3. Hot water for commercial warewashing equipment is generated by heat recovered from a furnace exhaust gas. A crossflow heat exchanger is used, with the hot gas (mixed) flowing over the tubes. The hot gas (cn = 1040 J/kg-C) enters the heat exchanger at a temperature of 450C with a flow rate of 2.5 kg/s. The water (cp= 4200 J/kg-C) flows through the tubes unmixed at 4.0 kg/s, entering the heat exchanger at 50C and must be heated to 86C to comply with the sanitation standard for warewashing equipment. The overall heat transfer coefficient for the exchanger is 232.4 W/m-C. Each tube has an external diameter of 25 mm and a length of 2.0 m. Using the effectiveness-NTU method determine the number of tubes required