Don't use the temperature limits are 600K and 290K - be careful which ones to use

3. A rectangular iron ingot 15cm15cm30cm is supported at the centre of a reheating furnace. The furnace has walls of silica-brick at 1400K, and the initial temperature of the ingot is 290K. How long will it take to heat the ingot to 600K ? It may be assumed that the furnace is large compared with the ingot-size, and that the ingot remains at uniform temperature throughout its volume; convection effects are negligible. The total emissivity of the oxidised iron surface is 0.78 and both emissivity and absorptivity are independent of the surface temperature. Density of iron =7.2Mg/m3; specific heat of iron =0.50kJ/kgK. You may need to use the following integration in solving this question: a4x4dx=4a31[lnxax+a+2tan1(ax)]+C