Heat Rejection Systems Utilizing Composites and Heat Pipes: Design and Performance Testing

Abstract

Polymer matrix composites offer the promise of reducing the mass and increasing the performance of future heat rejection systems. With lifetimes for heat rejection systems reaching a decade or more in a micrometeoroid environment, use of multiple heat pipes for fault tolerant design is compelling. The combination of polymer matrix composites and heat pipes is of particular interest for heat rejection systems operating on the lunar surface. A technology development effort is under way to study the performance of two radiator demonstration units manufactured with different polymer matrix composite face sheet resin and bonding adhesives, along with different titanium-water heat pipe designs. Common to the two radiator demonstration units is the use of high thermal conductivity fibers in the face sheets and high thermal conductivity graphite saddles within a light weight aluminum honeycomb core. Testing of the radiator demonstration units included thermal vacuum exposure and thermal vacuum exposure with a simulated heat pipe failure. Steady state performance data were obtained at different operating temperatures to identify heat transfer and thermal resistance characteristics. Heat pipe failure was simulated by removing the input power from an individual heat pipe in order to identify the diminished performance characteristics of the entire panel after a micrometeoroid strike. Freeze-thaw performance was also of interest. This paper presents a summary of the two radiator demonstration units manufactured to support this technology development effort along with the thermal performance characteristics obtained to date. Future work will also be discussed. Nomenclature mm= millimeter m = meter T = temperature, K W = watts

Cold Start of a Radiator Equipped with Titanium-Water Heat Pipes

“…1 Briefly, they are flat panels approximately 2.54 cm thick by 0.5 m wide and 1 meter long. High thermal conductivity carbon-polymer face sheets are adhesively bonded to an aluminum honeycomb core and three titanium-water heat pipes are embedded within the core to provide heat transport.…”

“…Heat pipe power loss through conduction down the wire and through the insulation was known to be 10% from a previous study. 1 Average analysis heat pipe power was the wattage applied to each heat pipe evaporator in the model. RDU maximum temperature is the maximum temperature generated by the model.…”

“…Thermal resistance incurred through the graphite foam saddle and adjoining adhesive layers was found to be somewhat disappointing owing to the adhesive and low areal density of contact. 1 The graphite fiber selected for construction was K13D2U from Mitsubishi. Although the graphite fiber was common to all three panels, different materials were used for the polymer matrix and adhesive, including, NASAdeveloped 6F-polyimides with a phenylethynyl endcap (HFPE), Cytec 5250-4 bismaleimide (BMI), and Bryte EX 1551 cyanate ester.…”

“…The performance of the three as-delivered RDU panels was evaluated in early 2007 and a paper summarizing the test results was presented. 1 In the previous work, panel performance was evaluated in a vacuum chamber equipped with liquid nitrogen (LN2) cold walls at the following steady state thermal inputs: 200, 300, and 350 watts per heat pipe. Simulated micrometeoroid impact with loss of a heat pipe, and freeze/thaw conditions, were also evaluated.…”