Search

Search Results

• 1. [Article] Comparative analysis of the Žukauskas method and data from the OSU MASLWR test facility steam generator

  Some of the next generation of small modular reactors have been designed with helically coiled steam generators integrated into the reactor vessel to enhance natural circulation. According to the developers ...

  Citation × Citation Citation Abstract Copy Title: Comparative analysis of the Žukauskas method and data from the OSU MASLWR test facility steam generator Author: Wuth, Bradyn J. Some of the next generation of small modular reactors have been designed with helically coiled steam generators integrated into the reactor vessel to enhance natural circulation. According to the developers of TASS/SMR, a one-dimensional thermal hydraulic code written to model the Korean Atomic Energy Research Institute's SMART reactor, the Žukauskas correlation, a heat transfer correlation designed for banks of straight tubes in crossflow, accurately models the heat transfer into helical steam generator tubes. Data has been collected using the Oregon State University Multi-Application Small Light Water Reactor (MASLWR) Test Facility to test whether the Žukauskas correlation can accurately predict the helical steam generator heat transfer coefficients for a natural circulation driven reactor. A one-dimensional, lumped parameter method was devised to use the limited instrumentation of the facility to calculate a temperature profile inside the tubes. From the calculated bulk fluid temperatures, wall temperatures were iteratively solved for and used to generate semi-local heat transfer coefficients. It was found that the instrumentation in the steam generator region of MASLWR Test Facility is too sparse to generate accurate heat transfer coefficients, but the calculated wall temperatures can be averaged over the length of the tubes to ind a good global wall temperature. This global wall temperature was used in a global analysis that found that the Žukauskas correlation works well when both systems are at high flow rates but becomes increasingly worse as the flow rates are lowered. Title: Comparative analysis of the Žukauskas method and data from the OSU MASLWR test facility steam generator Author: Wuth, Bradyn J. Some of the next generation of small modular reactors have been designed with helically coiled steam generators integrated into the reactor vessel to enhance natural circulation. According to the developers of TASS/SMR, a one-dimensional thermal hydraulic code written to model the Korean Atomic Energy Research Institute's SMART reactor, the Žukauskas correlation, a heat transfer correlation designed for banks of straight tubes in crossflow, accurately models the heat transfer into helical steam generator tubes. Data has been collected using the Oregon State University Multi-Application Small Light Water Reactor (MASLWR) Test Facility to test whether the Žukauskas correlation can accurately predict the helical steam generator heat transfer coefficients for a natural circulation driven reactor. A one-dimensional, lumped parameter method was devised to use the limited instrumentation of the facility to calculate a temperature profile inside the tubes. From the calculated bulk fluid temperatures, wall temperatures were iteratively solved for and used to generate semi-local heat transfer coefficients. It was found that the instrumentation in the steam generator region of MASLWR Test Facility is too sparse to generate accurate heat transfer coefficients, but the calculated wall temperatures can be averaged over the length of the tubes to ind a good global wall temperature. This global wall temperature was used in a global analysis that found that the Žukauskas correlation works well when both systems are at high flow rates but becomes increasingly worse as the flow rates are lowered. Close

• 2. [Article] Experimental Characterization of a Supercritical Carbon Dioxide Microchannel Solar Thermal Receiver

  Characterization of a microchannel solar thermal receiver for supercritical carbon dioxide (sCO₂) is presented. The receiver design is based on conjugate computational fluid dynamics and heat transfer ...

