(142cq) Hollow Polymer Three-Dimensional Micro-Lattice Heat Exchangers

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, 3^rd
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.