Strange air flow problem

In summary, when blowing air through a pipe, having your mouth against the pipe results in less air flow compared to blowing with your mouth away from it. This is because when your lips are against the paper, you are preventing air from coming in, which is necessary for air to go out. This can be explained by fluid mechanics.
  • #1
swerider
7
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if you use your mouth to blow air through a pipe (an A4 page rolled into a pipe for simplicity) with your mouth against the pipe, the outlet flow is much less compared to when you blow through the pipe with your mouth away from it. In terms of fluid mechanics, why does this happen?
 
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  • #2
Because if you have you lips against the paper, then the only air that can come out of the paper. Basically, in order for air to go out, air must come in. If your lips are against the paper, you're stopping air from coming in.
 
  • #3


This phenomenon can be explained by the concept of boundary layer in fluid mechanics. When you blow air through the pipe with your mouth against it, the air has to flow past your mouth before entering the pipe. This creates a thin layer of air, known as the boundary layer, which sticks to the surface of your mouth and slows down the airflow. As a result, the outlet flow is reduced.

On the other hand, when you blow through the pipe with your mouth away from it, the air can enter the pipe more directly without encountering the boundary layer. This allows for a smoother and faster flow, resulting in a higher outlet flow.

Additionally, when your mouth is against the pipe, the air has to make a sharp turn to enter the pipe, causing an increase in air pressure and further slowing down the flow. This is known as the Coanda effect, where a fluid tends to follow the curvature of a surface.

In summary, the difference in outlet flow when blowing through the pipe with your mouth against it or away from it can be attributed to the presence of a boundary layer and the Coanda effect. These factors affect the fluid dynamics and result in variations in airflow.
 

1. What causes a strange air flow problem?

There can be multiple causes for a strange air flow problem, such as a clogged air filter, a malfunctioning fan or blower, or a leak in the ductwork. It is important to identify the specific cause in order to properly address the issue.

2. How can I test for a strange air flow problem?

One way to test for a strange air flow problem is to use a flow hood to measure the air flow at various points in the ductwork. This can help identify any areas with reduced or abnormal air flow. Additionally, an inspection of the air filter, fan, and ductwork can also provide clues about the source of the problem.

3. Is a strange air flow problem dangerous?

In most cases, a strange air flow problem is not dangerous. However, it can lead to decreased efficiency and performance of the HVAC system, resulting in higher energy bills and discomfort. In rare cases, a blocked or leaky duct can compromise the air quality in the home, so it is important to address the issue as soon as possible.

4. Can I fix a strange air flow problem myself?

It depends on the cause of the problem. Some issues, such as a dirty air filter, can be easily fixed by the homeowner. However, more complex problems, such as a malfunctioning fan or ductwork issues, may require the expertise of a professional HVAC technician.

5. How can I prevent a strange air flow problem in the future?

Regular maintenance and cleaning of the HVAC system can help prevent a strange air flow problem. This includes changing the air filter regularly, inspecting the fan and ductwork for any issues, and scheduling annual tune-ups with a professional. It is also important to address any strange air flow issues as soon as they arise to prevent them from becoming more serious problems.

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