Tagged Questions
4
votes
0answers
72 views
Mechanical Equivalent of Heat
Recently I have been looking up James Joule's experiment regarding the mechanical equivalent of heat. After viewing some drawings of the apparatus, I assumed that the lines holding the weights would ...
0
votes
0answers
20 views
Total massflow through heat exchanger
I am working on a project and I stumbled on a problem. The project is to design a heat pump to replace the old system (actual problem, not some homework problem). There are 100 or so induction units ...
0
votes
3answers
72 views
How do you determine the heat transfer from a P-V diagram?
I doubt this question has been addressed properly before, but if there are similar answers, do direct them to me.
I am currently studying the First Law of Thermodynamics, which includes the p-V ...
0
votes
0answers
19 views
Heat transfer in fluid between two horizontal plates vs unconfined case
I often see the correlation for turbulent heat transfer between liquid cells published by Globe and Dropkin (1959). In the original paper the fluid was confined between two horizontal plates and ...
0
votes
1answer
679 views
Beginner Thermal Dynamics Question [closed]
A syringe is set up filled with air (mainly N2 and O2) as shown in the diagram below. The surface area of the syringe is 15.3 cm2. The initial pressure inside the syringe is Pi = 114 kPa and the ...
3
votes
1answer
52 views
How can I understand a Vortex Tube and its efficiency?
A Vortex Tube takes a pressurized input stream, most typically of a gas, and creates two output streams with a temperature differential. Apparently, it has been described as a Maxwell's Demon.
Both ...
1
vote
0answers
48 views
Calculate how hot PLA will become
I am trying to attach the shaft of a brass heating tip to a PLA component. My problem is that the tip will have to reach a temperature of about 200°C and the PLA can only handle a temperature of about ...
22
votes
6answers
2k views
How do whisky stones keep your drink cold?
From a discussion in the DMZ (security stack exchange's chat room - a place where food and drink are important topics) we began to question the difference between how ice and whisky stones work to ...
1
vote
0answers
29 views
Calculating the change in entropy in a melting process
I have a homework question that I'm completely stumped on and need help solving it.
I have a $50\, \mathrm{g}$ ice cube at $-15\, \mathrm{C}$ that is in a container of $200\, \mathrm{g}$ of water at ...
0
votes
1answer
46 views
Calculating the coefficient of thermal expansion in liquid
I am trying to write a matlab function that calculates the coefficient of thermal expansion of water from a given temperature. From what I understand the thermal expansion coefficient is calculated as ...
-2
votes
1answer
40 views
How do I calculate the heat lost or gained by surroundings? [closed]
How do I calculate the heat lost or gained by surroundings (Q surr) given mass ($m$), change in temp ($\Delta T$), and specific heat ($c$)? What equation would I use?
How can I tell whether it's lost ...
-1
votes
1answer
72 views
The effects of heat on gravitational fields
In boiling soapy water, globs of soap coalesce as the temperature increases to boiling. Does this mean that temperature increases the gravitational pull of bodies?
0
votes
1answer
48 views
Time constant of ice melt
I'm familiar with problems of "how much ice can you melt given some amount of energy", but I'm writing to get some clarification on the time constant of this event. This question might be somewhat ...
-1
votes
0answers
54 views
Newton's cooling law
I want to know few things regarding the practical of Newton's cooling law.
1). What are the other possible ways of making external conditions constant except using two calorimeters one within one?
...
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
$$ L' = L + L \alpha \Delta T$$
...
0
votes
0answers
26 views
Heat of adsorption from fugacity data
I have a set of data relating the fugacity ($\approx$ pressure) to the loading for a given set of temperatures. There are three temperature sets each having five fugacity vs. loading points.
The ...
1
vote
0answers
30 views
What is the meaning of $h_L - h_H$ for a heat engine?
My problem gives me a Carnot cycle heat engine with water as its working fluid, with $T_H$, $T_L$, and the fact that it starts from saturated liquid to saturated vapor in the heating process.
I need ...
-1
votes
1answer
88 views
Sensible heat question (solving for temperature)
If $55 034.175 \rm{kJ }$ of heat are transferred to $150 \rm{kg}$ of ice at a temperature of $-12.15 ^\circ \rm{C}$, calculate the temperature of the resulting water.
Using $Q = mc(t_2-t_1)$ or ...
3
votes
1answer
74 views
What pressure or tension occurs in a glass jar when I pour boiling water inside?
Sometimes it happens that when you pour a boiling water into a glass jar, it cracks. Since glass is very hard material and resilient to pressure, the tension must be very high. Is it possible to ...
3
votes
3answers
243 views
How can my water cool down more quickly?
I have a cup and I can only pour hot water inside, I wanna know whether the heat will dissipate more quickly with more water or less water?
How about the occasion when my cup is well covered?
1
vote
0answers
71 views
How much money does an unused but plugged-in cellphone-charger waste in a year, if its not getting warm?
Is it right as xkcd states:
You can use heat flow to come up with simple rule of thumb: If an unused charger isn’t warm to the touch, it’s using less than a penny of electricity a day.
Or, more ...
6
votes
2answers
147 views
When should I take wine out of the fridge - transient heat transfer problem
I am hosting a dinner tonight for which I'll be serving white wine (Riesling to be more specific). Generally white wine is best served chilled (not COLD!) at around ...
25
votes
1answer
931 views
Rubber band stretched produces heat and when released absorbs heat.. Why?
