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

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What role does gravity have on flame composition?

In 2000, Nasa conducted an experiment and found that gravity plays an indirect role in flame formation and composition (see the wikipedia article). What role does gravity play? Why does a flame ...
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5 views

Johnson Noise: Source of thermal fluctuations

I've read a lot online about Johnson noise being caused by thermal fluctuations, and the wikipedia page of thermal fluctuations attributes this to the fact that particles don't all have the same ...
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1answer
5 views

Best way to heat something in aluminum foil?

Let's say we have a wet piece of paper, wrapped in aluminum foil, that we need to heat up in the fastest and most energy efficient way possible (no flamethrower). What would that be? Details ...
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19 views

Difference between solid and gases thermal expansion

The coefficient of linear expansion is $$\Delta L = L \,\alpha \Delta T,$$ where $\Delta t$ can be the difference of any two temperatures. However, in volume expansion of gases, $$\Delta V = V ...
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17 views

Water behaviour under theoretical near-infinite pressure conditions

I've asked a similar question here but the answer given shows the behaviour of water under general conditions. I'd like to know what the behaviour of water is like as pressures increase towards ...
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22 views

Diameter of aluminium ring after it expands [on hold]

An aluminium ring has diameter $200.00$ mm at $25.00^0C$. What would be its diameter at $325.00^0C$? $\alpha$ for aluminium is $7.500 \times 10^{-5}K^{-1}$. Thanks for your help.
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15 views

Air unit selection and duct sizing [on hold]

I am not sure if this is the right place to post this. But would you please provide me with a concrete example showing the selection of an air heating/cooling unit along with the required duct sizing ...
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31 views

Deriving an Expression for Helmoltz free energy

Given the equations of states for an isolated system: $$E=\frac32 pV$$ $$p=aVT^4$$ I was asked to find the Helmoltz free energy per particle, $F=E-TS$, as a function of $T$ and $V$. I began with the ...
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15 views

Location of heat conversion in heat engines

If I put a large glass dome on a heap of coal, and burn it, I would expect the air to heat up certain amount. But if I put a coal power plant to that dome, and use it to burn the same amount of coal, ...
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38 views

How can q=mcp(deltaT) be made dimensionless?

Specifically, how can I make $m C_p$ dimensionless? I've tried using the Reynolds number and Peclet number definitions to plug into there but the closest I've gotten to was: $q=\pi D Re Pe ...
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18 views

Max thickness that can be cooled in a certain time

A frozen-food company freezes its spinach by first compressing it into large slabs and then exposing the slab of spinach to a low-temperature cooling medium. The large slab of compressed spinach is ...
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23 views

Non-steady state gas expansion

Please look at the following link for the sketch of the problem: Adiabatic Expansion with expanding control volume I have a certain amount of gas at a certain pressure and temperature at the start. ...
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17 views

why a engine convert all of its heat into work? [duplicate]

Why does heat is released to sink at lower temperature why all of the heat that is taken by a engine from heat reservior cannot be converted into work? I know that it has something to do with the ...
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33 views

In thermodynamic identity, dU=TdS-PdV. Are dS and dV orthogonal or is (T,P) defined in a conjugated space from (dS,dV)?

In thermodynamic identity, we say dU=TdS-pdV, and only Maxwell's relation is required for U to be a proper behaved thermodynamics variable. But from multivariable calculus, that result requires dS ...
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21 views

Adiabatic Relation in Plasma Invariant and Thermodynamics

In the problem above, I know how to do the 1D part. Basically, you just plug $V_{l\,l} = \frac{J}{L}$ into $\langle \frac{1}{2} m v^2\rangle = \frac{1}{2} k T$. After you get $T$ in terms of $L$, ...
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60 views

Is this Process Possible?

An inventor has devised a complicated non-flow process in which 1 mol of air is the working fluid. The net effects of the process are claimed to be: A change in state of air from 250$^{\circ}$C and ...
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37 views

Will the heat increases with the resistance?

