Covers the study of (mostly homogeneous) macroscopic systems from a heat/energy/entropy point of view. Maybe combine with [tag:statistical-mechanics].

learn more… | top users | synonyms (3)

0
votes
0answers
26 views

Water in pot with a heat source beneath it to boil it, does the water move?

I mean if there is there heat transfer by convection in the water? since convection requires motion. if it moves, then how can i determine the velocity of the water?
0
votes
1answer
31 views

How is conversion inside heat engines of heat (random motion) to work (organized motion) explained in quantum physics?

When heat engines convert heat into work, they change the random motion of millions of particles into motion in a single direction. What is the phenomenon responsible for this alignment of ...
0
votes
1answer
21 views

How would an increase in temperature affect ooblek's (non newtonian fluid) viscosity?

Due to the fact that Ooblek (cornstarch and water), contains so much water and from what I understand it is non newtonian due to the particles suspended in it, would it therefore be correct to say ...
-1
votes
1answer
52 views

I can get a heating strip - why can't I get a cooling strip?

A typical heating strip is a flexible silicone material containing a resistive heater. However, I would like the opposite - something I can wrap around my experiment and use in a similar way to the ...
1
vote
0answers
28 views

Temperature versus heat for water

What does the kink(abrupt rise and fall) in region of phase change from liquid to vapour state in the following graph indicate? Does it indicate that temperature rise and fall abruptly during phase ...
0
votes
0answers
23 views

How to model a cooling system?

Suppose a system with a coolant, a pump, a radiator, and a constant power load object with some constant heat capacity. How can we model the dependence of the load temperature on coolant flow rate (or ...
0
votes
1answer
28 views

Thermofluid mechanics Temperature

A steel alloy specimen (mass 4 kg) at 80 0C is submerged in water at 10 C0. At thermal equilibrium state the temperature of the steel-water system is 40 C0. Calculate the mass of the water used. The ...
2
votes
3answers
142 views

Why engines don't melt?

The temperatures of internal combustion engines are well above the melting points of the component materials. For example, temperatures can reach 2200° C whereas the melting point of aluminium is ...
5
votes
3answers
82 views

Do hot metals radiate? (Thermography)

I was looking into thermography which talks about emissivities of metals and other materials. Polished metals which have low emissivity appear to be colder in thermal imaging cameras even if they are ...
7
votes
2answers
260 views

Does the size of bubbles in water brought to a boil ever vary as a function of the amount of water?

Some discussion surrounding this answer on Worldbuilding got me curious. When water is brought towards a boil, bubbles are formed. Anyone who has ever cooked anything whatsoever knows about this. ...
1
vote
0answers
11 views

Heat transfer problems [closed]

A tank contains 4000 lts of chromic solution at 33 degree centigrade is surrounded by a nest of brass tubes. Water at 80 degree centigrade is flowing through the tubes. How to calculate the heat ...
0
votes
1answer
19 views

Does the thermal expansion of a conductor contribute to its change in resistance when it is heated?

We know that the resistance of a conductor varies with a change in temperature and we are taught that this change occurs due to the change in resistivity of the material but does the thermal expansion ...
0
votes
1answer
22 views

Convective heat transfer coefficients - how do you calculate them?

How do you calculate (or otherwise determine) h_i and h_o (convective heat transfer coefficients) for a heat exchanger? Standard thermodynamics equation below for reference. My specific situation ...
0
votes
0answers
16 views

Rankine Cycle Reheat Mass Flow Rate

Having worked through many examples on the rankine cycle both non-reheat and reheat, i just have one question. Can the mass flow rate of steam be calculated given only the data below? Boiler ...
0
votes
2answers
35 views

Why does hot water gets cooler on stirring instead it should have gotten hotter

When we keep on stirring hot water vigorously it starts getting cooler. But we are increasing the random kinetic energy of the molecules of water. Heat is as it is the energy of RANDOM motion of ...
0
votes
2answers
23 views

Is the energy change $\delta Q$ form 16C-15C the same as 72C to 73C?

As the tempreature change is the same. so the amount of energy change should also be same. According to the foumula $$\Delta Q=m s \Delta T$$ So no matter form what temperature to temperature change ...
-1
votes
1answer
36 views

Is there a way to prove information entropy?

