Questions tagged [compressible-flow]

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6 votes
2 answers
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What makes something like water so hard to change its density?

So I'm taking a compressible flow class soon, and I've been thinking beforehand about the topic. A substance like water can easily be pressurized, but its density doesn't change easily, meaning there ...
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5 votes
1 answer
1k views

How do gas flow regulators avoid choking?

According to compressible flow theory, a downstream pressure of 0.528 times upstream pressure is sufficient to choke a flow device. So, how do industrial grade pressure regulators throttle a wide ...
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4 votes
1 answer
176 views

Methane Gas Density in Adiabatic Compressible Flow

Hi.. The question above is one of the tutorial question from fluid mechanics textbook. In the textbook solution for this question, the density of the methane gas stream at downstream was computed with ...
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4 votes
1 answer
7k views

Determining mass flow rate and exit velocity of compressible flow

This one's a bit of a doozy, so please feel free to comment on any one single part or parts to this problem. The setup is simple--I have a container (an empty bottle) which I fill with a certain ...
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3 votes
1 answer
310 views

Shouldn't enthalpies be equal in isentropic process?

I have some questions about the enthalpies between two points during an isentropic process in a nozzle. By doing the energy balance between the two points, one gets: $h_1 + \frac{v_1^2}{2}+gz_1=h_2+\...
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  • 604
3 votes
1 answer
331 views

Why don't all gas pipe flows end up at sonic speed?

According to the 1D models of compressible fluid flow, the effects of pipe wall friction and the effects of heat addition from the environment both drive a flow toward Mach 1 (i.e. the speed of sound)....
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  • 133
2 votes
1 answer
9k views

How to determine the choke point in a compressed gas system?

I have a pressure regulator bringing an inlet pressure of 150 bar down to 10 bar which is then lead into a plenum followed by a nozzle of area 340 mm^2, exposed to atmospheric conditions. Weirdly ...
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  • 95
2 votes
3 answers
118 views

How do stators in axial compressors work?

How do the stators in axial compressors convert kinetic energy to pressure? Is this equivalent to a water hammer?
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2 votes
4 answers
146 views

If a fluid is incompressible,is it correct to say that the flow may or may not be incompressible?

From my understanding,when there is no change in volume due to pressure applied on a fluid,the fluid can be called as incompressible.As there can be still be change in volume due to other properties,...
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  • 129
2 votes
1 answer
125 views

Determination of blower mass flow from limited information

For a variable speed centrifugal blower, can a rough measure of mass flow be obtained from only motor speed and power when the outlet restriction is variable?
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  • 21
2 votes
2 answers
171 views

Why does exit pressure match back pressure in Converging Diverging Nozzles?

I am trying to understand why normal shocks are caused in Converging Diverging Nozzles. My textbook explains that since the exit pressure must match the back pressure, the normal shock is the only ...
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2 votes
2 answers
3k views

Using pressure drop to correlate mass flow

I am looking for a way to double check readings I am getting through a mass flow meter that appear to be reading lower than expected. Once flow starts in the system, the pressure regulator at the ...
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2 votes
1 answer
139 views

Combustion Chamber Back Pressure due to gas injection

I am trying to calculate prior to testing the expected back pressure resulting from injecting gaseous oxygen through an injector orifice (choked) into a rocket combustion chamber before ignition. I ...
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2 votes
1 answer
331 views

Determining required pressure drop for choked flow conditions to be met

I have pipework system with an inlet pressure, $P_0$, which passes from a pipeline of fixed diameter, $D_0$, through a tee with reducer to a smaller diameter pipe, $D_1$, before returning to another ...
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  • 23
2 votes
0 answers
64 views

How to balance flow and pressure in nitrogen purged chambers?

