# Questions tagged [airflow]

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### How does an airflow sensor work?

There are 4 piezoresistive sensors placed at position A, B, C and D.1 I searched for the working principle of an airflow sensor and I saw this. If I am trying to identify the expected displacement ...
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### How do I calculate the amount of watts that a heating element needs inside a box?

I have an aluminium box (6 mm thick) of about 13.6 m³. Inside the box is a ventilator that can move 140 m³/h and I want to keep the temperature inside this box at about 30 °C. The box is to be placed ...
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### Pressure drop in air flowing through an array of tubes

I have a pipe with ID=75 mm interrupted with an array of N=121 tubes (as shown in the drawing), forcing the air to flow inside the tubes (ID of each tube is 2mm) spaced apart by 5mm. Length of tubes ...
1 vote
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### Why don't AC units run condensate over the outdoor condenser coils?

As an AC cools the air it pulls condensate from inside. Ive noticed that this condensate is often discarded via drain a line away from the unit, why is this the case? Wouldn't it be more efficient to ...
67 views

### Theory of rotationally symmetric air cushion vehicle

I am trying to develop a theory for this situation: A small blown-up balloon is attached to the center of a compact disc; you let it float as the balloon discharges. Simplifying assumptions: ...
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### Does it matter where a reduction happens in a fluid system to the amount of back pressure at the source?

I currently have an exhaust hood that produces a lot of back draft due to limitations of the ducting and a 4" diameter exhaust. The hood has a 7" circular output. It uses a reducer ...
32 views

### How can I estimate the shape of stator vanes to straighten the flow of an axial fan?

I have an axial 140 mm fan which I need to connect to a duct and I need to design a converging duct as adaptor from circular to the shape and size of the duct I have. From past experiences, an axial ...
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### Is there any difference in performance when using a small pipe diameter for a greens bubbler?

So a greens bubbler is a setup that helps the farmer cleaning greens/ gets/ fruits by agitating the water. Details here: https://blog.uvm.edu/cwcallah/2021/10/06/building-a-better-greens-bubbler/. In ...
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### Backpressure vs Pressure Drop

We were asked by a customer to calculate the backpressure of an exhaust system we were supplying a muffler for. The system includes piping from the engine to our muffler, then from the muffler to the ...
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### Why does a centrifugal fan work better than an axial fan for high pressure drop systems?

I read that this is true, but I cannot understand why. Conversely, I heard that Axial fans are better for low pressure systems where large volumes of air need to be moved. More info on centrifugal vs ...
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### Calculate Air Conditioning Duct Pressure from Sources and Users

I am currently modeling a high fidelity simulation of Boeing 747-200 for a flight simulator, and I am now at the stage of programming what is essentially the HVAC system for the aircraft. I will try ...
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### Why robotic Lawn mowers are curved body structured?

Why robotic Lawn mowers are curved body structured as shown in image ? Is the curved body structure called aerodynamic ? What's the technical reason for it ? For reference image :
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### Efficiency difference of an evaporative air cooler based on its dimensions (wider or taller) given that all the other aspects are same

I own an evaporative air cooler of width 28 inches and height 34 inches, I was wondering if a taller air cooler with lesser width (but same surface area as the one I own) would have been more ...
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### Is it possible to determine how far a vacuum cleaner hose can suck an object in from?

I'm working on a project similar to a vacuum cleaner, where I have a suction pump connected to an open ended pipe that has a negative pressure gradient such that things are being sucked into it with a ...
1 vote
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### Why do axial compressor stages have to get smaller and smaller to increase fluid pressure?

Why can't we design axial compressor stages of which have the same length? We are adding kinetic energy to fluid and then get it back as potential energy-static pressure. So why do we need that they ...
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### Radial fan with both input and output on the same plane

An axial fan moves air from one side to the other, where the fan is placed on the plane normal to the axis: A radial fan, moves air from a normal axis to the same plane where the fan runs: Is there ...
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### Why would the compressor provide more pressure than necessary? Isn't the pressure determined by the resistance?

I clearly misunderstood something
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### The application of a Fluid (air) cooler on 20mm product, equations for temperature, moisture content and relative humidity (maybe modelling)

I currently have a fluid bed cooler which is cooling fine powder (around 20mm) product which enters upto 80 °C (minimum 40 °C) and leaves at a maximum of 25 °C. The mass flow rate is about 1200 kg/h. ...
812 views

### What are the downsides of reversing fan and filter direction on a Corsi-Rosenthal box so the fan blows air into the box?

I am trying to come up with a way to clean the air in my one-car garage/DIY-woodshop, removing fine sawdust particles smaller than 1-micron, and thought that maybe one or two Corsi-Rosenthal boxes ...
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### Multiple inline fans

I have a chimney with a single 100 cfm exhaust fan. If I would add a second similar fan in the same chimney,in line with the first fan, what would happen? Would I move 200 cfm? Would I still move 100 ...
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### How to convert volumetric flow rate of air into kg/hr?

