This study investigates the wettability of fluid-solid interactions of interest for oscillating heat pipe (OHP) applications. Measurements were taken using two techniques: the sessile drop method and capillary rise at a vertical plate. Tested surface materials include copper, aluminum, and Teflon PFA. The working fluids tested were water, acetone, R-134a, and HFO-1234yf. A novel low-pressure experimental setup was developed for refrigerant testing. Results show that the refrigerants have significantly lower hysteresis than the water and acetone-based systems, which is thought to lead to better heat transfer in OHP design.
An investigation using in situ pressure measurements was conducted on an oscillating heat pipe (OHP) to better understand its chaotic nature and the relation between the frequency of oscillations and the thermal performance. The working fluid used was HPLC grade acetone with a 0.8 fill ratio by mass. Three different orientations were tested: top, horizontal, and bottom heating from 100 to 500 W in increments of 50 W. An aluminum water block was used with water at approximately 0°C with a flow rate of 0.9 l/min for the condenser section of the OHP. The condenser and evaporator section were each fitted with a pressure transducer mounted perpendicular to the OHP channel. The pressure and temperature measurements were compared. Complex pressure wave forms were observed and a natural frequency could not be determined at the high filling ratio used.
Research at the AFRL Space Vehicles Directorate is being conducted to reduce schedule times for assembly, integration, and test, to make satellite-based capabilities more responsive to user needs. Structural Health Monitoring has been pursued as a means for validating workmanship and has been proven on PnPSat-1. Embedded ultrasonic piezoelectric wafer active sensors (PWAS) have been utilized with local and global inspection techniques, developed both in house and by collaborating universities, to detect structural changes that may occur during assembly, integration, and test. Specific attention has focused on interface qualification. It is now reasonable to believe that evaluation of interfaces through the use of such sensors can also be used to indirectly qualify the structure thermally and that tedious thermal-vacuum testing may be truncated or eliminated altogether. This paper focuses on the computational development of extracting thermal properties from ultrasonic transmission records. Methods are validated on simple bolted lap-joint cantilever beams.
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