Questions tagged [thermal-conductivity]

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Stirring the Pot: A Simple Question About Heat-Transfer

I was preparing hummingbird food. To get the feeders filled and hung quickly, I placed the pot in a sink with a similar or greater volume of cool water in it. I hypothesize that absent any other ...
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32 views

Why can't information be conducted out of a black hole? [closed]

Why can't information be conducted out of a black hole? Does gravity affect conduction? What is the temperature profile in equilibrium of a metal pole half in, half out of a very large BH such that ...
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1answer
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How to prove that a set of derived closed-form equations for a heat exchanger do not violate the second law of thermodynamics?

Recently I have been working on a problem involving a cross-flow heat exchanger (Two fluids flow orthogonal to each other on either side of a separating wall and exchange heat with each other through ...
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1answer
28 views

Drift of electrons in a conductor connected across battery terminals and constantly being heated

I came across this question which was suggested to me by a friend . In this question , the correct answer marked is d , which states that the conductor will have highest temperature near D end . I am ...
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8answers
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Why does holding a hot object with a cloth make it feel less hot?

Let's say that I held a hot object with a warm cloth. It instantly feels less hot and only warm to the touch. This is because the cloth is an insulator and doesn't allow as large a heat transfer as if ...
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1answer
23 views

Why heat flux is not related with specific heat capacity?

Rate of heat transfer across a solid material kept between two environments of different temperature (Assume a wall of a house) is mentioned to be dependent on the temperature gradient, length, and ...
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3answers
46 views

A thermally conductive gap filler does not conduct the heat as expected. Where does the heat go?

I have a mug warmer, which is a hot plate that I've measured heats up to 56C. It came with a mug with a flat bottom, which gets its contents warmed up to about 53C after some minutes. My understanding ...
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23 views

Heat relation of a isobaric expansion

A piston closed at the top contains $n=0,2$ $mol$ of a mono-atomic ideal gas at the temperature of $T_0$. The pressure of the gas is constant during the transformation and we don't have to consider ...
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32 views

What are operators for electric and thermal current in quantum mechanics?

Using Green's function formalism, I have derived a formula that can measure the expectation value of any operator $\hat{O}$ under temperature gradient $\nabla T$. The formula is more or less as ...
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1answer
45 views

Temperature of air coming out of a tyre due to a burst

I saw several questions where I had to calculate the temperature of the air coming out of a tyre due to a burst, given the external atmospheric pressure and the initial state of the gas present in the ...
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8 views

Convection/conduction simulation run from equal temp, but losing heat

I was investigating the effects of heated wall materials on outdoor air temperature and indoor air temperature with a certain software. The system is as the following: 1x1x1 meter cube of outdoor air ...
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3answers
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Are there thermodynamic obstacles to thermoelectric generation on the surface of Venus?

There has recently been a NASA design challenge for a clockwork Venusian terrain navigation system which uses no sensitive electronics or hydraulics. I was thinking that rovers and probes on Venus ...
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How to calculate vapor quality in a heated annular channel

Say I have a pipe of length L and an inner diameter of ID. Inside is a heated rod of diameter OD that is uniformly heated with power P. I have water flowing through the pipe with mass flow rate G ...
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1answer
33 views

Ideal gas equation for adiabatic process

In an adiabatic expansion or compression of gases, does the ideal gas equation change from $PV=nRT$ to $PV^{\gamma} = nRT$? If so, then why as pressure and volume are inversely related in both the ...
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Does the Mpemba Effect affect none-water substances?

Does the Mpemba Effect work on liquids other than water? If so, what are the similarities/differences, and what contributes to it(mainly the differences)?
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1answer
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Why does thermal conductivity decrease from solids to gases?

I am learning in my heat transfer class that the thermal conductivity decreases from solids to liquids to gases i.e. $$K_{solid} > K_{liquid}>K_{gas}$$ The reason cited is that (based on my ...
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Would a bread moving with infinite speed up and down a toaster, get toasted?

