a) Pillow plate exchangers
b) Plate fin exchangers
c) Lamella plate heat exchangers
d) Spiral plate heat exchangers

Answer: b
Explanation: Plate fin exchanger is also referred to as a matrix heat exchanger. In this heat exchanger, layers of corrugated sheets are made which is separated by flat metal plates therefore creating a series of finned chambers. The hot and cold fluid streams flow in alternate layers of the heat exchanger.