Browsing by Author "Lutz, Andrew"
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Item Advanced Hot Reservoir Variable Conductance Heat Pipes for Planetary Lander(2020 International Conference on Environmental Systems, 2020-07-31) Lee, Kuan-Lin; Tarau, Calin; Lutz, Andrew; Anderson, William; Huang, Cho-Ning; Kharangate, Chirag; Kamotani, YasuhrioThe next generation of Lunar rovers and landers require variable thermal links to maintain payload temperatures nearly constant over wide sink temperature fluctuations. It has been demonstrated on earth that a hot reservoir variable conductance heat pipe (VCHP) can provide a much tighter passive thermal control capability compared to a conventional VCHP with cold-biased reservoir. However, previous ISS test results revealed that the fluid management of a hot reservoir VCHP needs to be improved to ensure its long-term reliability. Under an STTR Phase I program, Advanced Cooling Technologies, Inc. in collaboration with Case Western Reserve University performed fundamental research to understand the complex transport phenomena within a hot reservoir VCHP. A novel loop VCHP configuration was developed during the program. This loop design allows a net flow to be induced and circulate along the NCG tubing system, which will continuously remove the excessive working fluid from the reservoir (i.e. purging) in a much faster rate compared to diffusion alone. Two potential mechanisms to induce net transport flow were identified: 1. By momentum transfer from vapor to NCG through shearing in the condenser/front region. It was called “DC” mechanism. 2. By filtering the pulses (via a tesla/check valve) generated in the heat pipe section of VCHP loop. It was called “AC” mechanism. Although these two mechanisms are independent, the AC mechanism can be further added/superimposed on the top of the DC mechanism to achieve a higher flow rate. This paper presents the work performed in Phase I to proof the existence of momentum transfer flow (“DC flow) and its effectiveness on VCHP purging. The work includes theoretical analysis, numerical modeling, prototype development and experimental demonstration.Item Advanced Two-Phase Cooling System for Modular Power Electronics(51st International Conference on Environmental Systems, 7/10/2022) Lee, Kuan-Lin; Hota, Sai Kiran; Lutz, Andrew; Rokkam, SrujanNASA envisions building future space power system architectures with many standardized, interchangeable, and reusable modular electronics to improve system adaptability and minimize the cost of development, operation, and maintenance. As the size of the electronics becomes smaller, future high-performance electronic modules will generate higher waste heat fluxes, which will be unmanageable by the current state-of-art cooling systems. More effective heat transfer devices and integrated cooling systems that can significantly reduce the overall thermal resistance from the semiconductors to the heat sink are highly desired. Under an SBIR program, Advanced Cooling Technologies, Inc. (ACT) developed a lightweight and effective cooling system for 3U modular electronics in a common enclosure. The system consists of multiple advanced thermal management components, including two-phase heat spreaders to move the heat from card center to edges and enhanced card locks to minimize card-to-chassis thermal resistance. Two types of two-phase solutions were identified and investigated. The first one is heat pipe embedded card (i.e. Hi-KTM plate) and the second is pulsating heat pipe (PHP) plate. ACT designed, fabricated, and thermally tested on a lab-scale mock modular electronics system. A comprehensive trade study and the overall improvement in heat transfer by these two heat spreaders in comparison to an aluminum plate were discussed.Item Development of High Heat Flux Titanium-Water CCHPs(2020 International Conference on Environmental Systems, 2020-07-31) Lutz, Andrew; Tarau, Calin; Anderson, BillCCHPs are the current method used for cooling almost all spacecraft, including NASA, DoD, and commercial satellites. The maximum heat flux for current aluminum-ammonia CCHPs is roughly 10-15 W/cm2. This limit will affect more and more spacecraft electronics systems as electronics continue to increase in power and decrease in size. Traditionally, CCHPs have achieved limited heat flux due to dry-out at the critical heat flux in the evaporator. During previous development, Advanced Cooling Technologies, Inc. (ACT) identified a hybrid wick configuration that allows an increased critical heat flux, and therefore increased maximum heat flux of the aluminum-ammonia CCHP. Under a NASA Phase IIX SBIR program, ACT demonstrated a hybrid wick (with grooves), high heat flux, titanium-water heat pipe capable of maintaining less than 10 K temperature difference from condenser to evaporator at heat flux values up to 90 W/cm2. Aluminum and ammonia were replaced by titanium and water because of a potential testing opportunity inside the ISS. The experiment was performed with the heat pipe operating against gravity to simulate a zero-gravity environment. The experimental performance of the hybrid wick heat pipe was compared to the performance of an otherwise identical baseline titanium-water heat pipe without the hybrid wick to enable high heat flux. The baseline heat pipe exceeded 10 K temperature difference at a heat flux less than 40 W/cm2. This work has been performed under NASA Small Business Innovation Research (SBIR) Phase IIX contract NNX15CM03C.Item Development of Variable View Factor and Deployable Two-Phase