Pulsed Heat Load Research Articles

The effect of pyrolytic carbon coating on gas emission and sublimation of graphite induced by pulse laser beams

The emission and sublimation of graphites coated with pyrolytic carbon (PyC) has been measured under irradiation with pulse laser beams to examine the effects of pulse heat load on the role of the coating. Under a heat load density of 640 MW/m 2 and a pulse length of 1 ms, gas emission, sublimation and vacuum degradation are enhanced by the PyC coating. This is mainly due to very low thermal conductivity of the PyC film in the surface normal direction resulting in an enhanced temperature rise during the heat load. On the other hand, the gas emission, sublimation and vacuum degradation of the coated specimens were small relative to the non-coated specimens when compared on the basis of the measured peak surface temperature. Thus the surface coating with PyC may be effective in reducing the gas emission when the carbon temperature increases gradually but can be harmful to vacuum and surface stability in the case of pulse high heat load.

Natural gas stored in underground pipes

A mathematical model of surface cracking under pulsed heat load was developed. The model correctly describes a smooth brittle–ductile transition. The elastic deformation is described in a thin-heated-layer approximation. The plastic deformation is described with the Hollomon equation. The time dependence of the deformation and stresses is described for one heating–cooling cycle for a material without initial plastic deformation.The model can be applied to tungsten manufactured according to ITER specifications. The model shows that the stability of stress-relieved tungsten deteriorates when the base temperature increases. This proved to be a result of the close ultimate tensile and yield strengths. For a heat load of arbitrary magnitude a stability criterion was obtained in the form of condition on the relation of the ultimate tensile and yield strengths.