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3answers
178 views

Heat flow in a hollow cylinder

Consider a hollow cylinder of different outer radius and inner radius and two different temperatures are maintained at the outer and inner surfaces such that inner temperature is higher. Because of ...
0
votes
1answer
99 views

What is the overall rate of heat conduction through two pipes of different dimensions if the thermal conductivity is not constant?

I am trying to work out how I would find the rate of heat transfer through two pipes made of the same material that are joined at their ends but which have different cross-sectional areas and lengths. ...
0
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2answers
50 views

Loss of temperature of a sphere [on hold]

I am trying to get an intuition of whether it theoretically seems possible for a living cell (a yeast for example) to regulate its own temperature. Let's consider a spherical living cell which radius ...
1
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1answer
81 views

How does the hot cup of tea cool down? [duplicate]

I am not sure about my answer. I think that the cup of tea cools down by the following modes: Radiation between the surface of the tea and the air molecules. Conduction between the tea and the cup ...
1
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0answers
35 views

Is thermal and electrical conductivity correlated for all phases of matter?

After reading this interesting post about why copper is a great heat conductor, I wondered if a plasma would conduct heat better than a gas. Or, are some properties like density more important for ...
2
votes
1answer
225 views

Calculating new temperature of an object when air temperature changes

I'm trying to calculate the new temperature of an object when the air temperature around it changes, given a period of time. Basically I get periodic readings from an air temperature sensor in a ...
0
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1answer
217 views

How to prove R value for insulation?

I ran some tests on different types of insulation. I heated water, and placed it into an insulated box. The temperature was recorded every minute, for the water, as well as the air. The insulation ...
-1
votes
1answer
70 views

Air Thermal Conductivity vs Humidity

If air of a certain temperature blows through a car radiator (or a computer case), what effect will air humidity (non-condensing) have on cooling rate?
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2answers
884 views

Stress due to the mismatch of thermal expansion coefficients of two different attached materials

I'm simulating the thermo-electro-mechanical behavior of a copper wire which is surrounded by silicon dioxide. In other words, the wire segments is under mechanical and thermal loads and at the same ...
1
vote
1answer
41 views

Single story, hotter outside, some shade from porch, enough to cool house with/without air flowing?

So, I know this question, without shade or one-story, has been answered many times on the 'net, so I have some actual physics for the one-story. I am fairly certain my roommate mixed up thermal ...
0
votes
1answer
65 views

Finding effective thermal conductivity multi-layer cylinder

How does one find the effective thermal conductivity of a cylindrical body made of multiple layers? E.g. Copper core (k1), insulator 1 (k2) and insulator 2 (k3). I need the effective properties for ...
0
votes
1answer
368 views

Ideal gas temperature and pressure gradients?

Consider an ideal gas in a $d\times d\times L$ box with the $L$ dimension in the $x$-direction. Suppose that the opposite $d\times d$ sides of the box are held at temperatures $T_1$ and $T_2$ with ...
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5answers
859 views

What causes contact resistance?

When two components are combined in an electric circuit, there is apart from their own resistances a contact resistance at their junction. This causes a sudden voltage drop of ...
3
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1answer
218 views

How can a material conduct heat but not electricity

Mica is a good conductor of heat but an electrical insulator. According to free electron theory (which applies only to metals) free electrons carry heat and electricity. Therefore, thermal ...
0
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1answer
52 views

Does paint affect the thermal conductivity of a metal?

We noticed that in our experiment that painting a metal increases its thermal conductivity; is this true? If so, can you guys send me a link to a research paper to support this claim.
1
vote
1answer
23 views

Is $\kappa_e$ caused by charge-carrier transport or electron transport?

$\kappa$ usually symbolises thermal conductivity, a material's ability to conduct heat. $\kappa$ can be expressed with other partial thermal conductivities: $\kappa=\kappa_e+\kappa_{ph}+...$ where ...
2
votes
1answer
91 views

How fast does heat travel via conduction?

