SIGNIFICANCE AND CORRELATION OF NUSSELT NUMBER (Nu), PRANDTL NUMBER (Pr) AND STANTON NUMBER (St) WITH VOLUME FRACTION OF VAPOUR IN A PHASE CHANGE SITUATION AROUND A CYLINDER IN STAGGERED ARRANGEMENT

摘要

The complexity of problem of fluid flow and heat transfer over an array of circular cylinders is quite common in industrial applications of fluid dynamics. The complex nature of the problem encountered in industry gives rise to certain significant dimensions in fluid dynamics theory. Some of them are fluid flow interaction, phase change phenomenon, interferences in flow and vortex dynamics which are typically found in compact heat exchangers, cooling of electronics equipment, nuclear reactor fuel rods, cooling towers, chimney stacks, offshore structures, hot-wire anemometry and flow control. In each of these situations, it is highly necessary to understand how mass, momentum and heat transfer take place and, due to which, many decisions are taken about the health of the equipment or the possible consequence of a situation. In addition to taking the impact of dynamics of fluid flow and heat transfer, the structures where these situations happen, are also subjected to air or water flows and therefore, experience flow induced forces which can lead to their failure over a long period of time. One of the significant cases is a two-phase change phenomenon that occurs due to heating of water flowing over a cylinder in a typical staggered arrangement. Basically, with respect to the free stream direction of flow water, the configuration of two cylinders can be classified as tandem (side-by-side) and staggered. Both the configurations are taken in the study and phase change of water is carried out by numerical simulation wherein Reynolds averaged Navier-Stokes (RANS) equations were solved along with Eulerian model for individual phases (water and vapour). The basic findings of the simulation such as drag coefficients and the necessary flow parameters were compared with the experimental and numerical results published by earlier researchers and presented in the paper. The phase change phenomenon considered in the paper was fundamentally due to nucleate boiling and the objective was to understand how volume fraction of vapour phase is getting affected by rise of temperature of cylinder surface and how a correlation of Nusselt number (Nu), Prandtl number (Pr) and Stanton number (St) exists with volume fraction of vapour phase of water. The dataset of Nu, Pr and St obtained from the computations were statistically analyzed to establish the significance and correlation of these non-dimensional numbers with volume fraction whose maximum value is one.