  Citation × Citation Citation Abstract Copy Title: Experimental Characterization of a Supercritical Carbon Dioxide Microchannel Solar Thermal Receiver Author: L'Estrange, Thomas Characterization of a microchannel solar thermal receiver for supercritical carbon dioxide (sCO₂) is presented. The receiver design is based on conjugate computational fluid dynamics and heat transfer simulations as well as thermo-mechanical stress analysis. Two lab scale receivers with a 2x2 cm² absorber area are fabricated and experimentally characterized - a parallel microchannel design and a microscale pin fin array design. Static pressure experiments are used to demonstrate receiver integrity at the design pressure of 125 bar at 750°C surface temperature. A concentrated solar simulator was designed and assembled to characterize the thermal performance of the lab scale receiver test articles. Results indicate that, for a fixed exit fluid temperature of 650°C, increase in incident heat flux results in an increase in receiver and thermal efficiency. At a fixed heat flux, efficiency decreases with an increase in receiver surface temperature. The ability to absorb flux of up to 100 W/cm² at thermal efficiency in excess of 90 percent and exit fluid temperature of 650°C using the microchannel receiver is demonstrated. Pressure drop for the pin array at the maximum flow rate for heat transfer experiments is less than 0.64 percent of typical line pressure of 200 bar. Following the successful test of the 2 x 2 cm lab-scale receiver, a larger 8x8 cm² integrated receiver was designed and fabricated. The integrated receiver is shown to withstand 200 bar of static pressure at 600°C. Furthermore, infrared imaging is used to glean the flow distribution from the headers into the microscale region of the receiver. While the integrated receiver could not be tested in the solar simulator due to limitations of the facility, receiver scale-up from 2 x 2 cm to 8 x 8 cm with more effective material usage is demonstrated. Title: Experimental Characterization of a Supercritical Carbon Dioxide Microchannel Solar Thermal Receiver Author: L'Estrange, Thomas Characterization of a microchannel solar thermal receiver for supercritical carbon dioxide (sCO₂) is presented. The receiver design is based on conjugate computational fluid dynamics and heat transfer simulations as well as thermo-mechanical stress analysis. Two lab scale receivers with a 2x2 cm² absorber area are fabricated and experimentally characterized - a parallel microchannel design and a microscale pin fin array design. Static pressure experiments are used to demonstrate receiver integrity at the design pressure of 125 bar at 750°C surface temperature. A concentrated solar simulator was designed and assembled to characterize the thermal performance of the lab scale receiver test articles. Results indicate that, for a fixed exit fluid temperature of 650°C, increase in incident heat flux results in an increase in receiver and thermal efficiency. At a fixed heat flux, efficiency decreases with an increase in receiver surface temperature. The ability to absorb flux of up to 100 W/cm² at thermal efficiency in excess of 90 percent and exit fluid temperature of 650°C using the microchannel receiver is demonstrated. Pressure drop for the pin array at the maximum flow rate for heat transfer experiments is less than 0.64 percent of typical line pressure of 200 bar. Following the successful test of the 2 x 2 cm lab-scale receiver, a larger 8x8 cm² integrated receiver was designed and fabricated. The integrated receiver is shown to withstand 200 bar of static pressure at 600°C. Furthermore, infrared imaging is used to glean the flow distribution from the headers into the microscale region of the receiver. While the integrated receiver could not be tested in the solar simulator due to limitations of the facility, receiver scale-up from 2 x 2 cm to 8 x 8 cm with more effective material usage is demonstrated. Close

• 3. [Article] Analysis of ceramic heat exchangers for use in a combined-cycle, wood-fired power plant

  This report presents the analysis of ceramic heat exchangers for use in a combined-cycle, wood-fired power plant. The combined-cycle system investigated is characterized by having a wood-fueled combustor, ...

