Questions tagged [heat-conduction]

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Source of light in a heating coil

When we connect a heater coil to an electric circuit then according to "joules law of heating effect" due to its resistance it will produce thermal energy . My question is why light is ...
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Quantum effects on phonon transport?

Phonons are the quanta of vibrations in a crystal lattice. As the name suggest, phonons are already a quantum phenomena but when studying heat transfer the phonons are mostly very classical (wave ...
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How to find external surface temperature with unknown heat transfer coefficient?

I am trying to calculate the thickness of insulation required for a certain design. The known properties are the inside temperature, target surface temperature and thermal conductivity. From what I ...
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Why water vapor condenses on glass? [closed]

I've read an answer to this question that stated glass was colder than air, causing this transfer of energy from the vapor to the glass, creating this condensation. But why is the glass colder than ...
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Understanding steady state in heat transfer on a molecular level

I am trying to get to a molecular understanding of what happens before a steady state is achieved. I understand that macroscopically, the temperature of any point along the rod won't change when ...
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Why is the tar condensing inside the Wood Pyrolysis retort?

I am facing some issues in wood pyrolysis. Doing in a 100 ltr drum. A lot of bamboo is not turning into proper charcoal. The tar is condensing inside the pyrolysis drum. It may be one of the reasons ...
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Why is heat current same in two different materials connected to each other?

I recently learned in my physics class that the heat current at a boundary between two materials with different thermal conductivities is equal. Why is this so? When these two materials are not ...
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Why is heat current constant in a cylinder?

In a hollow cylinder made of some uniform material with thermal conductivity k, length L and inner radius a and outer radius b, the total heat current (dQ/dt) has a constant value in the direction of ...
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Understanding thermal models of cavitation

Cavitation is a phenomena that occurs in liquids when the local static pressure drops below the vapor pressure; bubbles form within the liquid. I am studying cavitation in incompressible, two-phase (...
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How can I model convection in a simple and effective way?

I have a project in which we're trying to model heating of a room. We are modelling the room in 3D. The room has realistic walls, windows and a door, which will loose heat through them. To balance the ...
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Water heating up as it flows through a perfectly insulated pipe

I'm trying to solve the following problem: We want to know what the outflow temperature of the water, $\rm T_{water, out}$ is as a function of time. Knowing: Water is flowing through a thick pipe in ...
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Steady State Temperature Profile of a Centrally Heated Pipe (or rod)

This question is inspired by a question from 'Robomaze'. The OP now seems to have lost interest in it but I still think it's an interesting issue. I've cleaned up the original question and made it ...
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Thermal Conductivity and Specific Heat Capacity: Calculating the Time Required for a Volume of Water to Cool

I'm a chemist by training and have experience solving differential equations, though it has been insufficient in solving the problem I have. Here is the problem: I brew my own beer and I'm building a ...
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Is the gradient of temperature zero in case of steady state and no source of heat?

$$ k \frac{dT^2}{d^2 x} +heat generation =\rho c \frac{dT} {dt} $$ In steady state and in the absence of heat source, the equation becomes: $$ k \frac{dT^2}{d^2 x} =\ 0 $$ If the laplacian of ...
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Types of heat transfer

I’m having some problems to identify the type of heat transfer involved in a practical experiment I’ve carried out. In my experiment, I heat a metal rod by making water vapor flow inside the rod, then ...
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Gas to solid heating?

I am doing a study on the phenomenon of pyrolysis. This is purely a study of the underlying physics. Generally, in practice, pyrolysis feedstock is heated conductively but we are examining the energy ...
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What does divergence of heat flux mean?

Before stating my question I will start with two definitions: Heat flux also named as thermal flux, is referred to as heat flux density, heat-flow density is a flow of energy per unit of area per ...
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Is the heat flow $\dot{Q}$ in a series system is same for all its constituent parts? Question is wrong

Question is wrong. You can close it. Actually I was learning about the conduction method of heat transfer. I found that there is thermal resistance for a system which can either be series or parallel. ...
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Do inviscid fluids have thermal conductivity?

