Research Papers

Heat Transfer of Supercritical Carbon Dioxide in Printed Circuit Heat Exchanger Geometries

[+] Author and Article Information
Alan Kruizenga, Mark Anderson, Roma Fatima, Michael Corradini, Aaron Towne, Devesh Ranjan

 University of Wisconsin, Madison, WI 53711 Texas A&M University, College Station, TX 77843 University of Wisconsin, Madison, WI 53711 Texas A&M University, College Station, TX 77843

J. Thermal Sci. Eng. Appl 3(3), 031002 (Aug 10, 2011) (8 pages) doi:10.1115/1.4004252 History: Received May 11, 2010; Revised May 17, 2011; Published August 10, 2011; Online August 10, 2011

The increasing importance of improving efficiency and reducing capital costs has led to significant work studying advanced Brayton cycles for high temperature energy conversion. Using compact, highly efficient, diffusion-bonded heat exchangers for the recuperators has been a noteworthy improvement in the design of advanced carbon dioxide Brayton cycles. These heat exchangers will operate near the pseudocritical point of carbon dioxide, making use of the drastic variation of the thermophysical properties. This paper focuses on the experimental measurements of heat transfer under cooling conditions, as well as pressure drop characteristics within a prototypic printed circuit heat exchanger. Studies utilize type-316 stainless steel, nine channel, semi-circular test section, and supercritical carbon dioxide serves as the working fluid throughout all experiments. The test section channels have a hydraulic diameter of 1.16 mm and a length of 0.5 m. The mini-channels are fabricated using current chemical etching technology, emulating techniques used in current diffusion-bonded printed circuit heat exchanger manufacturing. Local heat transfer values were determined using measured wall temperatures and heat fluxes over a large set of experimental parameters that varied system pressure, inlet temperature, and mass flux. Experimentally determined heat transfer coefficients and pressure drop data are compared to correlations and earlier data available in literature. Modeling predictions using the computational fluid dynamics (CFD) package FLUENT are included to supplement experimental data. All nine channels were modeled using known inlet conditions and measured wall temperatures as boundary conditions. The CFD results show excellent agreement in total heat removal for the near pseudocritical region, as well as regions where carbon dioxide is a high or low density fluid.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 1

Thermophysical property variations for CO2 with both pressure and temperature. Maximum in specific heat represents pseudocritical temperature (Tpc ). The critical pressure for carbon dioxide is 7.377 MPa.

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Figure 2

Schematic of experimental facility at the University of Wisconsin

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Figure 3

Top and bottom of heat transfer test section

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Figure 4

Mixing manifold on test section. Also shown is the wall thermocouple implanted into the stainless steel.

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Figure 5

Test section assembled with water cooling block

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Figure 6

One of the ten subsections for the test section

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Figure 7

Diagram of water cooling block. Each cooling block (20 in total) is bolted to the heat exchanger. Thermocouples to measure water temperature are placed at the inlet and outlet.

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Figure 8

Bulk and wall temperatures (top) for experiments with a mass flux of 762 kg/m2 s and system pressure of 7.5 MPa. The bottom plot shows how the heat transfer coefficient changes as a function of length and inlet condition. Heat flux listed is the average heat flux over the test length.

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Figure 9

Heat transfer coefficient as a function of bulk temperature

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Figure 10

Decreasing pressure results in significant increases in HTC

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Figure 11

Reynolds and Prandtl numbers evaluated under bulk conditions for low mass flux tests. Differences in HTC are due to changes in the Prandtl number.

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Figure 12

Comparison of calculated Nusselt numbers to experimentally determined Nusselt numbers for several established correlations. Percentages indicate difference from a y = x of 1.

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Figure 13

Distribution of pressure losses between the local, acceleration, and frictional effects

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Figure 14

Friction factors that include roughness slightly over predict the frictional pressure losses, while smooth tube friction factors under predict the experimental data

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Figure 15

End view of mesh used in CFD model. The model extends into the page 500 mm. The wall temperature boundary profile is a best fit polynomial of the experimentally measured temperature.

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Figure 16

Total power removal comparison versus average bulk temperature between experiment and CFD. Results show an excellent agreement between experiments and CFD.

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Figure 17

Specific heat variation of carbon dioxide as a function of temperature at 7.5 and 8.1 MPa




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