Macro-Scale Modeling of Compact Heat Transfer Devices with Offset Strip Fins

In highly compact heat transfer devices, micro- and mini-channels with an array of periodic fins are commonly used to enhance the heat transfer or to increase the compactness. Due to their small dimensions, the flow through these channels mostly remains in the laminar regime. Moreover, after a certain development length, the flow and heat transfer in these devices become periodically developed such that their patterns around each fin become identical. Therefore, the flow and heat transfer are often described through an analysis of a single fin unit or a so-called unit cell. Alternatively, macro-scale models of the flow and heat transfer are employed to characterize the average velocity, pressure, and temperature fields in the channel. Only recently, an exact macro-scale description of the periodically developed flow and heat transfer has been given by Buckinx and Baelmans, unifying both approaches. Nevertheless, this macro-scale description has not been applied to any micro- and mini-channels with a periodic fin array. 

In this work, the exact macro-scale description of the periodically developed flow and heat transfer will be presented for micro- and mini-channels with an array of one of the most common fin geometry: the offset strip fin geometry. In particular, the macro-scale pressure drop and heat transfer coefficient will be determined for periodically developed flow and heat transfer in arrays of offset strip fins subject to an imposed heat flux and will be modeled through a friction factor and a Nusselt number correlation using a single unit cell simulation. Additionally, it will be assessed when the developed correlations are valid in the presence of channel entrance and side-wall effects, which have not been taken into account up to the present. Finally, an experimental investigation is performed to further support the numerical findings.