# Questions tagged [heat-conduction]

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1answer
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### How does a light source / laser transfer energy to a material?

I am trying to understand the physics of how a laser is able to heat a solid. My understanding so far is that when photons are incident upon a body (e.g. a metal) the momentum of the photons is ...
2answers
56 views

### 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 ...
1answer
40 views

### 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 ...
1answer
30 views

### Is there convection between two volumes of air at different temperatures?

As I have learned in my engineering classes convection takes place when a fluid meets a surface of both different temperatures. My question: can this also be evaluated for two volumes of air at ...
1answer
20 views

### Proof for net heat flow law for radiation

So this has been bothering me for quite a time: $$\frac{dq}{dt}=e \sigma A(T_1^4-T_0^4)$$ Net radiation is $emission-radiation$. According to that if you observe: Consider a situation where a body is ...
1answer
24 views

### Stefan Boltzmann law and absorptivity

I have this really big confusion , and it is about the Stefan Boltzmann law Does this law works for absorption? Or is it only radiation I have seen my textbook replacing emissivity with absorptivity ...
2answers
38 views

### How does Stefan Boltzmann law work for absorption?

I have come across the Stefan Boltzmann law and I have a couple of doubts based on its use in the net heat flow expression $$dq/dt = e A\sigma T^4$$ Now according to my textbook If the temperature of ...
0answers
39 views

### Transient heating of semi-infinite solid - time it takes for given depth to reach a specific temperature [closed]

Given a heat flux and the thermophysical properties of an object, how is the time to reach a specific temperature at a given depth determined for the case of no convective loss and with convective ...
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 ...
1answer
43 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 ...
1answer
27 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 ...
1answer
38 views

### Why does glass break into pieces rather than just melting or cracking

In the given link of a video. The maker puts hot lava on different kind of types of glass . https://youtu.be/wLNBLUm3CZQ my question is why does glass break into innumerable pieces rather than just ...
0answers
31 views

### Could this imaginary cooling solution work?

Imagine a perfectly insulated ideal closed cylinder. Inside, at the two ends there are two bodies, one with the temperature of T the other with temperature -T. Between the almost touching bodies with ...
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 ...
2answers
86 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 $k$ ...
0answers
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2answers
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### After sweating ,why do our body cool down faster under a fan?

The sweat on our body evaporate taking energy from our body in the form of heat.the temperature of our body decreases and we feel cool. Thus sweating cools down our body. Now why does our body cool ...
1answer
143 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 ...
4answers
2k views

### Why would frozen sausages defrost faster in water?

My mom uses frozen sausages for a soup. She defrosts frozen sausages by submerging them in water (room temperature I believe). She claims this makes them defrost faster. She learned this from some ...
2answers
40 views

### Will “stationary” air sorrounding a hot pipe from a wood stove act as insulation with a given time?

The inner pipe (colored in red) radiates considerable more heat than the current one so I'm planning on extending the more thermally conductive one so that it heats better. Will removing the outer ...
1answer
36 views

### Physical interpretation of the heat equation with variable coefficient

I would want to know what is the physical interpretation of the heat equation with variable coefficients such that: $$u_{t}-\frac{1}{1+t^2}u_{xx}=0$$ well, I think I got it, it means that the ...
1answer
39 views

### Heat transfer in glass top ranges

The "glass" in glass top ranges apparently has quite low heat conductivity as areas just a short distance from the heating element don't get so hot - especially compared to a metal surface which has ...
0answers
19 views

### Should I determine the wattage of my heater based on the heat conduction equation, or the specific heat capacity equation?

I know of the equation equating rate of heat flow to the product of a materials thermal conductivity, area of contact, temperature difference, divided by the thickness of the material. However, I ...
2answers
61 views

### Does heat flow always in the direction of maximum decrease?

I was wondering if at a given gradient temperature heat could flow in any direction satisfying moving from a higher to a lower temperature. Or it can only flow in the direction of gradient? Consider a ...
1answer
75 views

### Definition of the rate of heat flow

According to Wikipedia the rate of heat flow is:$$\frac{\Delta Q}{\Delta t}=-kA\frac{\Delta T}{\Delta x}$$ Where to evaluate? I can't understand where we must evaluate this rate. In the hottest ...
1answer
76 views

### Why did my water boil “differently” this time?

Yesterday, I put a pot of water on the stove and set it to boil to make some pasta. I have done this many times but this time the boiling was qualitatively different than normal. Why would it be ...