CFD SIMULATION OF HEAT TRANSFER WITH SPIRAL-WIRE DISPLACEMENT ON THE PIPE

The results of the study of the intensification of the heat transfer process under forced air convection in the annular gap of a pipe-in-pipe heat exchanger with a spiral-wire intensifier located near the outer surface of the inner pipe are presented. The intensifier does not touch the pipe surface. The height of the wire of the intensifier is taken as 1.5 mm. The change in the winding pitch varied within the range of 12-20mm. Boundary conditions of the first kind + 20 ° C are set on the inner surface of the inner pipe. The temperature of the air moving in the annular gap is 300 ° C. The air velocity varied from 6 to 15 m / s. For the CFD model of a pipe-in-pipe heat exchanger, the use of a computational grid with 4.7 million elements is justified. The CFD model was validated using literature data. Based on the analysis of the ratio of the intensified Nusselt number to the Nusselt number for a smooth pipe, a 1.7-fold increase in heat transfer was found for Reynolds numbers from 5000 to 7000. This result is explained by the periodic destruction of the boundary layer along the pipe. With a further increase in Reynolds numbers to 13000, the intensification of heat transfer decreases from 1.7 to 1.3, which is explained by an increase in the vortex zone immediately behind the wire and the appearance of recirculation zones that make a minimum contribution to heat transfer. It has been determined that the spiral-wire intensifier with the maximum possible step of 20 mm contributes to the greatest increase in heat transfer by 1.7 times and has the smallest coefficient of hydraulic friction of 0.076-0.06 for the studied range of Reynolds numbers.