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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127 views

Will humid air mitigate airborn dust due to neutralization of static electricity?

I have came to understand that humid air will help prevent electrostatic forces that can propel dust and cause it to cling to surfaces. My first question: is this above statement true? If the answer ...
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86 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 ...
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109 views

Temperature of the CMB when the Earth formed and the faint young Sun paradox

The cosmic microwave background (CMB) has a modern temperature of about 2.7 K. At the time of the origin of the CMB, about 13.6 billion years ago, it had a temperature of about 3000 K. ...
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184 views

Dissipation when the temperature is not constant

Consider a process where some chemical species diffuses from one part of a system (which I'll call $A$) to another ($B$) at a rate $r$ $\text{mol}\cdot \mathrm s^{-1}$. If the system's temperature is ...
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243 views

Centrifugal Compressor Flow Rate

For a centrifugal compressor, as found in most turbochargers on internal combustion engines, is there a noticeable change in flow rate versus a naturally aspirated flow rate? In other words, does the ...
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2k views

When do I know if energy stored in an object is 0 or nonzero? (Heat transfer)

There is uniform internal heat generation at $\dot{q}=5\times10^{7} \frac{W}{m^{3}}$ is occurring in a cylindrical nuclear reactor fuel rod of 50 mm diameter and under steady state conditions the ...
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2k views

What are typical values of the critical thickness of insulation?

As most people who've had any elementary heat transfer course are aware, when insulating a pipe, wire, etc, there is a critical thickness for the insulation below which it causes greater heat transfer ...
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437 views

Maxwell's Demon - laser cooling

There’s an interesting article on Scientific American that tells how to cool individual atoms to within a very tiny fraction of Absolute Zero. It uses two laser beams acting on a very cold rarified ...
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22 views

Heat loss by radiation reference

In our lab practice, we measured the rate of heat loss of a copper plate in atmospheric pressure and the rate of heat loss of the same plate in high vacuum ($\sim 10^5 torr$). So all I could find for ...
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79 views

Entropy of unattended music streaming and other useless processes

I just realized that on my work pc, I had an internet music streaming service turned on for the last week, but muted (=useless). I was wondering how much entropy in excess was generated by ...
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22 views

How exectly does Molecular potential energy change in change of state?

I have learn some basic knowledge of Heat in my class, and I got confused when dealing with the change of state. Basically, what the textbook say is that the molecular kinetic energy keeps constant ...
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39 views

Estimate heating wires temperature

Im design a power supply to work with heating wires and one of the task is to estimate the temperature of the bare wire for a given current or power consumption. I've tried to measure the ...
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21 views

Liquid Temperature Profile

Suppose I have a one meter cubed box of liquid and I know that it is in a $-4^\circ~\rm C$ room for some amount of time, but was at a uniform $25^\circ ~\rm C$ when it was placed inside. I know I can ...
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52 views

Maximum temperature possible on earth

What is maximum temperature that can we have on earth on a single day? Lets say an air mass is static over an area and there is no way for air mass to move, sun warming it up would increase ...
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44 views

Can the second law of thermodynamics be violated in a small enough system if tried repeatedly enough?

Second law of thermodynamics is observed in the universe because statistics favors it, right? And in large enough system this statistical tendency becomes certainty. Does it also mean that negative ...
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30 views

Thermal de Broglie wavelength - definition

The thermal de Broglie wavelenght is often defined by the formula $\lambda=\frac{h}{\sqrt{2\pi mkT}}$ but equally frequently is it defined as de Broglie wavelength for a free ideal gas of massive ...
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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 ...
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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 ...
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29 views

Heat capacity and fluctuation-dissipation theorem, meaning of energy fluctuations?

I have read that from the fluctuation-dissipation theorem that the heat capacity is proportional to energy fluctuations (or populations fluctuations). In this context what is the meaning of 'energy ...
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30 views

What is melting / boiling from the statistical viewpoint?

Microscopically, solids are usually described as "completely ordered" and "strongly bound", liquids "somewhat ordered", and gases "unbound" and "disordered". Thermodynamics predicts that the ...
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22 views

Optimal two-stage warming up of a bottle of baby milk

Here's a common two-stage method to warm up a bottle of baby milk to avoid uneven milk temperature: 1) Heat up a bowl of water in a microwave oven. 2) Put the bottle into the bowl of heated water to ...
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59 views

How much time it takes to boil water in a rigid body?

I have a question that bothers me. If we have a rigid container containing water at $P_1 = 1$ $atm$ and $T_1 = 25$ $°C$. If we add an electric resistance to heat the water inside, we go through ...
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23 views

Heat transfer with a small airgap - conduction v convection v radiation

I have a transducer approx 25mm dia x 25mm length which will sit inside a brass casing, but stood off from the walls by around 0.5mm. Obviously the brass is a far better conductor than the plastic of ...
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28 views

Reason behind the heat capacity of water

Water has a high specific capacity. Why can water release a large amount of energy without a great change in temperature?
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21 views

Calculating optimal heat dissipation/air-flow out-of/into an enclosure - hole size vs number of holes

I am not sure if this is the right place to ask, but I figured it would be a physics question. Essentially I have an enclosure that I will be using to house the components to build a computer. I am ...
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30 views

probability of striking the circular ring by gas molecules

In kinetic theory we use probabilistic case to derive pressure, no. Of molecules having speed c to c+dc or in such cases.and to derive such equations we introduce a term called "SOLID ANGLE" I come ...
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37 views

Why do different color materal differ temperature in the same sunlight?