  Citation × Citation Citation Abstract Copy Title: Analysis of ceramic heat exchangers for use in a combined-cycle, wood-fired power plant Author: Ranasinghe, Jatila This report presents the analysis of ceramic heat exchangers for use in a combined-cycle, wood-fired power plant. The combined-cycle system investigated is characterized by having a wood-fueled combustor, an indirect-fired gas turbine, and a Rankine steam cycle. The direct use of low-grade fuels, such as wood, in present gas turbines will present difficulties due to corrosion and erosion of the turbine components from the particulate matter in the exhaust gases. This difficulty can be overcome by indirectly firing the gas turbine with the transfer of energy from the combustion gases to the compressor air by means of a heat exchanger. Gas turbines suitable for this type of power plant operate at their maximum efficiency at the rated turbine inlet temperature, typically in the range of 1750 F. Modern ceramics exhibit excellent high temperature strength, and hence a ceramic heat exchanger is considered a very suitable candidate for such applications. In the power plant considered, air enters the heat exchanger at 540 F where it is heated to the turbine inlet temperature. Since a compact unit with low leakage was desired, a multiple gas-side pass, cross-flow heat exchanger was selected for the present application. A model was developed to simulate the ceramic heat exchanger. This model was used to size a heat exchanger for the power plant. The influence of the ceramic heat exchanger on the overall power plant performance were analyzed. The other plant components were simulated by using a computer code developed during previous studies of this power plant. The ceramic heat exchanger system was compared with a metallic heat exchanger system. Since leakage was recognized as a major difficulty in ceramic heat exchangers, the effects of leakage on the overall plant performance was analyzed. Finally, the ceramic heat exchanger system was compared to other possible methods of obtaining a high turbine inlet temperature. The results of the study indicate that the use of a ceramic heat exchanger has good potential for this type of power plant. It was also observed that losses due to heat exchanger leakage justify further research towards the development of better sealing arrangements, for high temperature and high pressure applications. Title: Analysis of ceramic heat exchangers for use in a combined-cycle, wood-fired power plant Author: Ranasinghe, Jatila This report presents the analysis of ceramic heat exchangers for use in a combined-cycle, wood-fired power plant. The combined-cycle system investigated is characterized by having a wood-fueled combustor, an indirect-fired gas turbine, and a Rankine steam cycle. The direct use of low-grade fuels, such as wood, in present gas turbines will present difficulties due to corrosion and erosion of the turbine components from the particulate matter in the exhaust gases. This difficulty can be overcome by indirectly firing the gas turbine with the transfer of energy from the combustion gases to the compressor air by means of a heat exchanger. Gas turbines suitable for this type of power plant operate at their maximum efficiency at the rated turbine inlet temperature, typically in the range of 1750 F. Modern ceramics exhibit excellent high temperature strength, and hence a ceramic heat exchanger is considered a very suitable candidate for such applications. In the power plant considered, air enters the heat exchanger at 540 F where it is heated to the turbine inlet temperature. Since a compact unit with low leakage was desired, a multiple gas-side pass, cross-flow heat exchanger was selected for the present application. A model was developed to simulate the ceramic heat exchanger. This model was used to size a heat exchanger for the power plant. The influence of the ceramic heat exchanger on the overall power plant performance were analyzed. The other plant components were simulated by using a computer code developed during previous studies of this power plant. The ceramic heat exchanger system was compared with a metallic heat exchanger system. Since leakage was recognized as a major difficulty in ceramic heat exchangers, the effects of leakage on the overall plant performance was analyzed. Finally, the ceramic heat exchanger system was compared to other possible methods of obtaining a high turbine inlet temperature. The results of the study indicate that the use of a ceramic heat exchanger has good potential for this type of power plant. It was also observed that losses due to heat exchanger leakage justify further research towards the development of better sealing arrangements, for high temperature and high pressure applications. Close

• 4. [Article] Experimental studies of a partially defluidized bed with immersed heat exchange tubes

  The object of this research study is to investigate and provide some fundamental information about bed slumping in a partially defluidized bed combustor. Due to the difficulty in making measurements and observations ...

