Asmall oxidized horizontal metal tube with an od of 0.0254 m and 0.61 m long with a surface temperature at 588 k is in a very large furnace enclosure with firebrick walls and the surroundings air at 1088 k. the emissivity of the tube is 0.60 at 1088 k and 0.46 at 588 k. calculate the heat transfer rate to the tube by radiation.