268734 Hollow Polymer Three-Dimensional Micro-Lattice Heat Exchangers

Monday, October 29, 2012
Hall B (Convention Center )
Christopher S. Roper, Kevin J. Maloney and Alan J. Jacobsen, HRL Laboratories, LLC, Malibu, CA

Title: Hollow Polymer Three-Dimensional Micro-lattice Heat Exchangers

Authors: C. Roper, K. Maloney, and A. Jacobsen

Abstract:

Compact heat exchangers with micro-scale flow paths offer higher overall heat transfer coefficients and higher surface area to volume ratios compared to traditional heat exchangers [1]. Polymer heat exchangers offer superior corrosion resistance and lower weight compared to metallic heat exchangers of similar size and geometry [2]. Compact polymer heat exchangers with micro-scale flow paths combine these benefits [3]; however, the inherent 2-D nature of each fabrication step used for traditional polymer microfluidics impedes production of compact polymer heat exchangers with sufficiently large overall size for many applications.

The recent development of a scalable 3-D micro-lattice material formed via a self-propagating photopolymer waveguide process [4] has enabled a new class of multifunctional mini- and micro-heat exchangers [5,6]. In the fabrication process, controlled feature sizes can be selected between 10 microns and 10 mm. Additionally, micro-lattice panels tens of mm thick, tens of cm long, and tens of cm wide can be fabricated with an exposure time of less than one minute. Utilizing a solid polymer micro-lattice as a sacrificial scaffold enables the fabrication of hollow micro-lattice heat exchangers. To date, the fabrication and testing of hollow micro-lattice heat exchangers constructed of nickel and copper have been reported [5,6].

In this presentation, we will for the first time discuss the design, fabrication, and testing of polymer wall hollow micro-lattice heat exchangers, thus overcoming previous limitations of compact polymer heat exchangers with micro-scale flow paths. Briefly, to form these heat exchangers, parylene is conformally coated onto a solid polymer micro-lattice. The solid polymer is then selectively removed, leaving behind a three-dimensionally ordered, interconnected network of hollow tubes (Figure 1). This tubular network separates two fluidically isolated, but interpenetrating volumes which have a high interfacial area to volume ratio (50 10,000 m2/m3 depending on the micro-lattice architecture). Headers formed in the fabrication process allow parallel distribution of flow inside each hollow tubular lattice member. Hollow polymer heat exchangers with internal tubular lattice member diameters ranging from 200 to 800 microns have been fabricated. Testing results of these hollow polymer heat exchangers will be presented.

Figure 1: Polymer hollow micro-lattice heat exchanger cores with lattice member internal diameters of (a) 800 microns and (b) 200 microns.

References:

[1] Kays and London: Compact Heat Exchangers, 3rd Edition, Krieger Publishing Company, 1984.

[2] T'Joena, Park, Wang, Sommers, Han, Jacobi: A review on polymer heat exchangers for HVAC&R applications, International Journal of Refrigeration, 32 (2009) 763-779.

[3] Harris, Kelly, Wang, McCandless, Motakef: Fabrication, Modeling, and Testing of Micro-Cross-Flow Heat Exchangers, Journal of Microelectromechanical Systems, vol. 11 no. 6 (2002) 726-735.

[4] Jacobsen, Barvosa-Carter, Nutt: Micro-scale Truss Structures formed from Self-Propagating Photopolymer Waveguides, Advanced Materials, 19 (2007) 3892-3896.

[5] Roper, Kolodziejska, Maloney, Fink, Schaedler, and Jacobsen: Recent Progress and Applications of Micro-Lattice Materials Formed Via a Self-Propagating Photopolymer Waveguide Process, Technologies for Future Micro-Nano Manufacturing Workshop, (2011) 251-253.

[6] Maloney, Fink, Schaedler, Kolodziejska, Jacobsen, and Roper: Multifunctional Heat Exchangers Derived from Three-Dimensional Micro-Lattice Structures, International Journal of Heat and Mass Transfer, 55 (2012) 2486-2493.


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