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Research Papers

Multiscale Transient Thermal, Hydraulic, and Mechanical Analysis Methodology of a Printed Circuit Heat Exchanger Using an Effective Porous Media Approach

[+] Author and Article Information
Eugenio Urquiza

Thermotive LLC,
8415 Fredericksburg Rd Suite 402,
San Antonio, TX 78229
e-mail: keno@cal.berkeley.edu

Kenneth Lee

Department of Mechanical Engineering,
University of California,
6141 Etcheverry Hall,
Berkeley, CA 94720

Per F. Peterson

Department of Nuclear Engineering,
University of California,
4155 Etcheverry Hall, MC 1730,
Berkeley, CA 94720

Ralph Greif

Department of Mechanical Engineering,
University of California,
6107 Etcheverry Hall, Mailstop 1740,
Berkeley, CA 94720

1Corresponding author.

Manuscript received February 7, 2013; final manuscript received April 4, 2013; published online October 3, 2013. Assoc. Editor: Jovica R. Riznic.

J. Thermal Sci. Eng. Appl 5(4), 041011 (Oct 03, 2013) (8 pages) Paper No: TSEA-13-1027; doi: 10.1115/1.4024712 History: Received February 07, 2013; Revised April 04, 2013

Printed circuit heat exchangers (PCHE) and the similar formed plate heat exchangers (FPHE) offer highly attractive economics due to their higher power densities when compared to more conventional shell-and-tube designs. However, their complex geometry makes them more vulnerable to damage from thermal stresses during transient thermal hydraulic conditions. Transient stresses far exceed those predicted from steady state analyses. Therefore, a transient, hydraulic, thermal, and structural analysis is needed to accurately simulate and design high performing PCHE. The overall length of the heat exchanger can be thousands of times larger than the characteristic length for the heat transfer and fluid flow. Furthermore, simulating the thermal hydraulics of the entire heat exchanger plate is very time consuming and computationally expensive. The proposed methodology mitigates this by using a multiscale analysis with local volume averaged (LVA) properties and a novel effective porous media (EPM) approach. This method is implemented in a new computer code named the compact heat exchanger explicit thermal and hydraulics (CHEETAH) code which solves the time-dependent, mass, momentum, and energy equations for the entire PCHE plate as well as hot and cold fluid streams using finite volume analysis (FVA). The potential of the method and code is illustrated with an example problem for a Heatric-type helium gas-to-liquid salt PCHE with offset strip fins (OSF). Given initial and boundary conditions, CHEETAH computes and plots transient temperature and flow data. A specially developed grid mapping code transfers temperature arrays onto adapted structural meshes generated with commercial FEA software. For the conditions studied, a multiscale stress analysis reveals mechanical vulnerabilities in the HX design. This integrated methodology using an EPM approach enables multiscale PCHE simulation. The results provide the basis for design improvements which can minimize flow losses while enhancing flow uniformity, thermal effectiveness, and mechanical strength.

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References

Figures

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Fig. 1

Heat exchanger design optimization process enabled using CHEETAH and the EPM method

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Fig. 2

Cut-away view through the OSF section showing alternating liquid and gas flow channels. Dark bands at the top of each fin indicate the location of diffusion-bonded joints between the plates.

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Fig. 3

Zones in the composite plate with varying thermal and hydraulic properties

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Fig. 4

The steady state temperature and corresponding stress distribution

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Fig. 5

Transient temperature distributions solved by CHEETAH for the composite plate of the PCHE after a step change in flow rate initiates a thermal hydraulic transient

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Fig. 6

The strain of a mechanical component with a complex geometry can be replicated with a component with a simple geometry when the two share effective mechanical properties such as an effective modulus of elasticity

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Fig. 7

The four unit cells characterizing the complex geometry of this composite plate

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Fig. 8

Local peak stresses on unit cells in the PCHX during a simulated thermal transient involving loss of forced gas heating

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Fig. 9

Local peak stresses on unit cells in the PCHX during a simulated thermal transient involving loss of forced liquid cooling

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