A counter-flow shell and tube exchanger is used to heat water with hot exhaust gases. The water (c = 41 80J/kg°C flows at a rate of 2 kg/s while the exhaust gas (1030 J/ kg°C) flows at the rate of...

A counter-flow shell and tube exchanger is used to heat water with hot exhaust gases. The water (c = 41 80J/kg°C flows at a rate of 2 kg/s while the exhaust gas (1030 J/ kg°C) flows at the rate of 5.25 kg/s. If the heat transfer surface area is 32.5 m2and the overall heat transfer coefficient is 200 W/m2°C, what is the NTU for the heat exchanger?

(a) 1.2                   (b) 2.4

(c) 4.5                    (d) 8.6