Question

When a steadily-flowing gas flows from a larger-diameter pipe to a smaller-diameter pipe, what happens to each of the following?
a. The density of the gas
b. The speed of the gas
c. The pressure of the gas
d. The temperature of the gas
e. The kinetic energy of the gas

Answer 1

You know that density=mass/volume. For the first part, as diameter decreases, the volume decreases as well and hence density increases, because it is directly proportional to the inverse of volume.

Answer 2

Presure=force/area or force/Pir^2 or force*4/Pid^2. Using proportionality, as diameter decreases, the pressure will increase, which is the answer for the C part.

Answer 3

Use Charles-Boyle law of gases, basing from the formula PV/T=K. Making Tthe subject you get T=PV/K. You can omit K, which is a constant... Say it is 1. As for V, remember as previously I said that when Diameter decreases, Volume decreases and I believe that the temperature will reduce too.

Answer 4

to answer the question properly you need to know whether the flow is incompressible of compressible

Answer 5

I think the expression 'steadily-flowing' tells you the thing.

Answer 6

I think that:
1) density increases, because your gas is constrained in a more little space,
2) consequently, being PV=nRT, pressure increase,
3) internal energy of our gas increases, because we perform a work on the gas, so by the first principle of Thermodynamics, temperature of gas increases
4) speed increases because we have a negative variation of entalpy
5)kinetic energy of our gas increases because the average speed of each its molecule is increased

Answer 7

@Michele_Laino, I think the answer for5 should be 'remains the same', because assuming that the gas in ideal, there are elastic collisions and therefore the kinetic energy is conserved or constant.

Answer 8

I think, since temperature increases, also kinetic energy of each molecule increases

Answer 9

Yes. It is debately. Anyway, are you satisfied with the other 4 parts, @deannapher?

Answer 10

Steady flow only refers to macroscopic properties not changing with time.
It says nothing about whether the flow is incompressible or compressible.

Answer 11

From what I just read, it says that a steady flow process is the process in which when matter travells in a space, the properties remain frozen with time.

Answer 12

Thank you Everyone! i have another question

Answer 13

Add or subtract as indicated.

Add or subtract as indicated.


When a 3-kg glass jar containing 3 kg of water is removed from the refrigerator, which material (if either) absorbs more heat from the room? Support your answer using 3 – 4 complete sentences.

Answer 14

Lol...the term steady state can be used for both compressible and incompressible flows.
Both you and the other person assumed the flow in this problem was both subsonic and compressible.

Answer 15

what?

Answer 16

I assume the flow is subsonic. A supersonic flow occurs in specific conditions and would be mentioned.
To answer the initial question, you need to know Bernoulli's principle, which is very non-intuitive.
Read this:
http://en.wikipedia.org/wiki/Bernoulli%27s_principle

Answer 17

Note: @Hoslos and @Michele_Laino have modeled the flow as compressible (ie:density changes)
@Vincent-Lyon.Fr is modeling the flow as incompressible (density is constant) since he is suggesting the use of the Bernoulli equation.
As I mentioned earlier, this is the first distinction which must be made for a fluid flow problem...incompressible or compressible flow.
In addition, there are three other conditions which must be met when using the Bernoulli equation...one of which is incompressible flow.