross-section displayed in the figure!), where gas flow is used to heat up the water. The water flows inside the steel tube, where the walls have been marked red. The heat ...
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2answers
163 views

What material is best suited for eating ice cream from, without the ice cream melting too fast on the edges?

When I buy some ice cream from a parlor or get some from the supermarket I find that the containers (also the standard bowls I can find in my kitchen) are not perfect for eating ice cream from. The ...
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1answer
30 views

temperature of each layer of a cooler

I have a cooler with five layers and I know the temperature outside and inside of the cooler. I created a Matlab model that demands me the temperature of each layer of the cooler. I want to know how ...
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1answer
41 views

Confusion about Thermal Resistance and Heat Distribution

I'm trying to understand the flow of heat between electrical components and circuit boards, and I'm having some trouble understanding some basic concepts. Suppose I'm considering a chip with a $\...
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1answer
31 views

Thermal Conductivity Conversion

I need to convert a thermal conduction unit W/m.K to Btu/ft.h.°F. I have 400 W/m.K and I ...
0
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1answer
292 views

Minimum Thickness of Insulation of a Pipe

We know that there is the critical radius of insulation where heat transfer is maximum at that radius. Heat Transfer vs Insulation Thickness]1 From the graph, we can see that as long as the radius ...
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1answer
69 views

Refrigerant vs water heatpipe [closed]

For a heatpipe that is connected to a 50 Celsius object on one side,and a heatsink at 23 Celsius air at other side, what fluid filling will give better heat conductivity? Plain water, or some kind of ...
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1answer
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Revisiting the choice of tungsten in light bulbs

I admit questions around why tungsten is used in light bulb tend to be very common, but hopefully what I'm asking here is not a duplicate. I am trying to understand which properties of tungsten make ...
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4answers
2k views

Why are compressed air tanks cold? [duplicate]

Why is a compressed air tank cold to the touch when it’s in a compressed state before use?
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2answers
358 views

Prevost Theory of Exchange

I am having a trouble in understanding this concept. If bodies are at thermal equilibrium, there is no heat transfer. Heat is transferred through three different ways: Conduction, convection and ...