I have a blue, red, and green cup and put a thermometer in each. Of the 3 the blue cup had the coldest temperature inside, then green, then red. I understand there may be differences in the ...
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30 views

Confusion about the number of micro states and approximating it for large number of particles

Hopefully after reading the meta site, I can now rephrase the question as more relevant to this site, this is a question related to statistical physics: Let us suppose we are given a system with ...
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24 views

Is frictional heat just electromagnetic interactions creating infrared radiation?

Example: Rub your index finger on a sheet of paper and you will feel that it will get noticeably hotter Is the reason you feel this increase in heat (technically an increase in kinetic energy of the ...
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25 views

How do I compute mass flow rate for a compressible fluid?

Consider the vacuum chamber in the figure. If a hole with cross section area $A_{cs}$ is created, how can I approximate the maximum mass flow rate, $\dot{m}$, for a compressible fluid (e.g. air)?
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49 views

Is it possible to consider PV diagrams without the equations of state?

Suppose that we have the equations of state for a particular system, or equivalently, that we have the fundamental relation $S = S(U,V,N)$. If we want to write down a PV diagram it will be quite ...
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60 views

In enthalpy, is PV the pressure energy?

In the case of a fluid, does the $PV$ contribution to the enthalpy correspond to the pressure energy in fluid mechanics? (Related: What is Pressure Energy?)
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34 views

Isentropic flow through nozzle

I've a question concerning the use of the Bernoulli principle. Let's say I have a pipe filled with air at atmospheric pressure, with a constricting section ala the figure below. The volume before the ...
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27 views

Thermodynamic equilibrium or thermal equilibrium and equipartition theorem

In all derivations of the equipartition theorem I can find a thermodynamic equilibrium distribution is used to show it's validity. But more vague sources (this site, wikipedia) state that only ...
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20 views

Black Body Radiation of a Home

If there is a home which is far away from all other buildings, what is the heat transfer due to radiation at night? Is the governing equation this: sigma*(T_home^4 - T_space^4)? Does the home radiate ...
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14 views

Thermodynamics: state change and process types

Why is change of state, for example: water to ice, considered an isobaric process as opposed to isothermal? I had always learnt that temperature does not change during change of state.
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61 views

What is the difference between thermodynamic and empirical temperature?

When I've studied Thermodynamics I did so in Callen's book and there the author talks about temperature as a single thing, which mathematically is simply defined as: $$T = \dfrac{\partial U}{\partial ...
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53 views

Why does cold air feel even colder when you are moving through it quickly?

My question is the following: Why does it feel colder (i.e. why does your body transfer more heat to the surroundings) when you are moving through the air at a high velocity, f.ex. when you are ...
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49 views

What is the relation between Clausius and Kelvin-Planck statement?

What is the relation between Clausius and Kelvin-Planck statement? In second law of thermodynamics, it is said that these two statement are equivalent and inverse to each other. Violation of one ...
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28 views

Expressing thermal efficiency for a closed Brayton cycle in terms of static enthalpies

I have a Brayton cycle made of a compressor (stage 2 to 3), a heat exchanger (stage 3 to 4) and a turbine (stage 4 to 5). The turbine and compressor are connected through a shaft. The cycle is closed ...
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13 views

What are the limitations of velocity selective coherent population trapping?

I'm somewhat familiar with limitations of Doppler cooling, particularly with the one photon recoil limit, but what I was curious about was what is the next barrier to cooling approaching absolute ...
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40 views

How to understand better this point of view on entropy?

On the book "Applied Differential Geometry" by William Burke we see a discussion about thermodynamics in which the following is said: A thermodynamic system is a homogeneous assembly that includes ...
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39 views

Definition of emissivity?

A have come across a definition of emissivity which is along the following lines: Emissivity is the power emitted per solid angle per frequency per surface area. This definition, however seems ...
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52 views

if copper is heated, does it become negatively charged?

i'm reading "Electronics for inventors" and there's this part where it says that free electrons never escape material due to electrostatic attraction with positive ions, but if heated, electrons are ...
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35 views

What is an extremal horizon?

In the contest of holography and thermodynamics, what is an extremal horizon? I am going through a paper by Hartnoll, Santos - Disordered Horizons: Holography of randomly disordered fixed points. They ...
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75 views

Is work only a change of kinetic or potential energy?

I find out on the internet that work is a transfer of energy essentially kinetic. What is the use of work if it does not consider all the types of energy applied , i mean sometimes an objects internal ...
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41 views

Did the universe have a temperature during inflation?

I've heard it said that inflation was not an equilibrium process. But I've also heard it said that during inflation, the temperature of the universe was much cooler than before or after. If the ...
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66 views

A question about ultimate computation capability

If we consider the physical limit of computational capability of a system with average energy $E$, then (1) According to Margolus and Levitin, a quantum system with average energy $E$ takes time at ...
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47 views

The Ideal Gas Equation in higher dimensions

Basically I wanted to know whether or not the ideal gas equation, $PV=NkT$ would hold in higher dimensions? If so, how would you go about proving this? I can't see any reason as to why it shouldn't ...
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24 views

solar energy on a specific location

How to find the amount of solar wattage in any specific place on earh in a monthly manner? by solar wattage I mean the energy recieved from the sun in a squared meters.