Questions tagged [thermal-conductivity]

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Thermal contraction for cooling

I've calculated by separation of variables function of temperature $T(x,y,z,t)$ for a cooling cube. I wanted to know how much the cube will contract in one dimension after 10 second of cooling, during ...
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Does adding cold water to evaporative air coolers actually produce colder air?

Or should it be the other way around, because hotter water evaporates easier than cold water? I know this sounds stupid, so just hear me out. I use an evaporative cooler and add normal room ...
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1answer
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Is 1D diffusion equivalent to diffusion in symmetrical coordinates?

Say you are modelling heat diffusion from hot air into a sphere. The thermal conductivity is the same at all positions on the sphere. Using the 1D diffusion equation, the temperature of the sphere is ...
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3-Omega method outside of um scale

Currently being fascinated by the 3-Omega method for measuring thermal conductivity. As a hobbyist, I'm currently not capable of making the sensors directly on the samples I would like to test. After ...
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1answer
56 views

Relighting a candle from its smoke, and being burned?

Having been extinguished, a candle can be relit from the resulting trail of smoke, even from meters away. However despite this apparently high level of heat, paper, bystanders, etc… are never ...
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1answer
26 views

Coefficient of thermal expansion [closed]

Is the coefficient of thermal expansion of a particular material under constant pressure constant?
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26 views

Pressure Drop in a Pipe due to Pressure Increase

I'm trying to calculate the pressure/temperature change in a pipe due to heating. Basically, assume there's a pipe, the pipe wall is at an increased temperature, how to calculate the pressure, ...
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3answers
92 views

Why do we cool water with ice? [closed]

I've came up with the following question: Why do we cool water with ice rather than with steel given that the last one has a bigger thermal conductivity?
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2answers
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Difficulty in theoretical understanding of Newton's law of cooling

Newton’s law of cooling states that the rate of heat loss of a body is directly proportional to the difference between the body’s temperature and that of the surroundings when there is a breeze. I can ...
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1answer
32 views

How do I calculate equilibrium temperature of a pot of water with some food in it, knowing only the equilibrium temperature of the pot of water? [closed]

Say I have a pot with 3L water on a stovetop, at an equilibrium temperature of 75ºC. I then add 1kg of meat at 20ºC to it. How do I calculate the final equilibrium temperature I should expect the pot'...
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1answer
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Heat Transfer on boiling water

Let's say I'll boil water on the stove from 25°C to 100°C, what heat transfer happens? Is it conduction (heat warms up the pot), or is it convection (causes water molecules to move away from the ...
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Analytical solution of the thermal conductivity equation [closed]

What is the exact analytical solution of a 1D thermal conductivity PDE: $\dfrac{\partial T}{\partial t} = \alpha\cdot \dfrac{\partial^2 T}{\partial x^2}$, where $T$ = temperature, $\alpha$ = thermal ...
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3answers
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Where would you sit? [closed]

Suppose on a summer afternoon, you have two chairs one made of steel and other of wood. Which one is better to sit on if you prefer colder one, provided they are at the same temperature?Would your ...
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1answer
57 views

Why heat flow perpendicular to the isothermal surface?

I was reading Feynman-Leighton-Sands 's physics lecture note in Volume 2 chapter 2 when deducing the equation $$h = -k\ \text{grad}T$$ It seems we use the assumption that heat flow orthogonal to the ...
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2answers
209 views

Characteristic timescale of a can of beer?

Modelling a 440 ml can of beer by Newton's law of cooling, the temperature difference between the can and its surroundings (e.g. a fridge) decays exponentially in time at a rate determined by the e-...
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1answer
27 views

What is the temperature profile of hot and cold fluids for a double pipe parallel flow heat exchanger?

In books, they just mention the temperature profile is exponential. Can someone help me come up with the exact temperature profile (the relation) for the hot and cold fluids in a double pipe parallel ...
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1answer
47 views

Is it wrong to derive Log mean temperature difference (LMTD) of a Heat Exchanger, this way?

I tried deriving the LMTD of a parallel flow double pipe heat exchanger by first finding the temperature profiles of the hot and cold fluid and then averaging them over the entire length of the Heat ...
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1answer
29 views

While determining LMTD for a heat exchanger do we assume, the tube wall to be at a constant temperature (no variation along radial direction)?

