Issue 37

E. Mihailov et alii, Frattura ed Integrità Strutturale, 37 (2016) 297-304; DOI: 10.3221/IGF-ESIS.37.39 303 Therefore, the application of insulation materials on water-cooled roofs should be limited in their safety working conditions, i.e. in the range of surfaces temperatures with low values of thermal gradients and thermal stresses across insulation thickness. As can be seen from Fig.10, magnesite can be recommended as an appropriate material with its own low values of emissivity, surface temperature of insulation and thermal gradient across insulation thickness. 4.C ONCLUSIONS detailed investigation of the water-cooled elements thermal performance under various options of application of additional insulation has been carried out. An analytical study was made to find the possible ways of reducing the thermal losses in the water-cooled roof of a 100t secondary steelmaking electric arc furnace. As a result of the study it was found that, magnesite can be recommended as an appropriate material with its own low values of emissivity, thermal losses and surface temperature of insulation during the work. R EFERENCES [1] Velchev, A., Mihailov, E., Petkov,V., Investigation of the parameters influence over the heat work of the water- cooling roofs for small electric arc furnace, International Conference “The Efficient Use of Energy in Metallurgy”, Varna, Bulgaria, 94 (1999) 100-105. [2] Lingorsky, N., Heat transfer in electric arc furnaces equipped with water cooled panels, Iron and Steel Engineer, 10 41(1988). [3] Toulouevski, Y., Zinurov, Il., Innovation in Electric Arc Furnaces: Scientific Basis for Selection, Springer-Verlag GmbH, (2013) 215-237 [4] Kreit, F., Black, W, Basic Heat Transfer, Harper and Row, Publishers, New York, (1980). [5] Mastrukov, B., Theory, Constructions and Calculations of metallurgical Furnaces, Moscow, Metallurgy, (1986) (in Russian). A PPENDIX List of symbols: C - coefficient of heat transfer through radiation W/m 2 K 4 ; C w - specific heat capacity of water, kJ/m 3 K; D p – diameter of cooling panel pipe, m; l c .el F , r c .el F , F m , F w-f -heat absorbing area of insulation, cooling element, metal and wall, m 2 ; i – consecutive number of iteration; k g - coefficient /  0,1/; k r - coefficient, marked the direct absorbing of the cooling element surface from the arc; k s - arc screening coefficient; l a - length of arc, m; m - volumetric flow of cooling water, m 3 /s; P a - heat generated by arcs, W; Pr , Re - Prandtl and Reynolds numbers; Q w-f , Q c.el , - heat removed by walls and cooling water, W; l c.el Q , r c.el Q - radiant heat flux fall on the roof and resultant heat flux, W; Q own , Q refl , Q abs – own, reflected and absorbed radiant heat flux by roof, W; Q m - heat observe by metal,W; Q c.el - heat removed by cooling water,W; Q g - heat outlet by gases,W; Q w - heat removed by walls,W; A