Stack Exchange Network

Stack Exchange network consists of 174 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [thermodynamics]

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

0
votes
1answer
9 views

Is spark from spark plug in SI engine(IC engine) not counted as a hot reservoir in Heat Engine

Are the Heat Engine(HE) and Internal Combustion Engine(ICE) not the same because ICE only exchanges the heat to the surrounding[only one reservoir]? And I have a question what if it's an SI engine ...
1
vote
4answers
24 views

Water mixture at different temperatures

Let's say that we mix homegeneously and instantly cold water at $t^\circ $ C and hot water at $T^\circ$ C (like in a water tap) in ratio $p:1$. My question is the following: What is the instant ...
1
vote
1answer
60 views

Thermodynamic Entropy seems to be contradictory

For an ideal gas the entropy change with energy is inversely proportional to temperature: This must yield: $$S=\frac 3 2 k_B \ln(T)$$ For various reasons, this equation is hard to find. However ...
3
votes
2answers
49 views

Question on the temperature dependence of the partition function

Let's just say we're looking at the classical continuous canonical ensemble of a harmonic oscillator, where: $$H = \frac{p^2}{2m} + \frac{1}{2} m \omega^2 x^2$$ and the partition function (...
0
votes
2answers
28 views

Is the *measured* temperature inside a hollow black body the same if we place a thermometer inside it or let it make contact with the body itself?

Imagine the inside of a black body shell with non-zero thickness. Inside the shell, there is photon gas produced by the shell [at a temperature much higher than zero, say $1000(K)$]. Is there is a ...
1
vote
1answer
35 views

Real gas heat calculation

For the Van der Waals gas we get a cycle consisting of 2 isobaric and 2 isenthalpic processes. The state equations are given as: $p = \frac {RT}{v-b} - \frac {a}{v^2}$ $\;$ and $\;$ $u = cRT ...
0
votes
2answers
47 views

Time for black body to cool to a given temperature

I'm trying to figure out the time required for a blackbody to cool assuming it only looses heat via radiation. I can estimate the mass, specific heat, surface area, emissivity, initial temperature, ...
0
votes
0answers
34 views

Maximum achievable mechanical work when heating water

I am doing a question about finding maximum achievable mechanical work when 1L of liquid water is heated from T₁ to T₂ at atmospheric pressure. The solution is $$W = \int_{T_1}^{T_2} \frac{T - T_1}{T} ...
2
votes
2answers
62 views

Work extracted from a pressure cooker

How much work can you extract from a turbine connected to a pressure cooker? The situation is modeled as a rigid adiabatic tank of volume $V_{tank}$, which initially contains water at a high ...
-1
votes
0answers
16 views

Determine Fuel Flow for the piston engine [on hold]

A piston engine produces 400 kW of power. Its sfc is 75 μg/J. Determine the fuel flow in kg/hr.
-1
votes
0answers
14 views

How to determine amount of heat absorbed by evaporator, power consumed by the compressor? [on hold]

A refrigerator having NH3 as refrigerant .Superheated vapor at 0c and 300 kpa enters the commpressor and compress isentropically till 2000kpa .water cooled condenser rejects heat from vapor till it is ...
1
vote
0answers
25 views

Advanced and Retarded Coordinates for Hawking Radiation

I am trying to solve the Klein Gordon equation near the horizon of a black hole. For a more accurate result I am using the Vaidya Metric in which the mass is a function of retarded time u. When ...
0
votes
0answers
17 views

Calculating the Variance of the Thermal state

We have a Harmonic Oscillator in the Thermal state $\tau(\beta)$ which is defined $$\tau(\beta) = \frac{e^{-\beta H}}{\mathrm{Tr}(e^{-\beta H})}$$ where $Z = \mathrm{Tr}(e^{-\beta H})$ is known as ...
0
votes
1answer
34 views

Calculate temperature decrease of an evaporating droplet

I have a small droplet of Cyclohexane which evaporates at room temperature and ambient pressure. I measured the volume at two different times ($\Delta V=1.5\times10^{-10}$ m$^3$). I would like to ...
0
votes
0answers
21 views

Conceptual meaning of Thermal States

Thermal states are generally defined as $$\tau(\beta)= \frac{e^{-\beta H}}{\mathrm{Tr}(e^{-\beta H})}$$ What are some physical statements one can make about them? A system in thermal equilibrium is ...
0
votes
0answers
18 views

