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Show CONCLUSIONS A water-cooled jacket was designed to enclose the transmitting- and receiving optics of a small fiber-optics LOV probe and to pennit velocity measurements in semi-industrial scale flames. This probe has been used in 2.5 MW natural gas, coal and oil flames, and in 12 MW natural gas flames. The furnaces internal diameters were 2 and 3.5 m. Cooling the LOV front side by means of two water-cooled quartz windows resulted in a complete absorption of the incident flame radiation, even after long exposure in a high temperature flame. Computer modelling of the purge flow in the probe tip helped design a very short tip which still produces a uniform outlet flow and efficiently prevents contamination of the LOV optics. Experiments showed that the front window remained clean even after long periods of measurements in coal flames with high particle loading. Data rates were always in the range of a few hundred to a few thousand Hertz, depending on the size and number density of the scattering particles. In coal and oil flames, simple particle size discrimination based on the Doppler signal amplitude enabled to assess the presence and direction of particle slip. The use of fiber-optics link, frequency domain processing and appropriate optics protection make it possible to perfonn laser velocimetry in semi-industrial flames with the same ease and speed as with standard furnace measurement techniques such as suction pyrometry. ACKNOWLEDGEMENTS The authors gratefully acknowledge the IFRF Members for their financial support for the development and testing of the water-cooled LOV probe. The measurements in a 12 MW natural gas flame were financed by the Gas Research Institute (GRI) of Chicago while the measurements in a 2.5 MW pulverized coal flame were financed by the Dutch Agency for Energy and Environment (NOVEM) and the IFRF. The measurements in a 2.5 MW heavy fuel oil flame were part of the Multi-Fuel Burner program supported financially by the European Community (Joule II) and the IFRF. The IFRF Joint Committee is acknowledged for permission to publish this paper. Further thanks are due to Henk Horsman for his continuous contribution to the experimental work reported in this paper. REFERENCES [1] Baker, R. J., Hutchinson, P. & Whitelaw, J.H. 1974 Preliminary measurements of instantaneous velocity in a twometer square furnace using a laser anemometer. J. of Heat Transfer, August, pp 410-414. [2] Barlow, S. M. 1982 Laser Ooppler_ anemometry measurements in a large gas-fired furnace. Proc. 1st Int. Symp. on Appl. of lAser Anemometry in Fluid Meclutnics, Lisbon .. [3] Thiele, K.U. & Brodbek, H. 1986 Velocity & turbulence measurements by two-color LOA in light and heavy fuel oil flames. Proc. 3rd Int. Symp. on Appl. of Laser Anemometry in Fluid Mechnllics, Lisbon .. (4) Ougue, J. & Abbott, M. 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