5,000 kg/h of water will be heated from 20°C to 35°C by hot water at 140°C. A 15°C hot water temperature drop is allowed. A number of double-pipe heat exchangers, each connected in series, will be used. Hot water flows through the inner tube. The thermal conductivity of the material is 50 W/m ⋅ K. 

Fouling factors: Ri = 0.000176 m2 ⋅ K/W 

Ro = 0.000352 m2 ⋅ K/W

Inner tube diameters: ID = 0.0525 m, OD = 0.0603 m

Annulus diameters: ID = 0.0779 m, OD = 0.0889 m

The heat transfer coefficients in the inner tube and in the annulus are 4,620 W/m ² ⋅ K and 1,600 W/m ² ⋅ K, respectively. Calculate the overall heat transfer coefficient and the surface area of the heat exchanger for both parallel and counter flow arrangements.