In a cogeneration plant, combustion gases at 1 atm and 800 K are used to preheat water by passing them through 6-m-long, 10-cm-diameter tubes. The inner surface of the tube is black, and the partial pressures of CO₂ and H₂O in combustion gases are 0.12 atm and 0.18 atm, respectively. If the tube temperature is 500 K, determine the rate of radiation heat transfer from the gases to the tube.