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Questions tagged [thermal-conductivity]

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why the bulk thermal conductivity of water-saturated soils is higher than that of water and dry soils alone?

According to wikipedia, the thermal conductivity of water is around 0.5-0.6 W·m-1·K-1, depending on the temperature (say 25 degree Celsius is 0.5918 W·m-1·K-1, and the thermal conductivity of dry ...
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1answer
23 views

Linear expansion over temperature change

From the equation $\Delta L=aL\Delta T$, $\frac{\Delta L}{\Delta T} = aL$ For small change $\frac{dL}{dT}=aL$ Solving we get $L(T)=e^{aT}$ (as differentiating it with respect to temperature gives $...
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What are ways or methods to calculate or measure the thermal conductivity of a hybrid nanoparticle?

I'm looking for ways of estimating or approximating the value of the thermal conductivity of two nanoparticles added or combined. Creating a hybrid nanoparticle.
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help: calculating surface temp for rotating planet from solar constant 1366 w/m2

I'm interested in calculating the maximum surface temperature for a rotating planet from the solar constant. I can calculate the solar constant for a planet at any distance from the sun, no problem, ...
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1answer
28 views

How to distinguish the radius from the electrical or thermal resistance? And how to distinguish thermal resistance from electrical resistance?

We know both the electrical resistance and the thermal resistance of a cylinder is inversely proprortional to the square of the radius of the cylinder. But the letters R and r are used sometimes for ...
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1answer
45 views

Why do purely harmonic interatomic interactions result in infinite thermal conductivity?

When interatomic interactions are purely harmonic, normal modes cannot interact, and therefore no phonon scattering occurs, thus resulting in infinite thermal conductivity. But why is anharmonicity ...
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1answer
53 views

How does the thermal conductivity works? What is the significance of thermal conductivity? [closed]

I'm newbie to thermal conductivity. I read an article from https://thermtest.com/what-is-thermal-conductivity that thermal conductivity refers to the ability of a material to transfer heat but I don't ...
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1answer
25 views

An Expression for $\Delta T$ for a Thermal Conductivity derivation

In kinetic theory, the thermal conductivity of a gas is $$K = \frac{1}{3} C vl.$$ In deriving this formula, why is the following equation valid? "Now $ \Delta T$ between the ends of a free path of ...
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33 views

How long does it take a gas to equilibrate with a container's temperature?

Initial Conditions in a vessel: P~my unknown, but ~100torr, V=5000cc, T=35C, gas is 50/50 N2/He Laser drill a hole in the initial volume of diameter=10mils through a chamber wall thickness of 0.75mm. ...
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1answer
25 views

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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37 views

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
28 views

Copper conductor thermal limitation [closed]

"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
131 views

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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19 views

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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0answers
38 views

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
33 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
59 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
29 views

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
70 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
16 views

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
31 views

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
69 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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30 views

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
57 views

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
25 views

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
159 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
109 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
49 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
38 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
906 views

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
273 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
20 views

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
159 views

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
35 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
35 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
30 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 ...
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1answer
209 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
90 views

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
27 views

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
137 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
77 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
62 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
196 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
40 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
207 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
118 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 ...