The derivation of Log Mean Temperature Difference (LMTD) for a Heat exchanger at preliminary level makes some assumptions like, constant specific heats, steady state operation, no changes in kinetic ...
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1answer
37 views

Heating of a metal rod

On heating a metal rod from one end ,after sometime it reaches a steady state. Is the temperature of the end directly receiving the heat is equivalent to the temperature of the heat source ? Even in ...
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1answer
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Effect of coloring on emissivity at temperatures below 150C?

I'm working on Aluminum/Copper heat sink design optimization and came across this thought. The heat source on which the heat sink is going to be placed is approx 100C. Forced convection is absent, so ...
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1answer
50 views

Heat diffusion in an oven

I have this problem where I am preheating an oven to reach $n^\circ$. So lets say within the oven there's a heating element at the bottom, which in turn heats up the rest of the oven. Assuming that ...
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Is there a Relationship between thermal Hall conductivity and coplanar/non-coplanar spin?

Does the magnitude of the thermal Hall conductivity depend on whether spins are coplanar or not? Also, if you have any theoretical references, it would be helpful if you could present them.
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3answers
45 views

Heat loss of an insulated pipe vs an uninsulated pipe

So I have this exercise: A hot water pipe consists of a copper tube of length $L = 1$ m, of thermal conductivity $\lambda_{1} = 380$, has an internal radius of $R_{1} = 6\cdot10^{-3}$ m and an ...
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3answers
51 views

Rate of Heat Flow

I was given a problem that asks me for the heat transfer power, also specifying that the heat transfer power is directly proportional to the difference in temperature. Does it refer to the rate of ...
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2answers
91 views

Deriving the time needed until Thermal Equilibrium

Two materials of mass $m_1$ and $m_1$, specific heat capacity $C_1$ and $C_2$ and temperature $T_1 > T_2$ are separated by a conductive solid with thickness $L$, area $A$ and heat conductivity $k$ ...
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4answers
56 views

Can an object in space have a high kinetic energy, but at the same time not release heat?

Can an object in space have a high kinetic energy, but at the same time not release heat? If the answer is no and the body has to radiate heat, why and how does it happen?
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Sanity check: Is water a good thermal insulator?

Last week, we had a few exceptionally cold days that froze a lot of ponds and rivers. On a hike through the forest, I broke through a weak spot in the ice, and soaked my boots with ice-cold water. I ...
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1answer
54 views

Estimating Debye and Fermi temperatures

Given the sketch of the behavior of the heat capacity against the temperature, How do I estimate the Debye and Fermi temperatures? Thank you in advance
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2answers
60 views

Does color have an effect on thermal conductivity?

I understand the color of a surface can affect its emissivity and albedo, but that is for radiation. For conduction does; for example, painting a bowl different colors affect its absorptivity when it ...
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Thermoelectric Seebeck Crystalline Structure

Recently reading about Crystalline Structure in metals and other forms of doping. Being that thermal energy has so called phonons could it be that crystals in metal having an effect like that for ex. ...
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25 views

What does it mean for resistance, as it appears in Ohm's law, to be an integral, evaluated over the body as a whole?

In literature I read: The three linear flux laws mentioned are: As seen, a correspondence exist between the hydraulic conductivity $K$, thermal conductivity $\lambda$, and electrical conductivity $\...
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1answer
19 views

Increase in temperature when a stretched wire suddenly snaps

When a wire is stretched under a force F so as to obtain an increase in length Δl the work done by the external force on the wire is (FΔl) Now the work done by the wire against the force is 1/2(FΔl)...
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32 views

Does a temperature gradient in a single metal rod generate an electric field?

Based on this question, I was trying to understand what happens with the electrons when there is a gradient of temperature between the ends of a metal rod. I put the contacts of a voltimeter at the ...
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2answers
258 views

A question about thermal conductivity and heat transfer

Put a piece of cold pizza on top of a sheet of aluminum foil and then stick it in the oven to heat up. After about 10 minutes, the pizza should be nice and hot—the aluminum foil is the approximately ...
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1answer
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Which one would represent complete combustion?

