At present hydrofluorocarbons (HFCs) such as R32, R-125, R-134a, and R-143a are widely used, and it is required to obtain accurate information of thermophysical properties, especially of the thermal conductivity of HFCs. In this paper new thermal conductivity equations for R-32, R-125, R134a, and R143a are proposed, applicable over a wide range of temperature and pressure including the critical region based on existing experimental data, and the reliability of the present equations is summarized. The problem that the thermal conductivity calculated from the thermal diffusivity in the critical region differs depending on the equation of state is also discussed.

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SynopsisThe effect of gas bottom-blowing condition on the refining characteristics of a top-and bottom-blowing converter in comparison with that of topblowing condition has been studied, on the basis of the amount of accumulated oxygen in the converter (Os), which represents the change in oxidation/reduction reactions between hot metal and slag.It is possible to express quantitatively the relationships between hard blow/soft blow by the manipulation of top-blowing jets and strong agitation/weak agitation by that of bottom-blown gas. The manipulation of the flow rate of bottom-blown gas permits to control the blowing reaction more effectively than that o f the top-blowing jet.In connection with the above fact, dynamic control of blowing reaction in the top-and bottom-blowing converter has been done, with the flow rate of bottom-blown gas as a manipulated variable and the variation of Os as a controlled variable. By the application of the multistep optimum control theory to the blowing reaction model, the stability of blowing operation and metallurgical characteristics, i.e., the ranges of changes in (T.Fe) of slag, phosphorus and manganese concentration of molten steel at blow end, were narrowed appreciably.

SynopsisThe possibility of blowing control based on exhaust gas data was studied. The amount of oxygen accumulated in LD converter (Os), which is calculated from the oxygen balance by using exhaust gas data, corresponds to the amount of FeO, Fe203 and MnO in the slag during blowing.When the refining reaction was controlled by Os control, the carbon, phosphorus and manganese contents of steel and the total iron content of slag at blow end were controlled at preferable levels and the fluctuations of levels were remarkably reduced. Namely, Os is an effective parameter representing the progress of the reaction and can be used to control the blowing at an optimum level.

Experiments were done on the prediction of slopping through direct observation of in furnace condition with an image fiberscope and by image processing and on the suppression of slopping by coke breeze injection. As a result, the following findings were obtained. (1) Slag foaming is detected by direct observation of the condition in converter with an image fiberscope. (2) The slag expansion rate at the occurrence of slopping is 1.2N 1.5 m3/s. Slopping is predicted about 30N40s before its occurrence by providing an observation hole at a location of 2.5 m below the converter top. (3) Slopping is automatically predicted by the identification of portions corresponding to the slag and the flame through processing of the image signals obtained by the camera, by the calculation of the ratio of area corresponding to the slag, and by the combination of change in ratio with the lapse of time with the process information. (4) Slopping is suppressed nearly 100 % by direct injection of coke breeze into the foaming slag at a rate of 200 kg/min for 1'-' 2 min. (5) It is considered that the suppression of slopping by direct injection of coke breeze into the foaming slag is attributable to the loss of foam stability by local reduction of slag (for example, decrease in local concentration of P205). (6) The occurrence ratio of slopping is been reduced from 22 to 2.7 % by the application of this slopping prediction and suppression system to the commercial process, resulting in the elimination of large disturbance for blowing control.