NUMERICAL STUDY OF FLOW AND HEAT TRANSFER CHARACTERISTICS IN SHELL-AND-PLATE HEAT EXCHANGERS

Abstract

The shell-and-plate heat exchanger is a completely welded heat exchanger that combines the best features of a shell-and-tube heat exchanger with a plate heat exchanger. The flow between the circular corrugated plates behaves as a first expanding then converging flow, leading to the intricate nature of flow structures, flow resistance, and phase-change heat transfer. The present paper numerically investigates the flow behaviors and heat transfer characteristics in the channel between the circular corrugated plates of 0.2 m in diameter, 0.0022 in corrugation depth, and 75° in corrugation angle. In the simulation, the gas velocity ranges from 0.25-6.00 m/s while the liquid velocity from 0.01-0.20 m/s. The wall is set as adiabatic and constant temperature condition of 350 K, respectively. For the single-phase flow, a longitudinal spiral flow along the main flow direction is formed, and the local velocity at the edge of the circular plate is generally higher and more turbulent than that in the central area. Additionally, the increase of Reynolds number leads to a more significant pressure drop but an apparent heat transfer enhancement. Based on the analysis of the friction factor and Nusselt number with Reynolds number, the empirical correlations for predicting the flow resistance and heat transfer characteristics in the channel are proposed. For the two-phase flow, we employed the VOF model to investigate the distribution of the phases in the downward flows. Compared with the experimental data, the numerical results are demonstrated to provide an accurate analysis of the phases distribution, particularly in the cross section of the channel. Accordingly, the flow patterns in the downward two-phase flows are identified as bubbly flow, slug flow, film flow, and churn flow. Based on the variation of the averaged void fraction, the film flow can be identified as α > 0.8 while bubbly flow as α < 0.5. Additionally, the void fraction in the cross section of the flow channel along the flow direction is analyzed in detail. Since the effect of the expansion and contraction of structures will go away with an increase in the gas mass flow rate, it can be anticipated that the effect of uniform distribution is more prominent for slug flow and is negligible for film flow.