A heat exchanger produces steam by boiling water within vertical tubes, as shown in Figure 3.1

i)Water is supplied at a rate of 2 kg s–1 and an initial temperature of 80°C. Calculate the rate of heat transfer required to produce saturated steam at 140°C. What would the pressure in the top of the heat exchanger be (in kPa gauge)?

ii)The water/steam passes through a bundle of 50 vertical tubes, each of 3 cm internal diameter, 4 cm outer diameter, and 4 m in length, made of stainless steel with thermal conductivity 19 W m–1 K–1. Calculate the overall resistance to heat transfer across the tube walls. Hence calculate the required temperature driving force to deliver the heat transfer rate calculated in part (i).