I have studied that the nichrome, which has high resistance, is used in heat coils to increase the heat released. But according to this equation, $$H=\frac{V^2}{R} t,$$ heat is inversely proportional ...
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1answer
30 views

Are there materials with an adiabatic compressibility higher than that of common gases?

Are there materials with an adiabatic compressibility, measured at atmospheric pressure, higher than that of common gases? Is there any fundamental upper limit to the differential compressibility of ...
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17 views

Pressure components in a film

I am performing molecular-dynamics simulations of a polymer near a crystalline substrate (polymer film). I am comparing the mechanical properties in the film with the properties in the bulk polymer. ...
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33 views

Calculating The Change in Thermodynamic Potentials for Reversible Adiabatic Expansion of Real Gas

The question asks to find which quantities have a change of zero for the reversible adiabatic expansion of a real gas: Entropy, Enthalpy, Internal Energy, Helmholtz Energy, and Gibbs Energy. Change ...
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56 views

Why does the Nusselt Number for a Constant Surface Temperature, Thermally Fully Developed Circular Pipe Converge To a Constant of 3.66?

I have flow in a pipe with a constant surface temperature boundary condition. The velocity profile is fully developed and the temperature profile is also fully developed. In my textbook, it says that ...
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1answer
80 views

Is the physics of $j = \rho v$ questionable? What are the consequences? [closed]

In electrodynamics you have the quantity $\mathbf{j}$, which represents density of current per surface area. It is often said that $\mathbf{j} = \rho\mathbf{v}$, for geometric reasons. When I make ...
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84 views

Derivation of the Maxwell-Boltzmann speed distribution

We're currently deriving the Maxwell-Boltzmann speed distribution, but I'm struggling to squeeze out the right answer. For the first exercise we have to derive the fraction of molecules travelling ...
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29 views

Where did the energy of the universe come from? [duplicate]

Last week my Physics teacher asked the class this question: If the internal energy of the universe is constant, then where did all the energy come from originally?
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9 views

Calculating vapor quality in a two-phase region

I'm currently trying to find the vapour quality of a refrigerant in a two-phase region of cycle. I know $v_l$ and $v_g$, the specific volumes of the liquid and gas. I also know the temperature and ...
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25 views

What is the formula to find the temperature at a specific location of a material as a function of time that is gaining or losing heat?

Imagine a scenario where there is a homogenous material and at a any location in that object I know the temperature at time 0. Given some properties of that material, how can I find out at any other ...
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23 views

Solution to a kinetic temperature problem

I have a particular equation that needs to be solved for the kinetic temperature of a stream of gas particles. If we let the kinetic temperature be designated by the letter x, the equation becomes, ...
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16 views

Callen's Second Postulate - Composite or Closed+Composite systems?

In section 1.9 of Callen's Thermodynamics he says: The single, all-encompassing problem of thermodynamics is the determination of the equilibrium state that eventually results after the removal of ...
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56 views

Boundary value problem

Consider the boundary value problem \begin{align} \frac{du}{dt}&= \frac{d^2u}{dx^2} , \\ u(0,t)&=0 \\ u(L,t)&=0 \\ u(x,0)&=f(x) \end{align} I know how to solve it using ...
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36 views

Entropy change at varying volumes

I have two questions both related to each other: 1.What is the effect of change in volume (whether increasing or decreasing), of a system, under isothermal conditions? How does this change in ...
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2answers
35 views

Clausius statement of 2nd Law

I'm slightly messed up with Clausius statement of 2nd Law. I've seen at least two versions, which seem to be conceptually different. a) It is impossible to transfer heat from a colder body to a ...
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32 views

Robin boundary conditions for the heat equation

Consider a 3D channel with fluid or gas with walls $\Gamma_1$, inflow part $\Gamma_2$ and outflow part $\Gamma_3$. The temperature is described by the heat equation: $$ \frac{\partial T}{\partial t} ...
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33 views

Problem Boltzmann distribution [closed]

I am trying to solve a problem about boltzmann distribution. If(A)=0.74 Uf(V)=0.037 Ia(A)=0.130 I have to find ...
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22 views

Boltzmann Distribution [duplicate]

I am trying to solve a problem about boltzmann distribution. If(A)=0.74 Uf(V)=0.037 Ia(A)=0.130 I have to find ...
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2answers
49 views

Only differences in chemical potential have physical meaning?

