This work is aimed at assessing the potential of winglet-type vortex generator (VG) “arrays” for multirow inline-tube heat exchangers with an emphasis on providing fundamental understanding of the relation between local flow behavior and heat transfer enhancement mechanisms. Three different winglet configurations in common-flow-up arrangement are analyzed in the seven-row compact fin-and-tube heat exchanger: (a) single–VG pair; (b) a 3VG-inline array (alternating tube row); and (c) a 3VG-staggered array. The numerical study involves three-dimensional time-dependent modeling of unsteady laminar flow (330⩽Re⩽850) and conjugate heat transfer in the computational domain, which is set up to model the entire fin length in the air flow direction. It was found that the impingement of winglet redirected flow on the downstream tube is an important heat transfer augmentation mechanism for the common-flow-up arrangement of vortex generators in the inline-tube geometry. At Re=850 with a constant tube-wall temperature, the 3VG-inline-array configuration achieves enhancements up to 32% in total heat flux and 74% in j factor over the baseline case, with an associated pressure-drop increase of about 41%. The numerical results for the integral heat transfer quantities agree well with the available experimental measurements.
This numerical study pertains to characterizing flow and heat transfer interactions for an interrupted fin design with wavy profile in compact tube-and-fin heat exchanger. Although designs with similar concept is prevalent in the HVAC&R industry not much literature exists on the subject combining wavy fins with periodic interruptions. Presently sinusoidal wavy fin is combined with slit fins to investigate thermalhydraulic performance relative to an un-interrupted fin design. This fin is referred to as Hybrid Slit Wavy (HSW) fin in this work. Commercial Computational Fluid Dynamics (CFD) software is used for 3D numerical solution of the complete Navier-Stokes and energy equations in the heat exchanger to study flow physics and predict performance. The modeling approach is first validated with available test data from the literature on a wavy (Herringbone profile) fin heat exchanger. The predicted friction factor was within 12% and the Colburn j-factor was within 7% of the reported test data over a Reynolds number range of 350-6500. In the case of the HSW fin it was found that the air-side heat transfer is enhanced by about 20-39% relative to the baseline un-interrupted fin with an associated pressure drop penalty of 20-38%. The area goodness factors of the HSW fins are up to 4 % higher compared to the wavy fins at various operating conditions indicative of favorable trade-off. It is further established that the local flow pattern including boundary layer modifications, wake structures and enhanced flow mixing correlates strongly with local Nusselt number distribution.
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