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Questions tagged [thermodynamics]

Questions relating to the various laws of thermodynamics, transformation or movement of a form of energy to another form, primarily but not limited to heating or cooling of a fluid.

691 questions
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Which is better: Defog a car windshield with cold or hot air?

So i had this experience when driving in a cold night, where my windshield just got all blurry. I knew that on the drivers manual they say you should turn the hot air and soon it will go off, but my friend that was on the passenger seat said the…
Alessandro Nardinelli
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How does humidity, specifically using a humidifier, affect the filtration of PM2.5 particles from a room?

I live in a very smokey and dry area where people are advised to use air purifiers. Since it's also dry I'm curious what affects, if any, adding a humidifier to a room with an air purifier would have? When I looked into it, it seems like moisture…
joeyfb
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How does expanding gas in isobaric process move a piston?

If we have a simple adiabatic cylinder with a piston on top and we heat the gas from the inside, the gas starts to expand and move the piston up. This process is isobaric; but if the pressure on the piston doesn't change, how does it move up?
noidK
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Why use steam in the rankine cycle?

In the rankine cycle, water is first pressurized and then heated to produce steam before it is used to turn a turbine. As far as i know, this is what is considered the best way to extract mechanical work on the turbine, but i want to understand why…
Paul
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Is vortex tube reversible?

If you inject cold and hot air in outlets of a vortex tube, do you obtain a greater pressure at inlet?
user3368561
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Otto Cycle Efficiency

A two-stroke engine equipped with a single cylinder having a bore of 12 cm and a stroke of 50 cm operates on an Otto cycle. At the beginning of the compression stroke air is at 100 kPa, 25 ℃. The maximum temperature in the cycle is 1100 ℃ . Use the…
Chris
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Derivation of the equation of the work done in a polytropic process

I am completing a question that is requiring calculation of the work done in a polytropic process. In the worked solutions the work equation seems to be reversed for the answer, as can be seen in the screenshot- the top row is p1v1-p2v2 insted of…
Harrison De George
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Why do we need to condense steam in the rankine cycle?

In my admittedly naive understanding of the rankine cycle, steam is condensed back into water after passing through the turbine. Why not reuse the steam instead? It would seem to require less effort to reuse heated steam than to intentionally…
Paul
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Finding the enthalphy of Helium given internal energy

I am trying to find the enthalphy of Helium if its internal energy is 200 kJ/kg. The answer is given as 333.42 kJ/kg, but I keep getting the wrong answer. I've tried the following: $\begin {align} H &= U + PV \\ H &= U + mRT \\ \end…
james
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What is the (thermodynamic) explanation for heat/temperature reduction due to wind?

Here is my fan in my office. Sometimes I used it if my air conditioner (AC) has problems, or I my self have problems with my health due to the freon. What I observed is that the heat (or probably temperature) will be reduced if I turn on the fan (I…
AirCraft Lover
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What are the differences between Gauge and Absolute pressure?

I am aware that Absolute pressure is zero-referenced to a perfect vacuum and Gauge pressure is zero-referenced to ambient air pressure. So, Absolute pressure is equal to Gauge pressure plus atmospheric pressure. However, the Part B of this problem,…
user13284
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Temperature when steam expands into a vacuum

Moran and Shapiro Fundamentals of Engineering Thermodynamics (p147) has a worked example: Steam at a pressure of $15$ bars and a temperature of $320^{\circ}C$ is contained in a large tank. Connected to the tank through a valve is a turbine…
peter2108
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Why does the torque of an internal combustion engine increase with its rpm at low rpm range?

Here is a simple schematic of the engine. The increase in angular momentum of the crankshaft in one complete cycle would be $\Delta L_{cycle}=\int_{\delta =0}^{\delta =4 \pi} F cos \theta Rdt$. where F is positive in combustion stroke and negative…
Raul369
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What is a thermodynamic process that is not polytropic?

In discussion under another question, it was pointed out: "Not every process is polytropic; that is just a special case when $pV^n$ is constant" Must have missed that in school. What is a real life example of a non-polytropic process in a closed…
mart
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Applicability of Gibbs' Phase Rule

The Gibbs Phase Rule indicates that for a two phase, single component thermodynamic system we will have one independent intensive parameter. Given that the Degree of Freedom is $1$ means that fixing one intensive parameter would fix the entire…
akshay rathore
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