Abstract
The transient cooling of rock surface by liquid nitrogen (LN2) jet was experimentally studied in this article. Experimental conditions cover a range of 1.4–2.4 MPa for jet pressure and 3–5 cm for stand-off distance. The nozzle diameter was fixed at 1 mm and the rock specimen was a circular plate, with diameter of 16 cm and thickness of 2 cm. The temperature curves at different radial locations in rock were measured during LN2 jet impingement. Based on these data we mapped the complete heat flux across the rock surface and attained the three dimensional temperature field within the rock. Thermal stresses inside the rock were further computed according to the experimentally determined temperature field. It is shown that the partial wetting of rock surface by LN2 jet created sharp thermal gradients in both radial and vertical directions. The induced thermal stress was in tensile state and the spatial range of thermal stress is consistent with the wetted region by LN2. The propagation speed of wetting front increases with increasing jet pressure and decreasing stand-off distance. Under the present experimental conditions, the maximum heat flux of LN2 jet was around 2.4 × 105 W/m2. The maximum tensile stress on rock surface was calculated to be ~5 MPa, which could potentially damage the rock structure and deteriorate rock’s strength.
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