  Citation × Citation Citation Abstract Copy Title: Experimental studies of a partially defluidized bed with immersed heat exchange tubes Author: Sitthiphong, Norkun The object of this research study is to investigate and provide some fundamental information about bed slumping in a partially defluidized bed combustor. Due to the difficulty in making measurements and observations at high temperature, a dynamically similar cold phase fluidized bed was used to model the high temperature case. Experiments were conducted in a 0.305 m by 2.44 m cold fluidized bed which has plexiglass windows along the sides to provide adequate visualization of the fluidizing phenomena. The heat exchange tube array comprising six staggered rows of horizontal tubes 0.0125 m O.D. was placed in the bed. Zirconia sand particles of diameter d[supscript p] = 305 microns were used to simulate the mixture of 1200 micron limestone and coal particles. Gas velocities used in the experiment were varied from minimum fluidizing velocity to six times minimum fluidizing velocity. On defluidizing half of the fluidized bed, bed material from the active portion of the bed began transferring to the slumped side of the bed, this caused a ridge of solids to form and grow on the slumped surface. Correlations were then developed to describe the changing contours of the slumped bed surface. A major factor in the entrainment of bed material from the fluidized beds is the ejection of particles when bubbles break the bed surface. The initial velocities of ejected particles can be associated with the velocity of rising bubbles from potential flow theory. A simple model was developed to predict the motions and trajectories of ejected particles in the freeboard region. This model predicted the rate of bed material transfer from the active side to the defluidized section of the bed. These predictions were tested by experiment and showed good agreement. A correlation of the experimentally found particle density function for transferred material is presented. This can be used to determine the total amount of bed material transfer at any defluidization time. The study of the gas flow in the slumped portion of the bed was also conducted by measuring the pressure profiles in both sections of the bed. The amount of gas bypass through the slumped bed was determined by the Ergun equation and these pressure profiles. The results indicate that the percentage of the gas bypass through the slumped section does not depend on the superficial velocity. Necessary conditions required to completely refluidize the slumped section of the bed after a long period of defluidization were obtained from the pressure-time trace study. It was found that complete refluidization of the slumped section could not be achieved by using superficial refluidizing velocities of less than two times minimum fluidizing velocity. Study of the lateral mixing of solids in a wide shallow fluidized bed was conducted by using the ferrite tracer technique. A simple unsteady diffusion equation was used successfully to model the dispersion of solids from the refluidized bed to the active bed. The lateral dispersion coefficient of solids was found to depend on the superficial velocity and so was the rate of the solids mixing. Finally, the results obtained from the room temperature bed were converted to those in the high temperature case by using similarity analysis. Comparison of the converted results with the available data from the high temperature bed indicated good agreement, and thus, a successful simulation. Title: Experimental studies of a partially defluidized bed with immersed heat exchange tubes Author: Sitthiphong, Norkun The object of this research study is to investigate and provide some fundamental information about bed slumping in a partially defluidized bed combustor. Due to the difficulty in making measurements and observations at high temperature, a dynamically similar cold phase fluidized bed was used to model the high temperature case. Experiments were conducted in a 0.305 m by 2.44 m cold fluidized bed which has plexiglass windows along the sides to provide adequate visualization of the fluidizing phenomena. The heat exchange tube array comprising six staggered rows of horizontal tubes 0.0125 m O.D. was placed in the bed. Zirconia sand particles of diameter d[supscript p] = 305 microns were used to simulate the mixture of 1200 micron limestone and coal particles. Gas velocities used in the experiment were varied from minimum fluidizing velocity to six times minimum fluidizing velocity. On defluidizing half of the fluidized bed, bed material from the active portion of the bed began transferring to the slumped side of the bed, this caused a ridge of solids to form and grow on the slumped surface. Correlations were then developed to describe the changing contours of the slumped bed surface. A major factor in the entrainment of bed material from the fluidized beds is the ejection of particles when bubbles break the bed surface. The initial velocities of ejected particles can be associated with the velocity of rising bubbles from potential flow theory. A simple model was developed to predict the motions and trajectories of ejected particles in the freeboard region. This model predicted the rate of bed material transfer from the active side to the defluidized section of the bed. These predictions were tested by experiment and showed good agreement. A correlation of the experimentally found particle density function for transferred material is presented. This can be used to determine the total amount of bed material transfer at any defluidization time. The study of the gas flow in the slumped portion of the bed was also conducted by measuring the pressure profiles in both sections of the bed. The amount of gas bypass through the slumped bed was determined by the Ergun equation and these pressure profiles. The results indicate that the percentage of the gas bypass through the slumped section does not depend on the superficial velocity. Necessary conditions required to completely refluidize the slumped section of the bed after a long period of defluidization were obtained from the pressure-time trace study. It was found that complete refluidization of the slumped section could not be achieved by using superficial refluidizing velocities of less than two times minimum fluidizing velocity. Study of the lateral mixing of solids in a wide shallow fluidized bed was conducted by using the ferrite tracer technique. A simple unsteady diffusion equation was used successfully to model the dispersion of solids from the refluidized bed to the active bed. The lateral dispersion coefficient of solids was found to depend on the superficial velocity and so was the rate of the solids mixing. Finally, the results obtained from the room temperature bed were converted to those in the high temperature case by using similarity analysis. Comparison of the converted results with the available data from the high temperature bed indicated good agreement, and thus, a successful simulation. Close

• 5. [Article] Half Array Architecture for Advancing Microchannel Heat Recuperation to Market

  High temperature microchannel heat recuperators (HTμRs) offer an efficient means of improving reactor process thermal efficiency by offering smaller form factors due to increased heat transfer surface ...

