- #1

erde

- 8

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## Homework Statement

Hello, i have the following assignment due for monday and i have truly no idea how to tackle it, i have already tried it many times but all my results have been wrong. the problem is as follows.

inside a sealed container is an amount of water: mass=90.26 kg; pressure 9.1842 bar; x=0.00051 ;

h´=745.14[kJ/kg]; h= 746.17 [kJ/kg]; h´´=2773.6[kJ/kg];

v´=0.001[m^3/kg]; v= 0.0011[m^3/kg] ; v´´=0.21338[m^3/kg];

u´=744.22[kJ/kg] ; u=745.15[kJ/kg]; u´´=2580.12[kJ/kg]

the container is heated using an electric heat source with P=? (im looking for this)

the container has an entry and an exit valve, both closed.

1) the exit valve is opened; now calculate the heater power P=? in kW required for a constant exit vapor mass(dm/dt) of 0.1[kg/s] while maintaining h´´=2773.6[kJ/kg]

## Homework Equations

(du/dt)=(du/dM) * (dM/dt)

take into account that the liquid water level inside the container sinks

only vapor h´´ leaves the container

## The Attempt at a Solution

M=90,26 kg; m=0,1 kg/s

deltaU=-deltaM*h+P*t |d()/dt

dm/dt * u+ du/dt *m = -m*h+ P

dm/dt* u + du/dt*m= -m * h +P |m=const-> dm/dt=0

du/dt * m=-m*h + P |du/dt= du/dM * dM/dt

du/dM * dM/dt*m= -m*h + P

du * (m^2)/dM= -m*h +P |* dM

integrate (m^2 * du ](0 to-> u) =-h* Integrate (m*dm] (0 to -> M) + integrate (P dM)(0 to->M)

(m^2)*u = -m*M + M*P

m*u= -m +P

[kJ]= [kg/s] + [kJ/s] --> so wrong

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