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 ...
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464 views
Heat Exchanger Calculation
I have a tank of oil at 55 degrees c. I plan to run a copper pipe 8mm in diameter (1mm thickness) into a coil 15m long inside the tank. For all purposes of assumption, the copper pipe is perfectly ...
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1answer
125 views
What is the ion drag mechanism in dielectric heating?
While reading about dielectric heating on Wikipedia, I read about the ion drag mechanism but there wasn't enough information about.
I know there is another Phys.SE question talking about the ion drag ...
3
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1answer
191 views
Why do non-stick frying pans work?
Modern non-stick frying pans use a mixture of titanium and ceramic that is sandblasted onto the pan surface, and then fired to 2,000 °C (according to Wikipedia).
Can anyone explain (at the molecular ...
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1answer
148 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 ...
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1answer
98 views
I need help with this question on Heat Capacity
A calorimeter has a Heat Capacity of $70 J/K$. There is $150g$ water with a temperature of $20^oC$ in this calorimeter. In this, you put a metal cube of $60g$ with a temperature of $100^oC$. The ...
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1answer
127 views
What would jumping into a pool and feeling cold be called? Conduction, or convection?
This was another question from my son's workbook. It said:
...
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0answers
168 views
Simple heat transfer question [closed]
You add an unknown volume of milk of $5.2 ^\circ C$ to a cup of coffee ($40 mL$ of water, temperature: $80.3 ^\circ C$). After a while of stirring the temperature reaches $73.2 ^\circ C$. The ...
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4answers
4k views
The difference between heat and temperature
So as I understand it, heat energy of an object is the SUM of all the kinetic
energies of the molecules of the object (upto constant factor).
The temperature on the other hand is the AVERAGE of the ...
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2answers
156 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.
...
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1answer
58 views
Could we really charge metal plates using microwaves?
While skimming through Dielectric heating, I read that they use microwaves to charge the plates. How do they do that?
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2answers
345 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 ...
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4answers
317 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 ...
21
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1answer
695 views
Energy in bolognese reduction - lid on or off?
Generally, to let my bolognese thicken, I leave the lid off in order to "let water vapor escape." I am however distracted from enjoying the taste because I'm having doubts that my physical reasoning ...
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0answers
54 views
Experimental Physics [closed]
A heater and thermocouple are used to measure and control the temp. T of a sample at $T_{0}=250^{o}C$. A feedback circuit supplies power P to the heater according to the equation $P=P_{0}+G(T_{0}-T)-D ...
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3answers
169 views
What forces are at play when molecules wiggle (due to heat)?
What forces are at play when molecules wiggle (due to heat)?
Or in other words, What makes them move?
3
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1answer
163 views
How to properly bake a ultra high vacuum chamber?
I need to get rid of water excess in my vacuum chamber, and for that there is the procedure of baking. In order to do that there are several things that one needs to consider, the power, heat load, ...
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1answer
166 views
Does a concave or flat bottom pan use heat more efficiently?
This may be anecdotal.
Playing in the kitchen I realized the frying pan comes with both a flat, and a concave bottom. So here's the question -
Given two pans made of brass, one has a concave base ...
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0answers
142 views
Air condition and net heat [closed]
I have attempted to solve a problem, but my answer is not quite the same as in the book. Thus, I would really appreciate it if someone could confirm/disconfirm whether or not my solution is correct.
...
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1answer
91 views
Physics of homebrewing heat exchangers
In homebrewing on of the key steps when brewing with extract is to rapidly chill the wort from boiling temperatures to about 80F in 30 min. This is needed to reduce risk of environmental ...
3
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1answer
91 views
Which heated, partially filled bottle will explode first?
This is in reference to a pasteurization discussion on a homebrewing forum.
I have four closed bottles which will explode if containing too much pressure. Two of them are 50% full (A and B), and two ...
1
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1answer
261 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. ...
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1answer
450 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?
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2answers
349 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 ...
3
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1answer
203 views
What is the difference between infrared heat and “regular” heat?
In Feynman's terms temperature is the speed at which atoms are 'jiggling'. Now, let's suppose I've just eaten a sizable dinner, and my body temperature just got a tad up. Am I emitting more photons in ...
3
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1answer
556 views
Where does the lost energy go in a rubber band powering a rotating shaft?
Okay, I'm no physics whiz, and this has me stumped. You know those toy airplanes you can get with the rubber-band driven propellers? You twist the propeller a bunch of times, and this stores ...
