EFFECT OF SPATIALLY PERIODIC HEATING OR AN ABRUPT CONTRACTION AT INLET ON TRANSITIONAL AND TURBULENT HEAT TRANSFER IN A DUCT (UNSYMMETRIC, INTERRUPTED WALL CONDITIONS, SEPARATED FLOWS, ENHANCED, FORWARD STEP).

摘要

A three-part investigation of convective heat and mass transfer from a one-sided-heated flat rectangular duct with fully developed transitional and turbulent flow was performed both experimentally and numerically. Quasi-local mass transfer results were obtained via the naphthalene sublimation technique. The heat/mass transfer analogy permitted conversion into heat transfer results.;For the first case, the experimental Sherwood number distributions displayed typical entrance region variations. The fully developed data agreed very well with well-established correlations. The numerically determined axial distributions were typically within 2% of the mass transfer data. For air, the Nusselt number distributions also displayed typical entrance variations, with thermal development at 40 hydraulic diameters from inlet.;Sherwood number distributions for the spatially periodic heated duct were characterized by higher mass transfer coefficients with increasing values of the adiabatic-to-active segment length ratio. The numerical distributions completely confirmed the experimental ones. A performance analysis showed that the decrease in the transfer area (delegated to the adiabatic segments) was greater than the increase in the transfer coefficient, causing a net decrease in the overall rate of heat transfer in the presence of periodic heating.;The duct with a contraction was characterized by a sharp increase in the transfer coefficient, followed by a peak and a decay to the fully developed value. These features are characteristic of separation, reattachment and redevelopment. The near-inlet coefficients were several times greater than the separation-free results. The effect of various candidate characteristic dimensions in the correlation of the results was investigated in detail.;First, the duct active wall is held isothermal. Experimental and numerical mass transfer results were generated for Sc = 2.5, supplemented by numerical results for heat transfer to air (Pr = 0.7). Second, the duct active wall is spatially periodically heated (i.e., successive adiabatic and heated segments). Experimental and numerical results were also obtained. Finally, experimental results are obtained for a duct with an unsymmetric contraction of the flow cross section.