In this paper, a numerical study on the flows in parallel and counter flow double tube heat exchangers with the inner tubes being eitheralternating horizontal or vertical oval cross section pipes or circular pipes is presented. The results include temperature and pressure contoursand velocity vectors at several selected cross sections, axial averaged Nusselt number distributions and distributions of overall heattransfer coefficient and heat transfer enhancement factor versus three different parameters. The computation shows that the introductionof the inner alternating oval tube produces axial vortices in both the inner and outer tube flows, and the tube’s heat transfer performanceis improved as a result. In general, the counter flow arrangement returns a higher level of overall heat transfer coefficient than the parallelflow arrangement. However, in terms of the magnitude of heat transfer enhancement, the performance of the parallel flow arrangement isslightly better than that of the counter flow.
Energy Conversion and Management 49 (2008) 1574–1583