Heat is energy transferred from one system to another by thermal interaction. In contrast to work, heat is always accompanied by a transfer of entropy. Heat flow is characteristic of macroscopic objects and systems, but its origin and properties can be understood in terms of their microscopic ...
1
vote
2answers
155 views
How does blow-drying a mirror keep it from steaming up again?
After a hot shower, the mirror in my bathroom steams up. When I try to clear it with a towel, it immediately refogs. Yet once I use my hair-dryer, it will clear the fog and the mirror will stay clear.
...
1
vote
3answers
260 views
Problem with an electricity / thermodynamics assignment
I've been trying to figure this one out for a while on my own, so I'd like to ask for your help if you could offer some.
The task states:
A heater made out of a wire with a diameter $R = ...
1
vote
2answers
79 views
Why not assimilate nuclear waste into “igneous” rock?
I was reading a question about why not to drop nuclear waste into volcanoes; the short answer is it would come back out and not be rendered safe.
Ignoring the cost and energy requirements, why can't ...
1
vote
1answer
91 views
Is $E=mc^2$ reserved to nuclear physics?
I was wondering, while putting a log in my fireplace, how much energy the piece of wood would give. The most famous formula poped into my head: $E=m \cdot c ^ 2$!
Is this formula applicable to a ...
1
vote
1answer
438 views
Will adding cold water to a hot iron pan harm it? Why/why not?
Adding cold water to a aluminum pan can be harmful.
Is this same with iron pan too?
How can it be explained?
1
vote
2answers
138 views
Using CO2 to air condition a room
I'm trying to determine how much dry ice or liquid nitrogen I would need to cool 3300 cubic feet, about 90,000 liters of air, from about 100F (37.78C or 310K) to about 90F (26.67C or 299.81K). I'm ...
1
vote
3answers
91 views
How can a strong water current be cold
This is a layman question.
If heat is the motion of atoms, how can a fast moving water current be cold?
1
vote
2answers
334 views
What causes the vacuum in my bento box?
I can't think of a good title for my post, sorry about that.
I've got a lunch box (called a bento box) Basically it's a plastic box with a plastic lid with a rubber rim around the lid to create an ...
1
vote
2answers
607 views
design of the heat exchanger…in chimney
I want to design a heat exchanger in a chimney in order to utilize heat from chimney. I have done several experiments, but I could not determine the exact length of tube (carrying water), such that ...
1
vote
1answer
365 views
Do materials cool down in the vacuum of space?
Do materials cool down in the vacuum of space?
If yes, how does it really work?
1
vote
2answers
472 views
Why did the microwave oven only heat my coffe half as much as expected?
A sticker on my microwave oven states its output effect to be 750W, which is 180 calories per second. This means that heating 250g of water by one degree celsius would take 250/180 = 1.4s.
Now, my ...
1
vote
2answers
1k views
Microwaves vs Gas or Electric Coil heating of a water boiler in a typical household
Wouldn't it be more energy efficient and or safe to use microwaves to heat our home's water boiler instead of using dangerous gas or hot electric coils that could catch other things on fire? I'm kinda ...
1
vote
1answer
248 views
Heat transfer, Cold vs. Hot
If you boil water inside a pot the outer rim bubbles first, I imagine because its hotter. Does that same concept apply for the inside of a refrigerator for example. Is the outer rim always more ...
1
vote
2answers
2k views
What happens to the absorbed light energy?
When light comes across with a solid material, some of it is reflected, some of it passes through and some of it is absorbed. I understand the reflection and passing through, but I don't understand ...
1
vote
2answers
171 views
If I put 3 bottles of water next to each other in the fridge, which one is cold first?
I was wondering: If I put three bottles of water next to each other in the fridge, which one is cold first? Does it matter? Is it the one in the middle because it gets refrigerated by the other two?
...
1
vote
2answers
2k views
How does watering your plants help protect against freezing?
I've always heard that watering plants if the temperature goes a few degrees below freezing will help prevent them from freezing, but I've never quite understood the physics behind it. Can you guys ...
