a heat transferring or transmitting apparatus characterized by an evaporator containing a semiconductive or heat generating device and being disposed below a condensor unit and connected thereto by two conduits substantially vertically arranged therebetween , such that a coolant gas is passed upwardly through one of the conduits and a coolant liquid is passed downwardly through the other of the conduits , features a resistant element , which may be in the form of a liquid reservoir , disposed in the coolant liquid passage so as to prevent flowing of the coolant gas into and through the coolant liquid passage . the paths of the flowing coolant gas and liquid are thereby kept separate whereby frictional contact therebetween is avoided while circulation is maintained through a phase transition process .