Mean squared velocity in Poiseuille flow

For fully developed laminar Poiseuille flow in a tube, I came across this relation: $$ \bar{u^2} = 2 u_b^2 $$ where $u_b$ is the bulk or mean velocity, defined by: $$ u_b = \frac{1}{\rho A} \int_A \...
0
votes
1answer
36 views

Is a Radiation Structured BH a Possible Alternative to a Singularity? [on hold]

A BH singularity implies an undefinable region of infinite density that cannot be explained by current scientific theory. There's got to be other explanations for the formation of a BH that do not ...
0
votes
1answer
30 views

Fire -Thermodynamics

Could a steel box lined with Rockwool (interior only) be an adequate shelter during a fire? How can I determine the temperature inside of the box at peak fire temp? How long could someone withstand ...
-2
votes
0answers
24 views

How can I plan my physics learning? [on hold]

i would like to start learning physics on my own, but the problem is i dont know where to start, and what topics i should do after, Im a 16 year old learning at a high school with high level phycics, ...
2
votes
2answers
30 views

How to see Planck's radiation law as a consequence of Bose Einstein statistics?

Planck's law comes about from the following ingredients. 1) The mode density per unit volume in a cavity is $8\pi\nu^2/c^3$. 2) Within each mode, assume Boltzmann statistics i.e the probability of ...
0
votes
1answer
25 views

Calculating initial average energy of a thermal state

We are given a system with the Hamiltionian $$H = \sum_i \omega_i a^{\dagger}_ia_i \tag{1}$$ where $a^{\dagger}_i, a_i$ are creation and anihilation operators. I did the calculations and got the ...
1
vote
1answer
51 views

Understanding conditional Entropy between two physical states

From the paper: https://arxiv.org/abs/1303.4686 Let us consider an ensemble of N identical quantum systems with Hamiltonian H and density matrix $$\rho^{(N)}$$ which is diagonal in the energy ...
-2
votes
0answers
14 views

What about the information related entropy? [on hold]

In the thought experiment Maxwell's demon what about the entropy related to sorting the molecules and also the entropy of Opening and closing the gates?
-5
votes
0answers
19 views

How is the graph of density-temperature in an isochoric process [on hold]

What will the graph between density and Temperature be like in an isochoric process?
-1
votes
0answers
11 views

Minimal energy required for distilling salt from water

Suppose we dissolve some salt into some water at room temperature. Then we want to get the salt back. How much energy is needed? There must be some minimal value, right?
2
votes
4answers
269 views

What are the differences between specific latent heat and latent heat?

What are the differences between specific latent heat and latent heat? As far as I know, latent heat is the heat required or released during the change of state, without change of temperature. So ...
-1
votes
0answers
23 views

Why do we take mean occupation number of particles? [on hold]

In statistical mechanics, when we find occupation number of particles using Bose-Einstein distribution or Fermi-Dirac distribution, why do we take the mean value of the occupation number? What does it ...
0
votes
1answer
70 views

Is it true that only living things and man-made objects can make an endothermic process that decreases entropy?

I'm not trying to apply the 2LOT to only part of a system. I'm asking if there is a related law or kind of a sub-law. My highschool physics teacher said that if I take an ice cube and shine a bright ...
-1
votes
0answers
13 views

Compression to Maintain Temperature

Can a liquid in a pressurized container maintain a very cold temperature merely because it is unable to expand and become a gas?
-1
votes
1answer
18 views

Energy recovery from refinery cooling tower

Is there any possibility of recovering exhaust energy from a cooling tower by putting a wind turbine above it? Would this affect the performance of the cooling tower?
0
votes
4answers
84 views

Why do we use heat engines if they are so inefficient?

Let's say I wish to build an engine which will launch a box vertically upwards. I propose two such engine designs: Engine 1 (finger, spring, box) Step 1: Orient uncompressed spring vertically. ...
0
votes
0answers
25 views

Conceptual understanding of Harmonic oscillators in Thermal states

my professor in the lecture defined a general thermal 'state' (which actually is a density matrix) in the following way $$\tau(\beta) = \frac{e^{-\beta H}}{Z}\tag{1}$$ where Z is the partition ...
1
vote
2answers
33 views

How to write equation of state in terms of partition function?

While studying quantum gases (fermions, bosons ), equation of state written were $PV = k_B T Z_{gr}$, where $Z_{gr}$ is the partition function of grand canonical ensemble. P and V are pressure and ...
0
votes
0answers
30 views

What formulas do I need to calculate the time it takes for a room with opened window to become the same temperature as outside?