Inviscid fluids are an idealization and they don't have viscosity. The no-slip boundary condition DOESN'T apply to them and consequently, these fluids won't display a hydrodynamic boundary layer. I've ...
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Confusion regarding effects of changing any mass in Principle of Equilibrium of Mixtures/Principle of Calorimetry

My book says that a calorimeter is made of thin copper sheets, and the thinner the better since less mass means less heat capacity, which means for the same temperature change, less heat is required ...
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Why is all heat released by a deflagration wave conducted upstream?

I'm having some trouble understanding the phenomenological analysis used to calculate the thickness of a 1D deflagration wave (Combustion Theory by Williams, page 135). I quote the text below: ...
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How does boiling work?

Let's assume that the exact boiling point of water is 100 degrees. Now I have a stovetop and a pot. I add the water to the pot, put it on the stovetop and turn the temperature to exactly 100 degrees. ...
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Is everything in nature a source of heat? [closed]

A source of heat is something from which heat is originated or obtained, whereas heat is the energy transferred due to temperature difference so heat is relative as the temperature difference is. Thus,...
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Questions about some analogies between heat and Shroedinger equations

Let $Z(x,t)=(4\pi t)^{-1/2}e^{-x^2/(4t)}$ and $G(x,t)=(4\pi t)^{-1/2}e^{-x^2/(4it)}$ be fundamental solutions of the heat $u_t=u_{xx}$ and Shroedinger $iu_t=u_{xx}$ equations. Function $Z(x,t)$ ...
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Trouble with deriving Fourier Number in Unsteady Heat Conduction analysis

Consider a metal ball being heated in a furnace. Thermal energy is convected to the ball while simultaneously getting conducted within. The Fourier Number, in unsteady heat conduction analysis like ...
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In case of heat transfer in a rod, why actually steady state occurs after a time (why sections of rod cant further absorb heat)?

In heat transfer across a rod, why actually steady state occur? why temperature of sections of rod don't further increase as heat is even flowing through them and as whole rod is of same material then ...
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Why does the steady state exist In thermal conduction?

In thermal conduction,why doesn't transient state go on continuously,why does steady state exist?why after some considerable time A metal bar sttached to a sink and source comes to steady state where ...
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How to determine qualitatively the metallic/semimetallic conduction behaviour by comparing chemical potential and thermal energy?

Suppose a material has a semi-metallic dispersion and we want to study electronic transport with small applied electric and magnetic field. Let the chemical potential be positive-valued (i.e. the ...
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1D Heat Equation with different materials

I'm trying to solve a 1D-Heat Equation with Finite Difference Method in python. The object I'm trying to depict has "Material A" with a high conductivity on the outside and a core of "...
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Transient heat equation in a tube (polar coordinates) with uniform initial temperature and uniform boundary temperature

I tried to solve this problem: I have a tube of inner and outer radius $R_1$ and $R_2$ (like coppers tube for fridges). The temperature at the exterior of the tube ($\rho = R_2$) is maintained to $...
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3 answers
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Is thermal conduction really radiation?

I have no doubt thermal conduction is a useful model for heat transfer, wherein kinetic energy is transferred between particles when they collide. However, according to explanations that I believe are ...
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Can conduction alone cause thermal equilibrium?

From the little I know about physics and conduction specifically, it seems to be that a system in which the heat transfer is done solely by conduction, cannot reach thermal equilibrium. I'll preface ...
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Is there a name for the type of boundary condition where the initial boundary values are known but are not held constant over time?

I'm exploring the heat equation to model a particular 1D scenario, and I understood the Dirichlet and Neumann boundary conditions, but neither are sufficient for my scenario. Assuming a rod of length ...
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Where should a cold carton of milk be placed in a styrofoam picnic box to keep it cold/cool for the longest time?

