entirely evaporated at those points only and not in the traps 27 above and below the conversion of this localized liquid in the gas running through the nozzles 28 28a 28b etc can elevate the gas pressure sufficiently to open the valve 30 and admit enough liquid from the adjacent device 29 to refill the one or two empty traps 27 of that particular column with vaporizable liquid simultaneously this same independent mode of operation can take place in every column throughout the entire heat exchanger to produce a truly regulated evaporative process and a truly controlled performance heat exchanger in a three dimensional sense that is controlled liquid vaporization and controlled transfer of heat between an exterior and an interior fluid can take place differentially over the area of the heat exchanger spanned by the plates 25 and over the thickness thereof defined by the columns consisting of the engaged extensions 26 it can be seen that the described construction and mode of operation brought about by the invention completely eliminates the inherent drawbacks of the prior art discussed previously and illustrated in fig1 and 2 because the system throughout contains only separated and isolated small volumes of liquid in the traps 27 instead of one continuous flowing mass of liquid the tendency for films of gas bubbles hindering heat transfer to develop is greatly minimized or eliminated and any bubbles which do develop are quickly carried off in the gas stream running through the nozzles 28 28a 28b etc fig5 through 8 show variations in the construction of the liquid trapping and counter flow gas discharging columns in the heat exchanger which can be substituted for the satisfactory arrangement shown in fig3 and 4 for example in fig6 heat exchanger plates 25a have formed integral.