Browsing by Author "Tarau, Calin"
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Item 24 Hour Consumable-based Cooling System for Venus Lander(49th International Conference on Environmental Systems, 2019-07-07) Lee, Kuan-Lin; Tarau, CalinTo support NASA future Venus in-situ exploration missions, Advanced Cooling Technologies, Inc (ACT) is developing a Venus Lander thermal management system based on venting of a mixture cooling fluids. This system will allow at least 24-hours of operation on Venus surface in the high temperature (460°C) and high pressure (~92 bar) environment. The consumable-based cooling system will reject both the electronics waste heat generated inside the vehicle as well as the incoming heat leaks from the Venus environment. The system consists of two pressure vessels (primary vessel and compressed gas vessel) and a network of flow channels that serve as environmental heat guard and are embedded within the lander’s shell. The primary vessel will be charged with working fluid (ammonia) and further pressurized by compressed gas (e.g. argon), so the resulted fluid mixture can be vented into the environment that has pressure higher than the saturation pressure of the coolant that corresponds to the temperature of the payload. The venting will provide effective refrigeration (through the combined effect of evaporation and Joule-Thompson cooling) of the electronics. As the vented fluid mixture travels through the flow channels (i.e. heat guard) in superheated state, it can further collect environmental heat (that leaks in through the shell) as sensible heat and exit into the Venus environment. This paper summarizes the feasibility study performed under a NASA Phase I SBIR program, which includes the development of a thermodynamic mathematical model and of a proof-of-concept sub-scale system. This work has been performed under NASA Small Business Innovation Research (SBIR) Phase I contract 80NSSC18P2186.Item 3D Printed Thermal Management System for the Next Generation of Gallium Nitride-based Solid State Power Amplifiers(49th International Conference on Environmental Systems, 2019-07-07) Ababneh, Mohammed; Tarau, Calin; Anderson, WilliamCurrent Gallium Nitride (GaN)-based solid state power amplifiers (SSPAs) are limited in their operational capabilities due to the limitations of the overall thermal management system in dissipating the high heat fluxes. However, GaN based SSPAs are desirable for satellite communication due to their superior linearity, built-in redundancy, reliability, power density and energy efficiency as compared to current technologies such as traveling wave tube amplifiers (TWTAs). In order to enable higher power GaN amplifiers and next generation phased arrays, it is critical to reduce the heat flux on the thermal management system by spreading the heat efficiently across a larger area. Aluminum/ammonia constant conductance heat pipes have been a proven technology for spacecraft thermal control for more than 40 years with both high heat transport capability (76 to 254 Watt-m) and reasonably low mass. Unfortunately, ammonia only works up to about 80°C, while the use of high- temperature electronics such as GaN power amplifiers, allows operation up to 150 °C. This further allows significant reduction in radiator size and mass. Advanced Cooling Technologies, Inc. (ACT) is devloping a novel, low-cost and low-mass thermal management system (TMS) which is capable of handling power densities and temperatures of next generation GaN power amplifiers and phased arrays. The design is based on integration of 3D printed vapor chamber and freeze/thaw tolerant titanium-water heat pipes with several novel features designed to ensure cooling of GaN devices during start-up or operation in space (vacuum and zero gravity) as well as earth environments.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 Passive Thermal eXperiment (APTx) for Warm Reservior Hybrid Wick Variable Conductance Heat Pipes on the International Space Station(48th International Conference on Environmental Systems, 2018-07-08) Tarau, Calin; Ababneh, Mohammed; Anderson, William; Alvarez-Hernandez, Angel; Ortega, Stephania; Farmer, Jeff; Hawkins, RobertAs NASA prepares to further expand human and robotic presence in space, it is well known that spacecraft architectures will be impacted by unprecedented power requirements and thermal environments in deep space. In addition, there is a need to extend the duration of the missions in both cold and hot environments, including cis-lunar and planetary surface excursions. The heat rejection turn–down ratio of the increased thermal loads in the above-mentioned conditions is crucial for minimizing vehicle power needs. Therefore, future exploration activities will have the need of thermal management systems that can provide higher reliability and performance, and power and mass reduction. In an effort to start