WIRELESS METHANE DETECTOR WITH TEMPERATURE MODULATED HEATING PROFILE

The results of development of an autonomous methane detector in a dynamic measurement mode are presented. Industrial catalytic sensor was used as a sensitive element. To prevent burnout of the catalytic sensor microheater which often occurs during pulsed heating, the special form of heating pulse has been developed. The proposed dynamic mode of the sensor heating provides the measurements with low power consumption and the required level of safety in the measurement range of pre-explosive methane concentrations from 0.1 to 2 vol.%. Based on the analysis of the obtained results, the estimation of autonomous operating time of the detector is given.

A Study of the Effect of Post-Heating Pulse on Hot Cracking Susceptibility in Pulsed Laser Welding of Invar Alloy

Hot cracking is one of the major challenges in laser welding of Invar alloy. In this study, welding hot cracking susceptibility experiments are conducted with fish-bone‐type Invar alloy sheets under pulsed laser welding condition. The pulse wave consists of two distinct power levels: welding pulse and post-heating pulse. The welding temperature field can be controlled by changing the duration of the post-heating pulse. The results of experimental measurements and finite element method calculation show that increasing of the post-heating pulse duration leads to a decline in the cooling rate of weld metal within the brittle temperature range, although the welding hot cracking susceptibility decreases at first and then increases. Neither the heat input nor the cooling rate is the only decisive factor for hot cracking during the welding process.

Coupled thermo-hydro-mechanical behaviour of a deep clay

An experimental study on Ypresian clays –one of the potential deep formations in Belgium for the geological disposal of heat-emitting radioactive waste– was undertaken to systematically study its thermal properties and coupled hydro-mechanical response during fast heating pulse tests. An accurate characterisation of the thermal properties is required for assessing the near-field perturbations around disposal galleries that the sedimentary host rock formation will undergo. A new experimental cell adapted to apply the high in situ stresses and with thermal flux sensors was used to directly measure the thermal conductivity at different sample orientations (heat flux orthogonal and parallel to bedding planes). A clear influence of the degree of saturation – despite being close to saturation – and anisotropic features on thermal conductivity have been detected. The study was complemented by performing fast heating pulse tests under constant volume on a new and fully-instrumented axisymmetric cell. The cell allowed recording the pore pressure build-up and dissipation along a heating pulse and under water-undrained conditions.