A set of partial differential equations is formulated which describes the
transient behaviour of parallel-flow multichannel heat exchangers. In the
model, the heat capacitance of walls is neglected and heat is assumed to
be transferred only in the direction perpendicular to the direction of flow
of fluids. The set is solved by the MacCormack predictor-corrector method
for a sample four-channel heat exchanger. Three cases of transient behaviour
of the exchanger are investigated: uniform initial temperatures in all channels,
a step change in flow rate in one channel, and a step change in inlet
temperature of one fluid. In the last two cases, the exchanger is initially
at steady state.