through the first unit 10 to the first manifold 38 which directs the heat exchange fluid back through the second unit 10 to the second manifold 40 which then directs the fluid back through the third unit 10 to the third manifold 42 the fluid is there directed back through the fourth unit 10 and out of the outlet 44 in another embodiment as shown in fig v heat exchange fluid from inlet 46 flows through two units 10 to a manifold 48 which directs the fluid flow back through the upper two units 10 and out through the outlet 50 the embodiment of fig vi shows how heat exchange fluid enters through inlet 52 and is distributed by a first manifold 54 to all four units 10 the fluid flows directly through all four units 10 in parallel to the second manifold 56 which directs the fluid out through outlet 58 a model of the phase change heat exchanger of the present invention was constructed using six units as described above two units each were stacked on top of each other and the three pairs were lined up in series this arrangement provides both the axial and the vertical heat exchange characteristics the entering and exiting air temperature was measured versus time and the storage and discharge capacity of the test unit was determined by the integration of the area between two curves of the entering and exiting air temperature.