Figure 5.44 shows the thermal circuit for a furnace wall. The outside surface has a known tem perature T2=625K. The temperature of the surroundings Tiur is 290K. We want to estimate the temperature of the inside surface T1. The wall consists of three layers: deposit kk=1.6 W ((mK),Ax0=0.080m), brick (kgg=1.7W/(mK),Axg=0.15m), and steel [kS=45W/(mK) Ax5=0.00245m. The outside surface loses heat by two parallel mechanisms-convection and radiation. The comvective heat transfer coefficient hc=5.0W(m2.k). The radiative heattransfer coefficient ho =16,3W/(m2,K). The latter is calculated from