shell - and - tube heat exchangers that utilize one or more foam heat transfer units engaged with the tubes to enhance the heat transfer between first and second fluids . the foam of the heat transfer units can be any thermally conductive foam material that enhances heat transfer , for example graphite foam . these shell - and - tube heat exchangers are highly efficient , inexpensive to build , and corrosion resistant . the described heat exchangers can be used in a variety of applications , including but not limited to , low thermal driving force applications , power generation applications , and non - power generation applications such as refrigeration and cryogenics . the foam heat transfer units can be made from any thermally conductive foam material including , but not limited to , graphite foam or metal foam . in an embodiment , the heat exchanger utilizes tubes that are twisted around a central foam heat transfer unit .