Steel slag is a by-product from the steelmaking process, and its yield is about 10-15% of steel production. [1] Steel slag, which contains a lot of valuable elements including Fe, Mn, Ca, Mg, Si, etc, can be reused as the raw materials for the metal recovery, engineering backfilling, road construction, sewage treatment and glass-ceramics preparation. [2] However, the reuse ratio of steel slag is still low due to volume expansion caused by the presence of free CaO and MgO in steel slag. [3][4][5] Therefore, the effective utilization of steel slag is an urgent issue to achieve the emission reduction in metallurgy industry. [6][7][8][9] Hot steel slag with temperature over 1773 K carries a lot of high-grade physical heat, and thus adding modifiers into the hot slag to make the slag modification through utilizing waste heat can significantly improve the physicochemical property of hot slag and stabilization of free CaO and MgO, which is needed for the valuable element recycling and steel slag valorization. During the hot slag modification stage, the temperature control of hot slag is one of the major factors contributing towards the modification effect of hot slag. The rapid temperature drop of hot slag surface may cause the uneven temperature distribution of hot slag and premature solidification on hot slag surface, which is detrimental to the modifier addition. Mechanical stirring is considered as an effective way to promote the temperature distribution uniformity of hot slag and intensive mixing between hot slag and modifiers, which is beneficial to improve the dynamic conditions of hot slag modification. Meanwhile, mechanical stirring can prevent the surface of hot slag from solidification and crusting, so as to facilitate the modifier addition and modification of hot slag.The heat transfer behavior of hot slag is complicated including forced convection and conduction heat transfer in hot slag, fluidsolid phase coupling heat transfer between hot slag and pot wall, natural convection and radiation heat transfer through the pot wall and hot slag surface. Up to now, metallurgists have conducted many researches on the thermal behavior of high temperature molten melt in metallurgical process. [10][11][12][13][14] Lu et al. [15] studied the effect of different casting parameters on the flow and heat transfer of hot slag, but the surface temperature of hot slag was assumed to be constant, which may lead to a large error in the simulation results. Li et al. [16] investigated the temperature variation of hot slag and the heat loss through slag surface at different preheating temperatures in a slag pot, but the convection effect of hot slag was ignored. Tripathi et al. [17] developed a mathematical model for the temperature prediction of ladles and molten steel during the whole process cycle of ladles, and the effects of various factors on the temperature drop were