  Citation × Citation Citation Abstract Copy Title: Half Array Architecture for Advancing Microchannel Heat Recuperation to Market Author: Brannon, Samuel T. High temperature microchannel heat recuperators (HTμRs) offer an efficient means of improving reactor process thermal efficiency by offering smaller form factors due to increased heat transfer surface area density and volumetric heat transfer rate over traditional heat exchanger designs. To date, HTμRs face cost and reliability challenges. In this work, a HTμR design was developed capable of utilizing high volume manufacturing methods to improve raw material utilization and cost. The design utilizes a microchannel flow insert (MFI) to resist differential pressures within low pressure channels eliminating the need for photochemical machining. The MFIs are placed within a laser-welded microchannel half array which is inserted within a metal housing to establish the counter flow path. Analytical and computational models were developed to guide the structural, thermal and fluidic design of the sub-millimeter MFI for waste heat applications. A forming process was developed for producing the MFIs and experimental investigations were used to validate structural, thermal and fluidic performance. A robust microforming fabrication process was developed capable of providing average MFI heights of 529 μm with 0.5% standard deviation. MFIs were analyzed for out-of-plane compressive stiffness and compressive strength over multiple loading cycles to validate both analytical and finite element models. A finite element model provided a model error of 6.8% for compressive stiffness. The unbonded μPTN design presented yields an 88% decrease in structural panel size compared to macro-pyramidal truss networks for a given loading condition while maintaining similar panel area. Single layer fluid flow experiments were conducted to determine the average Nusselt number and pressure drop in microchannels both with and without an MFI installed. The MFI increased the average Nusselt number by 2.9x due to increased fluid mixing. The pressure drop through the MFI was found to be on average five times higher than the empty channel due to reduced flow cross-section area. The network pressure drop model yielded a percent error at low Reynolds numbers of 5.2%. Subsequently, a 3.5 kW HTμR made of Inconel 625 was designed for waste heat recovery with an inlet temperature of 850°C. A subscale HTμR was fabricated and tested to validate the 3.5 kW design. The sub-scale five layer HTμR was tested with a hot side inlet temperature of 300°C. The sub-scale device performed as expected in terms of effectiveness (4.3% error), duty (4.3% error), and MFI channel pressure drop (-2.6% error). These results were used to scale a 3.5 kW Inconel 625 HTμR with a heat transfer surface area density of 1,633 m²/m³, a volumetric heat transfer coefficient of 2.3 MW/(m³K), and a volumetric heat transfer rate of 32 MW/m³ providing improved results versus high temperature recuperator designs in literature. Title: Half Array Architecture for Advancing Microchannel Heat Recuperation to Market Author: Brannon, Samuel T. High temperature microchannel heat recuperators (HTμRs) offer an efficient means of improving reactor process thermal efficiency by offering smaller form factors due to increased heat transfer surface area density and volumetric heat transfer rate over traditional heat exchanger designs. To date, HTμRs face cost and reliability challenges. In this work, a HTμR design was developed capable of utilizing high volume manufacturing methods to improve raw material utilization and cost. The design utilizes a microchannel flow insert (MFI) to resist differential pressures within low pressure channels eliminating the need for photochemical machining. The MFIs are placed within a laser-welded microchannel half array which is inserted within a metal housing to establish the counter flow path. Analytical and computational models were developed to guide the structural, thermal and fluidic design of the sub-millimeter MFI for waste heat applications. A forming process was developed for producing the MFIs and experimental investigations were used to validate structural, thermal and fluidic performance. A robust microforming fabrication process was developed capable of providing average MFI heights of 529 μm with 0.5% standard deviation. MFIs were analyzed for out-of-plane compressive stiffness and compressive strength over multiple loading cycles to validate both analytical and finite element models. A finite element model provided a model error of 6.8% for compressive stiffness. The unbonded μPTN design presented yields an 88% decrease in structural panel size compared to macro-pyramidal truss networks for a given loading condition while maintaining similar panel area. Single layer fluid flow experiments were conducted to determine the average Nusselt number and pressure drop in microchannels both with and without an MFI installed. The MFI increased the average Nusselt number by 2.9x due to increased fluid mixing. The pressure drop through the MFI was found to be on average five times higher than the empty channel due to reduced flow cross-section area. The network pressure drop model yielded a percent error at low Reynolds numbers of 5.2%. Subsequently, a 3.5 kW HTμR made of Inconel 625 was designed for waste heat recovery with an inlet temperature of 850°C. A subscale HTμR was fabricated and tested to validate the 3.5 kW design. The sub-scale five layer HTμR was tested with a hot side inlet temperature of 300°C. The sub-scale device performed as expected in terms of effectiveness (4.3% error), duty (4.3% error), and MFI channel pressure drop (-2.6% error). These results were used to scale a 3.5 kW Inconel 625 HTμR with a heat transfer surface area density of 1,633 m²/m³, a volumetric heat transfer coefficient of 2.3 MW/(m³K), and a volumetric heat transfer rate of 32 MW/m³ providing improved results versus high temperature recuperator designs in literature. Close

