Development and validation of Nusselt number and friction factor correlations for laminar flow in semi-circular zigzag channel of printed circuit heat exchanger

Abstract

Friction factor and heat transfer correlations have been developed for printed circuit heat exchangers (PCHEs) as a function of geometric parameters. These correlations summarize the thermal hydraulic performance of PCHEs and allow for accurate determination of their cost and effectiveness. Although there have been previous studies of the thermal-hydraulic performance of zigzag channel PCHEs, explicit correlations for friction factor or Nusselt number as a function of geometric parameters have not yet been reported. In this study, computational fluid dynamic (CFD) predictions were used to aid in the development of friction factor and Nusselt number correlations for laminar flow in semicircular zigzag-channel PCHEs. Two CFD models were developed to investigate the thermal-hydraulic characteristics of fluid flow in zigzag channels. A single-channel isothermal CFD model was used to investigate friction factors in PCHE zigzag channels. A two-channel CFD model was used to investigate the Nusselt number in zigzag channels and the effect of temperature-dependent fluid properties on the pressure loss. The effects of geometric parameters such as relative length ratio, zigzag angle and radius of curvature of bend were investigated. From the extensive CFD analysis database, friction factor and Nusselt number correlations were developed by implementing a least squares method with a non-linear Generalized Reduced Gradient algorithm. The friction factor correlation is valid for 50≤Re≤2000, 5°≤α≤45° and 4.09≤lR/Dh≤32.73. The Nusselt number correlations are valid for 200≤Re≤2000, Pr≤1.0, 5°≤α≤45° and 4.09≤lR/Dh≤12.27. The correlations were validated against experimental data from The Ohio State University (OSU) and Korea Advanced Institute of Science and Technology (KAIST). The friction factor for zigzag-channel PCHEs is mainly influenced by the zigzag channel geometry while the Nusselt number is influenced by the overall heat exchanger design including the plenum sections.