I want to calculate how long I have to open my window to become the same temperature as outside. To make things more easy let’s assume there’s almost no wind helping the exchange of temperature.
1
vote
3answers
31 views

Will the particles from 2 objects in thermal equilibirum still collide?

Suppose that we have 2 objects and both of them reached thermal equilibrium. Do the particles of the two objects still collide with each other? If so, do any of the collisions result in the transfer ...
0
votes
2answers
43 views

Does heat transfer actually from high temperature to low temperature?

Consider Object A which has a temperature of 70°C and Object B which has a temperature of 20°C. The objects are placed right next to each other. Now, as far as i know, the temperature is defined as ...
0
votes
1answer
54 views

Determine the entropy $S(U,V,N)$ from the Helmholtz free energy $F(T,V,N)$ for a Van der Waals fluid

The entropy $S$ of a Van der Waals fluid is: $$ S(U,V,N) = S_0 + NR\ln\left[\left(\frac{V}{N}-b\right)\left(\frac{U}{N}+a\frac{N}{V}\right)^c\ \right] $$ I understand how to get from the equation of ...
2
votes
1answer
44 views

Boltzmann distribution derivation from maximum entropy principle

I'm stuck halfway through a derivation of the Boltzmann distribution using the principle of maximum entropy. Let us consider a particle that may occupy any discrete energy level $\mathcal{E}_i$. The ...
0
votes
1answer
53 views

Why is work done by the system in a Carnot engine?

In a Carnot engine, represented above, it is said that work is done by the system, but in reality , work is done by the system only in the isothermal and adiabatic expansions (from 1 to 3 in the ...
0
votes
1answer
28 views

Caloric equation of state for the Van der Waals gas

I'm currently trying to reproduce a specific derivation of the caloric equation of state for the Van der Waals gas, which I saw a couple of months ago in a Thermodynamics lecture. I'm well aware of ...
2
votes
1answer
35 views

Increase of entropy as statistical necessity via Fundamental Assumption of Statistical Mechanics

My statistical physics books reasons that the increase of entropy for a closed system arises naturally from statistics. Outline: 1) Fundamental Assumption of Statistical Mechanics: For a system at ...
0
votes
0answers
38 views

Are Thermal states Harmonic oscillators?

Excuse me if I use somewhat wrong terminology. But I've always been confused about this. So firstly when we talk about a 2-state system, like a qubit, it has dimension d=2, no? But what if we ...
2
votes
1answer
26 views

Probability of a system in the canonical ensemble

In the canonical ensemble, we have the state of system $x_s$ and the state of the environment $x_e$. The probability of the total system is $$P(x_s,x_e)= const.$$ and that is independent of the states ...
0
votes
0answers
39 views

Is fire matter? [duplicate]

Anything that has mass, occupies space and whose presence can be perceived by our senses is called matter, isn't it? If that is so, then what state of matter is fire? Is fire matter?
2
votes
2answers
53 views

Critical point of a pure substance

What I've understood is no matter how much pressure we apply to a gas present at its critical temperature, it will never liquefy, and that there will be no 'distinction' between the 2 phases, liquid &...
0
votes
0answers
44 views

Why are thermodynamic potentials minimized?

In thermodynamics one says that in equilibrium the corresponding thermodynamic potential is minimized. Why? For example take the case of a canonical ensemble. Based on the assumption that the ...
0
votes
1answer
39 views

Material with discontinous conductivity

Is there a material whose thermal conductivity can be modeled by the function $$k(T) = \begin{cases}k_1, & T<T_0 \\ k_2, & T\geq T_0\end{cases}$$ where $k_1$, $k_2$ are constants. I ...
1
vote
0answers
68 views
+100

Is there any use of a quadratic equation of state in FLRW cosmology?

Consider standard FLRW cosmology. Usually, the relation between energy density $\rho$ and pressure $p$ of a cosmological fluid component is linear: \begin{equation}\tag{1} p = w \, \rho, \end{...
0
votes
0answers
14 views

Potential energy of molecule [duplicate]

Does potential energy of molecule and therefore bond length change with temperature?
0
votes
0answers
18 views

Bond energy and tempetature

Does bond energy depend on temperature? Also why is it defined at 298 Kelvin if some substances cant be in gas phase in that temperature?