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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How to find Entropy of system in terms of Magnetic Field and Temperature

I'm studying for final exams and I have a question about how to find the entropy of a particular system. The system is a lattice of paramagnetic atoms fixed to the lattice sites, with an external ...
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26 views

Why is Cv greater than Cp during anomolous expansion of water?

Well, in general $c_p> c_v$ for most cases but for water having anomolous expansion from $0^{\circ}\mathrm{C}$ to $4^{\circ}\mathrm{C}$ the order is just opposite, $c_v >c_p$, why?
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22 views

Does the orientation matter by a heat mirror?

I have a roller blind, which has a heat mirror, so one side seems to be covered with some sort of metal. In summer the metallic side faces outwards, so it can reflect the sunlight. Now in the winter ...
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15 views

temperature and velocity exchange

So there is a relation between total temperature and velocity of a fluid. In an adiabatic flow what determines how much one property (velocity or temperature will change)? I know the equation. But ...
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15 views

Schottky Anomaly - Heat Capacity

I'm having a little bit of a difficulty understanding the origins of the schottky anomaly at low temperatures in the heat capacity of certain materials with restricted energy levels. As I understand, ...
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11 views

Work done by heating a balloon with $H_2$ ideal gas

I have a difficulty treating this problem. Could you help me to understand the questions, please (I did my attempt)? Problem Consider a spherical balloon filled with $H_2$ gas. Due to a ...
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9 views

Isentropic efficiency of gas expansion process

let a compressed gas expand. If the process is isentropic, the relationship between its temperature before expansion, and its temperature after expansion is related to its heat capacity ratio. The ...
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18 views

why do we use absolute pressure in thermodynamics

One of my university doctors asked a question and I couldn't find an answer for so If anyone can help I will appreciate that. The question is why in thermodynamics we usually work with absolute ...
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26 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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34 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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57 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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52 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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66 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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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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40 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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10 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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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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18 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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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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24 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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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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17 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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34 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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25 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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23 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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31 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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19 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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20 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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48 views

Euler Equation Arbitrary Quantities

I have a question about the Euler equation. For some state I can write down: $$ U = TS - pV + \mu N$$ In this equation $T$, $p$, $V$, and $N$ are directly measurable so they have fixed values. ...
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16 views

dynamic structure factor for nucleation

I know that using the peak position/moment of structure factor or may be by first zero or minimum of pair correlation function we can estimate the characteristic length scale in a phase separating ...
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52 views

Chemical potentials at triple point

How to prove that chemical potential of each phase at triple point are equal? My attempt: At phase transition, $P$ and $T$ are constant and using $dG=0$(Gibbs free energy at minimum) at equilibrium ...
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29 views

What makes fluorescent lamps lower in heat than high pressure lamps coated with phosphorus?

Why does a fluorescent lamp give off more pure visible light (without heat) than a high-pressure lamp? Is the heat given off by high-pressure lamps caused by the intensity of light being emitted from ...
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57 views

I have got some weird data after a homemade battery experiment

Okay, so i've been searching for some time, for perpetual motion machines of the second kind. So things got into my mind, such as this homemade solar cell. And i thought in my mind:" It's not the ...
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45 views

gibbs free energy and maximum work

I'm getting confused between two important results.... Gibbs free energy G = H-TS where h is the enthalpy and S is the entropy. This relation indicates only when the temperature and pressure are ...
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184 views

What is the minimum volume in which, for a given temperature difference $\Delta T$, natural convection would occur?

I'm trying to figure out if convection will occur in a plastic bottle slice and what length of slice would be optimal to achieve high R value transparent insulation on the cheap. The bottle slice is ...
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51 views

Temperature dependence for specific thermal diffusivity in the diffusion formula

I recently found this answer about the diffusion equation (nice one actually), but have one doubt about the temperature dependence of this formula. If the "packet" of energy (terminology suggested ...
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15 views

Creating correlated Szilard engines

A demon has a large number of boxes with a single particle in. He / she adiabatically introduces a wall in the box, dividing it in two with a particle in one of the two halves (L, R). The demon does ...
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39 views

How much energy does a powerlifter need to perform a session of squats?

So I started the math myself and I'm hoping someone can look this over and improve on my idea. Let's say that a powerlifter performs the following sets of squats: % 1RM = lifted weight in percent ...
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37 views

Is the rapid compression of a non-insulated/insulated cylinder “practically” the same process?

I recently had an exercise which had us examine the following 4 situations: A quasi-static isothermic compression of a mono-atomic ideal gas. A rapid compression of a mono-atomic ideal gas, where ...
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12 views

Which constant is required to calculate the energy in a thermal analysis?

I want to calculate the energy in a thermal analysis. I want to do it in analogy to the electrostatic field, because I'm interested calculating the $H_1$ error in a Finite Element analysis. For ...
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101 views

Quadratic versus other types of degrees of freedom

In my text book I have the following question and after thinking about this one for hours, I can't figure out what they're getting at: In Section 2.5* I quoted a theorem on the multiplicity of any ...
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52 views

Simple Conduction Simulation

What is the simplest way to simulate heat conduction on a 2D plane? What I want to do is have 1024x1024 2D plane of uniform temperature 0°C and specify the temperature of a cartesian coordinate. ...
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76 views

Steam Turbine Inlet Velocity

Consider an ideal steam turbine. The power generated by a steam turbine comes down to the torque and the angular velocity, which is ultimately dependent on the velocity at which the flow enters the ...
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133 views

Derivation of Van der Waal's Equation from Helmholtz Free Energy

From the following equation $$ f(T,v) = f_{id}(T,v) - RT \ln\bigg(1-\frac{b}{v}\bigg)-\frac{a}{v}$$ how do I derive Van der Waal's equation. In the equation above, $f$ and $f_{id}$ are the Helmholtz ...
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109 views

Heat engine efficiency, compression ratio vs temperatures

I want to understand the role or even existence of a cold reservoir in the Otto cycle gasoline engine. The efficiency of the Otto engine is given as a function of compression ratio $$ ...
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49 views

Modeling an Adiabatic Expansion (EES)

How would one model an isentropic (reversible) adiabatic expansion using thermodynamic software in order to determine isentropic work? What I am looking for is an actual pressure-volume curve for the ...