Refrigerant134a is to be cooled by water in a condenser The

Refrigerant-134a is to be cooled by water in a condenser. The refrigerant enters the condenser with a mass flow rate of 6 kg/min at 1 MPa and 70 degree C and leaves at 35 degree C. The cooling water enters at 300 kPa and 15 degree C and leaves at 25 degree C. Neglecting any pressure drops, determine the mass flow rate of the cooling water required and the heat transfer rate from the refrigerant to water.

Solution

solution

a)

h₁ = h_f@15C = 62.99 kJ/kg

h₂ = h_f@25C = 104.89 kJ/kg

The refrigerant enters the condenser as a superheated vapor and leaves as a compressed liquid at 35^oC.

P₃ = 1MPa, T₃ = 70^oC, h₃ = 302.34 kJ/kg.

P₄ = 1MPa, 35^oC, h₄ = h_f@35C = 98.78 kJ/kg

Substituting,

m_w (62.99 – 104.89) = 6(-302.24)

m_w = 29.15 kg/min

(b) Heat transfer from the refrigerant to the water:

Choosing volume occupied by the water as control volume,

Q_w,in + m_w h₁ = m_w h₂

Q_w,in = m_w(h₂ – h₁) = 29.15 (104.89 – 62.99)

       = 1221 kJ/min