ANALYSIS OF UNSTEADY FORCED-CONVECTION IN TURBULENT DUCT FLOW

The results of a theoretical analysis and experimental study of unstea dy forced convection with turbulent dow in the thermal entrance region of a circular duct, subjected to a periodically varying inlet tempera ture, are presented. The related unsteady energy equation for the ther mal entrance region is analytically solved under a general boundary co ndition of the fifth-kind, accounting for the effects of both external convection and wall heat capacitance. Together with empirical models for expressing both eddy viscosity and turbulent velocity profiles, th e generalized integral transform technique is used to provide hybrid a nalytical-numerical solutions for the thermal response of the fluid wi th a prescribed accuracy, An experimental setup was built and used to validate the mathematical modeling wherein the thermal response of the fluid is obtained in terms of amplitudes and decay indices with respe ct to the inlet condition for fully developed turbulent flow, due to a sinusoidal variation of the inlet temperature. Satisfactory agreement prevailed between the theoretically and experimentally determined hea t transfer characteristics for a succession of axial positions, thereb y establishing the theoretical model and numerical technique. To furth er enhance the model's practical applicability to engineering problems , the analytical technique is extended in obtaining results on the eff ects of the modified Blot number, fluid-to-wall thermal capacitance ra tio, and the Reynolds number, on the thermal response of the fluid wit hin the temperature field, which are presented in tabular forms.