Information entropy is a very general term involving everything from the tendency of material to decay (in all the 3 meanings) to the fact that you need energy to sort your books alphabetically. ...
0
votes
1answer
15 views

refrigerating power of a cooling system

So i need to find the power of a cooling system. I have the $T_{coil}=-2^{\circ}C$. $T_{input}=6^{\circ}C$ and $T_{output}=1^{\circ}C$ . I also have mass flow rate of the fluid along with its specific ...
1
vote
2answers
38 views

Time taken for a layer of ice to form

The book I have gives the following derivation: Let the temperature of the atmosphere be $-\theta$ and the temperature of the water be $0$. Consider unit cross sectional are of ice, if layer of ...
1
vote
0answers
24 views

What is the relation between temperature and electromagnetic radiation emitted by a body? [duplicate]

I have read in thermodynamics that a body with high temperature radiates electromagnetic radiation. Does the frequency of waves increases with temperature? What is the mechanism? How does temperature ...
10
votes
5answers
2k views

Milk or sugar first to maximize temperature of a hot cup of tea?

If there is a hot cup of tea and we were asked to add milk and sugar, which mixing order would make the hottest tea? I personally think that the order doesn't matter, since sugar wouldn't change the ...
0
votes
1answer
28 views

Temperature of the System right after mixing water at different temperature

Let's assume that 100gm of water at temperature 25$^{\circ}$C and another of 300gm at 90$^{\circ}$C. After mixing both samples, we would eventually get a constant temperature (say $T^{\circ}_f$) and ...
0
votes
1answer
42 views

Temperature difference with continuous pumping

So, one of my friends gave me this problem to work out and I am stuck at a critical juncture -- guess I need to brush up on my thermodynamics. Basically, if I have a vessel and keep pumping it with ...
1
vote
1answer
32 views

What is the word describing the pairs: temperature and energy, chemical potential and particle number?

I keep forgetting the word describing the pairs of coupled quantities in stat. mech. e.g. inverse temperature $\beta$ and internal energy $E$ or chemical potential $\mu$ and particle number $N$. I ...
0
votes
2answers
39 views

Equations describing a counterflow heat exchanger [closed]

One of my experiments has a water-cooled apparatus. I plan on building a heat exchanger to keep the apparatus cool. However, I am not very good at thermodynamics and could use a hand. Also, from a ...
-3
votes
1answer
56 views

Convert ambient heat into electricity without violating laws?

This is an idea I've been playing around with for a while, even though many people tell me it's impossible. However, as far as I can tell, it does not actually violate the laws of physics. I am ...
0
votes
1answer
45 views

Newton's Law of Cooling [closed]

As shown in Figure 3.3.11, a small metal bar is placed inside container A, and container A then is placed within a much larger container B. As the metal bar cools, the ambient temperature $T_A(t)$ ...
0
votes
1answer
67 views

Is $\mathrm d(PV)$ the same with work received OR produced?

When I write energy conservation in thermodynamics problems, I write the internal energy before, the pressure energy before (so these two are the enthalpy) and then I add/substract the work and heat ...
0
votes
0answers
20 views

Fuel cell HHV vs LHV

I am calculating the maximum efficiency for a fuel cell, based on both HHV and LHV. For hydrogen and oxygen in a PEMFC I calculated these at STP as 82.9% (based on HHV) and 94.5% (based on LHV). I do ...
4
votes
2answers
97 views

Why is heat transfer reversible when temperature difference is infinitesimal?

I don't understand why heat transfer from hot reservoir to the system is considered reversible in this case: $T_{reservoir}$ = $T_{system}$ + dT but it's considered irreversible in this case: ...
1
vote
1answer
25 views

What is the temperature of compress air entering the atmosphere?

Hi to all of you enthusiasts, I have a 1 liter compressed air tank with around 207 bar of air pressure inside. It has been sitting out for a while and I am assuming its temperature has almost reached ...
1
vote
0answers
23 views

Is there a limit to how hot an object can be? [duplicate]

We know that speed of physical object cant exceed speed of light, a body cant be cooler than 0k, thus does there exist a limit to hotness of an object?
0
votes
2answers
55 views

What's the origin of electrical resistance?

i know relation ohm : $$R=\rho\frac{L}{A} $$ i want to know about resistance from view point small particle like atom,dipole: when we have a resistor,with a special voltage it has loss power: whats ...
1
vote
2answers
48 views

Why water's temperature is less than air?

