OCR Text |
Show The experiments have shown that while longitudinal pressure gradient exerts essential influence on the flow pattern in the dimple during combustion, nevertheless it practically has no effect on flame stabilization. As the pressure gradient, whether favourable or adverse, varies, the sizes and shapes of the secondary flows in the dimple undergo changes. Thus the experiments carried out allowed to estimate the possibility of the use of the vortex generators, i.e. spherical dimples, to establish the combustion and the flame stabilization. It may be concluded that the spherical dimples can be used not only to effectively enhance the heat transfer but also to improve the process of gas combustion. All these properties, which manifest while using the vortex generators, can successfully be put to practical use. As an illustration, we consider one of the possible alternatives to use the vortex generators to establish the natural gas combustion on waterwall surfaces of the boilers. In this case, some advantages over traditional ways of gas combustion and heat transfer in the boilers can be gained. The essence of the way proposed to establish gas combustion in boilers is the following. The vortex generators or the spherical dimples with the relative depth h/d=Q. 2-0.5 are installed on the heat transfer surface of the wall, as shown on Figure 8. On the opposite side of the wall, flows the coolant, for instance, water. In the first, downstream dimples, natural gas combustion process is established and an intensive wall heatmg takes place. In this case, natural gas is supplied into the back, with respect to the air flow direction, region of the dimples. The holes for gas feeding should be made Figure 8. S C H E M E OF A N E L E M E N T OF W A T E R W A L L SURFACE: 1 - AIR, 2 - C O O L A N T , 3 - G A S SUPPLY MANIFOLD approximately on the depth (0.2-0.9)/? from the bottom of the dimple. The excess air should be aa=1.3-1.5 to secure a high level of the temperatures and, close to the optimal values of other parameters. The following series of the dimples are designated to enhance the heat transfer from gas combustion products to the wall. In this case, the combustion process need not be established in the air flow core of the channel. Convex surfaces on the side of the coolant also enhance the heat transfer. Elements of the waterwall surfaces, one of which shown in Figure 8, can be assembled together as a unit depending on the required power of heat transfer device. 9 |