A numerical study of the supercritical CO plate heat exchanger subject to U-type, Z-type, and multi-pass arrangements.

This study proposes a numerical model for plate heat exchanger that is capable of handling supercritical CO fluid. The plate heat exchangers under investigation include Z-type (1-pass), U-type (1-pass), and 1-2 pass configurations. The plate spacing is 2.9 mm with a plate thickness of 0.8 mm, and the size of the plate is 600 mm wide and 218 mm in height with 60 degrees chevron angle. The proposed model takes into account the influence of gigantic change of CO properties. The simulation is first compared with some existing data for water-to-water plate heat exchangers with good agreements. The flow distribution, pressure drop, and heat transfer performance subject to the supercritical CO in plate heat exchangers are then investigated. It is found that the flow velocity increases consecutively from the entrance plate toward the last plate for the Z-type arrangement, and this is applicable for either water side or CO side. However, the flow distribution of the U-type arrangement in the water side shows opposite trend. Conversely, the flow distribution for U-type arrangement of CO depends on the specific flow ratio (C*). A lower C* like 0.1 may reverse the distribution, i.e. the flow velocity increases moderately alongside the plate channel like Z-type while a large C* of 1 would resemble the typical distribution in water channel. The flow distribution of CO side at the first and last plate shows a pronounced drop/surge phenomenon while the channels in water side does not reveal this kind of behavior. The performance of 2-pass plate heat exchanger, in terms of heat transfer rate, is better than that of 1-pass design only when C* is comparatively small (C* < 0.5). Multi-pass design is more effective when the dominant thermal resistance falls in the CO side. [ABSTRACT FROM AUTHOR]