Performance and Optimization of Microchannel Condensers

Abstract

This study is the first to document the condensation heat transfer performance of small
\ndiameter, microchannel tubes in crossflow heat exchange, and this study provides the fIrSt
\nsystematic evaluation of the effect of port ~hape on microchannel tube performance. Furthermore,
\nthis study is the flI'St to suggest methods for improving microchannel heat exchanger designs.
\nWe collected experimental data for flat, multiport tubes with hydraulic diameters in the
\nrange 0.6 mm S Db S 1.5 mm. The port shapes considered were circles, squares, triangles,
\nenhanced squares, and small squares. We found that established relationships describe singlephase
\ncircular-tube heat transfer and pressure drop behavior in microchannel tubes. Circular-tube
\ncorrelations are appropriate for noncircular tubes if dimensionless numbers are formed with
\nappropriate length scales. The wavy flow correlation of Dobson [1994] was found to predict
\naccurately condensing heat transfer in flows predicted to wavy. A slightly modified form of the
\nDob~n [1994] annular flow correlation was found to predict accurately condensing heat transfer in
\nflows predicted to be annular.
\nAn analytical study??of methods to improve microchannel condenser design was performed.
\nWe found that volume minimization is a comprehensive and reasonable objective for. the
\nsuboptimization analysis. As condenser volume is reduced, system charge, condenser mass, and
\nmaterial costs all decrease ???
\n. ' . Refrigerant-side circuiting flexibility is the key that unlocks the potential of the
\nmicrochannel technology. With unconstrained refrigerant circuiting, smaller port diameters always
\nlead to reduced condenser volume. However, the pressure-drop effect drives optimal condenser
\ndesigns toward many tubes of short length, and the crossflow-heat-exchanger effect drives optimal
\ncondenser designs toward many tubes of short length and few ports.
\nWe found that port shape significantly impacts condenser design. To achieve reduced
\ninternal volume, the order of preference for port shapes is circle, square, and triangle. To achieve
\nminimized external volume, the order of preference for port shapes is triangle, square, and circle.