I measured the temperature of water and found that it's less than room temperature. I think evaporation is the main reason of it. Are there any reason except evaporation for the less temperature of ...
0
votes
1answer
16 views

The difference between Gibbs and grand canonical potentials

To my understanding, Helmholtz free energy is a measure of the amount of work a thermodynamical system can perform. Following the same reasoning Gibbs and Grand-canonical free energies measure the the ...
1
vote
3answers
35 views

Heat transfer between water tank and room temperature

I have 20 gallons of water (salt water, but this might be irrelevant). These 20 gallons have a heater that maintains a minimum of 78º F. With the increasing temperatures during summer, the water ...
0
votes
0answers
19 views

Is there a temperature drop at the rotor plane of a wind turbine?

A wind turbine rotor produces power from the torque generated by the rotor blades. This torque arises from forces on blade elements which in turn are the consequence of pressure differences on each ...
3
votes
1answer
131 views

Why don't we observe spontaneous symmetry restoration in nature?

Why do we always observe spontaneous symmetry breaking in nature and not restoration? Does there exist some argument with the 2nd law of thermodynamics and the entropy of the universe increasing? If ...
0
votes
1answer
39 views

Will there be any heat transferred between water at 100 degrees Centigrade and steam at 100 degrees Centigrade if they are brought into contact?

Since heat transfer needs a finite temperature difference, it seems unlikely. However, the enthalpy of steam is greater than water (due to the latent heat of vaporisation) so is there a possibility ...
1
vote
1answer
45 views

Helmholtz Free Energy Representation of Ideal Gas

It is asked to find the fundamental equation of a monoatomic ideal gas in Helmholtz Representation, where $$F = U - TS$$ My Attempt :: $S$ of a monoatomic ideal gas is given by: $$S = Ns_0 + ...
1
vote
1answer
28 views

Using the central equation for inelastic collisions entropy change

I have what appears to be a simple question but I seem to be missing something. Take a constant temperature system where a ball travelling at $5ms^{-1}$ strikes a stationary ball and sticks to it in ...
0
votes
2answers
60 views

Free Expansion Of and Ideal Gas

We know that in free expansion of an ideal gas, no heat enters or leaves the system. We also know that $P_\text{initial}V_\text{initial}=P_\text{final}V_\text{final}$ is valid. If heat exchange ...
1
vote
0answers
8 views

Energy Per Dry Ice Mass Required By de Laval Expansion of Air?

There has been a lot of talk lately about CO2 extraction from air. Since there are rocket engines in which ice crystals precipitate in the exhaust when expanding into near vacuum, it seems dry ice ...
0
votes
4answers
58 views

Is the speed of sound in air constant?

In Optics lecture we took a formula for the speed of a wave which is: $$ v=\frac{\omega}{k} $$ where $\omega$ is number of complete vibrations per second: $$ \omega=\frac{2\pi}{\tau} $$ and: $$ ...
0
votes
1answer
62 views

What is the difference between a white object and a mirror in terms of heat absorption?

Will a white object be cooler than a mirror when exposed to direct sunlight? Or will it be the other way around? If mirrors bounce all visible light and some of the other elements of electromagnetic ...
0
votes
0answers
18 views

Can we define a whole body thermodynamic model for human?

we can consider human body as a thermodynamic system and an energy exchange system, so we can investigate efficiency, entropy, exergy, is there any thermodynamic model for whole body?
0
votes
0answers
28 views

Reversibility principle for classical mechanic

I'm studying this colloquium about quantum fluctuation relations for nonlinear thermodynamic, but I'm having a problem. Reading about the principle of micro-reversibility of the dynamic of a system i ...
0
votes
2answers
41 views

Does the increase of pressure of a gas also increase the energy?

It says that in adiabatic process, the heat is constant but the temperature is not. My question is, if you increase the pressure, the temperature is going to rise as pV = kT. But we know that the ...
0
votes
1answer
37 views

Why can't an ocean liner be powered by an engine that takes heat from the ocean water and eject ice cubes?

The following excerpt comes from the physics textbook Understanding Physics, by David Cassidy, Gerald Holton, and James Rutherford: A ball lying on the floor will not somehow gather energy from ...
0
votes
2answers
34 views

Maximum Work for A engine

We are asked to find the maximum work obtainable from an engine. Which the engine operates between two reservoir, one at T1 and another at T2. Given T2 > T1 , and the final common temperature is T3. ...