Three different approaches are developed for the prediction of transie
nt performance of cross-flow finned-tube, liquid/gas heat exchangers f
or the step change in the inlet temperature of the hot fluid. These ar
e called the zero solid capacity, one solid capacity and two solid cap
acity approaches (ZCA, OCA and TCA respectively). In the analysis usin
g ZCA, the heat capacities of the wall and tins are added to the capac
ities of the hot and cold fluids. The temperature variation of both fl
uids between inlet and exit is assumed to be linear, and the effective
rate of heat transfer is assumed to be proportional to the difference
of the average temperatures on both sides. In the analysis using OCA
the fins and tube wall are considered as one thermal capacity and the
thermal resistance between them is neglected. However, in the analysis
using TCA the capacities of the fins and tube wall are considered sep
arately. Energy equations for the hot and cold fluid, tube wall and th
e fins, if they are to be considered, are derived for each of these ap
proaches and solved numerically using a finite-difference method. The
variation of the dimensionless exit temperature of the hot and cold fl
uid with time is obtained for a step change in the inlet temperature o
f the hot fluid. To show the appreciability of these approaches, an ex
perimental study is performed and the numerical results are compared w
ith the experimental results.