3
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5answers
316 views
What is the meaning of following expresion $C=\frac{\delta Q}{dT}$ mathematicly
Our professor raised the following question during our lecture in Statistical Physics (even so it's related to Thermodynamics):
Many text books (even wikipedia) writes wrong expressions (from ...
3
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2answers
207 views
Why does it take until the middle of summer before lakes have warm water, but desert sand heats up in hours?
My sister asked me this question and I keep thinking that water would conduct heat much faster than sand. Hence the energy transfer of heat across the lake does not allow it to heat up soon. Sand on ...
2
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3answers
136 views
Heat Equation Equalities
While studying the heat equation, I ran into a few equalities that I cannot understand.
For example, Fourier's law of heat conduction claims that
$$\varphi(x,t)=-K_0\frac{\partial u}{\partial x},$$
...
4
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1answer
70 views
Where does the heat flow in the Earth's crust switch from primarily solar to geothermal?
Ok, maybe more of a geology question than physics, but maybe somebody has been involved in modeling these heat flows?
Essentially I'm asking if we know what sort of depth the heat source becomes ...
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2answers
224 views
Is carbon dioxide a greenhouse gas? [duplicate]
Possible Duplicate:
What experiments prove the greenhouse effect?
I am seeking for a proof that CO2 is a greenhouse gas. I posted this on Skeptic.SE recently but found no help in seeking ...
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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.
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1answer
193 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 ...
3
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1answer
439 views
Calculating time to heat cold water in bowl of hot water
How would I calculate the time it takes to heat a given volume of water to a given temperature with a given temperature T1 when it is submerged in a volume of water with a temperature T2
Estimation ...
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3answers
279 views
How can there be heat in a vacuum?
I keep reading in the Physics World focus issue on vacuum technology about scientists creating high temperatures in the vacuums etc.
If heat is caused by thermal energy being radiated from particles ...
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2answers
614 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 ...
2
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2answers
328 views
Why water will stay on a piece of toilet paper?
I think everyone has tried to blow air (breath) on toilet papers. The papers will get wet. I believe the holes diameters on a toilet paper should be much larger than diameters of water molecules. (The ...
2
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1answer
65 views
Is Joule heating only between charged particles?
The Wikipedia page for Joule heating explains
"It is now known that Joule heating is caused by interactions between the moving particles that form the current (usually, but not always, electrons) and ...
2
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0answers
100 views
Problems in the modern semiconductor/electronics technology?
From what I have read, the problem with modern semiconductors/electronics seems to be quantum tunnelling and heat. The root of these problems is the size of the devices. The electrons are leaking out, ...
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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?
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0answers
64 views
How is pool boiling dealt with by today's process design methods?
Designing evaporators and industrial reboilers often requires at initial stages of dimensioning (i.e. when the support from a finite element software tool to model the system of interest, isn't yet ...
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1answer
505 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: ...
2
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1answer
118 views
Why is the crust of my meat pie only slightly warm?
I just cooked a meat pie in the oven. Almost immediately after pulling it out of the oven, I felt that the crust was only slightly warm, but when I cut it open the filling felt very warm. I can't ...
1
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1answer
104 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 ...
2
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2answers
1k views
Why I will feel colder when I get out from a swimming pool?
A friend of mine told me that because water heat capacity is higher. He also mentioned that it was similar to alcohol on skin effect.
Assume that there are 3 situations.
1. I did not get wet
2. I got ...
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1answer
114 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 ...
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1answer
57 views
What is the average total heat incident on Earth's surface each hour?
Just what the title states
Some part or the other of this Globe faces approximately towards the Sun during each 24 hour period. What is the total amount of heat (in calories) incident on average ...
3
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2answers
177 views
Density of states via a Laplace transform
Is this formula correct?
$$ \frac{-1}{\pi}Im\int_{0}^{\infty}\!dt~\exp(Et)\Theta (t)\exp(i \epsilon t) ~=~ \sum _{n}\delta (E-E_{n}), $$
$$ \Theta (t)~=~ \sum_{n}\exp(-tE_{n}) ,$$
and I have used ...
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1answer
493 views
How to calculate specific heat capacity of an alloy
I have done an experiment in which I measured the specific heat capacity of a coin. I would like to compare the results to the actual value. I have found out that the coin is made of Cupronickel alloy ...
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2answers
157 views
Second Law of Thermodynamics, heat and quantum-level explanation
I heard somewhere that the second law of thermodynamics is stating that some heat (energy) becomes unusable for work (at the scale of the whole universe). Why is it like that? Can't heat be converted ...
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1answer
372 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?
