**Abstract**

A conjugate heat transfer problem on the shell side of a finned double pipe heat exchanger is numerically studied by suing finite difference technique. Laminar flow with isothermal boundary conditions is considered in the finned annulus with fully developed flow region to investigate the influence of variations in the fin height, the number of fins and the fluid and wall thermal conductivities on the hydraulic and thermal design of the exchanger. The governing momentum and energy equations have been solved by a finite difference-based numerical algorithm. The improvement in heat transfer rates, the exchanger performance and the optimum configurations are discussed.

**Keywords:** incompressible, laminar flow, convective heat transfer, finned double pipe, fully developed flow, conjugate heat transfer, isotherms
