Flow Pattern and Turbulence Intensity in Stacks of Interrupted Parallel-Plate Surfaces

Wen-Jei Yang Department of Mechanical Engineering and Applied Mechanics, The University of Michigan, Ann Arbor, Michigan 1 A n experimental study is performed to investigate the pressure drop distribution and turbulence intensity for airflow through a stack of parallel plates with periodic interruptions. The interrupted surfaces are constructed in an offset-strip f6rm and a perforated form. Hot-wire measurements of the flow stream in the test core are made to determine turbulence intensity variations as a function of the Reynolds number. Results on the pressure drop and turbulence intensity are compared with those of the uninterrupted flow case. The offset-strip surface yields higher flow with higher turbulence intensity than the perforated and uninterrupted surfaces, an indication of superior heat transfer performance. Flow visualization by the dye injection method is performed on flow through a stack of offset-strip surfaces in a vertical water tunnel. Steady laminar flow, vortex shedding, oscillating flow, and turbulent flow are observed in sequence along the flow passage. The effects of Reynolds number on the location of the transition from steady to unsteady (oscillating and turbulent) flow regimes are determined. The study provides evidence to support the theory of secondary laminar-flow enhancement and transition-turbulent flow enhancement of heat transfer in compact heat exchangers [1-3].