Is the statement in the title true? Does the chemical potential of a single pure substance that does not undergo any chemical reactions or phase changes have any physical meaning?
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23 views

maximun work in a reversible process

I often read maximum work done is by a reversible process. Shouldnt the more appropriate sensence should be maximum work done per unit of heat is maximum in a reversible process. ?
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What is the overall rate of heat conduction through two pipes of different dimensions if the thermal conductivity is not constant?

I am trying to work out how I would find the rate of heat transfer through two pipes made of the same material that are joined at their ends but which have different cross-sectional areas and lengths. ...
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32 views

What does negative absolute temperature mean? [duplicate]

I always understood that the concept of absolute temperature stems from the third law of thermodynamics and that the lowest theoretical possible temperature is zero degrees Kelvin. However, ...
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40 views

Why can thermal shocks damage/break materials?

When an object is heated a lot and then brutally cooled down or vice-versa, it can crack or even break spectacularly. What happens inside that makes it do that? Is it only because the hot core swells ...
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14 views

final state when Saturated liquid-vapour mixture contained in a rigid tank is heated

I have this question: Determine the final state when a 2 kg of Saturated liquid-vapour mixture at 50 °C contained in a rigid tank is heated so that the it reaches a single phase for each of the case ...
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28 views

How does Brake specific fuel consumption vary with Brake mean effective pressure?

I'm aware that there is a certain relationship between brake specific fuel consumption (BSFC) and brake mean effective pressure (BMEP), but I am wondering if someone could explain how each varies with ...
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22 views

Trying to calculate the length of a tube to heat Ar gas

If one were trying to heat Argon gas from ambient (~20C) through a mild steel tube of some diameter 'd' how long would it need to be? Additional unknown includes flow rate of Ar gas so some general ...
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19 views

How do we compute the volumetric efficiency of an engine which is based on forced induction?

The volumetric efficiency of a naturally aspirated engine is computed by: $$n= \frac{V_1}{V_2}$$ With n: volumetric efficiency $V_1$: actual volume of air drawn $V_2$: volume swept by piston ...
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30 views

Two Limits in Thermodynamics - Reducing Driving Force and Increasing Resistance

I just wanted to clarify what is probably a very obvious idea. Suppose I'm holding a a piston separating two containers at different pressures. If I release the piston, it will naturally move, ...
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1answer
35 views

Compute convective heat transfer coefficient for a condensing steam

I have a question about convective heat transfer coefficients. I am trying to figure out how much steam I can condense in this specific heat exchanger. Steam at 9 MPa is condensed in a 1 shell pass, ...
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25 views

joule-thomson effect and linde process

According to the j-t effect the decrease in the temperature is a result of the work done by molecule to expand thus increasing their PE and decreasing their KE, but in the linde process the next step ...
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16 views

Can the effectiveness of a heat sink be increased with surface texturing?

Some supercapacitors use chemical etching to increase their surface area by several orders of magnitude. Could a similar process be used on a heat sink to increase its surface area and thus its ...
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17 views

Recommend books on thermodynamics [duplicate]

I want to take on thermo I will be analysing boilers, gas cycles ,ic engines etc. I want to Analyse all of these by using the basic laws gof thermo on my own (if i could) .I have cengel boles book and ...
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18 views

Thermal resistance of an aluminium plate to ambient?

I have heaters mounted on an aluminium plate inside an enclosure, and I would like to know what the temperature of the plate will be at thermal equilibrium for a given heating power. For this I need ...
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1answer
23 views

Work done in adiabatic reversible process

I was solving a problem on turbine.the steam works on turbine adiabatic reversibly .Is change in enthalpy or is it change in internal energy which equal this work?