addressing the current technical gaps in thermal management systems, novel new passive thermal technologies have been selected and tested on the board of the International Space Station (ISS). This testing was performed under the Advanced Passive Thermal eXperiment (APTx) project that is a collaboration between the Johnson Space Center (JSC), Marshall Space Flight Center (MSFC), University of Texas, and Advanced Cooling Technologies, Inc. (ACT) with funding from ISS Technology Demonstration Office at JSC as well as NASA’s Small Business Innovative Research Program. A hybrid-wick copper-Monel-water Variable Conductance Heat Pipe (VCHP) with warm reservoir design that consists of a copper evaporator (with sintered wick), a monel adiabatic section and a condenser both with grooved wick inside was developed and tested successfully on ground. The VCHP worked on the board of the ISS, but at higher temperatures than expected. Hence, a new flight VCHP design is currently under development to mitigate the shortcomings encountered in microgravity. The final paper will include some results and conclusions from the original flight testing and the ground test results for the improved VCHP.Item Advanced Passive Thermal Experiment for Hybrid Variable Conductance Heat Pipes and HiK™ Plates on the International Space Station(47th International Conference on Environmental Systems, 2017-07-16) Ababneh, Mohammed T.; Tarau, Calin; Anderson, William G.; Farmer, Jeffery T.; Alvarez-Hernandez, Angel R.; Ortega, StephaniaAs NASA prepares to further expand human and robotic presence in space, it is well known that spacecraft architectures will be challenged with unprecedented thermal environments in deep space. In addition, there is a need to extend the duration of the missions in both cold and hot environments, including cis-lunar and planetary surface excursions. The heat rejection turn–down ratio of the increased thermal loads in the above-mentioned conditions is crucial for minimizing vehicle resources (e.g. power). Therefore, future exploration activities will have the need of thermal management systems that can provide higher reliability and performance, and power and mass reduction. In an effort to start addressing the current technical gaps in thermal management systems, novel new passive thermal technologies have been selected to be included as part of suite of experiments to be tested on the board of the International Space Station (ISS), tentatively in 2017. Advanced Cooling Technologies, Inc. (ACT), together with NASA Marshall Space Flight Center and NASA Johnson Space Center, are working to test and validate hybrid wick VCHP with warm reservoir and HiK™ plates on the ISS under the Advanced Passive Thermal experiment (APTx) project. The APTx consists of two separate payloads that will be tested sequentially: • Payload 1 contains a VCHP/HiK™ plate assembly: a hybrid-wick copper-Monel-water VCHP design consists of a copper evaporator (with sintered wick inside), a monel adiabatic section and a condenser both with grooved wick inside and a NCG reservoir thermally and physically attached to the evaporator. In turn, the VCHP evaporator is mounted on an aluminum HiK™ plate. • Payload 2 contains a HiK™ plate and the ElectroWetting Heat Pipe (EWHP) experiment, developed by the University of Texas at Austin. This paper will cover the results to date for the flight test, which is planned for 2017.Item Demonstration of Copper-Water Heat Pipes Embedded in High Conductivity (HiK™) Plates in the Advanced Passive Thermal eXperiment (APTx) on the International Space Station(48th International Conference on Environmental Systems, 2018-07-08) Ababneh, Mohammed; Tarau, Calin; Anderson, William; Alvarez-Hernandez, Angel; Ortega, Stephania; Farmer, Jeffrey; Hawkins, RobertCopper-water heat pipes are commonly used for thermal management of electronics systems on earth and aircraft, but have not been used in spacecraft thermal control applications to date, due to the satellite industry’s requirement that any device or system be successfully tested in a microgravity environment prior to adoption. Recently, Advanced Cooling Technologies Inc., (ACT), in coordination with engineers from NASA’s Marshall Space Flight Center (MSFC) and Johnson Space Center (JSC) demonstrated successful flight operation of these heat pipes in low-Earth orbit. The testing was conducted aboard the International Space Station (ISS) under the Advanced Passive Thermal eXperiment (APTx) project, a project to test a suite of passive thermal control devices funded by the ISS Technology Demonstration Office at NASA JSC. The heat pipes were embedded in a high conductivity (HiK™) aluminum base plate and subject to a variety of thermal tests over a temperature range of -10 to 38 ºC for a ten-day period. Results showed excellent agreement with both predictions and ground tests. The HiK™ plate underwent 15 freeze-thaw cycles between -30 and 70 ºC during ground testing, and an additional 14 freeze-thaw cycles during the ISS testing. The following was demonstrated during 10 days of testing on the ISS: 1. Successful operation of the copper-water heat pipes and HiK™ plate 2. Ability of the copper-water heat pipes and HiK™ plate to survive multiple freeze/thaw cycles 3. As-designed heat transport via Copper-water heat pipes. 