Method and apparatus for generating a nitrogen / water vapor - fog, in particular of a contaminating nitrogen / water vapor - mist for visualisation of flow paths

摘要

In a process and assembly to generate a non contaminating nitrogen/steam fog to enable visual detection of flow paths, liquid nitrogen is mixed with ultra-distilled water. The liquid nitrogen is dosed and then introduced to the distilled water. Distilled water is pre-heated within a vessel (3) under controlled conditions such that part of the vessel which is not filled by liquid is filled by steam generated from the distilled water. The liquid nitrogen is dosed into the distilled water vapour in vessel (3) from which it is led to the application. The input of liquid nitrogen and the heat applied to the distilled water depends upon the distilled water vapour pressure within the vessel, and the temp. of the emerging nitrogen-steam fog, such that the fog temp. is the same as that of the ambient environment and that the fog moves at slow speed. A suuitable assembly incorporates a heat-insulated vessel (2) for liquid nitrogen (2a) and a vessel for ultra-pure distilled water, an electric heating element (19) for the ditslled water (3a), inlets (9, 22) from the vessel (2) for liquid nitrogen to the vessel (3), a dosing assembly (23) and an outlet pipe for the nitrogen-water vapour fog. A pressure sensor (26) is located in the vapour section of the distilled water vessel. A temp. sensor (27) is located in the fog outlet pipe (24), while a control assembly (28) determines the heat liberated by the heating element (19). USE/ADVANTAGE - Liquid nitrogen and distilled water mixed together form a visible trail which reveals the flow path taken and does not contaminate objects with which it comes into contact. The addition of dosed liquid nitrogen produces a trail which remains visible at slow speeds, facilitating detailed examination of flow paths in small areas, the pattern of which would not otherwise be visible for inspection.