Mixing steam at different pressures

In summary, the problem involves calculating the mass of throttling steam needed to achieve a final mixture of 800 kpa dry steam. This is done by using the enthalpy rates of the entering steam and the specific enthalpies of the 2000 kpa and 800 kpa streams. Through heat balance, the mass of throttling steam is determined to be 48.7 kg/s.
  • #1
Morey
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Homework Statement


steam flow through a line is 3.5 kg/s at 650 kps and .9 dry. It enters a mixing line where it exits at 800kpa, dry and saturated. The mixing steam is throttle from 2000kps to 800kpa. What is the mass of throttling steam added to have a final mixture of 800 kpa dry steam.


Homework Equations


steam tables
q=mcΔT


The Attempt at a Solution



@650: hf=684 hfg=2076 hg=2552
@800: hf=721 hfg=2048 hg=2769
@2000:hf=908 hfg=1890 hg=2798
 
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  • #2
To do this, we need to assume that the throttled steam was saturated. Otherwise the problem can't be solved.

Enthalpy rate of entering 650 kpa stream = 3.5((0.1)(684)+(0.9)(2552))=8278.2 kJ/s
Specific enthalpy of 2000 kPa steam = 2798 kJ/kg
Specific enthalpy of 800 kPa product steam =2769 kJ/kg

From heat balance on system, 8278.2 + 2798 w = (3.5+w) 2769

w = 48.7 kg/s
 

1. What happens when steam at different pressures is mixed together?

When steam at different pressures is mixed together, the resulting pressure will be equal to the sum of the individual pressures. This is known as the law of partial pressures.

2. Can steam at different pressures be mixed without any consequences?

No, mixing steam at different pressures can result in turbulence and energy loss, which can impact the efficiency of the system. It is important to carefully consider the pressure differentials before mixing steam.

3. How does the temperature of steam at different pressures affect the mixing process?

The temperature of steam at different pressures is directly related to its pressure. When steam at different pressures is mixed together, the resulting temperature will be equal to the average of the individual temperatures.

4. What factors should be considered when determining the ideal pressure for mixing steam?

The ideal pressure for mixing steam depends on the specific application and the desired outcome. Factors such as energy efficiency, temperature requirements, and equipment limitations should be taken into consideration when determining the ideal pressure for mixing steam.

5. Is there a limit to the pressure differential that can be safely mixed?

Yes, there are limits to the pressure differential that can be safely mixed. It is recommended to keep the pressure differential below 10% to avoid any potential damage to the system.

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