Questions tagged [thermal-conduction]
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117 questions
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I have some questions about heat transfer (heat evaporative minichannel heat sink)
Problem Description
As shown in the diagram, an evaporative minichannel heat sink with 48 minichannels is being analyzed. A glass plate is attached to the top of the minichannels for flow ...
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Dark baking pan versus light baking pan
There are a ton of articles on baking websites that state baking in a dark colored pan works different than using a light colored pan.
The only thing I can think of is that the pans are of different ...
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The origin of Joule heating from scattering
My understanding is that Joule heating originates from the transfer of electronic energy to the lattice. This post states that impurities contribute to the dissipation of electrical energy. However, ...
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Physical Significance of power density of a point source of heat
What does the power density of a point source of heat signify?
I'll illustrate this with the help of an example
Consider a sphere of radius R and thermal conductivity k with a point source kept at ...
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Finite difference scheme for solving 3D stationary diffusion equation in inhomogeneous medium using spatially irregular orthogonal discretisation grid
I try to numerically solve the 3D stationary diffusion equation in a medium with spatially inhomogeneous conduction.
Analytical problem
In the context of this post, heat diffusion is considered. The ...
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Heat current through a material with variable conductance
Can anyone explain how temperature at any point on the rod (or any material in general) varies with distance when conductivity is variable. This question came to my mind from my physics test last week,...
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Physics behind gold+silver space blanket placement
In the first aid and mountaneering, "space blanket" or "astro foil" is used for protection against cold enviroment or as first aid after burns. There are many different versions of ...
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Factoring the volume of the water inside the pipe in a heated pipe calculation
I have been using a formula to calculate how much heat needs to be generated by a heated pipe in order to raise the temperature of the water flowing through the pipe by a certain amount, e.g. from 10𝑜...
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How does a pizza heat up in the oven?
Sometimes if you bake a frozen pizza (and are impatient) it can happen that the center of the pizza is still cold while the edges are already burning hot. How is this possible?
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Measuring the thermal resistance of a window
I would like to compare the R-value (thermal resistance) of several windows in my house. Is there a simple experiment I can do, with home equipment, to measure it with reasonable accuracy?
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Let say we have two different fluids, what are the main properties they have that is needed in order to determine convection constant h
I have searched a lot on the thermal interaction by convection between two different fluids having different properties, but did not find anything useful, all of results were talking about only ...
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Heating a piece of metal using a circuit - calculating the time [closed]
If I have a circuit sitting on the surface on the top of a rectangular slab of metal, and I want to heat the metal using resistance heating in the circuit, how can I calculate how much in watts the ...
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Is there a general equation for calculating the heat gained from drag?
Not just the amount of energy converted to heat, but specifically, the amount of energy a part would heat up? I am trying to calculate the heat imparted on the fins of a rocket as it passes through ...
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Why is the heat curve of water a straight line?
This excellent video plots the heat curve of water experimentally by measuring the temperature every second (see below). The apparatus was a Corning PC-400D Hot Plate with a Vernier Go!Temp ...
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Simplified scenario: evaporative cooling vs convective heating between water and air
While thinking through this question I thought of a simplified scenario that would model one of the extremes:
A body of water with mass $M_W$, temperature $T_W$, and surface area $S_W$ is surrounded ...
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Analogy between Galilean relativity and thermal physics?
So I was thinking about an analogy, that could potentially be used for an explanation or at least to take a different perspective on thermodynamics as it is. But I don't want to abuse the analogy, so ...
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How to calculate the thickness of ice formed on a lake with a known temperature gradient?
I've been working on a problem involving the formation of ice on a small lake. The surface of the lake is in thermal equilibrium with the air at $-4^{\circ} \mathrm{C}$, while the bottom remains at $4^...
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Effect of starting temperature on thermistor still air time constant measurement
The still air time thermal time constant is stated in datasheets and is understood to be the time it takes for the sensor to cool to 63.2% of the difference between itself and the ambient temperature. ...
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How to estimate thermal conductivity of a sample?
There is a rectangular sample whose emissivity is known, and I want to estimate its thermal conductivity. A heater with a known heat flux is applied to one end of the sample and a fixed temperature is ...
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Can a thermistor's heat capacity be calculated using the still air thermal time constant and dissipation constant? (using $C = τ·h·A$)
Thermistor data sheets typically state the thermal time constant in still air and the dissipation constant in still air.
For a body heating or cooling, the thermal time constant can be calculated as $\...
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Why is transfer of heat very slow as compared to transfer of sound in solids?
If I heat a one-meter long iron rod at one end, the heat takes several seconds to reach the other end, while sound takes fractions of a second. Why is it so?
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For a 2D anisotropic medium, how can it be shown that $k_a = \sqrt{k_1 k_2}$ when $\theta = 45^{\circ}$ and $W/L=1$?
where $k_1$ and $k_2$ are the principal conductivities of the medium and $k_1 \ne k_2$; $\theta$ is the angle between the $k_1$ axis and the $x$-axis; $W$ and $L$ are the width and length of the ...
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Heat transport in earth's gravitational field
Consider a Carnot machine that exploits the earth's atmospheric temperature gradient using air at lower altitude as a warm reservoir and air at higher altitude as a cold reservoir. Due to the ...
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Effect of humidity and $CO_2$ on heat transfer coefficient for a small object (breath on a thermistor)
I am writing a paper on monitoring breathing using small thermistors (in my case a narrow cylinder of 1.5 mm x 3 mm) placed just beyond the nose and mouth (e.g. 1–2 cm) and I need to explain the ...
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Why does capillary in gas thermometer have a temperature and pressure gradient?
I have been learning thermodynamics using Heat and Thermodynamics by Zemansky, in which he mentions
The gas in the capillary connecting the bulb with the manometer has a temperature gradient, that is,...
