A gas that behaves as randomly moving, non-interacting molecules. This allows a simplified equation of state.

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Stagnant Air Deep Inside Vintage Mines

This is really a question more about mining ventilation than true "physics." I occasionally explore a southwest desert mine, but am aware of the hazards - typically passing over half a dozen vintage ...
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1answer
111 views

error propagation and collision in ideal gas

When dealing with gas, a statistical approach is needed because For N particles, you have to solve 6N equations which cant be done analytically. To know our time step for numerical solving, you can ...
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17 views

Rate of collision of gas molecules

On what factors does the rate of collisions of gas molecules with walls of a container depends? I know one would be temperature but are there any other factors like density,pressure,volume etc. I ...
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1answer
78 views

What is the difference between the Method of Characteristics being formulated in terms of theta & alpha and theta & nu?

So I'm doing an MSc thesis involving the method of characteristics in rocket nozzles. My lecture notes have the MoC formulated such that the positive characteristics are defined as: C+ = Tan ( $\...
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44 views

On the definition of the compressibility`

The compressibility factor for a real gas can be defined in two equivalent ways, $$Z = \frac{V_{measured}}{V_{ideal}} \equiv \frac{p_mV_m}{nRT} $$ where the subscripts $m$ stand for measured ...
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336 views

Gas compressed and cooled

If a certain amount of a gas is compressed into a cylinder by the action of a piston that reduces its volume (lets say at a low speed), the kynetic energy of the gas molecules increases, what is ...
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78 views

Is it possible to have a line rather than a point where the three states of a substance can exist?

Most of us are familiar with state diagrams that define which of the three states a substance will take given the pressure and temperature. And that some substances, such as water for example, exhibit ...
3
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43 views

Can I always assume that a vapour pressure over a liquid is ideal?

Can I assume that the vapour of a subject over its liquid is ideal-ish? I'm thinking that if the vapour pressure is low the subject in question wont interact with itself, but it doesn't necessarily ...
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103 views

Sound level of organ pipe driven by helium

The sound pressure level of an organ pipe is a function of the gas flow rate delivered to the pipe. Source Would the sound level of an organ pipe driven by helium be lower than that of a pipe driven ...
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35 views

How Quickly Do Gasses Mix?

When I pick up my scuba tanks from the dive shop, I measure the nitrogen and oxygen levels in it. I check that they are close to what I specified and calculate the maximum depth it's safe to go to to ...
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25 views

Ratio of Stagnation to Normal Flow Properties in Incompressible Flows

I know in compressible flows the ratio of stagnation to normal flow variables is a function of the Mach number and usually the specific heat ratio. Does this ratio mean anything for incompressible ...
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85 views

Why do we need to suppose the chemical potential is zero in this situation?

I've been working on some statistical mechanics problems and one of them asks to compute the pressure with chemical potential zero of a boson gas whose particles do not interact and whose energies are ...
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50 views

How is convection possible in fluids, in the absence of a contact surface for any buoyant force?

I don't understand why liquids and gases are acted upon by a buoyant force. In a solid immersed on some fluid medium, the pressure pressure difference caused by gravity exerts a force on the surface ...
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178 views

Simple gas in cylinder modeling

I want to do a simple (physically plausible but not physically accurate) simulation of a gas in a cylinder as it works on or is worked on by a piston. Wikipedia gives a good example of an adiabatic ...
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749 views

How can I interpret negative values of potential evapotranspiration?

If I extract Potential Evaporation (PET, W/m$^2$) from the National Centers for Environmental Prediction (NCEP), climate reanalysis data (downloadable as netCDF files here), there are some negative ...
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244 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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48 views

Mixed Gas Absorbtion

Consider a gas misture that contains two type of atom, A and B. The gas is in equilibrium at temperature $T$. If on the surface of the gas container there are M sites that can absorb an atom gas, and ...
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27 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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50 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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28 views

Doubt about Hard Sphere Model

I couldn't find a proper answer about this question: if I have a gas formed by a single species (ex: biatomic gas like O2), what is the diameter $\sigma$ of the relative hard sphere model? Is it the ...
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59 views

Necessity of infinitesimal steps for reversible processes

Is there a mathematical proof for why a reversible process is one that has many infinitesimal equilibrium steps, rather than fewer large steps? Maybe something along the lines of this?: \begin{...
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46 views

Nitrogen generator maximum flow check

We have a N2 PSA unit with following specs Now I have done some calculations as shown in the image. Assuming 0.8% of the air is (N2+inerts) rest being O2 can someone tell me that how 160CFM air ...
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88 views

Dielectric constant of gases - constant?

A number of questions related to the topic: Is the dielectric constant actually constant as a function of temperature and frequency (when used in a capacitor)? Is it constant as a function of field ...
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83 views

Recombination time for ionized atoms in a low pressure gas?

I am looking into some new physics and had the following question come up: You have a neutral gas of let's say, CO atoms at 1 nanoTorr. An electron(s) comes passing through the gas ionizing only 1% ...
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97 views

logarithm of ideal gas law

This question is about taking the logarithm of the ideal gas law. In a fluids text book the author writes: First recall a couple of ideal gas relationships involving potential temperature, $\theta$...
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196 views

Effusion of particles from one box to another - pressure calculation

Suppose we have a container divided into equal halves. Right half is fixed at temperature $T$, volume $\frac{V}{2}$. Initially it has pressure $P_0$, a hole of area $A$ is opened between them. I ...
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73 views

If air was significantly compressed, and then the force compressing it suddenly disappeared (no container), what would happen?

