Strained Ultra-High Molecular Weight Polyethylene Heat Exchanger

Desire for low-cost and corrosion-resistant heat exchangers (HXs) has driven development of polymer HXs over several decades; however, these approaches are typically limited by materials with low thermal conductivity between 0.11 and 0.35 W/m-K, rendering earlier attempts with uncompetitive volume and performance. Attempts to improve thermal conductivity have involved polymer composites; however, these attempts use expensive thermal conductivity enhancers or expensive processing techniques. Mainstream proposes increasing polymer thermal conductivity without expensive particle or processing costs. Metallic-like thermal conductivities of ultra-high molecular weight polyethylene (UHMWPE) are possible using processes analogous to processing metal sheets. The high thermal conductivity coupled with aggressive HX design results in strained UHMWPE HXs having 5X the thermal performance of commercial-off-the-shelf (COTS) polymer HXs while using base material that is 2.5X cheaper than aluminum. Mainstream developed a process to increase the thermal conductivity of UHMWPE by 9.11X while retaining practical fin thicknesses. We also computationally demonstrated that an asymmetric out of phase dimpled surface can increase convective heat transfer by 51.2% over a plain fin with the same pumping power. Using these results, Mainstream designed a UHMWPE HX that is 47% smaller than a COTS polymer HX and only slightly larger than a metallic HX under equivalent heat load. Mainstream will refine the design and manufacturing process from Phase I to design, fabricate, and test an UHMWPE HX for use in an industrial heat pump. We will retain the mechanical and thermal interfaces and demonstrate equivalent thermal performance of the metallic HX within the heat pump. We will then perform long-term testing to demonstrate significantly reduced performance degradation due to corrosion and particulate airside fouling. Decarbonizing industrial heat is an effective way to reduce greenhouse gases. With the inclusion of inexpensive polymer-based HXs, the upfront investment in decarbonizing industrial heat pumps reduces, improving its return on investment. In addition to upfront cost savings, the elimination of metallic joints eliminates corrosion mechanisms that causes HX failure, and therefore, significantly increases industrial heat pump service life. While these HXs can provide improvements in a range of applications, the best initial application is the lumber drying industry because a) they form a very large market share of industrial heat pumps, b) the application is at moderately elevated temperatures amenable to a large range of polymers, and c) the total capacity is tenable for a first article.