Thierry Meier

Numerical investigation of thermal spallation drilling using an uncoupled quasi-static thermoelastic finite element formulation

ABSTRACT In this work, we examine thermal spallation drilling through finite element modeling of the uncoupled quasi-static thermoelastic problem describing the stresses induced by rapid and localized heating of a uniaxially pre-stressed rock core. The numerical procedure is verified using the method of manufactured solutions, and the optimal order of accuracy is demonstrated. From a series of numerical experiments, we present the temperature and stress profiles along the centerline of the rock core which are discussed qualitatively with respect to the corresponding laboratory experiments. Our numerical results, in agreement with the experiments, emphasize that the efficiency of thermal spallation drilling increases linearly with the vertical stress.

Design and convective calibration of a transverse heat flux sensor

In this work, a transverse heat flux sensor built from alternating layers of K-Type thermocouple materials is presented. In the first step, the sensor is calibrated in radiation heat transfer, and its behavior is compared to existing sensors found in the literature. Subsequently, a secondary calibration is performed in a stagnation heat transfer facility, where surface temperatures up to 400°C and heat flux up to 550 kW/m2 are achieved. The radiative sensitivity is found to be 1.35 μV m2/kW, while in a convective environment, the value varies between 0.8 and 1.8 μV m2/kW. This difference is attributed to the temperature-dependent material properties and the angle formed by the heat flux and the surface of the anisotropic material. The experimental sensitivities compare well with a parametric model able to account for this angle. Eventually, we emphasize the use of transverse sensors for stagnation heat transfer investigations, especially for applications where chemical compatibility and mechanical robustness are required.