In this book, our objective is to design and optimize Plate and Frame heat exchanger. The plate and frame heat exchanger was originally introduced in the 1930s and is used extensively in the oil industries . Plate and frame heat exchangers consist of several metal sheets with corrugated surfaces that are clamped together .The irreversibility of any heat exchanger is due to two factors; The transfer of heat across the stream-to-stream temperature difference and the frictional pressure drop that accompanies the circulation of fluid through the apparatus. The fluid friction and heat transfer irreversibility can systematically be reduced by showing down the movement of fluid through the heat exchanger. In other words, optimization process is synonymous with employing larger heat exchanger, where there is more heat transfer area and less heat exchanger volume. Hence, after designing a heat exchanger the optimization process is a key stage due to economical considerations.