Performance and Optimization of Microchannel Condensers

摘要

This study is the first to document the condensation heat transfer performance of smalldiameter, microchannel tubes in crossflow heat exchange, and this study provides the fIrStsystematic evaluation of the effect of port ~hape on microchannel tube performance. Furthermore,this study is the flI'St to suggest methods for improving microchannel heat exchanger designs.We collected experimental data for flat, multiport tubes with hydraulic diameters in therange 0.6 mm S Db S 1.5 mm. The port shapes considered were circles, squares, triangles,enhanced squares, and small squares. We found that established relationships describe singlephasecircular-tube heat transfer and pressure drop behavior in microchannel tubes. Circular-tubecorrelations are appropriate for noncircular tubes if dimensionless numbers are formed withappropriate length scales. The wavy flow correlation of Dobson [1994] was found to predictaccurately condensing heat transfer in flows predicted to wavy. A slightly modified form of theDob~n [1994] annular flow correlation was found to predict accurately condensing heat transfer inflows predicted to be annular.An analytical study??of methods to improve microchannel condenser design was performed.We found that volume minimization is a comprehensive and reasonable objective for. thesuboptimization analysis. As condenser volume is reduced, system charge, condenser mass, andmaterial costs all decrease ???. ' . Refrigerant-side circuiting flexibility is the key that unlocks the potential of themicrochannel technology. With unconstrained refrigerant circuiting, smaller port diameters alwayslead to reduced condenser volume. However, the pressure-drop effect drives optimal condenserdesigns toward many tubes of short length, and the crossflow-heat-exchanger effect drives optimalcondenser designs toward many tubes of short length and few ports.We found that port shape significantly impacts condenser design. To achieve reducedinternal volume, the order of preference for port shapes is circle, square, and triangle. To achieveminimized external volume, the order of preference for port shapes is triangle, square, and circle.