Air at 0.1 kg/s is to be cooled from 140 C to 40 C in a heat exchanger. The coolant water is at 20C constant throughout the heat exchanger. The convective heat transfer coefficients are 100 W/m2K and 500 w/m2K on the air and water sides respectively. The air and water are separated by material 100mm thick, thermal conductivity 10 W/mK and the surface area is 4m2 per meter length of the unit.
Calculate the overall heat transfer coefficient between the air and the water (answer in W/m^2K).