Polymeric materials hold several advantages over metal components in heat exchangers such as cost savings, lighter weight and corrosion resistance. However, it is challenging to engineer plastics with good heat transfer characteristics, processability and required strength. Neat polymer resins have inferior mechanical and thermal properties relative to metals, requiring careful consideration of the entire heat exchanger system from materials to system design, to achieve sufficient performance. This review summarizes the physical parameters governing polymer and composite thermal conductivity, as well as the latest research on augmenting thermal conductivity. Highly filled composites containing carbon or metal have achieved thermal conductivity an order of magnitude higher than that of neat polymers. The effects of critical additive characteristics, such as interfacial compatibility, filler shape factor, loading level and processing technique, are reviewed. In addition to lower material costs, high volume processing technologies such as injection molding and extrusion are responsible for the cost savings of polymers over metals. Thus, the manufacturing considerations for the most promising high thermal conductivity polymer composites are also reviewed. (C) 2016 Elsevier Ltd. All rights reserved.

H2 permeation through Pd–Cu alloy membranes was carried out using pure H2, simulated syngas, and binary H2 gas mixtures of N2, CO, CO2, or H2O, respectively, along with and without H2S in the feed to investigate the impact of non-hydrogen gas species on H2 permeability at temperatures between 350 °C and 500 °C under pressures from 2.03 bar to 13.79 bar. When H2S was added to the feed, the H2S concentration was varied from 5 ppmv to 39 ppmv. The testing results indicated that the H2 permeability through the Pd–Cu alloy membranes from pure H2 followed Sievert's law. H2S in the feed did not affect the H2 permeability at H2S concentrations below 39 ppmv and temperatures between 400 °C and 500 °C, indicating that the Pd–Cu separator was sulfur tolerant. From the H2 permeation experiments with H2 gas mixtures, it appeared that no inhibition effect from N2, CO, CO2 and H2O on H2 permeation was observed at temperatures between 400 °C and 500 °C. However, the inhibition effect from N2, CO and H2O on the H2 permeation was observed at 350 °C. Furthermore, the Pd–Cu separator was tested for 1031 h including 618 h exposure to 5–39 ppmv H2S and showed stable H2 permeation flux without N2 leakage detected, suggesting that the separator had a good thermal and structural stability.

The main objective of this project was to construct, test, and demonstrate a Pd-Cu metallic tubular membrane micro-channel separator capable of producing 2 lb day{sup -1} H{sub 2} at 95% recovery when operating downstream of an actual coal gasifier. A key milestone for the project was to complete a pilot-scale gasifier test by 1 September 2011 and demonstrate the separation of 2 lb day{sup -1} H{sub 2} to verify progress toward the DOE's goals prior to down-selection for larger-scale (100 lb day{sup -1}) hydrogen separator development. Three different pilot-scale (1.5 ft{sup 2}) separators were evaluated downstream of coal gasifiers during four different tests and the key project milestone was achieved in August 2011, ahead of schedule. During three of those tests, all of the separators demonstrated or exceeded the targeted separation rate of 2 lb day{sup -1} H{sub 2}. The separator design was proved to be leak tight and durable in the presence of gasifier exhaust contaminants at temperatures and pressures up to 500 °C and 500 psia. The contaminants in the coal gasifier syngas for the most part had negligible impact on separator performance, with H{sub 2} partial pressure being the greatest determinant of membrane performance. Carbon monoxide and low levels of H{sub 2}S (<39 ppmv) had no effect on H{sub 2} permeability, in agreement with laboratory experiments. However, higher levels of H{sub 2}S (>100 ppmv) were shown to significantly reduce H{sub 2} separation performance. The presence of trace metals, including mercury and arsenic, appeared to have no effect based on the experimental data. Subscale Pd-Cu coupon tests further quantified the impact of H{sub 2}S on irreversible sulfide formation in the UTRC separators. Conditions that have a thermodynamic driving force to form coke were found to reduce the performance of the separators, presumably by blockage of effective separation area with carbon deposits. However, it was demonstrated that both in situ and ex situ (laboratory) air regeneration at 450 °C could restore separator performance by burning out such deposits. Gasifier testing revealed that high molecular weight hydrocarbons have the potential to retard H2 separation. Unconverted coal tars with carbon numbers greater than 14 have a boiling point such that they can act as a reversible poison to the Pd-Cu membranes even at temperatures above 500 °C. The use of real-time, physics-based, performance models revealed the effect of these coal tars. It is believed that this project provided the first evidence for the impact of coal tars on H{sub 2} separator performance. Final down-selection of candidate alloys for non-membrane materials of construction proceeded by evaluating the alloys in both UTRC laboratory tests and testing downstream of an actual gasifier at the National Carbon Capture Center (NCCC). The overall alloy ratings were calculated by multiplying the projected cost of a 100 lb day{sup -1} H{sub 2} separator outer shell by the projected oxide scale thickness for 5 years of operation. The alloy with the lowest resulting rating parameter was stainless steel 309 (SS-309) followed by stainless steel 310 (SS-310). However, it was noted that approximately half of the alloys showed susceptibility to pitting and localized corrosion. SS-309 was one of the alloys that exhibited heavy localized attack after 2000 hours of laboratory testing. As this localized corrosion can potentially lead to accelerated end of life, it was determined that SS-310 would be the best alloy selection for this application as it does not show signs of localized pitting corrosion.