I have to convert volumetric air flow rate into kg/hr. In my system I have 2 ducts, one for ambient air and one for hot air.
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### How to make my kiln airtight?

I need to maintain temperatures of 900 C in a kiln. Making the kiln airtight is very important. After considerable research, I have zeroed in on sheet metal box and mylar space blankets. Am wary of ...
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### Pneumatic pressure sensing in a moving air compressor line

I am building an automatic control system for an compressor that stops at a designated pressure. Here's a rough sketch of the system: The compressor should receive the on signal from the ...
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### Scroll design for off the shelf tangential/cross flow fan rotor

I'm trying to figure out a somewhat optimized fan scroll shape for a cross flow fan rotor I aquired. However I seem to have vastly underestimated the complexity as I have a lot of trouble finding ...
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### Do curves and bends in an airduct (or airpipe) influence the energy that can be captured from that airflow?

To better explain my question, I've included a schematic below. Let's assume that the water level rises. As the water rises in the wide chamber, it displaces the volume of air and essentially pushes ...
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1 vote
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### Removing air from voids plastic powder

A cylinder contains a powder made up two substances - spherical grains of metal and spherical grains of plastic. In between the grains are voids, so that the cylinder is made up of 75% powder grains ...
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### Vacuum cleaner hose length & diameter vs air resistance

I have 1600 Watt vacuum cleaner, I need to use 32 ft of hose (10 meters), I have a choice here, whether I buy a hose with diameter 3 inches (75 mm) or 2 inch (50 mm) or 1 inch (25 mm). Which hose ...
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1 vote
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### Is supersonic flow not possible in a venturi tube?

I'm trying to design a venturi tube that will have a pressure drop of 91525 Pascals where the inlet pressure is at 1 atm and the throat pressure is at 9800 Pascals. I calculated the minimum throat ...
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### How do water tunnel experiments compare to wind tunnel experiments?

I recently stumbled across the water tunnel videos by this guy: https://youtu.be/quDLzxmJl5I?t=838 He states that for his "high flow" experiments the water speed is at 0.668 m/s. The car ...
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### How to connect a 1/4 NPT pressure gauge to a schrader valve while being airtight

I need to attach this pressure gauge - https://www.amazon.co.uk/gp/product/B07CXM3ZGT/ref=ask_ql_qh_dp_hza - to a schrader valve with a pipe to measure the pressure. The valve has a 1/4 NPT thread. I ...
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### How (mathematically) does pressure in the intake manifold vary based on size of throttle opening?

I have the intuitive picture somewhat down: the intake manifold is partially opened; during the intake stroke of a four-stroke process, the piston moves rapidly moves downwards creating a short-term ...
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### Gas temperature control with a mixing chamber

I am currently trying to figure out how to set up an automatic controller in order to get a precise air temperature at a specific flow rate with a hot and fresh air mix system. Picture the system like ...
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### How to determine time taken for tyre to deflate using CFD analysis?

I am working on my final year project, and am at a point which requires us to deflate a tyre in 0.8 seconds. This needs to be simulated using CFD. We have drilled a hole into the rim and attached a ...
1 vote
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### Increasing airflow of fan

I learned at at young age from a physics kit that one can blow up a large bag with your mouth by blowing into it from a distance and letting the air pick more air with it. Later in life when Dyson ...
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### is there a difference in performance between these two fan designs

These two fans are usually used in hairdryer is there a difference between them in performance if both have same rpm and same outer diameter.
1 vote
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### Can airflow through an HVAC duct be considered inviscid? Does viscid flow ever occur for HVAC?

Can airflow through an HVAC duct be considered inviscid? Does viscid flow ever occur for HVAC? If the answer to (1) is yes, how do we know airflow in an HVAC pipe is inviscid? In general, what's a ...
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### Routing the flow from an axial "box" fan

I have a project where I need to generate a certain flow rate to levitate a ping pong ball using the Bernoulli principle. From some rough calculations, I found that it would take about 30 CFM through ...
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### Airflow theory in wing design

In a race car rear wing with 2 airfoils, why does the second airfoil have a greater angle of attack compared to the leading airfoil? Also, what is the best offset distance between the 2 airfoils in a ...
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### How does temperature not affect fan airflow?

Please correct me if I am wrong : fans are devices moving a constant volume of air, given a constant rotation speed. Though, flowrate depends of the total resistance of a circuit and the ability of ...
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### Thrust force of a fan

If I have a fan with these attributes Category Value Air flow 108.2 CFM (3.03 $m^3/min$) RPM 3100 Dimensions LxHxW (mm) 120x120x25 Is it correct to calculate the thrust force at max rpm like this:...
1 vote
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### What is the difference between a 100 USD professional pitot tube and a 5 USD hobbyist pitot tube?

I would like to measure air flow speeds in a duct system for dust collection in a workshop. Relevant air speeds in the ducts are around 10-30 m/s. The ducts are circular tubes with a diameter of 160 ...
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