Experimental and theoretical investigation of unsteady forced convection in ducts

In the first phase of this project, an experimental apparatus was designed, built and used to study transient forced convection in a duct for sinusoidal variation of heat input at the inlet, covering both laminar and turbulent flow. The experimental study covered a wide range of Reynolds numbers and the frequencies of heat input in the thermal entrance region. The temperature variation along the rectangular duct in response to the timewise variation of inlet temperature was recorded and the amplitudes at various locations along the rectangular duct were presented in graphical form for various values of inlet frequency and the Reynolds number.In the second phase of the project, some of the experimental study has been repeated for the thermal entrance region. The effects of the thermal boundary conditions on the amplitude along the length of the duct were studied for various values of the Reynolds number and inlet frequency. The theoretical analysis of laminar flow in the thermal entrance region under the assumption of constant wall temperature has been compared with the experimental findings.In the final phase of the project, a general boundary condition of the fifth kind that accounts for both external convection and wall thermal capacitance effects is considered, and an analytical solution is obtained through extending the generalized integral transform technique. The variations of amplitudes and phase lags of the centerline and bulk temperatures along the duct are determined as functions of modified Biot number, fluid-to-wall thermal capacitance ratio and dimensionless inlet frequency.The theoretical dimensionless temperature amplitudes along the duct for both laminar and turbulent flow have been compared with experimental findings to provide validation of the mathematical model employed. Good agreement is obtained when the non-uniform sinusoidally varying inlet temperature profile obtained by experiments is incorporated into the theoretical model. The effects of inlet temperature frequency, Reynolds number and boundary conditions on temperature amplitudes have been studied for both laminar and turbulent flow regimes