1
vote
2answers
28 views
Heating and Recooling of an Object
Consider a piece of metal of length $L$ and linear thermal expansion coefficient $\alpha$. We eat the metal $\Delta T$ degrees, causing the metal to increase to length
$$ L' = L + L \alpha \Delta T$$
...
1
vote
2answers
73 views
Is it possible to condense heat?
Suppose that I have a warm room. Is it possible to condense the heat of the room into a small object so that the room turns cold and the small object very hot?
If it's possible: How?
If it's not: ...
1
vote
3answers
119 views
Unclear how heat interacts with Navier Stokes
I am playing around with an Navier stokes solver and I'm having trouble introducing heat.
Am I right in thinking this would be introduced in the ${\bf f}$ term of ${\partial{\bf u}\over\partial t} = ...
1
vote
2answers
189 views
A hot object exposed to low temperature in a vacuum doesn't lose heat?
I heard somewhere that if the human body were exposed to outer space where the temperature is extremely low, the human won't actually feel cold because in a vacuum, the heat energy doesn't have ...
1
vote
3answers
191 views
Can one heat up a vacuum?
I've got a question about heating a vacuum. If there were, say, a container in space, at 2.7 degrees kelvin (the typical temperature of space, if I'm not mistaken) and as empty as space (as close to ...
1
vote
2answers
119 views
How cold should it be outside for a hot coffee mug to break?
So I like to go outside for a morning coffee with a cigarette. In winter here it's usually between -5C to -25C, and sometimes it gets down to -30C and colder. Assuming that my coffee is about 75-80C, ...
1
vote
1answer
98 views
Why does the aligning of magnetic dipoles in a material cause its heat capacity to decrease?
This is with regards to adiabatic magnetisation.
1
vote
2answers
658 views
Specific heat capacity
Which of two objects at the same tempreature can cause more intense burns when you touch it: the one with the greater specific heat capacity or the one with the smaller specific heat capacity and why?
...
1
vote
3answers
352 views
Maximum efficiency for a counter-current heat exchanger (double flux controlled motorized ventilation)
I am not sure if I can explain the question correctly because I don't know the name of this mechanism in English.
This is my explanation attempt: In a house, a tube is expelling the air from the ...
1
vote
1answer
207 views
Per unit area, is there more heat transfer through the open top of a mug or the side walls?
I had a mug of hot coffee cool too rapidly for my liking the other day, which made me wonder what was the greater contributor to heat loss for a typical open-top ceramic mug: the open top, the walls, ...
1
vote
1answer
468 views
How does heat transfer between two atoms in solid material?
Been looking at heat equation and it's derivation, according to Wikipedia it uses 2 mathematical assumptions. My problem is that although it all seems OK, what is the physics of heat transfer in ...
1
vote
1answer
98 views
What are the patterns appear after kernel averaging?
Having a 2D map filled uniformly by random values (Figure:top-left) to demonstrate a disordered phenomena, the next maps are ...
1
vote
2answers
534 views
Extracting heat energy from a material
Does it violate any physical laws to take a portion of the energy out of a system and use it? Specifically I'm referring to heat. (Kinetic energy).
For example, if you have a material which has a lot ...
1
vote
1answer
55 views
What is the term for heat generation by a flowing fluid?
I would like to know more about the heat distribution over time in a flowing liquid. To this end, I consider the Navier-Stokes equation (where the coefficients may be temperature dependent) and the ...
1
vote
3answers
93 views
What's the physical difference between a convective heater and an infrared heater?
Could someone please explain why there are 2 types of space heaters-- one that is convective and one that is infrared? Why does the first one not radiate and why does the second one not heat the air?
...
1
vote
2answers
341 views
Why can't I evaporate water without wind, just heat? (not boiling,evaporating!) Or can I?
So here is the thing, I searched all over the internet for this but all the sources say that I need wind because the process of evaporation goes as follow:
Water particles at the top layer with ...
1
vote
1answer
189 views
Physics of the electric hot plate
For an electronics experiment, I began wondering about the electric hot-plates (specifically the temperature dependence over time). If I were to measure the given temperature over time, I assume that ...
1
vote
1answer
490 views
Why does burning magnesium explode when sprinkled with water?
