Used cooking oil can be converted to biodiesel through a transesterification process. In this process, the refined cooking oil needs to be heated first. An opposite flow heat exchanger with 3.5 cm diameter thin -walled copper was used to heat cooking oil from 35C to 70C at a rate of 0.5 kg/s. The heat source is from condensed steam that enters the heat exchanger at a temperature of 140C (Figure 2). If the total heat transfer coefficient in the tube is 750 W/m2 . C, the heat specificity for cooking oil, cp = 2,300 J/kg C, and specific enthalpy for water hfg = 2,174 kJ/kg. Calculate:

a) Heat transfer rate

b) The length of the heat exchanger tube

c) If the length tube is reduced, what will happen to the output temperature of the used cooking oil. Why?

Steam 140C Used cooking 35*C, 0.5 kg/s 70C