• 6. [Article] A microchannel-based thermal management system for hydrogen storage adsorbent beds

  Hydrogen has been shown to be a promising replacement for fossil fuels for use in light duty vehicles because it is a clean, renewable and plentiful resource with a high gravimetric energy density. However, ...

  Citation × Citation Citation Abstract Copy Title: A microchannel-based thermal management system for hydrogen storage adsorbent beds Author: Steigleder, Leif J. Hydrogen has been shown to be a promising replacement for fossil fuels for use in light duty vehicles because it is a clean, renewable and plentiful resource with a high gravimetric energy density. However, in order to obtain an acceptable volumetric energy density, densification of the hydrogen is required. Adsorptive materials have been shown in the literature to increase volumetric and gravimetric storage densities. A major issue with adsorptive storage is that the adsorption process generates heat and optimal storage conditions are at temperatures below 100 K at pressures up to 50 atm. There is a need to develop heat exchanging architecture that enables adsorbents to be a viable method for hydrogen storage by managing the thermal environment of the storage tank. Based on previous modeling efforts to determine an acceptable bed module height for removal of heat via microchannel cooling plates, a thermal management system has been designed and tested capable of removing the heat of adsorption within adsorbent-filled hydrogen storage tanks. The system uses liquid nitrogen cooling to maintain tank temperatures of below 80 K at 50 atm. System studies show that the microchannel architecture offers a high cooling capacity with about a 6% displacement volume. Simulations and experiments have been conducted to evaluate the design for the cooling capacity, pressure drop, and flow distribution between and across the cooling plates, stress due to the pressurized environment, and thermal stress. Cost models have been developed to demonstrate that the system can be manufactured for a reasonable cost at high production volumes. Experimental results show that the modular system offers an acceptable cooling capacity and pressure drop with good flow distribution while adequately managing thermal stresses during operation. Title: A microchannel-based thermal management system for hydrogen storage adsorbent beds Author: Steigleder, Leif J. Hydrogen has been shown to be a promising replacement for fossil fuels for use in light duty vehicles because it is a clean, renewable and plentiful resource with a high gravimetric energy density. However, in order to obtain an acceptable volumetric energy density, densification of the hydrogen is required. Adsorptive materials have been shown in the literature to increase volumetric and gravimetric storage densities. A major issue with adsorptive storage is that the adsorption process generates heat and optimal storage conditions are at temperatures below 100 K at pressures up to 50 atm. There is a need to develop heat exchanging architecture that enables adsorbents to be a viable method for hydrogen storage by managing the thermal environment of the storage tank. Based on previous modeling efforts to determine an acceptable bed module height for removal of heat via microchannel cooling plates, a thermal management system has been designed and tested capable of removing the heat of adsorption within adsorbent-filled hydrogen storage tanks. The system uses liquid nitrogen cooling to maintain tank temperatures of below 80 K at 50 atm. System studies show that the microchannel architecture offers a high cooling capacity with about a 6% displacement volume. Simulations and experiments have been conducted to evaluate the design for the cooling capacity, pressure drop, and flow distribution between and across the cooling plates, stress due to the pressurized environment, and thermal stress. Cost models have been developed to demonstrate that the system can be manufactured for a reasonable cost at high production volumes. Experimental results show that the modular system offers an acceptable cooling capacity and pressure drop with good flow distribution while adequately managing thermal stresses during operation. Close