I always used to wonder why this happens..
when one stretches a rubberband to nearly it snapping point holding it close to your skin - preferably cheek(helps feel the heat), it emits heat. While ...
3
votes
2answers
136 views
What's the basic difference between heat and temperature?
Temperature is usually seen as a calibrated representation of heat but what about latent heat?
Eg. Ice and water have different amounts of heat at 0 degree c.
2
votes
2answers
197 views
Heat transfer between two surfaces
Suppose I have surface A in contact with surface B, if I apply Fourier's law of heat transfer, which $K$ should I use, $K_a$ or $K_b$?
Essentially asking whether the same block of material heats ...
0
votes
1answer
58 views
Indicators on how even the heat is distributed?
I'm wondering if there are any good indicators on how even the heat is distributed on an object (for simplicity, a flat object maybe)? What are the possibly reasonable ways to maximize the evenness if ...
1
vote
2answers
190 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
0answers
24 views
Does a flame produce free electrons? [duplicate]
Possible Duplicate:
Does Fire Conduct Electricity? Why?
Is fire plasma?
Does a flame produce free electrons ? Or is the answer sometimes depending on the chemicals ? Does the answer depend ...
0
votes
1answer
125 views
Confused about fire?
Im confused about fire.
The way I see it :
Heat creates (kinetic) energy in mass and this creates stronger vibrations of atoms.
When those vibrations are strong enough the electrons interact ...
3
votes
1answer
128 views
Why aren't two systems in thermal equilibrium the same as one system?
I am reading Molecular Driving Forces, 2nd ed., by Dill & Bromberg.
On page 53, example 3.9, we consider why energy exchanges between two systems from the point of view of the 2nd law.
We ...
5
votes
1answer
138 views
Can an induction coil heat two layers of metal?
Imagine we have an induction coil which is strong enough to heat a sheet of metal. We can put a sheet of ferromagnetic metal close to the coil at distance $h_1$, and it gets heated to temperature ...
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?
...
8
votes
4answers
733 views
What happens when you heat vodka in a microwave?
Since ethanol has a lower dielectric constant than water would the water heat up and boil before the ethanol? Would the water transfer heat to the ethanol and, since ethanol has a lower boiling point, ...
3
votes
1answer
115 views
How can gas from compressed air can “take” heat from surrounding environment?
I have recently been reading about why a can of compressed air gets cold when the air it contains is discharged. From what I understand the change from a liquid to a gas requires energy and therefore ...
3
votes
0answers
75 views
Thermal imaging camera [closed]
I'm making a tea bag experiment (Make a hollow cylindrical tube from light paper e.g. from an empty tea bag. When the top end of the cylinder is lit, it takes off.) I need to know how hot air is ...
2
votes
0answers
31 views
In a non-degenerate plasma, why are e-e collision negligible compared to e-ion for thermal conduction?
I'm trying to make some order of magnitude estimates of heat transfer in stars - to better understand 1) why conduction is said to be negligible (for non-degenerate matter) and 2) when convection ...
0
votes
2answers
96 views
Stealing heat, or not?
Say I hook a 1KW steam engine to the steam heat in my apartment, and generate 1KW of electricity (the engine is 1KW mechanical, not 1KW thermal) from it, so I don't have to pay ConEd.
That means I ...
0
votes
0answers
131 views
Constant volume specific heat
A monatomic ideal gas is confined to move in two dimensions. What is the constant volume specific heat for this gas?
Consider a system of N independent harmonic oscillators moving in two dimensions. ...
0
votes
1answer
69 views
What is the difference of work $W$ and thermal energy $Q$ in thermodynamic Stirling-process for ideal gas?
What is the difference of work $W$ and thermal energy $Q$ in thermodynamic Stirling-process (in simple form) for ideal gas?
I think that you need work to preserve this process and you bring thermal ...
3
votes
1answer
144 views
Rayleigh-Benard Convection
I found this nice paper about RB convection. However I am confused by what is going on page 6. In particular why we are suddenly using Helmholtz equation to find spatially periodic solutions. Aren't ...
4
votes
0answers
121 views
Thermodynamic relations from Gibbs-Duhem
Given the Gibbs-Duhem relation
$V dp = S dT - N d \mu$, I am having trouble deriving the following identity:
$\ (\frac{\partial N}{\partial \mu})_{V,T} = N (\frac{\partial \rho}{\partial p})_T$
...
4
votes
3answers
319 views
Can I take heat from the air and convert it to electricity?
Its a summer day and the air in my house has been heated up. I could switch on my air conditioning, but then I'd be using energy from the grid in order to reduce the amount of energy in my house.
...
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, ...
5
votes
4answers
1k views
After what speed air friction starts to heat up an object?
I understand that air friction cools off an object at low speeds. For example, if you blow on a spoon of hot soup, it cools off. Or if you swing a hot frying pan in the air, it cools off faster.
But ...
7
votes
4answers
668 views
Why does pizza cheese seem hotter than the crust?
When I eat hot pizza or a melted cheese sandwich, the cheese feels a lot hotter than the crust or bread: in particular, the cheese might scald the roof of my mouth. but the crust will not. Is this
...
5
votes
1answer
101 views
Which came first, movement or heat?
According to my measly understanding of the universe, when particles hit one another, some of their kinetic energy is transformed into heat. But when we heat particles (for instance, putting a bucket ...
0
votes
1answer
460 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 ...
0
votes
1answer
121 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
votes
1answer
190 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 ...
-1
votes
1answer
96 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 ...
