Relaxation of Probe Geometry Requirements for Soil Thermal Properties Measurements with Transient Heated Needle Techniques. (3926)

Relaxation of Probe Geometry Requirements for Soil Thermal Properties Measurements with Transient Heated Needle Techniques. (3926) Authors: D.R. Cobos* - Decagon Devices G.S. Campbell - Decagon Devices C.S. Campbell - Decagon Devices Abstract: Thermal properties of materials are commonly measured using transient heated needle techniques. The application of this theory depends on the heater needle approximating an infinitely long line heat source, a criteria that cannot be met for certain applications. We are currently developing a Thermal and Electrical Conductivity Probe (TECP) to measure thermal properties of the Martian surface in situ, that will fly aboard NASA’s Phoenix Scout Lander in 2007. Because the probe will be inserted by a robot arm into the Martian surface with undetermined hardness it is likely that long, thin needles could be damaged or destroyed during insertion. Hence, this application requires violation of the assumptions outlined above. We evaluated the effects of using a shortened, conical heater instead of the more common long, cylindrical heater. First, we used a finite element analysis (FEA) software package to simulate the heat flow from conical needle geometries in several materials. To verify the model analysis, the shortened, conical probes were also evaluated in the laboratory with media of known thermal properties. The results of the FEA and laboratory studies indicate that the use of simple calibrations can account for errors associated with the violation of the heated needle theory, and accurate determination of material thermal properties are still possible. Speaker Information: Doug Cobos, Decagon Devices, 950 NE Nelson Ct., Pullman, WA 99163; Phone: 509-332-2756; E-mail: doug@decagon.com Session Information: Monday, November 1, 2004, 5:00 PM-6:00 PM Presentation Start: 5:00 PM (Poster Board Number: 2504).