Semi-numerical analysis of heat transfer performance of fractal based tube bundle in shell-and-tube heat exchanger

A bundle of topologically arranged tubes based on fractal is proposed in this work to enhance the flow of shell-side fluid. The space for arranging tubes is separated into some periodic regions and the tubes are symmetrically arranged in these regions. The topological arrangement of tubes is in the radial direction starting from the shell center. Fractal treatment is applied to divide each periodic region into two smaller symmetric ones. With the alternately installed disc and doughnut baffles, the shell-side fluid converges to shell center or diverges away from the center, and the uniform shell-side flow is realized. According to the periodic characteristic of tube bundle, numerical heat transfer unit models are established and the characteristic temperatures in heat exchanger are obtained using the semi-numerical simulation algorithm. Comparing the results with the analytical solution to the outlet temperatures of shell-side and tube-side fluids based on the Bell-Delaware method, it is revealed that, even though the number density of tubes is reduced compared to the conventional version, the new structure has a higher heat transfer efficiency due to the full use of tubes. The fluid outflows from the tube near the shell center has a higher temperature, and the concurrent and countercurrent flows result in the different temperature increasing trends of tube-side fluid as well as the different temperature decreasing trend of shell-side fluid. The countercurrent results in a larger decrease of shell-side fluid temperature.