Follow up question:Differentiate a contact type from a non-contact type heat exchanger.
A heat exchanger (HE) is used to move heat from one location or zone to another, usually for the purpose of cooling one zone. A direct-contact HE is explained in the link below - heat transfer between hot and cold streams of two phases in the absence of a separating wall. So you could have a gas being bubbled through a liquid to cool it. A non-contact HE could be, for example, one where cooling pipes (with coolant inside them) have the liquid to be cooled flowing around them. It comes down to whether there is a wall separating the two phases or not.