One of the more promising applications of ultraviolet photocatalytic oxidation (UVPCO) technology is air purification for improved indoor air quality (IAQ). Successful implementation has been hindered by lack of understanding of the behavior of UVPCO systems in real, constantly evolving ambient air environments. The focus of most published research is on the demonstration of the rate of removal of various single compounds in a laboratory experiment, often at high concentrations relative to those encountered in ambient air. UVPCO products have been released worldwide with wildly varying claims of effectiveness and lifetime, but limited data is available relative to the long term effectiveness of this promising technology.This study presents results from laboratory photocatalyst deactivation studies, and field testing of prototype reactors in two office building locations in CT, USA. The goal was both to investigate deactivation by silicon-containing volatile and semi-volatile organic compounds (VOCs and SVOCs) and to determine the durability of the photocatalyst in situ in an office environment. Ambient air quality was monitored by total VOC sensors, and relative humidity and temperature were documented. Limited air analysis was performed. Photocatalysts employed in the testing were either Degussa P25 or a 3% WO(3) coated P25. The results indicate that rapid catalyst deactivation is observed in photocatalytic air purifiers deployed in ambient office air. (C) 2010 Elsevier B.V. All rights reserved.

The overall objectives for this project were to: (1) confirm the high stability and resistance of a PdCu trimetallic alloy to carbon and carbide formation and, in addition, resistance to sulfur, halides, and ammonia; (2) develop a sulfur, halide, and ammonia resistant alloy membrane with a projected hydrogen permeance of 25 m{sup 3}m{sup -2}atm{sup -0.5}h{sup -1} at 400 C and capable of operating at pressures of 12.1 MPa ({approx}120 atm, 1750 psia); and (3) construct and experimentally validate the performance of 0.1 kg/day H{sup 2} PdCu trimetallic alloy membrane separators at feed pressures of 2 MPa (290 psia) in the presence of H{sub 2}S, NH{sub 3}, and HCl. This project successfully increased the technology readiness level of palladium-based metallic membranes for hydrogen separation from coal-biomass gasifier exhaust or similar hydrogen-containing gas streams. The reversible tolerance of palladium-copper (PdCu) alloys was demonstrated for H{sub 2}S concentrations varying from 20 ppmv up to 487 ppmv and NH{sub 3} concentrations up to 9 ppmv. In addition, atomistic modeling validated the resistance of PdCu alloys to carbon formation, irreversible sulfur corrosion, and chlorine attack. The experimental program highlighted two key issues which must be addressed as part of future experimental programs: (1) tube defects and (2) non-membrane materials of construction. Four out of five FCC PdCu separators developed leaks during the course of the experimental program because {approx}10% of the alloy tubes contained a single defect that resulted in a thin, weak point in the tube walls. These defects limited operation of the existing tubes to less than 220 psig. For commercial applications of a PdCu alloy hydrogen separator under high sulfur concentrations, it was determined that stainless steel 316 is not suitable for housing or supporting the device. Testing with sulfur concentrations of 487 {+-} 4 ppmv resulted in severe corrosion of the stainless steel components of the separators. The project identified an experimental methodology for quantifying the impact of gas contaminants on PdCu alloy membrane performance as well as an atomistic modeling approach to screen metal alloys for their resistance to irreversible sulfur corrosion. Initial mathematical descriptions of the effect of species such as CO and H{sub 2}S were developed, but require further experimental work to refine. At the end of the project, an improvement to the experimental approach for acquiring the necessary data for the permeability model was demonstrated in preliminary tests on an enhanced PdCu separator. All of the key DOE 2010 technical targets were met or exceeded except for the hydrogen flux. The highest flux observed for the project, 125 ft{sup 3}ft{sup -2}h{sup -1}, was obtained on a single tube separator with the aforementioned enhanced PdCu separator with a hydrogen feed pressure of 185 psig at 500 C.

The cost of delivering the payloads to space increases dramatically with distance and therefore missions to deep space place a strong emphasis on reducing launch weight and eliminating resupply requirements. The Vapor Phase Catalytic Ammonia Removal (VPCAR) system, which is being developed for water purification, is an example of this focus because it has no resupply requirements. A key step in the VPCAR system is the catalytic oxidation of ammonia and volatile hydrocarbons to benign compounds such as carbon dioxide, water, and nitrogen. Currently, platinum-based commercial oxidation catalysts are being used for these reactions. However, conventional platinum catalysts can convert ammonia (NH3) to NO and NO2 (collectively referred to as NOX), which are more hazardous than ammonia.