Supercritical Carbon Dioxide Heat Transfer Research

by by Alan Kruizenga1, Mark Anderson1, Michael Corradini1, Devesh Ranjan2, & Roma Fatima2
1University of Wisconsin, Madison
2Texas A&M University

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The increasing importance of improved efficiency and reduced capital cost has led to significant work studying
advanced Brayton cycles for high temperature energy conversion. One particular improvement in the operation
of an advanced carbon dioxide cycle is the use of compact, highly efficient, diffusion bonded heat exchangers
for recuperators. These heat exchangers will operate near the pseudo critical point of liquid carbon dioxide
making use of the drastic variation of the thermo-physical properties. This work focuses on the experimental
measurements of heat transfer and pressure drop characteristics within mini-channels, typical of diffusion bonded
heat exchangers under cooling conditions, with supercritical carbon dioxide as the working fluid. Two test
section channel geometries were studied; a straight channel and a zig-zag channel; both configurations are 0.5m
in length and constructed out of 316 stainless steel with a series of 9 parallel 1.9mm semi-circular channels.
The zig-zag configuration has an angle of 115 degrees and an effective length of ~0.6m. Heat transfer measurements
were conducted for varying ranges of inlet temperatures, pressures, and mass flow rates. Local and average
heat transfer coefficients near the critical point were determined from measured wall temperatures and calculated
local bulk temperatures. The experimental results are compared to several correlations developed from
previous miniature channel experiments under cooling conditions1, 2 along with predictions produced from the
CFD package Fluent© and Star-CD.