So, assume I have a vertical toaster and a slice of bread. If we assume it would take $t=5$ minutes to toast the bread usually and I am able to move the bread up and down the toaster with an infinite ...
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2answers
28 views

Increasing boiling point without change in physical conditions

Recently while going through the chapter calorimetry of class 10 I came across a passage saying "if we add impurities to water such as salt in proper proportion the boiling point of water ...
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0answers
30 views

Best color for pool cover [closed]

I couldn't find a stack* forum for pools, so I hope this is the next best place to post. I have an 18 foot diameter above ground pool in the north west, and I don't like the pool cover that came with ...
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0answers
45 views

Lagrange Equation for thermal system

I am working on modeling of a multi-physical system using Lagrange based modeling and we know that Lagrange function, $L$, can be defined as below; $L= T-V$ where: $T=$Kinetic Energy $V=$Potential ...
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16 views

How to protect glass from direct, excessive hot air?

I need to use a hot air gun directly next to a one-way mirror glass window which is embedded in a wooden frame. I've read that a heat gun can shatter the glass easily because the excessive direct heat,...
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29 views

What is the physical meaning of ΔG = q(irr) - q(rev)?

Why is change in enthalpy ΔH equal to heat exchanged following whether reversible or irreversible path whereas TΔS is equal to the heat that would be exchanged if the process was reversible? What is ...
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3answers
64 views

Which substance cools faster a glass bottle or the liquid inside it?

I had an argument with a friend who says that the temperature of the glass of a beer decreases faster than the liquid inside. for example if there's a beer bottle in the fridge for 10 minutes the ...
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22 views

How many dry ice produced by a 5lb co2 cylinder at 860 psi and room temperature (30 C)?

just wonder how many lb dry ice could be produced from $5$ lb $CO_2$ cylinder at $860$ psi and $30$ C , assuming no recyle co2 stream) ?
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2answers
49 views

Melting ice under pressure

If we put a cube of metal on ice (ice with a certain thickness), under which conditions the cube will penetrate the ice? and how can we calculate the velocity of penetration?
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1answer
39 views

Heat absorbed from a reservoir by a moving object [closed]

Imagine two bodies, say a body A with an infinite heat capacity(reservoir) and the another body B with some finite heat capacity($C = \alpha \ T_{B}(t) $). They come into direct contact with each ...
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11 views

Nusselt number for a rectangular fin under forced convention

I am looking for the correct Nusselt Equation to calculate the heat transfer coefficient for a rectangular fin acted upon by air with a certain speed
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15 views

Coupled solid-fluid heat transfer over a rectangular plate heated from the bottom (Boundary value problem)

I have the two-dimensional temperature Laplacian $(\nabla^2 T(x,y)=0)$ coupled with another fluid equation (which is one-dimensional). The Laplacian is defined over $x\in[0,L], y\in[0,l]$. On ...
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1answer
23 views

Specific heat capacity in gas vs solid

If in general the specific heat capacity is low in gas then why doesn't it raise it's temperature more quickly compared to a solid that is given similar conditions as to the gas. (By the reason of the ...
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2answers
45 views

Heat equation with a source and homogenous boundary and initial conditions

I am trying to solve the following: $$\frac{\partial^2u}{\partial x^2}-3\frac{\partial u}{\partial t}=-9$$ $$u(0,t)=0=u(\pi,t)$$ $$u(x,0)=0$$ So solving the homogenous case first by separation of ...
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2answers
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How much hotter will an object get if I paint it black?

