4. A 'heat exchanger' may be defined as an equipment which transfers the energy from a hot fluid to a cold fluid, with maximum rate and minimum investment and running costs. In heat exchangers the temperature of each fluid changes as it passes through the exchangers, and hence the temperature of the dividing wall between the fluids also changes along the length of the exchanger. One of the type of heat exchanger is the recuperator where the two fluids are not allowed to mix and according to the relative directions of two fluid streams the heat exchangers can have either parallel-flow or counter-flow mechanism. a. Hence you are required to distinguish the differences between the parallel- flow and counter-flow recuperator heat exchangers. (4 marks)

Fig: 1