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• 1. [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

• 2. [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

• 3. [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