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Does the isotropy definition of a perfect fluid imply no heat conduction?
Weinberg defines a perfect fluid (Chapter 2, Section 10) as one where each fluid element appears isotropic in a reference frame moving with that element.
From the definition of the stress-energy ...
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Does Pipe Temperature Directly Correlate To Water Temperature? [closed]
I need to know if just by taking a boiler flow pipe temperature that will tell me the water temperature that is flowing through the pipe.
For example if the water from the boiler travelling through ...
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Entropy change of an isolated system consisting of two thermally conductive blocks of equal isochoric heat capacity at different temperatures
A classic example considered in most introductory treatments of elementary thermodynamics consists of two thermally conductive (e.g., metal) blocks placed in thermal contact. In particular, I find ...
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Should I hold a baby formula bottle to cool it down faster?
This is an interesting and somewhat surprising physics problem - holding a hot object in your hand will cool it down faster, even if the air around is colder. I guess that 90% of people would be ...
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Estimating Heat transfering by measuring [closed]
Consider the setup with closed chamber with two flat metal objects with know dimensions.
The first object can be heated or cooled by peltier module and the second one is placed on top of the first one....
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Definition of convection heat transfer not unambiguous? [duplicate]
What is actually the definition of convection in the context of heat transfer, if there is one?
Wikipedia states:
Convection (or convective heat transfer) is the transfer of heat from one place to ...
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Heat equation two stage process - Additivity? some other approach?
I'm struggling a bit how to apply a standard solution to the heat equation to my own practical problem. I have some intuition, but do not know whether this intuition is justified. I don't understand ...
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Why clothes keep us warm?
I want to understand why clothes keep us warm. I understand that they reflect back thermal radiation and also trap air thus significantly reducing cooling due to thermal convection. My question is, do ...
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Heat exchange speed of two liquids separately vs their mixture
I'm quite oblivious about basic high school physics, so pardon my misuse of terms and inability to google the answer.
I want to solve a puzzle that I face in my daily routine. Suppose I want to make a ...
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Why are absorbing bodies hotter over time than reflecting bodies?
I recently learnt about energy transfer by EM Waves and came across the formula for momentum transfer, i.e.
Δp = U/c → perfect absorption
Δp = 2U/c → perfect reflection
then why do absorbing bodies ...
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Temperature of plasma sputtering magnetron
This question is in regards to DC magnetron sputtering for coating surfaces. My main goal is to determine how much heat will be seen by the anode, cathode and the target. As well as to determine what ...
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Thermal resistance in heat transfer
Can a material experiencing heat generation be represented by thermal resistance and
included in a circuit analysis? If so, why? If not, why not?
Consider a case with the solid cylinder with the heat ...
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Rate of heat flow through rod of variable conductivity
Incase wher we have an object( a rod ) with its conductivity not uniform say varying with temprature. Then will heat flow through it at same rate from every cross section of the object?
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Glass having huge thermal mass when stirring drinks
In the book "Liquid Intellegence: The Art and Sience of the Perfect Cocktail", David Arnold says this:
My question is how the glass affects the chilling? What does he mean by the glass ...
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Lumped body analysis
$k$ - thermal conductivity,
$h$ - heat transfer coefficient,
$\rho C_p$ - Volumetric heat capacity,
$T$ - temperature
$T_\infty$ - Temperature of exposed cooling surrounding environment
Consider two ...
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At what circumstances is Nusselt's theory of evaporating falling films valid?
Nusselt's theory of evaporating falling films assumes no convection and neglects the effect of inertia. At what circumstances is that valid? Any books or articles that discuss this in depth would be ...
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How to deal with temperature drift when computing thermal conductivity with molecular dynamics?
Background
In the $NVE$ ensemble, thermal conductivity, $\lambda_T$, can be computed from molecular dynamics (MD) using the Green-Kubo relation (Allen and Tildesley)
$$\lambda_T = \frac{V}{k_B T^2} \...
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Fully coupled thermal-stress analysis in Abaqus/Standard- equations
I'm simulating a fully coupled thermal-stress problem with linear elastic material in Abaqus and comparing the results with my own implementation of the same problem in FEniCSx. The weak form in ...
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Physics of microwave oven
I am looking for a definitive discussion of the physics of microwave oven - I mean I would like to see actual evidence in favor of this or that explanation, rather than just popular physics/...
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Why some materials expand linearly on heating while others have areal and volumetric expansion for the same temperature difference?
Why some materials expand linearly on heating while others have areal and volumetric expansion for the same temperature difference? What actually cause materials to expand?
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Heat equation in 1D with Robin conditions [closed]
I am tasked with analytically solving the boundary value problem as follows: the 1D heat equation for temperature $T \equiv T(x,t)$ in a solid extending from $x = 0$ to $x = L$ and located in air at ...
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General differential equation for Energy transfer
In my textbook of Fundamentals of Momentum, Heat, and Mass Transfer by Welty, it is said that $$\nabla \cdot k\nabla T + \dot q + \Lambda = \rho \frac{Du}{Dt}+\rho\frac{D(gy)}{Dt}+\mathrm v \cdot \rho ...
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Approximating the temperature of the wall of the heating jack of a reactor
Suppose we have a reactor containing some fluid that we heat through a heating jacket containing some other fluid.
I am interested in approximating the temperature of the wall of heating jacket. I ...
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Why slow compression with conducting walls should be isothermal?
I know that for an isothermal process heat transfer is necessary so process should be slow and walls should be conducting for heat transfer to occur as a process cannot be isothermal and adiabatic at ...
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Conduction in liquid and gas
Is this condition correct, "if liquid and gas heated from top, then it will be possible for 'conduction' to occur" ?
One reason i can think is :
when liquid or gas is heated from sideways or ...
