|Abstract:||This study is the first to document the condensation heat transfer performance of small
diameter, microchannel tubes in crossflow heat exchange, and this study provides the fIrSt
systematic 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 the
range 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 singlephase
circular-tube heat transfer and pressure drop behavior in microchannel tubes. Circular-tube
correlations are appropriate for noncircular tubes if dimensionless numbers are formed with
appropriate length scales. The wavy flow correlation of Dobson  was found to predict
accurately condensing heat transfer in flows predicted to wavy. A slightly modified form of the
Dob~n  annular flow correlation was found to predict accurately condensing heat transfer in
flows 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. the
suboptimization analysis. As condenser volume is reduced, system charge, condenser mass, and
material costs all decrease •
. ' . Refrigerant-side circuiting flexibility is the key that unlocks the potential of the
microchannel technology. With unconstrained refrigerant circuiting, smaller port diameters always
lead to reduced condenser volume. However, the pressure-drop effect drives optimal condenser
designs toward many tubes of short length, and the crossflow-heat-exchanger effect drives optimal
condenser designs toward many tubes of short length and few ports.
We found that port shape significantly impacts condenser design. To achieve reduced
internal volume, the order of preference for port shapes is circle, square, and triangle. To achieve
minimized external volume, the order of preference for port shapes is triangle, square, and circle.