4. Reliable, repeatable start up of Copper-water heat pipes and HiK™ plate from a frozen state. This paper describes the test hardware, ground and flight test campaign, and discusses the results and conclusions of the testing.Item Design Analysis and Performance testing of a Novel Passive Thermal Management System for Future Exploration Missions(48th International Conference on Environmental Systems, 2018-07-08) Alvarez, Angel; Ortega, Stephania; Farmer, Jeff; Breeding, Shawn; Tarau, Calin; Ababneh, Mohammed; Anderson, WilliamIn response to an announcement of opportunity from the NASA’s Science Mission Directorate (SMD) Discovery Program, the Southwest Research Institute in collaboration with the Aerospace Corporation and the NASA Johnson Space Center (JSC) proposed a lunar lander science mission. The Moon Age and Regolith Explorer (MARE) would use a lunar lander to reach a young, nearside lunar lava flow for the collection and analysis of the lunar soil. This would be used for the determination of the impact history of the inner solar system and the evolution and differentiation of the interiors of one-plate planets. The lunar lander proposed was based on the NASA JSC Morpheus lander vehicle. The thermal environments for the proposed mission were both challenging and unprecedented, since survival of multiple lunar day/night cycles at the south-west region of the Aristarchus plateau were required. Other thermal design challenges included the need of a low mass, simple, robust and reliable thermal management system that would assure the success of the proposed mission. As part of the proposal effort, and leveraging on existing NASA Small Business Innovative Research (SBIR), a completely passive thermal control system concept was used to meet mission requirements. The thermal management system proposed uses a novel type of hybrid grooved and sintered wick variable conductance heat pipe and a high conductivity heat spreader; the thermal management systems tested wer developed by Advanced Cooling Technologies, Inc. (ACT) in Landcaster, Pennsylvania. This publication will present the design, analysis and prototype component and system level performance testing done at NASA JSC.Item Development of a Heat Exchanger with Integrated Thermal Storage for Spacecraft Thermal Management Applications(47th International Conference on Environmental Systems, 2017-07-16) Lee, Kuan-Lin; Tarau, Calin; Van Velson, NathanIn order to reduce the mass of on-board thermal management systems for NASA future space missions, Advanced Cooling Technologies, Inc. (ACT) has developed an innovative heat exchanger that integrates phase change material (PCM) within a vapor chamber. The developed PCM-based heat exchanger consists of multiple ultra-thin aluminum drawers charged with bulk PCM (Tm~25°C). The exterior of each drawer was wrapped with screen mesh, which serves as the wick structure to transport the working fluid (acetone) back to the heated regions. Depending on the sink temperature, the developed device can either function as a thermal capacitor or a two-phase heat exchanger with heat storage capability. During the spacecraft launching stage, the excessive heat carried via the saturated vapor will be stored within the PCM and then released back to the heat exchanger during the orbiting stage. The aluminum-acetone heat exchanger with multiple drawers can potentially achieve a high PCM/total mass ratio (~0.7). This paper reports on the development of the PCM-based heat exchanger, including conceptual designs, mathematical modeling, prototype fabrication and the experimental system.Item Development of Flight Demonstration Hot Reservoir Variable Conductance Heat Pipes for Microgravity Testing and Future Lunar Landers and Surface Systems(2023 International Conference on Environmental Systems, 2023-07-16) Lee, Kuan-Lin; Tarau, Calin; Abdelmaksoud, Ramy; Anderson, William G.; Kharangate, Chirag; Kamotani, YasuhiroThe lunar landers and rovers require a reliable tight passive thermal control technology due to their exposure to the ambient's harsh temperature conditions such as the lunar night where the temperature drops to about -280?F (-173.3?C) and lasts for a continuous 14-day period. Advanced Cooling Technologies Inc. (ACT) has devised and demonstrated a hot reservoir variable conductance heat pipe (HR-VCHP) to be an ideal passive variable thermal link between the payloads and the radiator for such lunar landers since HR-VCHP can offer much tighter thermal control capability when compared to a regular cold-biased reservoir VCHP. Under NASA Small Business Technology Transfer (STTR) program, ACT and Case Western Reserve University (CWRU) further matured this technology by introducing a novel fluid management feature that enables a non-condensable gas (NCG) flow to generate inside the device. This flow can maintain the moisture level of the reservoir and lead to more reliable VCHP operation in space. Two flight demonstration units (FDU) of HR-VCHPs with NCG flow are under development: one for microgravity testing on International Space Station (ISS) and another one for lunar lander thermal control applications. The FDU for microgravity testing is made from copper where the working fluid is water while the HR-VCHP for the future lunar landers is made from aluminum where the working fluid is ammonia or propylene. This paper will present a compact HR-VCHP prototype description, reliability testing results, and the development status of two FDUs.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 High Heat Flux (>50 W/cm^2) Hybrid Constant Conductance Heat Pipes(48th International Conference on Environmental Systems, 2018-07-08) Ababneh, Mohammed; Tarau, Calin; Anderson, William; Fisher, JesseNovel hybrid wick aluminum-ammonia constant conductance heat pipes (CCHPs) are developed to handle heat flux requirements for spacecraft thermal control applications. The 5-10 W/cm^2 heat density limitation of aluminum-ammonia grooved heat pipes has been a fundamental limitation in the current design for space applications. The recently demonstrated >50W/cm^2 capability of the hybrid high heat flux heat pipes provides a realistic means of managing the high heat density anticipated for the next generation space designs. The hybrid wick high heat flux aluminum-ammonia CCHP transported a heat load of 275 Watts with heat flux input of > 50 W/cm^2 and with a thermal resistance of 0.015 ºC/W at 0.1 inch adverse elevation. This demonstrates an improvement in heat flux capability of more than 5 times over the standard axial groove aluminum-ammonia CCHP design.Item Hot Reservoir Variable Conductance Heat Pipe with Advanced Fluid Management(50th International Conference on Environmental Systems, 7/12/2021) Lee, Kuan-Lin; Tarau, Calin; Adhikari, Sanjay; Anderson, William; Kharangate, Chirag; Huang, Cho-Ning; Kamotani, YasuhiroA hot reservoir variable conductance heat pipe (VCHP) can offer a significantly tighter passive thermal control than a regular VCHP with a cold-biased reservoir. This attribute makes the hot reservoir VCHP an ideal thermal management device for future planetary landers and rovers and especially for the moon where surviving of the lunar night is energetically challenging. Since the hot reservoir cannot be wicked, it becomes a challenge to properly manage the presence of working fluid within the reservoir. To ensure a long-duration operation of the hot reservoir VCHPs in reduced gravity and in microgravity, advanced fluid management strategies and features must to be developed. Advanced Cooling Technologies, Inc (ACT) in collaboration with Case Western Reserve University (CWRU) is developing a reliable VCHP configuration under the NASA STTR program. The novel VCHP consists of a loop with well-engineered tubing configuration, that would generate a momentum induced continuous flow within the device. This induced flow would provide continuous maintenance of the NCG humidity in the reservoir as well as enable a much faster purging process (i.e. removal of moisture from the hot reservoir) if needed, significantly enhancing device�s reliability. The development of hot reservoir VCHP with advanced fluid management features will be presented in this paper, including both numerical and experimental efforts.Item Hybrid Heat Pipes for Lunar and Martian Surface and High Heat Flux Space Applications(46th International Conference on Environmental Systems, 2016-07-10) Ababneh, Mohammed; Tarau, Calin; Anderson, William; Farmer, Jeffery; Alvarez-Hernandez, AngelNext generation of polar rovers and equatorial landers is among the immediate NASA planetary applications. These landers and rovers have a Warm Electronics Box (WEB) and a battery, both of which must be maintained in a fairly narrow temperature range. So, a variable thermal link between the WEB and radiator is required. During the day, the thermal link must transfer heat from the WEB to the radiator as efficiently as possible, to minimize the radiator size. On the other hand, the thermal link must be as ineffective as possible during the Lunar night. This will preserve the electronics and battery warm with minimal power, even with the very low heat sink temperature. This variable thermal link can be a variable conductance heat pipe (VCHP) would require hybrid wick to allow liquid return during operation under unfavorable orientation of the evaporator. Also, future spacecraft and instruments developed for NASA's Science Mission Directorate will involve highly integrated electronics, such as for CubeSat/SmallSat. This high density electronics packaging leads to substantial improvement in performance per unit, mass, volume and power. However, it also results in requirement of sophisticated thermal control technology to dissipate the high heat flux generated by these electronics systems. For example, the current incident heat flux for laser diode applications is on the order of 5-10 W/cm2, although this is expected to increase towards 50 W/cm2. This is a severe limitation for the commonly employed axial groove aluminum/ammonia constant conductance heat pipes (CCHPs). Hence, high flux heat acquisition and transport devices are required. The paper reports on the development of VCHPs and CCHPs with a hybrid grooved and sintered wick.Item Hybrid Heat Pipes for Planetary Surface and High Heat Flux Applications(45th International Conference on Environmental Systems, 2015-07-12) Ababneh, Mohammed T.; Tarau, Calin; Anderson, William G.Novel hybrid wick Constant Conductance Heat Pipes (CCHPs) were developed to solve the high heat flux limitation for future highly integrated electronics. In addition to carrying power over long distances in space, the hybrid CCHP evaporator can also operate against an adverse tilt on the planetary surface for Lunar and Martian landers and rovers. These hybrid heat pipes will be capable of operating at the higher heat flux requirements expected in NASA’s future spacecraft and instruments such as on the next generation of polar rovers and equatorial landers. The thermal transport requirements for future spacecraft missions continue to increase, while at the same time the heat acquisition areas have trended downward, thereby increasing the incident heat flux from 5-10W/cm2 to the projected > 50W/cm2. This exceeds the performance of standard axial groove CCHPs and loop heat pipes (LHPs). Aluminum/ammonia and stainless steel/ammonia hybrid CCHPs to demonstrate high heat flux capability and for planetary (Lunar and Martian) rovers and landers were designed, fabricated and tested. The CCHPs had a sintered powder metal wick in the evaporator and axial grooves in the adiabatic and condenser regions The hybrid wick high heat flux aluminum/ammonia CCHP transported a heat load of 175 watts with heat flux input of 53W/cm2 at 0.1 inch adverse elevation. This demonstrates an improvement in heat flux capability of 3 times over the standard axial groove CCHP design. The hybrid wick high heat flux stainless steel/ammonia CCHP transported a heat load of 165 watts with heat flux input of 51W/cm2 at 0.1 inch adverse elevation. The Thermal Link planetary aluminum/ammonia CCHP transported approximately 202 watts at a 4.2° adverse inclination before dryout, exceeding the 150W target. Also the Thermal Link planetary aluminum/ammonia CCHP was tested for maximum transport power at three different adverse elevations to extrapolate zero-g power. The maximum power at zero-g is 288 watts, exceeding the 150W target. The X-ray micrographs for the interface between the sintered powder metal wick and the axial grooves in the stainless steel hybrid CCHP shows much better contact in comparison to the aluminum CCHP because of the successful internal sintering technique developed during this project.Item Integrated Hot Reservoir Variable Conductance Heat Pipe with Improved Reliability(51st International Conference on Environmental Systems, 7/10/2022) Lee, Kuan-Lin; Tarau, Calin; Anderson, William; Huang, Cho-Ning; Kharangate, Chirag; Kamotani, YasuhiroA hot reservoir variable conductance heat pipe (VCHP) that can offer tight and passive thermal control is an ideal thermal link for future planetary landers and rovers. This is especially useful for the moon operation as surviving during the lunar night is energetically challenging. Under a Small Business Technology Transfer (STTR) program, Advanced Cooling Technologies (ACT) and Case Western Reserve University (CWRU) developed an advanced integrated hot reservoir VCHP with improved reliability. This novel design enables a momentum-induced flow to circulate through a non-condensable gas (NCG) loop, which can continuously and effectively remove the excessive working fluid vapor from the reservoir (i.e. purging) without using an electric heater. Based on the purging test results, the bulk induced flow velocity is in a cm per second range. Without the flow, purging is dominated by diffusion and it will take hours to complete. With momentum-induced flow, the purging rate is much faster and the heat pipe can get back to normal operation within 20 minutes. This paper summarizes prototype development and experimental study of hot reservoir VCHP loop, including a detailed analysis of the VCHP purging process, purging, and startup testing of VCHP loop. A compact hot reservoir VCHP loop prototype with both reservoir and NCG tube integrated was developed and tested.Item Launch Vehicle Avionics Passive Thermal Management(44th International Conference on Environmental Systems, 2014-07-13) Anderson, William G.; Corday, Cameron; DeChristopher, Mike; Hartenstine, John R.; Maxwell, Taylor; Schwendeman, Carl; Tarau, CalinA passive thermal management system was designed to cool avionics on a launch vehicle for 3 different thermal modes. Prior to launch, the heat sink for the avionics is purge duct flow. During the 10 minute launch period, the thermal energy is stored in phase change material (PCM). On orbit, the heat sink is a radiator. The system consists of 1. A high conductivity thermal shelf, 2. A PCM thermal storage system, 3. Heat pipes to conduct the heat from the shelf to the heat sinks, 4. Fins to reject the heat to the purge duct, and 5. A radiator to reject the heat on orbit. A unique aspect of the system design is the avionics shelf, which contains embedded heat pipes. While the electronics locations are fixed before manufacturing with encapsulated high conductivity material, this design allows the avionics boxes to be positioned anywhere. A second benefit is the much higher thermal effective thermal conductivity, which can approach 2500 W/m K in long systems. A low-cost, simplified version of the system to fabricated to verify the design during ground testing, consisting of the high conductivity plate, the heat pipe, and the purge duct sink. The general performance matched expectations, except that the overall ΔT was higher than expected, due to the thermal interface materials. This can be improved with a better material.Item Multiple Loop Heat Pipe Radiator for Variable Heat Rejection in Future Spacecraft(45th International Conference on Environmental Systems, 2015-07-12) Velson, Nathan Van; Tarau, Calin; DeChristopher, Mike; Anderson, William G.As NASA refocuses its human mission ambitions to colder areas of exploration beyond Low Earth Orbit, the need for improved variable heat rejection thermal control systems increases. To account for large variations in heat loads and environment temperatures, a thermal control system with a large turndown ratio is required. This paper presents a variable heat rejection system that uses multiple Loop Heat Pipes (LHPs) to reject large heat loads from a single-phase pumped loop, with high turndown ratios. A novel method of LHP control through local flow rate modulation of the single-phase fluid is developed and demonstrated. Systematic Thermal Desktop modeling of multiple LHP systems was performed to demonstrate the potential of this method. A modeled 2.5 kW three LHP system was shown to have a turndown ratio of 10:1 at a sink temperature of -41°C K and a turndown of 1.5:1 at a sink temperature of -269°C. Finally, an experimental study of a two-LHP system was performed to support the conclusions of the modeling effort.Item Non-Integrated Hot Reservoir Variable Conductance Heat Pipes(51st International Conference on Environmental Systems, 7/10/2022) Diebold, Jeff; Tarau, Calin; Smay, Joshua; Hahn, Timothy; Spangler, RyanAs NASA prepares to further expand human and robotic presence in space, it is well known that spacecraft architectures will be impacted by unprecedented power requirements and extreme thermal environments. Thermal management systems need to reject large heat loads into hot environments and have high heat rejection turn-down ratios in order to minimize vehicle power needs during periods of darkness, such as the 14-day lunar night. Variable conductance heat pipes (VCHP) are capable of passively transporting large quantities of heat and provide high thermal turn-down ratios ideal for surviving extreme cold environments. In this paper, Advanced Cooling Technologies, Inc. (ACT) will discuss the design and testing of two unique non-integrated warm reservoir VCHPs. The first VCHP is flight hardware designed to fly onboard Astrobotic Technology�s lunar lander Peregrine. The Astrobotic VCHP is designed to operate during transit and on the lunar surface and utilizes a hybrid wick design. The evaporator wick was 3D printed while the adiabatic and condenser sections utilized grooved wicks with high permeability optimum for operation in a microgravity environment. The second VCHP was designed for NASA�s lunar rover VIPER. A unique feature of the VIPER VCHP was the flexible adiabatic section. In order to accommodate relative motion between the heat spreader panel and the radiator panel, due to launch induced vibrations, nested flexible lines for the VCHP envelope and internal non-condensable gas tube were used in the adiabatic section. Both VCHPs utilized a non-integrated warm reservoir of non-condensable gas. The non-integrated reservoirs provided high thermal turn-down ratios and the ability to independently heat the reservoir in order to purge working fluid increasing the reliability of the device.