figures on the bottom of page 17 show an infrared image of a

figures on the bottom of page 17 show an infrared image of a methanol pan fire. Liquid methanol was poured into this pan and ignited. On the picture is a scale which shows the temperature of the methanol fire. This scale is linear and ranges from 68.0degreeC to 783.9degreeC. Most of the image is the fire plume. In the fire plume, air is entrained from the surrounding air into the plume. For methanol, 20% of the energy released (i.e., heat of combustion) is radiated to the surroundings, while the other 80% goes up in the fire plume. You can assume that when methanol is burned that only carbon dioxide and water are produced. In addition, due to air entrainment, there is a significant amount of excess air in the fire plume If the mass flow rate of air supplied to this fire is 4 kg/min and the average temperature of the fire plume is 400 degree C, calculate the mass flow rate of methanol in kg/hr supplied to the fire. Why is air entrained into the fire plume? Give a physical argument.

Solution

From the above given data we can calculate mass flow rate by the following formula .

So mass flow rate = 1.5 kg/hr