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• 1. [Article] Adhesive microlamination protocol for low-temperature microchannel arrays

  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 ...

  Citation × Citation Citation Abstract Copy Title: Adhesive microlamination protocol for low-temperature microchannel arrays Author: Paulraj, Prawin 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. Title: Adhesive microlamination protocol for low-temperature microchannel arrays Author: Paulraj, Prawin 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. Close

• 2. [Article] Enhancement and modeling of cryogenic solid-state hydrogen storage systems with a novel microchannel thermal management device

  Compact storage systems demonstrating increased hydrogen storage capacity are the key to advancing the growth of the hydrogen economy throughout the world and reducing the global dependence on fossil fuels ...

  Citation × Citation Citation Abstract Copy Title: Enhancement and modeling of cryogenic solid-state hydrogen storage systems with a novel microchannel thermal management device Author: Loeb, Christopher S. Compact storage systems demonstrating increased hydrogen storage capacity are the key to advancing the growth of the hydrogen economy throughout the world and reducing the global dependence on fossil fuels for transportation. The use of highly porous adsorbent materials for reversible hydrogen storage is a promising pathway towards achieving storage densities capable of reaching driving ranges comparable to gasoline automobiles without high-pressure compressed gas storage systems (>200 bars H₂). The focus of this effort is the enhancement of solid-state hydrogen adsorption systems through the development and inclusion of a microchannel thermal management device for efficient heat removal and uniform gas distribution in compressed beds of activated carbon and metal organic framework. The stainless steel microchannel device utilizes 250 μm walls to remove heat from the contacting adsorbent bed with liquid nitrogen coolant flow through 250 μm channel. Cryogenic (<140 K) hydrogen adsorption experiments were completed with and without liquid nitrogen cooling at pressures between 50 and 55 bars. The experiments demonstrate that the use of liquid nitrogen coolant effectively lowers the adsorbent bed temperature by removing the majority of the heat generated during the adsorption process, resulting in an 11% increase in stored H₂ gas with MOF-5 and a 3% increase with activated carbon compared to their respective non-cooled counterparts. The liquid cooled MOF-5 adsorbent bed increases average hydrogen storage throughout the experimental vessel by 14% compared to a cryo-compressed gas system at similar conditions (121 K and 55 bars). A functional development tool representing the experimental adsorption system was developed in COMSOL Multiphysics and utilized derived conservation equations and the modified Dubinin-Astakhov equation to characterization the gas flow, energy transport, and physical adsorption of supercritical hydrogen on MOF-5 adsorbent. Simulated adsorption experiments, modeled with development tool, were validated against experimental data; the predicted temperature responses at embedded thermocouple locations show a strong correlation to experimental data. The development tool may assist in the design and development of future storage systems utilizing adsorbent materials with known physical, thermal, and adsorption parameters. Title: Enhancement and modeling of cryogenic solid-state hydrogen storage systems with a novel microchannel thermal management device Author: Loeb, Christopher S. Compact storage systems demonstrating increased hydrogen storage capacity are the key to advancing the growth of the hydrogen economy throughout the world and reducing the global dependence on fossil fuels for transportation. The use of highly porous adsorbent materials for reversible hydrogen storage is a promising pathway towards achieving storage densities capable of reaching driving ranges comparable to gasoline automobiles without high-pressure compressed gas storage systems (>200 bars H₂). The focus of this effort is the enhancement of solid-state hydrogen adsorption systems through the development and inclusion of a microchannel thermal management device for efficient heat removal and uniform gas distribution in compressed beds of activated carbon and metal organic framework. The stainless steel microchannel device utilizes 250 μm walls to remove heat from the contacting adsorbent bed with liquid nitrogen coolant flow through 250 μm channel. Cryogenic (<140 K) hydrogen adsorption experiments were completed with and without liquid nitrogen cooling at pressures between 50 and 55 bars. The experiments demonstrate that the use of liquid nitrogen coolant effectively lowers the adsorbent bed temperature by removing the majority of the heat generated during the adsorption process, resulting in an 11% increase in stored H₂ gas with MOF-5 and a 3% increase with activated carbon compared to their respective non-cooled counterparts. The liquid cooled MOF-5 adsorbent bed increases average hydrogen storage throughout the experimental vessel by 14% compared to a cryo-compressed gas system at similar conditions (121 K and 55 bars). A functional development tool representing the experimental adsorption system was developed in COMSOL Multiphysics and utilized derived conservation equations and the modified Dubinin-Astakhov equation to characterization the gas flow, energy transport, and physical adsorption of supercritical hydrogen on MOF-5 adsorbent. Simulated adsorption experiments, modeled with development tool, were validated against experimental data; the predicted temperature responses at embedded thermocouple locations show a strong correlation to experimental data. The development tool may assist in the design and development of future storage systems utilizing adsorbent materials with known physical, thermal, and adsorption parameters. Close