I have an instrument that is technically a humidity controlled chamber. It measures how much moisture is picked up by the sample through a microbalance(Zone 1). Nitrogen gas flows from zone 3 and ...
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2 votes
1 answer
1k views

Isentropic flow equation derivation

I am trying to derive the isentropic flow equations for a compressible gas by myself and at the end, I have different formulation than the one in the literature. Can you please tell me what am I doing ...
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  • 604
1 vote
1 answer
27 views

Linear pneumatic actuator opening time - pressurise connection pipe

I would like to estimate the time needed to open a linear single-acting pneumatic actuator. The actuator's piston is loaded with a spring pushing downwards and the operating fluid (air or nitrogen) ...
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1 vote
1 answer
189 views

Isentropic Flow and Conservation of Mass

I have some doubt on fluid mechanics that need some confirmation. I am on the section that discusses about compressible flow and the effect of variation of flow cross section area. It stated that ...
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  • 51
1 vote
0 answers
36 views

Confusion between Steady flow and Space-Time invariant density field

Let's take the example of a steady flow with velocity field as $u=βr(\tilde{r})$. Now, we can find a density field $ρ(r,t)$ that satisfies the mass conservation equation of $∂ρ/∂t+∇(ρu)=0$. First, ...
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1 vote
0 answers
42 views

Can any Air rotameter be used for refrigerant gas by using equation conversion?

Currently, I am trying to find rotameter calibrated for R134A gas flow. However, most companies only sell rotameter or variable area flowmeter for water/Air/Nitrogen flow. Is it possible to use any ...
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1 vote
0 answers
69 views

Water Valve Functionality

Before to present my question, I have to say that I'm not a hydraulic expert. I'm working on a water valve design and I found this model which work with a diaphragm and a spring. I want to consider ...
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0 votes
1 answer
756 views

Natural gas mass flow conversion

I have a question about gas valve selection and working out the CV. The equation I have needs the mass flow in kg/hr, but I have been given the volumetric flow rate in litres/minute. How do I go about ...
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0 votes
1 answer
39 views

How are the conditions after the shock calculated for a shockwave formed on a cone?

How do oblique shockwaves differ from 2D to 3D problems? More specifically, how are the conditions after the shock calculated for a shockwave formed on a cone (e.g. the inlet cone on a ramjet)? I am ...
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  • 19
0 votes
2 answers
56 views

What should be the density of a compressed gas while measuring the flow rate using Rotameter?

Say we have a required mass flow rate, in order to have equivalent volume flow rate, we need to consider density of the operating fluid (compressible fluid). To measure the volume flow rate in LPM, ...
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  • 101
0 votes
1 answer
30 views

Determination of solid bed fluidisation

How would one determine if a fluidised bed (with liquid flow) is determined to be a stable fluidised bed, which subsequently doesn't form a plug or bed at the top of a column (bounded by frits), when ...
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0 votes
0 answers
25 views

Joule Thompson Effect and Isenthalpic Processes

We are trying to compute the Joule Thompson (JT) coefficient for air going through a valve from P1 to P2 (where P2 is a much lower pressure). Beginning this we were thinking that the water in the air ...
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  • 41
0 votes
1 answer
215 views

Solving 1D Unsteady Homentropic Flow using Method of Characteristics

I am looking to solve the 1D Unsteady Homentropic Flow equations using the Method of Characteristics (MOC). I am using Zucrow and Hoffman's Gas Dynamics Volume 1 as a reference and I am currently ...
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0 votes
1 answer
161 views

Is the pressure of the gas identical to the static pressure of the liquid in the diagram?

In my application the liquid would be tapped from a fast-varying flowrate, and I want to measure the static pressure change during this by measuring the air pressure above it. Will this work?
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0 votes
1 answer
35 views

What are some concepts I can look into to aide in creating a 'compression funnel'(?) without the aide of a motor? [closed]

In short I'm designing a 'Humane fly swatter' for my University application into bachelor of Industrial Design. The idea is to utilise the energy of swatting a fly to capture air through an intake, ...
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  • 3
-1 votes
1 answer
120 views

Ideal Exhaust velocity of a rocket nozzle

In a youtube video, they defined exit exhaust velocity of a rocket nozzle as $$v_2 = \sqrt{\dfrac{2k}{k - 1}RT_1 \left[1 - \left(\dfrac{p_2}{p_1}\right)^{(k - 1) / k}\right]}$$ How can I derive this ...
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