I have read these threads If black is the best absorber and radiator, why does it get hot? Black and white matters. But why and how? If a black body is a perfect absorber, why does it emit anything? ...
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1answer
33 views

Thermal Wheatstone Bridge

I am currently studying about the thermal conductivity of rods, as I am reading a Idea popped up in my mind that is , Is the concept of wheat stone bridge Valid to thermal resistors ?
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Need help with heat exchanger requirements [closed]

Disclaimer: Not an engineer I need some help determining the required performance from a heat exchanger for a pseudo-instant hot water system on a boat. Using a heat exchanger, and a reserve of hot ...
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1answer
108 views

Analytical Solution to Heat Equations

I have the steady state equation with an internal source as $$\frac{1}{r^2}\frac{\partial}{\partial r}\left(r^2k\frac{\partial T}{\partial r}\right)+Q=0$$ which has the analytic solution $$T(r)=-\frac{...
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1answer
38 views

Materials to Insulate Against Convection, But Not Radiation

Are there any materials which could effectively insulate against convection (and/or conduction), that don't insulate against radiation? Specifically, I want to make a water-heater that uses solar ...
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0answers
19 views

Heat loss calculation and Energy Balance

The image shows the CAD model of the annealing zone in a galvanization simulator. The zone is electrically heated with a AC current of 5597A at 2.09V. This whole zone is surrounded by insulating ...
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27 views

What microscopic and microscopic parameters are involved if room is filled with normal air?

Let us suppose that in my room an air conditioner is working at $25^\circ\ C$. Now if I want to calculate the macroscopic and microscopic coordinates in the room if it's completely filled with normal ...
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1answer
140 views

Calculate rate of heat gain of a steel chain in a campfire [closed]

Up front: I'm trying to be scientifically accurate about heating up a length of steel chain in a campfire to use as a surprise attack tactic in a D&D campaign, but I'm not sure I'm using the ...
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0answers
18 views

Convective Air Velocity

Consider there is a hot plate which causes natural convection in a closed environment of air over the hot plate. Is there any exact formula to find velocity of air flow? If there is please cite the ...
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2answers
114 views

Black body radiation problem [closed]

Three concentric thin spherical shells are given their radius are $R$, $2R$ and $3R$. Outer most sphere can't radiate in outer space. The inner most and the outer most shells are maintained at $T_{1} ...
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Why there is no perfectly transmitting surface?

My teacher was teaching us about the process radiation in heat transfer. He told us there are Perfectly absorbing surface i.e. Black body. Perfectly reflecting surface. Then I asked him about ...
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3answers
353 views

Why does an ice stupa not melt for 6 months?

https://www.youtube.com/watch?v=-1s0K_MKAgI&t=303s In this video at 3:55, Mr. Wangchuck explains that the ice stupa doesn't melt because it has less surface area for a given volume compared to ...
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2answers
51 views

Is aluminium better for insulation or heat dissipation?

Aluminium (-containing) foils are used for insulation, eg. in emergency situations where injured people are covered in them, to prevent heat loss. On the other hand, aluminium is used for heatsinks, ...
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1answer
43 views

Thermal Heat Transfer [closed]

I work for a large plant bakery and we have recently coated the inside steel walls of our very large oven with a reflective coating. I have taken temperature readings inside the insulation void and ...
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4answers
6k views

Why are steel thermal mugs much better than plastic ones?

I have several thermal mugs, two of them by the same brand, have the same look, shape and size except that one is in steel (inside and outside) and the other one, plastic. Both have an insulating ...
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0answers
30 views

How thermal conductivity affects sound propagation

I would like to better understand how thermal conductivity is related to sound propagation in an insulator. In particular I have read that sound attenuation due to thermal conductivity is given by $$\...
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1answer
34 views

Thought experiment: Could the Earth be cooled by pumping refrigerant?

Possibility of Using a Refrigerator to Cool the Earth I understand that the Earth as a whole cannot be cooled directly by radiating energy away for theoretical reasons. Waste heat has low entropy; ...
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31 views

Optimum insulation for minimal temperature variation [closed]

I have little knowledge of physics and have been unable to find a general mathematical analysis of this problem. I’ve tried to present it in a general way but the underlying principles are applicable ...
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1answer
74 views

Question about the definition for the scalar magnitude of a symmetric 2nd-rank tensor in a given direction

The scalar magnitude $S$ of a symmetric 2nd-rank tensor $S_{ij}$ in a given direction having direction cosines $l_i$ is given as: $$\tag{1} S=S_{ij} l_i l_j$$ This result is obtained by starting with ...

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