Question

Example 5 10, P 236 9th edition Refrigerant 134 a at 700 kPa , 70 deg C and 8 kg/min is cooled by water in a condenser until it exists as a saturated liquid at the same pressure. The cooling water enters the condenser at 300 kPa and 15 deg C and leaves at 25 deg C at the same pressure. Determine the mass flow rate of the cooling water required to cool the refrigerant.

Answer 1

The mass flow rate of the cooling water is determined from the energy balance equation. The enthalpies of the refrigerant at the initial and the final states were obtained from A-13 and A-12 for the given parameters.

Therefore by energy balance equation,

`$\dot m_r h_(r1)=\dot m_w \Delta h_w +\dot m_r h_(r2) $`

`$\dot m_w = (\dot m(h_1-h_2)_r)/(c \Delta T)$`

`$\dot m_w = (8(308.34-88.82))/(4.18 * 10)$`

= 42 kg / min