- #1

Andrew Pierce

- 8

- 0

## Homework Statement

An insulated piston-cylinder device contains 5 L of saturated liquid water at a constant pressure of 175 kPa. Water is stirred by a paddle wheel while a current of 8 A flows for 45 min through a resistor placed in the water, If one-half of the liquid is evaporated during this constant pressure process and the paddle -wheel work amounts to 400 kJ, determine the voltage of the source. Also, show the process on a P-v diagram with respect to saturation lines.

## Homework Equations

ΔE = E

_{in}- E

_{out}

W

_{electric}= VIΔt

if ΔP = 0, ΔH = m(h

_{2}- h

_{1})

ΔH = ΔU + W

_{boundary}

## The Attempt at a Solution

V = 5 L

m = 5 kg (by conversion)

P = 175 kPa

I = 8 A

Δt = 45*60 sec = 2700

Assuming that KE, and PE = 0,

ΔE = ΔU

Also since it is insulated we are assuming that the heat lost is 0

W

_{e}+ W

_{sh}- W

_{boundary}= ΔU

W

_{e}+ W

_{sh}= ΔU + W

_{boundary}

W

_{e}+ W

_{sh}= ΔH

W

_{e}+ W

_{sh}= m(h

_{2}- h

_{1})

Here is where I get lost. I know that we can find h

_{1}from the saturated water tables

h

_{1}= 487.01 kj/kg (at P

_{sat}= 175 kPa)

I'm confused as to where the second enthalpy value comes from since our state has constant P.

Also the P-v should look something like this I believe: