Laura Ottenstein

Temperature oscillations in loop heat pipe operation

Loop heat pipes (LHPs) are versatile two-phase heat transfer devices that have gained increasing acceptance for space and terrestrial applications. The operating temperature of an LHP is a function of its operating conditions. The LHP usually reaches a steady operating temperature for a given heat load and sink temperature. The operating temperature will change when the heat load and/or the sink temperature changes, but eventually reaches another steady state in most cases. Under certain conditions, however, the loop operating temperature never really reaches a true steady state, but instead becomes oscillatory. This paper discusses the temperature oscillation phenomenon using test data from a miniature LHP.

Flight Testing of the Capillary Pumped Loop Flight Experiment

The Capillary Pumped Loop 3 (CAPL 3) experiment was a multiple evaporator capillary pumped loop experiment that flew in the Space Shuttle payload bay in December 2001 (STS‐108). The main objective of CAPL 3 was to demonstrate in micro‐gravity a multiple evaporator capillary pumped loop system, capable of reliable start‐up, reliable continuous operation, and heat load sharing, with hardware for a deployable radiator. Tests performed on orbit included start‐ups, power cycles, low power tests (100 W total), high power tests (up to 1447 W total), heat load sharing, variable/fixed conductance transition tests, and saturation temperature change tests. The majority of the tests were completed successfully, although the experiment did exhibit an unexpected sensitivity to shuttle maneuvers. This paper describes the experiment, the tests performed during the mission, and the test results.

Thermal Vacuum Testing of a Novel Loop Heat Pipe Design for the Swift BAT Instrument

An advanced thermal control system for the Burst Alert Telescope on the Swift satellite has been designed and an engineering test unit (ETU) has been built and tested in a thermal vacuum chamber. The ETU assembly consists of a propylene loop heat pipe, two constant conductance heat pipes, a variable conductance heat pipe (VCHP), which is used for rough temperature control of the system, and a radiator. The entire assembly was tested in a thermal vacuum chamber at NASA/GSFC in early 2002. Tests were performed with thermal mass to represent the instrument and with electrical resistance heaters providing the heat to be transferred. Start‐up and heat transfer of over 300 W was demonstrated with both steady and variable condenser sink temperatures. Radiator sink temperatures ranged from a high of approximately 273 K, to a low of approximately 83 K, and the system was held at a constant operating temperature of 278 K throughout most of the testing. A novel LHP temperature control methodology using both temperat...

Investigation of Low Power Operation in a Loop Heat Pipe

This paper presents test results of an experimental study of low power operation in a loop heat pipe. The main objective was to demonstrate how changes in the vapor void fraction inside the evaporator core would affect the loop behavior, The fluid inventory and the relative tilt between the evaporator and the compensation chamber were varied so as to create different vapor void fractions in the evaporator core. The effect on the loop start-up, operating temperature, and capillary limit was investigated. Test results indicate that the vapor void fraction inside the evaporator core is the single most important factor in determining the loop operation at low powers.

Testing of A Loop Heat Pipe Subjected to Variable Accelerating Forces, Part 2: Temperature Stability

Testing of A Loop Heat Pipe Subjected to Variable AccelerationsPart 2: Temperature StabilityJentung KuLaura OttensteinGoddard Space Flight CenterGreenbelt, Maryland(301) 286-3130jentung.ku@gs fc.nasa.govTaril KayaInternational Space UniversityFrancePaul RogersUS Army TARDECWarren, MichiganCraig HoffKettering UniversityFlint, Michigan30 th International Conference on Environmental systemsJuly 10- 13, 2000, Toulouse, Francehttps://ntrs.nasa.gov/search.jsp?R=20000101592 2020-07-13T13:22:19+00:00Z

Thermal Performance of Capillary Pumped Loops Onboard Terra Spacecraft

The Terra spacecraft is the flagship of NASAs Earth Science Enterprise. It provides global data on the state of atmosphere, land and oceans, as well as their interactions with solar radiation and one another. Three Terra instruments utilize Capillary Pumped Heat Transport System (CPHTS) for temperature control: Each CPHTS, consisting of two capillary pumped loops (CPLs) and several heat pipes and electrical heaters, is designed for instrument heat loads ranging from 25W to 264W. The working fluid is ammonia. Since the launch of the Terra spacecraft, each CPHTS has been providing a stable interface temperature specified by the instrument under all modes of spacecraft and instrument operations. The ability to change the CPHTS operating temperature upon demand while in service has also extended the useful life of one instrument. This paper describes the design and on-orbit performance of the CPHTS thermal systems.

Thermal Vacuum Testing of a Miniature Loop Heat Pipe With Multiple Evaporators and Multiple Condensers

This paper describes thermal vacuum testing of a miniature loop heat pipe (MLHP) with two evaporators and two condensers designed for future small systems applications requiring low mass, low power and compactness. Each evaporator contains a wick with an outer diameter of 6.4 mm, and each has its own integral compensation chamber (CC). Multiple evaporators provide flexibility for placement of instruments that need to be maintained at the same temperature, and facilitate heat load sharing among instruments, resulting in a reduced auxiliary heater power requirement. A flow regulator is used to regulate heat dissipations among all condensers, thus providing flexibility for placement of radiators on the spacecraft. A thermoelectric converter (TEC) is attached to each CC for operating temperature control and enhancement of start-up success. Tests performed include start-up, power cycle, sink temperature cycle, high power and low power operation, heat load sharing, and operating temperature control. The MLHP demonstrated excellent performance in the thermal vacuum environment. The loop started successfully and operated stably under various evaporator heat loads and condenser sink temperatures. The TECs were able to maintain the loop operating temperature within ±0.5K of the desired set point temperature at all power levels and all sink temperatures. The un-powered evaporator would automatically share heat from the other powered evaporator. The CC control heater power was reduced by more than 50 percent when a TEC was used instead of conventional electrical heaters. The flow regulator was able to regulate the heat dissipation among the radiators and prevent vapor from flowing into the liquid line.

Technology Overview of a Multi-Evaporator Miniature Loop Heat Pipe for Spacecraft Applications

Aminiature loop heat pipe with multiple evaporators andmultiple condensers was developed for thermal control of small spacecraft and instruments requiring low mass, low power, and compactness. Multiple evaporators afford flexible placement of instruments inside the spacecraft and facilitate heat-load sharing among instruments. Multiple condensers allow the radiators to be placed at various locations on the spacecraft surface and exposed to different thermal environments. Thermoelectric converters are used to provide heating and cooling to the reservoir for loop operating temperature control. A breadboard and a protoflight unit of the miniature loop heat pipe with two evaporators and two condensers were built and tested in a thermal vacuum chamber to demonstrate the thermal performance. In addition, an analytical model was developed to simulate the steady-state and transient behaviors of the miniature loop heat pipe during thermal performance tests.

Multi-Evaporator Miniature Loop Heat Pipe for Small Spacecraft Thermal Control

Under NASA s New Millennium Program Space Technology 8 (ST 8) Project, four experiments Thermal Loop, Dependable Microprocessor, SAILMAST, and UltraFlex - were conducted to advance the maturity of individual technologies from proof of concept to prototype demonstration in a relevant environment , i.e. from a technology readiness level (TRL) of 3 to a level of 6. This paper presents the new technologies and validation approach of the Thermal Loop experiment. The Thermal Loop is an advanced thermal control system consisting of a miniature loop heat pipe (MLHP) with multiple evaporators and multiple condensers designed for future small system applications requiring low mass, low power, and compactness. The MLHP retains all features of state-of-the-art loop heat pipes (LHPs) and offers additional advantages to enhance the functionality, performance, versatility, and reliability of the system. Details of the thermal loop concept, technical advances, benefits, objectives, level 1 requirements, and performance characteristics are described. Also included in the paper are descriptions of the test articles and mathematical modeling used for the technology validation. An MLHP breadboard was built and tested in the laboratory and thermal vacuum environments for TRL 4 and TRL 5 validations, and an MLHP proto-flight unit was built and tested in a thermal vacuum chamber for the TRL 6 validation. In addition, an analytical model was developed to simulate the steady state and transient behaviors of the MLHP during various validation tests. Capabilities and limitations of the analytical model are also addressed.

Effect of Variable Emittance Coatings on the Operation of a Miniature Loop Heat Pipe

As the size of spacecraft shrink to accommodate small and more efficient instruments, smaller launch vehicles, and constellation missions, all subsystems must also be made smaller. Under NASA NRA 03‐OSS‐02, Space Technology‐8 (ST 8), NASA Goddard Space Flight Center and Jet Propulsion Laboratory jointly conducted a Concept Definition study to develop a miniature loop heat pipe (loop heat pipe) thermal management system design suitable for future small spacecraft. The proposed loop heat pipe thermal management system consists of a miniature loop heat pipe (LHP) and deployable radiators that are coated with variable emittance coatings (VECs). As part of the Phase A study and proof of the design concept, variable emittance coatings were integrated with a breadboard miniature loop heat pipe. The entire system was tested under vacuum at various temperature extremes and power loads. This paper summarizes the results of this testing and shows the effect of the VEC on the operation of a miniature loop heat pipe.