This paper presents a semi-analytical solution of a set of partial differential
equations describing the transient temperature field in a parallel-flow
three-fluid heat exchanger. The set of partial differential equations
is Laplace-transformed and the resultant set of ordinary differential equations
is solved analytically. The inverse of the solution is obtained numerically.
Exemplary calculations are performed for the case of a step change
in the inlet temperature of one fluid and steady state initial conditions.