Question

Water is being heated in a vertical piston-cylinder device. The piston has a mass of51 kg and a cross-sectional area of 100 cm2. If the local atmospheric pressure is 100kPa, determine the temperature at which the water starts boiling

Answer 1

The temperature at which the water starts boiling is 111.35 °C.

Step-by-step explanation:

First, we have to determine the total pressure experimented by water inside the piston-cylinder device. The total pressure is the sum of atmospheric and gauge pressures, the gauge pressure is the weight of piston divided by its cross-sectional area, that is:

`P_(g) = (m_(p)\cdot g)/(A)`

Where:

`P_(g)` - Gauge pressure, measured in pascals.

`m_(p)` - Mass of the piston, measured in kilograms.

`g` - Gravitational constant, measured in meters per square second.

`A` - Cross-sectional area, measured in square meters.

`P_(g) = ((51\,kg)\cdot \left(9.807\,(m)/(s^(2)) \right))/((100\,cm^(2))\cdot \left((1\,m^(2))/(10000\,m^(2)) \right))`

`P_(g) = 50015.7\,Pa`

`P_(g) = 50.016\,kPa`

The total pressure of water is:

`P_(t) = 100\,kPa + 50.016\,kPa`

`P_(t) = 150.016\,kPa`

Temperature at which water starts boiling is the saturation temperature associated with total pressure, which can be obtained from property tables:

`T_(sat) = 111.35\,^(\circ)C`

The temperature at which the water starts boiling is 111.35 °C.