Study On Combustion And Heat Transfer In An Oil Boiler With Omega-Type Flue Gas Flow

Oil boilers which are efficient, environmental friendly and also easy to control, have been widely used in social production and people’s daily life. Researchers pay much attention to the overall efficiency of the boilers and grow great interesting in combustion and heat transfer inside the boilers at the same time. We can obtain how flue gas flows and how the temperature distributes in the boilers by the method of numerical simulation which does not cost too much. The method can help researchers know the boilers well so that is helpful to design a better production and to operate a boiler.In this paper, a small-scale oil boiler with an omega-type flue gas flow was studied using the software FLUENT. The spray combustion, heat transfer and flue gas flow was simulated through numerical method. The standard k-ε model was chosen to describe the turbulent flow. The discrete phase model was chosen to describe the interaction between fuel droplets and the continuous flow. The non-premixed combustion model seemed to simulate the spay combustion very well. As to radiation in the boiler, P-1 model was chosen.As the simulation on the spray combustion conducted, a few information can be obtained. The gas flow inside the furnace can be complicated due to the long narrow outlet. Most flue gas can’t flow out directly that enhance the turbulence in the furnace. Some locations in the corner are out of the flow path of flue gas where there may be some ash deposits. The flow at the top of furnace tend to run to the outlet of furnace. An area where multi-flue gases confluence happens comes near the outlet. The mean temperature at the bottom is higher than that at the top location and smaller temperature difference also happens. Temperature decrease along radial direction. The high temperature area tend to lean towards the outlet of the furnace. The velocity distribution along height appear to be uniform, whereas the temperature is higher at the bottom, lower at top. The turbulence near the outlet have shown effects on the velocity and temperature distribution.The simulation was also conducted in different conditions of combustion load. As we can see, when the oil and air increase, the mean and the highest temperature increase in a degree. But, as the load becomes too high, the high temperature area will move down that causes the temperature distribution doesn’t get well with the shape of furnace. To reduce the oil in the furnace, the air must be reduced at the same time, or the high exceed air number will cause bad combustion.Due to the simulation on the flow and heat transfer in the flue gas channel, some conclusions can be drawn. As the flue gas flows between the water cooling tubes, the velocity and temperature decrease. Flue gas rushes over the surface which near the main flow of tube will reduce the thickness of boundary layer so that will enhance the heat transfer effect. The flue gas can’t flow across the area between adjacent tubes so that the heat transfer is bad here.