New thermal-hydraulic correlations for printed circuit heat exchangers (PCHEs) with zigzag channels under high Reynolds numbers

Purpose The purpose of this paper is to investigate the impact of semi-circular zigzag-channel printed circuit heat exchanger (PCHE) design parameters on heat transfer and pressure drop of flows under high Reynolds numbers and provide new thermal-hydraulic correlations relevant to conditions encountered in natural gas processing plants. Design/methodology/approach The correlations were developed using three-dimensional steady-state computational fluid dynamics simulations with varying semicircular channel diameter (from 1 to 5 mm), zigzag angle (from 15° to 45°) and Reynolds number (from 40,000 to 100,000). The simulation results were validated by comparison with experimental results and existing correlations. Findings The results revealed that the thermal-hydraulic performance was mostly affected by the zigzag angle, followed by the ratio of the zigzag channel length to the hydraulic diameter. Overall, smaller zigzag angles favored heat transfer intensification while keeping reasonably low pressure drops. Originality/value This study is, to date, the only one providing thermal-hydraulic correlations for PCHEs with zigzag channels under high Reynolds numbers. Besides, the broad range of parameters considered makes the proposed correlations valuable PCHE design tools.

THEORETICAL MATHEMATICAL MODELING OF HEAT EXCHANGE IN PIPES WITH TRIANGULAR AND SQUARE TURBULATORS WITH d/D=0.95÷0.90, t/D=0.25÷1.00 AND HIGH REYNOLDS NUMBERS Re=106

Mathematical modeling of heat exchange process in straight and round horizontal pipes with protrusions and d/D=0.95...0.90, t/D=0.25...1.00 of triangular and square sections with large Reynolds numbers (RE=106) are carried out on the basis of multiblock computing technologies based on solutions of factored and finite-volume algorithm of RANS equations and energy equations. It is shown that for higher square protrusions and at higher Reynolds numbers, a limited increase in NU/NUgl is accompanied by a significant increase in relative hydro resist ance in accordance with the higher Reynolds number; for triangular turbulators, this persists and even deepens.

Experimental PIV investigation of the PZT fans array coupling effect at high Reynolds numbers

Piezoelectric fan arrays are being increasingly emphasized for heat dissipation in small-sized electronic devices. In this study, PIV experiments were conducted to investigate the flow fields induced by piezoelectric fan arrays with different vibration modes and pitches at high Reynolds numbers (324< Re <509) in a stationary air environment. As a result, when the PZT fan array is vibrating in-phase, the saddle points in the time averaged flow field are formed and separated gradually as the pitch increases, the remnant vortex and the induced vortex interact to form a jet with a periodic oscillation in the direction. Jet velocity reaches a maximum at P = 3A. In counter-phase vibration, saddle points are separated from one region under large pitches, the interaction of counter-rotating induced vortices forms a vertical upward jet. The morphology of induced and remnant vortices with different vibration modes and array pitches are responsible for the jet formation and flow field pattern. The interaction of counter-rotating vortices in counter-phase vibration leads the jet intensity higher than in-phase vibration induced jet, the optimal setting of the PZT fan under this study is determined as P = 2.5A with counter-phase vibration. The experimental results provide validation for the simulation study and give guidance to the application

How Turbulence Models Perform in Simulating Pipeflow Response to Targeted Wall-Shapes?

This study evaluates how Reynolds-Averaged-Navier-Stokes (RANS) models perform in simulating the characteristics of mean three-dimensional perturbed flows in pipes with targeted wall-shapes. Capturing such flow features using turbulence models is still challenging at high Reynolds numbers. The principal objective of this investigation is to evaluate which of the well-established RANS models can best predict the flow response and recovery characteristics in perturbed pipes at moderate and high Reynolds numbers (10000-158000). First, the flow profiles at various axial locations are compared between simulations and experiments. This is followed by assessing the well-known mean pipeflow scaling relations. The good agreement between our computationally predicted data using Standard k-epsilon model and those of experiments indicated that this model can accurately capture the pipeflow characteristics in response to introduced perturbation with smooth sinusoidal axial variations.