Magnesium powder burns extremely well and reaches temperatures of 2500°C. However, attempts to extinguish such a magnesium fire with conventional water (e.g. from a garden hose) only make it worse: ...
1
vote
1answer
342 views
When a color LCD/LED display is off it is black, when on it is colored. What color to light is an LCD/LED display
When a modern display using pixels is turned on its colors are different than the black that the screen is actually made up of. When put in light, such as sunlight, does the screen react to the color ...
1
vote
1answer
316 views
Heat absorbed by a room
How can one calculate the amount of heat absorbed inside a room in a single day using the temperature readings of the day?
If the temperature has to be reduced from 30C to 20C how much heat should be ...
1
vote
1answer
271 views
Given two boiling temperatures and pressures, how can I find the latent heat?
I am given the fact that at a certain pressure a liquid boils at a corresponding temperature, at a different pressure it boils at a different temperature, and then I am asked to find the latent heat ...
1
vote
1answer
367 views
Understanding the Seebeck effect
Thermoelectricity is, as I understand it, the difference in voltage between the hot and cold ends of two dissimilar materials. If two materials are connected at two different junctions, the hot ...
1
vote
1answer
493 views
How does liquid convert to gas on getting thermal heat energy?
Say for example, when we heat, water converts to steam gas. How does it happen? What happens underneath giving rise to breaking of bond between molecules in liquid state and spreading them in gas ...
1
vote
1answer
3k views
How to calculate heat exchange/deltaT in a moving volume of fluid?
I am building a preheater for a maple syrup evaporator and am going to use the steam generated by the heating process to pre-heat the incoming sap from, say 5 degrees C to (hopefully) something on the ...
1
vote
1answer
189 views
Why do regular lattice elements heat up faster?
For example iron. A metal spoon heats up much quicker than a wooden/plastic one.
Why?
1
vote
1answer
139 views
What arrangement of sound waves would be needed to heat air in a typical sized room?
From what I understand, sound is simply the jostling of the molecules that make up the air in a specific pattern, widely known as waves. I also know that these are longitudinal waves. If we were to ...
1
vote
4answers
298 views
Physics of a burning log of firewood
According to my knowledge, heat is nothing but the result of the vibrations of atoms and molecules. I guess this mean that in heating up a gas or liquid, we are increasing the rate at which the ...
1
vote
1answer
260 views
ratio between work and heat [closed]
I am really stuck on a problem in my textbook:
Water is heated in an open pan where the air pressure is one atmosphere. The water remains a liquid, which expands by a small amount as it is heated. ...
1
vote
1answer
103 views
Temperature and latent heat
Building a bronze stature we make a mold and pour in the liquid bronze when the bronze hardens we remove the mold.
The mold is made of 3 Kg of steel and the statue has a mas of 1 Kg. The specific ...
1
vote
1answer
113 views
Determine the flow and amplitude equation for thermal energy (with Del operator)
It is a question vector calculus and Maxwell's laws. I put it this way. Let's say, we are working in a $3$-Dimensional space ( e.g $x\cdot y\cdot z = 4\cdot3\cdot2$, a certain room/class of that size ...
1
vote
1answer
178 views
Efficiency of parallel and sequential heat pumps
Consider two identical heat pumps, for example, split-system air conditioners. There're two ways to make them work - in parallel or sequential. Parallel means that "hot" radiators of the machines are ...
1
vote
1answer
257 views
How would I calculate the convection coefficient in transient convection?
So I have faced a problem dealing with transient conduction and I need a little help with the problem solving concepts. I need to determine how long it would take to reach the final temperature but I ...
1
vote
1answer
667 views
How much disolved oxygen is removed by boiling water?
Apologies if this is a chemistry question
I've read that drinking water contains dissolved oxygen to the tune of $10\:\rm{ppm}$.
I've also read that raising the temperature of water will remove some ...
1
vote
1answer
134 views
2d or 1d conduction in this scenario?
There is a rectangular fin attached to a heat exchanger with a base temperature of 350K. The fin has uniform properties and experiencesa uniform heat generation. It also experiences heat transfer with ...
