Hot gases flow better than cold gases why?

In summary, hot gases flow better than cold gases due to the decrease in density and increase in viscosity. This is because with higher temperatures, molecules have greater momentum and can transfer more energy in collisions. This is demonstrated by the effect of increased viscosity seen in the provided link. The same principle applies to liquids, where warmer temperatures decrease intermolecular bonds and reduce adhesion, allowing for easier flow.
  • #1
5.0stang
63
0
I have read that hot gases flow better than cold gases.

Why is this so? Less dense? Any good readings on it.

I am thinking of incoming intake charge (cool) in an engine, and the outgoing (hot) gases.

Thanks.
 
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  • #2
I don't know, but I'm thinking that hot gasses flow better because there is more distance, and thus less interaction, between the molecules.
As for a cold intake flow, the main reason that one wants that is because you get a denser charge (ie: more air and fuel per unit of volume). That means more released energy when you light it.
 
  • #4
Thanks, Astro. Now here's a chance for my ignorance to really shine.
I'm starting to question my understanding of viscosity. Isn't it the tendency of molecules to cling to each other? If so, how does heat increase that? Motor oil flows better hot, so why would a gas be contrary? :confused:
 
  • #5
Well, in a liquid, the warmer the liquid the lower the intermolecular/interatomic bond, so that reduces the adhesion if you will. In gas, there is already low intermolecular interaction or force, but with an increase in temperature, each molecule has a greater momentum, and thus more momentum can be lost/transferred in a collision (e.g. molecular collision with the containment).

BTW, Danger - congrats on 5000 posts. :approve: :cool:
 
  • #6
Astronuc said:
congrats on 5000 posts. :approve: :cool:

Y'know, I never even noticed that. Thanks.
Also thanks for the very clear and concise explanation of gas viscosity. That makes perfect sense to me.
 
  • #7
Gas molecules are like billiard balls in that they move in little straight lines and collide with the walls and sometimes with each other. It may seem like we can "push" as gas through the length of a a tube, but really we have to wait until the molecules get to their new location by bouncing around. A higher temperature means that their average speed is greater.
 

1. Why do hot gases flow better than cold gases?

Hot gases have a higher kinetic energy, meaning that their molecules are moving faster and have more force to push against their surroundings. This results in a faster and more efficient flow compared to cold gases with lower kinetic energy.

2. How does temperature affect gas flow?

Temperature plays a significant role in gas flow because it directly affects the kinetic energy of the gas molecules. Higher temperatures result in higher kinetic energy and faster flow, while lower temperatures result in slower flow due to lower kinetic energy.

3. Does the type of gas affect its flow rate?

Yes, the type of gas does affect its flow rate. In addition to temperature, the size, shape, and mass of the gas molecules also play a role in determining its flow rate. Heavier gases, such as carbon dioxide, will typically flow slower than lighter gases, such as helium.

4. Why do we use hot gases in certain applications instead of cold gases?

In certain applications, hot gases are preferred because of their faster flow rate and higher kinetic energy. This can be beneficial in processes that require a quick and efficient flow, such as in power generation or propulsion systems. Additionally, hot gases can also have a lower viscosity, making them easier to work with in certain situations.

5. Can hot gases ever flow slower than cold gases?

While it may seem counterintuitive, there are certain situations where hot gases can flow slower than cold gases. This can occur when the gas is highly compressed, which can increase its density and decrease its flow rate. In these cases, the temperature of the gas may be high, but its density can still affect its flow rate.

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