Radiator(2020 International Conference on Environmental Systems, 2020-07-31) Diebold, Jeff; Tarau, Calin; Lutz, Andrew; Rokkam, Srujan K.Radiators for manned spacecraft, satellites, planetary rovers and unmanned spacecraft are typically sized for the highest power at the hottest sink conditions, so they are oversized most of the time. In order to address the need for light-weight and efficient radiators capable of a significant thermal turndown ratio, Advanced Cooling Technologies, Inc. (ACT) has developed a novel vapor-pressure-driven variable-view-factor and deployable radiator that passively operates with variable geometry (i.e., view factor). The device, utilizes two-phase heat transfer and novel geometric features that passively (and reversibly) adjusts the view factor in response to internal pressure in the radiator. This paper extends previous 2D structural modeling to three dimensions. A set of important geometric variables are identified and their influence on the view factor is parametrically investigated. In addition, a thermal model of the variable-view-factor two-phase radiator is introduced and used to demonstrate the thermal control capabilities of the concept. This work has been performed under NASA Small Business Innovation Research (SBIR) Phase I contract 80NSSC18P2187 and Phase II contract 80NSSC19C0209.Item Fabrication and Experimental Testing of Variable-View Factor Two-Phase Radiators(51st International Conference on Environmental Systems, 7/10/2022) Diebold, Jeff; Tarau, Calin; Lutz, Andrew; Rokkam, Srujan; Eff, Michael; Lindamood, LindseyRadiators for manned spacecraft, satellites, planetary rovers and unmanned spacecraft are sized for the highest power at the hottest sink conditions, so they are oversized and prone to freezing at low sink temperatures. In order to address the need for light-weight, deployable and efficient radiators capable of passive thermal control and a significant heat rejection turndown ratio, Advanced Cooling Technologies, Inc. (ACT) has developed a novel vapor-pressure-driven variable-view-factor and deployable radiator that passively operates with variable geometry (i.e., view factor). The device utilizes two-phase heat transfer and novel geometric features that passively (and reversibly) adjust the view factor in response to the internal vapor pressure in the radiator. The variable-view-factor two-phase radiator (VVFTPR) consists of hollow curved and straight panels, filled with a two-phase fluid. An increase in internal vapor-pressure, due to an increase in fluid temperature, results in elastic bending of the curved panel and an increase in view-factor. In addition, since the radiator is a two-phase device, its efficiency will approach unity. ACT and the Edison Welding Institute (EWI) have successfully manufactured and tested VVFTPR panel prototypes from aluminum 7075 via ultrasonic welding. Two radiator prototypes will be presented. The first prototype was made of several separate channels containing a two-phase working fluid. The second prototype utilized a continuous channel design that allowed the working fluid to flow continuously through the prototype and could function as a radiator for loop heat pipes. This paper discusses the manufacturing process and experimental testing of the prototypes.Item Variable View Factor Two-Phase Radiator(49th International Conference on Environmental Systems, 2019-07-07) Lutz, Andrew; Tarau, Calin; Rokkam, SrujanVariable View Factor Two-Phase Radiator Variable view factor radiators are needed for manned missions and satellites to maintain a target temperature band of the cooled media or environment over widely varying power and heat sink conditions. Under a NASA SBIR program, Advanced Cooling Technologies is developing a vapor-pressure-driven variable-view-factor radiator that is deployable, operates with variable geometry and offers high turndown ratio of its thermal resistance to the sink. The proposed device, utilizes two-phase heat transfer and novel geometric features that adaptively (and elastically) adjust the view factor in response to internal (vapor) pressure and, implicitly, temperature. The radiator folds into a teardrop shape to minimize view factor when cold, and opens to maximize view factor when heated. This is facilitated by dynamic feedback between pressure inside the hollow curved panels of the radiator and the radiator structure itself, which permits a change of shape within the elastic limit of the material – thereby resulting in a reversible, deployable and variable view factor radiator that works via a two-phase heat rejection mechanism. The paper will discuss the proof-of-concept development that includes lab-scale experimental results, structural studies describing opening sensitivity including design optimization for environmental conditions, and overall TCS performance when utilizing the variable view factor radiator. Initially, a baseline design of the radiator was modeled, fabricated, and tested in a laboratory environment. Subsequently, structural studies were performed to understand how opening sensitivity is effected by geometric parameters including wall thickness, gap space, major radius, and other features. Design optimization seeks to maximize the opening sensitivity thus lowering the temperature difference between heat source and sink across the range of shapes between closed and fully open. Geometric features that increase opening sensitivity will be presented as well as their impact on TCS performance. Work performed under NASA (SBIR) contract 80NSSC18P2187.