A new adhesive bonding method is introduced for microlamination architectures, for producing low-temperature microchannel arrays in a wide variety of metals. Sheet metal embossing and chemical etching processes have been used to produce sealing bosses and flow features, resulting in approximately 50% fewer laminae over traditional methods. These lamina designs are enabled by reduced bonding pressures required for the new method. An assembly process using adhesive dispense and cure is outlined to produce leak-free devices. Feasible fill ratios were determined to be 1.1 in general and 1.25 around fluid headers, largely due to gaps between faying surfaces caused by surface roughness. Bond strength investigation reveals robustness to surface conditions and a bond strength of 5.5-8.5 MPa using a 3X safety factor. Dimensional characterization reveals a two sigma (95%) post-bonded channel height tolerance under 10% (9.6%) after bonding. Patterning tolerance and surface roughness of the faying laminae were found to have a significant influence on the final postbonded channel height. Leakage and burst pressure testing on several samples has established confidence that adhesive bonding can produce leak-free joints. Operating pressures up to 413 kPa have been satisfied, equating to tensile pressure on bond joints of 1.9 MPa. Higher operating pressures can be accommodated by increasing the bond area of devices. A two-fluid counterflow microchannel heat exchanger has been redesigned, fabricated and tested to demonstrate feasibility of the new method. Results show greater effectiveness and higher heat transfer rates, suggesting a smaller device than the original heat exchanger. A maximum effectiveness of 82.5% was achieved with good agreement between theoretical and experimental values. Although thermal performance was improved, higher pressure drops were noted. Pressure drops were predicted with a maximum error of 16% between theoretical and experimental values. Much of the pressure drop was found to be in the device manifolds, which can be improved in subsequent designs. Fluid flow simulation results show a 45-65X reduction in fluid leakage velocity past sealing bosses, thereby mitigating adhesive erosion concerns. Theoretical models indicate that the worst-case adhesive erosion rate is 1/12th the rate of aluminum and 1/7th the rate of stainless steel, implying satisfactory reliability in high fluid velocity applications. Economic comparison indicates an 83% reduction in material cost and 71% reduction in assembly cost with the new adhesive bonding process, when compared to diffusion bonding for the recuperator investigated in this study. Adhesive compatibility with common refrigerants is reviewed through literature references, with no adverse compatibility issues noted. The findings of this research suggest a fairly quick path to commercialization for the new bonding method. Future studies required to pursue commercialization are liquid and gas permeability evaluations, and long term strength and performance testing of adhesives in targeted applications. / Graduation date: 2012 / Access restricted to the OSU Community at author's request from Mar. 26, 2012 - Mar. 26, 2013

Microchannel process technology (MPT) offers several advantages to the field of nanomanufacturing: 1) improved process control over very short time intervals owing to shorter diffusional distances; and 2) reduced reactor size due to high surface area to volume ratios and enhanced heat and mass transfer. The objective of this thesis was to consider how nanomaterials, produced in part using MPT, could be used to solve problems associated with the fabrication of MPT devices. Specifically, many MPT devices are produced using transient liquid-phase brazing involving an electroplated interlayer consisting of a brazing alloy designed for melting temperature suppression. Unfortunately, these alloys can form brittle secondary phases which significantly reduce bond strength. In contrast, prior efforts have shown that it is possible to leverage the size-dependent properties of nanomaterials to suppress brazing temperatures. In this prior work, thin films of off-the-shelf elemental nanoparticles were used as interlayers yielding joints with improved mechanical properties. In the present investigation, efforts have been made to characterize the synthesis and deposition of various elemental nanoparticle suspensions for use in the transient liquid-phase brazing of aluminum and stainless steel. Advances were used to demonstrate the nanoparticle-assisted diffusion brazing of a microchannel array. In the first section, a silver nanoparticle (AgNP) interlayer was produced for the diffusion brazing of heat exchanger aluminum. Efforts are made to examine the effect of braze filler particle size (~5 nm and ~50 nm) and processing parameters (heating rate: 5ºC/min and 25ºC/min; brazing temperature: 550ºC and 570ºC) on thin coupons of diffusion-brazed 3003 Al. A tensile strength of 69.7 MPa was achieved for a sample brazed at 570°C for 30 min under 1 MPa with an interlayer thickness of approximately 7 μm. Further suppression of the brazing temperature to 500ºC was achieved by sputtering a 1 µm thick layer of Cu before depositing a 5 nm thick film of AgNPs resulting in a lap shear strength of 45.3±0.2 MPa. In the middle section of this thesis, several techniques are investigated for the synthesis of sub 10 nm diameter nickel nanoparticles (NiNPs) to be used in the diffusion brazing of 316L stainless steel. The average NiNP size was varied from 9.2 nm to 3.9 nm based on the synthesis technique, solvent and reducing agent used. Conventional wet-chemical synthesis using NiCl₂.6H₂O in ethylene glycol (solvent) and N₂H₄.H₂O (reducing agent) resulted in the formation of 5.4 ± 0.9 nm NiNPs. Continuous flow synthesis using a microchannel T-mixer (barrel diameter of 521µm) and a 10 second residence time of reactants in a bath temperature of 130ºC resulted in a particle size of with 5.3 ± 1 nm. To make the synthesis safer and less energy intense, microwave heating was used along with less toxic Ni(CH₃CO₂)₂·4H₂O (nickel salt), propylene glycol (solvent) and NaPH₂O₂ (reducing agent) yielding 3.9 ± 0.8 nm diameter NiNPs. For the final section, nickel nanoparticles were synthesized using NiCl₂.6H₂O (nickel salt), de-ionized water (solvent), NaBH₄ (co-reducing agent), N₂H₄.H₂O (reducing agent) and polyvinylpyrolidone (capping agent) yielding 4.2 ± 0.6 nm NiNP. Several deposition techniques were investigated for controlling film thickness and uniformity in the diffusion brazing of 316L stainless steel (SS). Using in-house prepared NiNP and automated dispensing, a hermetic joint up to 70 psi (tested pressure) was obtained in 316L SS substrates under brazing conditions of 800ºC, 2 MPa and 30 min. Throughout the course of this thesis, techniques used for characterizing nanoparticles, films and joints included FT-IR, XRD, SEM, TEM, HRTEM, EDS, EPMA, DSC, mass spectrometry, and lap-shear testing. / Graduation date: 2012