Question: If air was significantly compressed, and then the force compressing it suddenly disappeared (no container), what would happen? Side Question: I'm imagining significantly compressed, but ...
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81 views

Do I need mass to calculate the rms speed of diatomic Nitrogen?

Calculate the rms speed of diatomic Nitrogen ($N_2$) at an altitude of $600$ km, where the temperature is $1500$ K. I'm confused because only an altitude and a temperature is given, and I feel like ...
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257 views

Sound velocity in ideal Bose gas

Speed of sound is related to the derivative of pressure with respect to density: $v_s=\sqrt{(\frac{\partial P}{\partial \rho})_S}$ where S tells us the derivative must be taken while keeping entropy ...
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387 views

ideal gas law modelization in a vacuum chamber

I am trying to model a pressure sensor in COMSOL. The basic work is that there is current flowing inside it, if the pressure of the gas around it drops down, the temperature goes down as well (ideal ...
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13 views

Maxwell's distribution analogue for angular velocity

Consider hydrogen ($\mathrm{H_2}$) as an ideal gas. We know that distribution of translational velocities is given by Maxwell's distribution. However our gas is diatomic, which means every molecule ...
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13 views

How to calculate static air temperature

Let's suppose I have an airplane flying at an unpecified altitude and the following data are given: Flight Mach number: $M=0.76M$ Ground speed: $v_{kts}=470kts$ My goal is to estimate the air ...
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15 views

Kinetic gas theory: How large are rotational and vibrational energy for a linear diatomic molecule?

Let's say one has given a temperature of a simple linear diatomic gas like Hydrogen $H_2$. From the temperature one knows the energy of the gas, but how does this energy "split up" to the different ...
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21 views

If Earth's atmosphere would be cooled, how would its pressure change relative to its temperature?

I have a feeling it would not behave like an ideal gas? For example, if the atmosphere were to cool down at a constant 1 atm to 90 K, oxygen would liquefy. If changing of pressure would be considered,...
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20 views

pipette waterfountain

Place the tip of a pipette in some hot water. Cover the other end with you thumb. Invert the pipette and water sprays out nearly two metres. Is the cool air in the pipette being heated by the hot ...
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69 views

When does $PV = const$ stop being true?

My problem is the following: a 15-liters cylinder contains air compressed at 370 bar. How many liter will flow out of the cylinder once uncompressed at 1 bar? I thought that I could use $PV = const$ (...
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42 views

Thermal conductivity of a binary gas mixture

I want to estimate the thermal conductivity of binary gas mixture, say water vapor+nitrogen. I assume the mixture as ideal gas. The molar fraction and thermal conductivities of the components are ...
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98 views

Time between two collisions in a 2D gas

I'm trying to code a simulation of a 2D gas in a box. The molecules are represented by circles of radius $R$ having elastic collisions with the walls only (for now). I read that the average time step ...
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32 views

Can a point particle experience deformation?

One of the assumptions in an ideal gas is that the particles are small hard spheres. Another assumption is "All collisions between gas molecules are elastic and all motion is frictionless". Assuming ...
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21 views

Temperature and air flow - are they related?

If I open a window, does the air "changes" (e.g. the $O_2$ concentration) in the room more quickly if there was a temperature difference between inside and outside?
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60 views

Difficulty in understanding Maxwell Boltzmann distribution in case on ions in a field

I learned that the velocity of molecules obey Maxwell Boltzmann (MB) distribution at a Temperature T. If I have ions of mass 'M' accelerated to 2eV in a specific region. As the ions are not "...
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52 views

Can a flowing gas create a static charge?

On the Static Electricity page of Wikipedia the claim is made that "The flowing movement of gases in pipes alone creates little, if any, static electricity" with a cited reference [ref 19] being made ...
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77 views

Pressure profile and output of a coil heated burner

In a hot air balloon burner (and probably lots of other burners) liquid gas is passing through a heating coil before it exits at a hose. I realize that the point of having a heating coil is to ...
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125 views

Efficiency of a compressed air engine

I am doing some personal research on the efficiency of compressed air cars. I am currently trying to come up with an 'ideal' cycle to use as a reference for efficiency (c.f. Otto Cycle for petrol cars)...
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94 views

Modelling the diffusion of gas in a container with non uniform temperature

I want to model diffusion of a gas (e.g. water vapor diffusion in air) in a container with a temperature gradient. One side of the container has a hole, but for simplicity of boundary conditions I can ...
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30 views

Temperature Frequency relationship for gas?

I am getting something like this T (C) = Constant*log(Frequency) I do not have background of physics and I am wondering, if there is any formula which can explain the physics behind it? Something ...
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93 views

How does a heated constant volume flow behave, for an expanding flow tube leading into the free atmosphere

I have a helium gas flow with a flow rate that has been set to a constant value ($0.3\,m^3/h$). It's streaming upwards in the picture, and beyond the upper big red dot position, it meets the ...
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38 views

Nonlinear constitutive state equation

Between the Tait equation, and the B/A type of equation, which one is better suited to approximate the isentropic equation of state? Why B/A type is mostly used in nonlinear acoustics?
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Experimental data for gas flow through pipelines

Maybe some of you could point a good source of experimental data of gas flow through pipelines? What I need is a very simple flow of some gases through some diameter simple linear pipeline. A graph of ...
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115 views

Using thermodynamics and Kinematics together to solve a parachuter problem?

I need to find a parachutist's displacement after a given height (nearly 37000m) and at a given latitude. I have his mass, area, parachute area, drop height, parachute deployment height, data about ...