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Anna [14]
2 years ago
8

Helium gas expands in a piston-cylinder in a polytropic process with n=1.67. Is the work positive, negative or zero?

Engineering
1 answer:
IRINA_888 [86]2 years ago
3 0

Answer:

work will be positive when it is under polytropic expansion process

Explanation:

It states a polytropic  process with n equal to 1.67. there is a polytropic expansion that mean work is positive and if it was polytropic compression then it would   be negative

PV^n = const

P_1V_1 = P_2V_2

Also work during the process of polytropic is given as

W_{1-2} =\frac{P_1V_1 -P_2V_2}{n-1}

the work will be positive when it is under the polytropic expansion process

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A vacuum pump is used to drain a basement of 20 °C water (with a density of 998 kg/m3 ). The vapor pressure of water at this tem
lord [1]

Answer:

The maximum theoretical height that the pump can be placed above liquid level is \Delta h=9.975\,m

Explanation:

To pump the water, we need to avoid cavitation. Cavitation is a phenomenon in which liquid experiences a phase transition into the vapour phase because pressure drops below the liquid's vapour pressure at that temperature.  As a liquid is pumped upwards, it's pressure drops. to see why, let's look at Bernoulli's equation:

\frac{\Delta P}{\rho}+g\, \Delta h +\frac{1}{2}  \Delta v^2 =0

(\rho stands here for density, h for height)

Now, we are assuming that there aren't friction losses here. If we assume further that the fluid is pumped out at a very small rate, the velocity term would be negligible, and we get:

\frac{\Delta P}{\rho}+g\, \Delta h  =0

\Delta P= -g\, \rho\, \Delta h

This means that pressure drop is proportional to the suction lift's height.

We want the pressure drop to be small enough for the fluid's pressure to be always above vapour pressure, in the extreme the fluid's pressure will be almost equal to vapour pressure.

That means:

\Delta P = 2.34\,kPa- 100 \,kPa = -97.66 \, kPa\\

We insert that into our last equation and get:

\frac{ \Delta P}{ -g\, \rho\,}= \Delta h\\\Delta h=\frac{97.66 \, kPa}{998 kg/m^3 \, \, 9.81 m/s^2} \\\Delta h=9.975\,m

And that is the absolute highest height that the pump could bear. This, assuming that there isn't friction on the suction pipe's walls, in reality the height might be much less, depending on the system's pipes and pump.

8 0
3 years ago
Which of the following is NOT associated with Urban Sprawl?
pochemuha

The option that is not associated with the given term called urban sprawl is; Option A: Blocking high views

What is Urban Sprawl?

Urban sprawl is defined as the rapid expansion of the geographic boundaries of towns and cities which is often accompanied by low-density residential housing and increased reliance on the private automobilefor movement.

Looking at the given options, "blocking high views" is the option that is not typically a problem associated with urban sprawl because urbanization usually takes place on relatively flat levels.

The missing options are;

a. blocking high views

b. destroying animal habitats

c. overrunning farmland

d. reducing green space

Read more about urban sprawl at; brainly.com/question/504389

8 0
2 years ago
I gave 15 min to finish this java program
lisov135 [29]

Answer:

class TriangleNumbers

{

public static void main (String[] args)

{

 for (int number = 1; number <= 10; ++number) {

  int sum = 1;

  System.out.print("1");

  for (int summed = 2; summed <= number; ++summed) {

   sum += summed;

   System.out.print(" + " + Integer.toString(summed));

  }

  System.out.print(" = " + Integer.toString(sum) + '\n');

 }

}

}

Explanation:

We need to run the code for each of the 10 lines. Each time we sum  numbers from 1 to n. We start with 1, then add numbers from 2 to n (and print the operation). At the end, we always print the equals sign, the sum and a newline character.

4 0
3 years ago
Bằng lý luận và thực tiễn, bạn hãy trình bày ý kiến của mình về quan điểm sau đây: "Quá trình dạy học là quá trình truyền thụ tr
mrs_skeptik [129]

Answer:

can you please ask in English I can't understand this language

7 0
2 years ago
You guys are amazing :D
Sloan [31]
Ik i am thank you tho xoxo
3 0
3 years ago
Read 2 more answers
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