I have read this question which seems to ask an identical question, but I'm not sure - it had far too many words I don't understand, let alone the equations. Perhaps someone can answer with a ...
0
votes
1answer
150 views

Does doping silicon affect its coefficient of thermal expansion (CTE)?

Everywhere I have searched I always see the CTE of silicon listed as 2.6*10e-6 °C^-1. However, I have silicon that was phosphorus-doped to an ion concentration of of 2.41*10e11 atmos/cm^3, and I would ...
4
votes
4answers
4k views

Improving our homemade hot tub design? [closed]

My brother and I built a wood burning, convection based, thermal circulating hot-tub. (With and oxyacetylene torch, lots of 1.5" pipe, a brake drum, and a thirty year old jacuzzi). Our design is ...
2
votes
3answers
63 views

Different materials have different temperatures?

Why do two materials, under the same weather, have different temperatures? I have a small clue about it. For example, iron and wood supposed under the sun's radiation, and if we touch both of them, ...
1
vote
1answer
140 views

Why bodies lose heat faster in water than in air?

A simple question. In several places, including this very recent and already famous paper http://www.sciencemag.org/content/348/6236/786.short it is stated that bodies lose heat in water very fast ...
2
votes
1answer
101 views

How much heating Earth inner core provide to the surface?

Compare to the energy that the Earth surface receives from the sun, how much power comes from the inner melted core ? How important is this contribution to the surface temperature ?
1
vote
1answer
67 views

Is “eco” shower mode actually using less power? [closed]

At work we have electronic showers in the gym, they have three modes: * (A snowflake, Which I guess means no heating at all) ...
9
votes
2answers
286 views

How does the sun's surface conduct thermal energy from the convective zone to the corona?

How does the surface of the photosphere conduct thermal energy from the convective zone to the corona, while remaining at such a relatively low temperature itself? It seems odd to me that the ...
1
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0answers
38 views

Heat transfer coefficients

I am trying to make a model of non-stationary heating on a plate and I have questions considering coefficients. I am using explicit method to solve it (have to use it). I am not sure if I am using the ...
0
votes
0answers
49 views

High resistance wire as a heating element

I'm redesigning one of the labs for our senior lab class at my university. It's a thermal conductivity experiment meant to measure aluminum's thermal conductivity in a thin (1.1 cm diameter) rod. I ...
4
votes
4answers
168 views

What does thermal conductivity actually measure?

Forgive my layman, non-physicist terminology used here. Hopefully I'm not too much of a caveman to express myself properly. What does thermal conductivity actually express? Is it measuring the amount ...
0
votes
0answers
27 views

Ratio between thermal conductivity heat transfer coefficient

Consider the Robin boundary condition for the diffusion/heat equation $u_t=a(t)u_{xx}+f(x,t)$: $$\mathrm{-k(t)u_x(0,t)=h(t)u(0,t)}$$ or $$\mathrm{u_x(0,t)+\frac{h(t)}{k(t)}u(0,t)=0}$$ where ...
3
votes
3answers
9k views

The relation between permittivity and conductivity

I am able to measure relative permittivity $\varepsilon_r$ of a fluid, and I want to calculate conductivity of same fluid. Can anyone suggest me how to do this? I found one formula to calculate ...
1
vote
0answers
28 views

Why the whole object cannot be observed to vibrate when energy is transferred through conduction (solid)?

Conduction is the transfer of thermal energy when particles in an object vibrate and collide with neighbouring particles thereby transferring their kinetic energy to them, why doesn't the whole object ...
0
votes
4answers
164 views

Is it possible to “add cold” or to “add heat” to systems?

Amanda just poured herself a cup of hot coffee to get her day started. She took her first sip and nearly burned her tongue. Since she didn't have much time to sit and wait for it to cool down, ...
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votes
0answers
36 views

Activation energy as a function of defects

Electrical conductivity has a form of Arrhenius equation. It is assumed that activation energy decreases with defect density in the insulating state and becomes zero in the conducting state. Can one ...
1
vote
2answers
156 views

An equation to describe a process of heating one room using hotter air from another room

There are two rooms completly isolated from the outer world (a closed system, no heat losses). They are connected with each other through a ventilation tube. Temperature in room A is 32 degrees ...
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3answers
7k views
0
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1answer
53 views

What are the units in the heat equation?

