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

Solution :

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,

$\dot m_r h_{r1}=\dot m_w \Delta h_w +\dot m_r h_{r2}$

$\dot m_w = \frac{\dot m(h_1-h_2)_r}{c \Delta T}$

$\dot m_w = \frac{8(308.34-88.82)}{4.18 \times 10}$

     = 42 kg / min