If you have a cold carton of milk that you place on the floor of an otherwise empty (apart from air) styrofoam picnic box (and replace the lid after) in a room at room temperature, should you place it ...
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How do we justify the equation of heat current through a perpendicular cross section?

Fourier's equation for heat flow: $$ \frac{dQ}{dt} =-KA\frac{dT}{dx} $$ is usually derived by quoting its similarity with electric current and comparing variables to arrive at a similar equation. ...
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How can you determine how fast (m/s) heat will travel through a material being heated on one end?

I was wondering how fast heat will travel through rectangular glass bottle, heated on a tray under vacuum. I work in a lab where an inert atmosphere glovebox is used, and when moving glass bottles ...
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ODE or PDE heat conduction

question about heat conduction. I was casually reading through an ebook and came across the following: Could you tell me where this last equation comes from? I can follow the solution to the problem ...
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Isn't the Newton's cooling law for heat convection too macroscopic for CFD simulations?

In Computational Fluid Dynamics simulations, the space is discretised into a huge number of tiny cells and, therefore, one has the opportunity to use a model of heat transfer that takes into account ...
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Different definitions for Thermal Resistance

I have been reading on the topic of thermal resistance and I came across these two different definitions multiple times. The first one: $R = \Delta T/\dot{Q} = L/kA $ and the second one $R = \Delta T/\...
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Heat equation with specific boundary conditions

I am interested in a specific problem of 1-dim. heat transfer. A rod (metal) with coordinate $0 \le x \le d$ of length d is in contact with two reservoirs $i = 1,2$ with fixed temperatures $T_1 < ...
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What does the concept of "Entropy Flow" mean in detail?

Recently a found a paper on the thermoelectric effect: https://williamsgj.people.cofc.edu/Thermoelectric%20Effect.pdf When I started with Chapter 5 "Irreversible Thermodynamics" I struggle ...
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Will a reflective surface inside a lit tube increase luminosity disproportionately more than heat?

Okay, so I have a long tube, shaped like an irregular octagon across its Cross section (wider than tall), with vertical slats running along the length of the tube (like in this picture) The tube is ...
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A room with a heater in contact with walls as a heat sink

I have to calculate the increase of my room temperature as a function of the heater's power. The easiest way of doing it is: $$T_1=\frac{P\Delta t}{C_v V n }+T_0$$ $T_1$ is the final room temperature, ...
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1 vote
1 answer
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What are phonons actually?

I was reading about heat conduction in solids wherein it was stated that in crystalline solids heat conduction takes place via lattice vibrations. In relation to this, the word phonon was used. In ...
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3 answers
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What is the difference between thermal conductivity and thermal diffusivity?

Please excuse me, for any inability in my way to frame the question. I myself had a hard time making myself understand what was the doubt I really had :P. Also, I'm studying heat transfer at ...
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Casimir heat transfer (Ballistic heat transfer) paper

In general, in the paper Casimir assumes that between the boundaries of a crystal the heat transfer can be imagined as electromagnetic radiation between two hollow bodies connected by a tube (at least ...
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3 answers
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Why can a very large body of water not store summer heat?

On this page, it states "The key disadvantage of using a very large body of water to achieve heat exchange with a relatively constant temperature is that you are not able to store summer heat in ...
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Radiative heat transfer inside opaque solids?

The heat equation assumes that the heat transfer inside of a conductive solid is proportional to the temperature gradient. However, we might imagine that every element of the solid radiates energy to ...
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Inverting the heat equation

I have a wire that stretches from $x=0$ to $\infty$. The temperature at $x=0$ is given by the unknown function $f(t)$ for $t$ from $-\infty$ to now ($t=0$). I can measure the temperature of the wire ...
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1D flow equation with source inside the medium

How do I set up and solve a 1D flow problem which looks like this - i.e There is a source of water injecting directly into the medium at a point $a$ distance away from the origin. The source is time-...
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