1. The total enthalpy of 15.000kg of steam at 2250.000kPa is 34191.510kJ. Determine the dryness of the steam.

ANS = %

2. Determine the quantity of heat required, to raise 11.100kg of water at 80.000 degrees Celsius, to saturated steam at 2250.000kPa and 71.400% dry.
ANS = kJ

Not sure where to start. I need a little help please. I do have a chart with the properties of saturated steam. Thank you.

Since you've posted this question about eight times in the last few days, I think we can assume that none of our tutors can help you.

Sorry.

(A)Ht=Hs•ζ+(1-ζ)Hw,

where
Ht = total (actual) enthalpy (kJ/kg),
Hs = enthalpy of steam (kJ/kg),
Hw = enthalpy of saturated water or condensate (kJ/kg)
Using steam-pressure table
http://enpub.fulton.asu.edu/ece340/pdf/steam_tables.PDF
we can find the magnitudes for p=20 bar
(the given data in the problem is p=2250 000 Pa = 22.5 bar)
Hs =2800 kJ/kg
Hw = 908.8 kJ/kg and.
Ht=34191. 510/15 =2279.434 kJ/kg

Ht=Hs•ζ+ Hw –Hw•ζ
ζ(Hs-Hw)=Ht-Hw
ζ= (Ht-Hw)/ (Hs-Hw)=
=(2279.434-908.8)/(2800-908.8) =
=1370.634/1891.2=0.725
Answer: 72.5% (the answer may differ due to using of 20 bar instead of 22.5 bar)
(B)
Q=Q₁+Q₂+Q₃
Q₁=cmΔt =4186•11.1•20 = 929292 J = 929.292 kJ
Q₂= = mL =11.1•2260000 =25086000 J= 25086 kJ
Q₃= Ht ≈34191.510 kJ (I believe that we can use the result of part (a)
Q = 929.292+25086+ 34191.510 ≈ 60206.802 kJ

Thank you, Elena. I was wrong.

Another table http://www.chem.mtu.edu/~tbco/cm3230/steamtables.pdf

gives more precise values
Hs =2801.7 kJ/kg
Hw = 936.48 kJ/kg
As a result
ζ= (Ht-Hw)/ (Hs-Hw)=
=(2279.434-936.48)/(2801.7-936.48) =
=13.42.954/1865.22=0.7199 => ≈72%

Using Problem 5 page 234 from

http://books.google.com.ua/books?id=PQRo3XuHHvYC&pg=PA262&lpg=PA262&dq#v=onepage&q&f=false

From steam table
at 22.5 bar
Hw= 936.48 kJ/kg
He = 1865.2 kJ/kg - enthalpy of evaporation (Latent heat)
Enthalpy of 1 kg of wet steam is
H=Hw+ζ •He=
=936.48 +0.714•1865.2 = 2268.23 kG/kg
Heat already at water (water is at 80℃) = 4.186•80= 334.9 kJ/kg
Heat required per 1 kg of steam = {Enthalpy (or) heat required to raise 1 kg of steam from water at 0℃} – {Heat already present in water} = 2268.23 -334.9 = 1933.33 kJ/kg
Heat supplied per kg = 1933.33 kJ/kg.
Heat required for 11. 1 kg =11.1• 1933.33= 21459.963 kJ

To solve these problems, we need to use the properties of steam from the chart you mentioned. Here's how you can approach each problem:

1. To determine the dryness of the steam, we can use the definition of dryness fraction (x). The dryness fraction is the ratio of the mass of dry steam to the total mass of the steam. We are given the total enthalpy of 15.000kg of steam at 2250.000kPa, which is 34191.510kJ. To find the dryness (x), we can use the formula:

Enthalpy of dry steam (h) = dryness fraction (x) * enthalpy of saturated steam (hfg) + enthalpy of water (hf)

From the chart, find the values of hfg and hf corresponding to the given pressure of 2250.000kPa. Once you have those values, substitute them into the formula along with the given enthalpy value to solve for x.

2. To determine the quantity of heat required, we need to calculate the total energy required to heat the given water mass (11.100kg) from its initial temperature (80.000°C) to saturated steam at the given pressure (2250.000kPa) and dryness fraction (71.400%). We need to consider two separate processes: heating the water to its boiling point and changing the phase from water to steam.

a. Heating the water: To calculate the energy required to heat the water, use the specific heat capacity formula:

Q = mcΔT

Where Q is the heat energy, m is the mass of water, c is the specific heat capacity of water, and ΔT is the temperature change. Substitute the given values into the formula and calculate the heat energy for this process.

b. Changing phase from water to steam: To calculate the energy required for this process, we can use the following formula:

Q = m(hfg) * dryness fraction

Where m is the mass of steam, hfg is the enthalpy of vaporization (from the chart), and the dryness fraction is given as 71.400%. Substituting the values into the formula will give you the heat energy for this process.

Finally, add up the heat energies from both processes to get the total energy required.

Remember to pay attention to units while performing calculations. Let me know if you need any further assistance!