• 7. [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

• 8. [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

• 9. [Article] Integrated dual cycle energy recovery using thermoelectric conversion and an organic Rankine bottoming cycle

  Hot engine exhaust and industrial process exhaust represents a resource that is often rejected to the environment without further utilization. This resource is prevalent in the transportation and industrial ...

  Citation × Citation Citation Abstract Copy Title: Integrated dual cycle energy recovery using thermoelectric conversion and an organic Rankine bottoming cycle Author: Miller, Erik W. Hot engine exhaust and industrial process exhaust represents a resource that is often rejected to the environment without further utilization. This resource is prevalent in the transportation and industrial process sectors, but stationary engine-generator systems also typically do not utilize this resource. Engine exhaust is considered high grade heat and can potentially be utilized by various approaches to produce electricity or to drive heating and cooling systems. This thesis describes a model system that employs thermoelectric conversion as a topping cycle integrated with an organic Rankine bottoming cycle for waste heat utilization. This approach is being developed to fully utilize the thermal energy contained in hot exhaust streams. This thesis investigates several system configurations each composed of a high temperature heat exchanger which extracts thermal energy for driving the thermoelectric conversion elements and a closely integrated bottoming cycle to capture the large amount of remaining thermal energy in the exhaust stream. The models differ by how they arrange specific heat exchangers in the system. Many interacting parameters that define combined system operation are employed in the models to determine overall system performance including output power, efficiency, and total energy utilization factors. In addition, the model identifies a maximum power operating point for the combined system. That is, the model can identify the optimal amount of heat to remove from the exhaust flow to drive the thermoelectric elements for maximizing the combined cycle output. The model has been developed such that the impact of heat exchanger UA[subscript h] values, thermal resistances, and the thermoelectric figure-of-merit (ZT) can be investigated in the context of system operation. The model also has the ability to simultaneously determine the effect of each cycle design parameter on the performance of the overall system, thus giving the ability to utilize as much waste heat as possible. Key analysis results are presented showing the impact of critical design parameters on power output, system performance and inter-relationships between design parameters in governing performance. Title: Integrated dual cycle energy recovery using thermoelectric conversion and an organic Rankine bottoming cycle Author: Miller, Erik W. Hot engine exhaust and industrial process exhaust represents a resource that is often rejected to the environment without further utilization. This resource is prevalent in the transportation and industrial process sectors, but stationary engine-generator systems also typically do not utilize this resource. Engine exhaust is considered high grade heat and can potentially be utilized by various approaches to produce electricity or to drive heating and cooling systems. This thesis describes a model system that employs thermoelectric conversion as a topping cycle integrated with an organic Rankine bottoming cycle for waste heat utilization. This approach is being developed to fully utilize the thermal energy contained in hot exhaust streams. This thesis investigates several system configurations each composed of a high temperature heat exchanger which extracts thermal energy for driving the thermoelectric conversion elements and a closely integrated bottoming cycle to capture the large amount of remaining thermal energy in the exhaust stream. The models differ by how they arrange specific heat exchangers in the system. Many interacting parameters that define combined system operation are employed in the models to determine overall system performance including output power, efficiency, and total energy utilization factors. In addition, the model identifies a maximum power operating point for the combined system. That is, the model can identify the optimal amount of heat to remove from the exhaust flow to drive the thermoelectric elements for maximizing the combined cycle output. The model has been developed such that the impact of heat exchanger UA[subscript h] values, thermal resistances, and the thermoelectric figure-of-merit (ZT) can be investigated in the context of system operation. The model also has the ability to simultaneously determine the effect of each cycle design parameter on the performance of the overall system, thus giving the ability to utilize as much waste heat as possible. Key analysis results are presented showing the impact of critical design parameters on power output, system performance and inter-relationships between design parameters in governing performance. Close

• 10. [Article] Biaxial fatigue behavior of commercially pure titanium Ti-50A (Grade 2) and low-alloy titanium Ti-Code 12 (Grade 12) heat exchanger materials

  Material failures in heat exchangers are often closely tied to events associated with the conditions of service and operating parameters. These events can generally be attributed to adverse load application ...