If we write the heat equation as: $$ \frac{\partial}{\partial t}u-\alpha \nabla \cdot (\nabla u) = f $$ Then, Temperature of the material: $u: m^3\times s\rightarrow K$ Thermal diffusivity: ...
2
votes
1answer
312 views

Heat equation: boundary conditions?

Say we have a bar centered at $x=0$, that is heated. We have the 1D Heat equation which we can solve to find a parabolic temperature profile : $$\kappa \frac{d^2 T}{d x^2}=-\frac{Q}{L S}$$ with ...
1
vote
1answer
76 views

Where do limits of integration come from in the equation of heat transfer by conduction?

I was watching the third lecture of Diffrential equations on OCW. As an application, the model of heat transfer by conduction is provided. We derived this equation which models the system where $T$ is ...
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0answers
24 views

Does illuminating a conductor with light energy less than its workfunction change the measured conductivity?

For example, does the light absorbed in an exposed metal wire increase the average velocity of the electrons, hence increasing mobility and conductance?
5
votes
1answer
189 views

How does temperature in a solid sphere change with time when moving through a gas?

I'm interested in the following problem: There is a solid sphere with radius $r$ and mass $m$ at temperature $T_{s0}$. It is moving at velocity $v_s$ through a gas of temperature $T_g$. How does the ...
1
vote
1answer
57 views

Spherical Shaped Electrical Leads for Thermal Conductivity Mitigation?

I am designing a thermionic converter and one of the biggest inefficiencies is the thermal conductivity and limited electrical conductivity of the leads. I'm trying to mitigate the loss of heat ...
1
vote
0answers
27 views

What is the boundary of restorable thermal expansion?

As every book indicates, thermal expansion is a linear process $\frac{\Delta L}{L}=\alpha \Delta T$. Upon heating an object the result is thermal expansion. If we cool it down it is restored its ...
3
votes
2answers
189 views

What's the true reason behind thermal expansion?

Thermal expansion is a normal concept everyday. There are 2 explanations: 1, thermal expansion result in stress, then result in deformation 2, thermal expansion result in deformation, then result in ...
0
votes
1answer
140 views

What type of glass is used in oven glass doors? [closed]

I understand that the glass used in convection oven door must be able to withstand high heat. But what should be the exact specification if I am thinking of replacing my broken oven door and ...
1
vote
2answers
259 views

Why does room temperature water and metal feel almost as cool as each other?

From what I've read about heat, temperature and conductivity, I understand that the reason water at room temperature feels colder than most other things at the same temperature (like wood, air, ...
2
votes
1answer
161 views

Copper Bath Keeping the Water Warm

I was watching a home improvement program the other day and the presenter mentioned that a copper bath kept the water warmer for longer. She didn't say what it was being compared with but I have ...
1
vote
1answer
89 views

Thermal conduction through 1D rod with changing thermal diffusivity?

I've been working with solving partial differential equations in 1D numerically using the finite difference scheme. My case is for example this: I've got a rod that's insulated around the sides such ...
0
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0answers
45 views

How water and honey behave with increasing pressure?

Is there any relation between pressure and viscosity of water and honey? I hardly found the topic. Is it related to the Laplace law?
0
votes
0answers
155 views

Thermal conductivity in vacuum

It is my assumption that material objects preserve/gain heat via: 1) material contact (air or other touching material/object) and/or 2) absorbing radiation / electromagnetic waves So, imagine that ...
0
votes
0answers
32 views

Thermal conductivity of semiconductors - theoretical function?

Below is a plot of the thermal conductivity coefficient for Gallium Arsenide, reproduced from 3: I would like to interpolate the data, but I don't know what fit function to use. I tried a generic ...
4
votes
2answers
103 views

How does aerogel attain its enormous heat isolation properties?

In a text about properties of aerogel I read some interesting facts - clothes with aerogel proved to be impractical, being far too warm to wear. If you isolated a house with aerogel and lit a candle ...