Question

A rigid tank has a volume of 0.01 m3. It initially contains saturated water at a...

A rigid tank has a volume of 0.01 m3. It initially contains saturated water at a temperature of 200 oC and a quality of 0.4. The top of the tank contains a pressure regulating valve which maintains the vapor at constant pressure. This system undergoes a process where it is heated until all the liquid vaporizes. How much heat in (kJ) is required? You may assume there is no pressure drop in the exit line.

Homework Answers

Answer #1

V = 0.01 m3 = 10 L

sat water at 200°C, x = 0.4

Q = ? until x = 1

find H

this is deffinetively an isobaric process

so

Q = m*Cp*dT

since this is at equilibrium

Q = Hf-Hi

Hf = saturated vapor , 1.0 quality

Hi = sat. liquid, 0.4 quality

a)

step 1, find Pressure saturation

at T = 200°C, P = 1.5538 MPA (from thermo tables)

H of liquid = 852.45 kJ/kg

H of gas = 2793.2  kJ/kg

Hfg = 1940.7 kJ/kg

We need the mixed Enthalpy:

H = x*Hfg + Hf

H = 0.4*1940.7 + 852.45 + = 1628.73kJ/kg

then

we need mass of system

vf = 0.001157 ---> 0.01 m3

mass = vf/V = 0.01 m3 /0.001157 m3 / kg *= 8.6430 kg

Q = m(Hf-Hi)

substitute data

Q = 8.6430* (2793.2 -1628.73) = 10064.51421 kJ

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