  Citation × Citation Citation Abstract Copy Title: Biaxial fatigue behavior of commercially pure titanium Ti-50A (Grade 2) and low-alloy titanium Ti-Code 12 (Grade 12) heat exchanger materials Author: Tobias, Benjamin C. Material failures in heat exchangers are often closely tied to events associated with the conditions of service and operating parameters. These events can generally be attributed to adverse load application and higher than optimum operating temperatures that could lead to changes in the microstructure of the materials and fatigue failure of the component. However, fatigue failure in heat exchangers is usually associated with the presence of a biaxial stress condition. Two nonparallel forces create a two-dimensional stress field at the free surface of the structural element where the process and mechanism of fatigue failure normally initiate. An experimental investigation was conduct6d to evaluate the biaxial fatigue behavior of commercially pure titanium Ti-50A (Grade 2) and low-alloy titanium Ti-Code 12 (Grade 12) heat exchanger materials. The biaxial state of stress was composed of an axial stress and a superimposed torsional stress, applied in a thin-wall tubular specimen machined from titanium tubing. Torsional stress was applied independently using a torsion machine and a torque fixer assembly devised as part of this study. After applying the desired torsion, the torsionally stressed specimen was mounted on a closed-loop electrohydraulic machine for the application of axial cyclic loading. A minimum of four tests were conducted for each of three alternating stress levels at both high and low torsional stresses. The biaxial fatigue test under load control condition was done under fully reversed cycles equivalent to a biaxiality ratio of -1. These test parameters were determined from an analytical formulation based on Mohr's circle. The results are presented in terms of the various measured or calculated quantities versus number of cycles to fracture. Biaxial fatigue curves were drawn through the experimental points corresponding to Weibull's mean life criterion. The four data points exhibit scatter that appears to be related to the applied stress amplitude. It was also found that a correlation exists between the magnitude of applied cyclic biaxial stress and fatigue life to failure. In addition, the results have been discussed taking existing failure criteria into account. Title: Biaxial fatigue behavior of commercially pure titanium Ti-50A (Grade 2) and low-alloy titanium Ti-Code 12 (Grade 12) heat exchanger materials Author: Tobias, Benjamin C. Material failures in heat exchangers are often closely tied to events associated with the conditions of service and operating parameters. These events can generally be attributed to adverse load application and higher than optimum operating temperatures that could lead to changes in the microstructure of the materials and fatigue failure of the component. However, fatigue failure in heat exchangers is usually associated with the presence of a biaxial stress condition. Two nonparallel forces create a two-dimensional stress field at the free surface of the structural element where the process and mechanism of fatigue failure normally initiate. An experimental investigation was conduct6d to evaluate the biaxial fatigue behavior of commercially pure titanium Ti-50A (Grade 2) and low-alloy titanium Ti-Code 12 (Grade 12) heat exchanger materials. The biaxial state of stress was composed of an axial stress and a superimposed torsional stress, applied in a thin-wall tubular specimen machined from titanium tubing. Torsional stress was applied independently using a torsion machine and a torque fixer assembly devised as part of this study. After applying the desired torsion, the torsionally stressed specimen was mounted on a closed-loop electrohydraulic machine for the application of axial cyclic loading. A minimum of four tests were conducted for each of three alternating stress levels at both high and low torsional stresses. The biaxial fatigue test under load control condition was done under fully reversed cycles equivalent to a biaxiality ratio of -1. These test parameters were determined from an analytical formulation based on Mohr's circle. The results are presented in terms of the various measured or calculated quantities versus number of cycles to fracture. Biaxial fatigue curves were drawn through the experimental points corresponding to Weibull's mean life criterion. The four data points exhibit scatter that appears to be related to the applied stress amplitude. It was also found that a correlation exists between the magnitude of applied cyclic biaxial stress and fatigue life to failure. In addition, the results have been discussed taking existing failure criteria into account. Close