Say that I want to burn some fuel, so I'm aiming for a complete combustion, hence CO = 0 So I have 2 possibilities a) CO2 quantity = maximum, CO quantity = 0 (complete combustion) and O2 quantity = ...
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2answers
27 views

Why is the rate of energy conducted in a rod equals the rate of energy released from the surface at the other end?

Assuming energy is released as convection only,we always do questions by equalizing, $$P_{\text{conducting}} = Q/t = KA (T1 - T2)/L = eA(dT).$$ Assume the system is at Steady State. Why does this ...
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1answer
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Derivation of general equation of heat transfer & entropy

In Landau & Lifshtiz Volume 6 on fluid mechanics we derive the general equation of heat transfer by starting with the expression $$ \partial_t \left( \frac{1}{2} \rho v^2 + \rho \varepsilon \right)...
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Why doesn't ice in a glacier feel as cold when I touch it as the ice I get from my freezer?

When I was in Iceland, I went to a tour in a glacier and I remember the ice that was there. It looked and felt like a huge amorphous block of glass: hard, smooth, not wet, and not that cold. Not as ...
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Prior probability for transient cooling time constant

I am trying to fit the Transient Cooling equation to data, but I need the prior probability for the time constant $ \tau $. The error function for my data is, $$ \epsilon = \tau \dot{T} + T - T_{env} ...
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2answers
86 views

Why does porridge start steaming more after the hob is switched off?

I have noticed that when I cook porridge in a saucepan, and stir it with a spatula, it only steams a little bit. But the moment I turn off the (gas) hob underneath, and keep stirring it with a spatula,...
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27 views

Through which medium is most of the heat transferred down (downwards) a glass tube filled with water: the glass walls or the water column?

If a much hotter object is attached to the tube from the outside, and the heat in question is transferred to the part of the tube that is below the source of heat, so there is no convection. ¨ The ...
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1answer
39 views

What is the difference between rate of cooling and rate of heat loss?

I had a perception that rate of cooling and rate of heat loss are synonymous because the rate at which it looses heat indicates the rate at which it is cooling but this question changed my view There ...
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1answer
32 views

Steady State conduction of cylindrical pipeline

I have this problem involving conduction of heat: Suppose that $z = 0$ represents the ground level on a street where an electric cable is buried at $x = 0$ and $z = −D$. The ground is kept at a fixed ...
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Does the time of heating of multicomponent system depend on the order, in which the components are heated?

Let's say I have a source of heat, an engine, and two systems - cooling tubes and the air inside the car. Let the temperature of the engine be $T_e$, temperature of the other two components $T_s < ...
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1answer
33 views

Wind velocity dependence of the temperature of a cylinder

I am currently looking for a way to model the temperature as a function of time $t$ and velocity $v$ (of the wind rushing past), of a metal cylinder that is being supplied with some heat $Q$ (a ...
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1answer
14 views

Will the temperature reading of a thermostat change as a result of direct skin contact? [closed]

If I was to place my hand on a thermostat for an extended period of time, would this eventually result in the temperature reading rising after a period of time - or would the reading not be impacted ...
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2answers
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Why does thermal conductivity of an alloy becomes nearly flat from $0.2<x<0.8$ composition?

I am trying to understand the effect of alloying on the thermal conductivity of an crystalline alloy. I have found a great many papers where I see thermal conductivity sharply decreases from 0 to 0.2 ...
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1answer
84 views

How long should I wait to steep my tea?

This is not a homework question, this is a real question that I have. I like to drink green tea, and I use an electric kettle which brings the water to boiling. You can purchase kettles which bring ...
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1answer
26 views

Is there any formulated relationship between the concentration of s solution and its specific heat capacity?

I've seen in this answer that there is an inverse relationship between the two, as illustrated by the image below. Is there any formula describing this relationship though? Thank you very much!
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1answer
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Two identical solid cylinders, which transfers energy faster?

Two scenarios: Solid metal cylinder of $43^\circ$ C is placed in room of $23^\circ$ C Identical solid metal cylinder of $3^\circ$ C is placed in another (identical) room of $23^\circ$ C at the ...

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