tailieunhanh - GasTurbine Engineering HandbookSecond Edition phần 7

Nghiên cứu gần đây cho thấy giảm 85% NOx bằng hơi nước hoặc phun nước với tối ưu hóa khí động học buồng đốt. Trong một buồng đốt điển hình như trong hình 10-19, dòng chảy vào các khu vực trọng điểm được giới hạn trong khoảng 10%. Phần còn lại của dòng chảy được sử dụng để trộn không khí đốt và làm mát buồng đốt có thể. | Bearings and Seals 477 BEARING TYPE LOAD CAPACITY SUITABLE DIRECTION OF ROTATION RESISTANCE TO HALF-SPEED WHIRL STIFFNESS AND DAMPING CYLINDRICAL BORE GOOD K WOF INCRE BE 1ST r ASING ST MODERATE CYLINDRICAL BORE WITH DAMMED GROOVE GOOD A MODERATE LEMON BORE GOOD MODERATE THREE LOBE MODERATE GOOD OFFSET HALVES GOOD EXCELLENT TILTING PAD o MODERATE GOOD Figure 13-6. Comparison of general bearing types. This groove or channel covers an arc of 135 and terminates abruptly in a sharp-edge dam. The direction of rotation is such that the oil is pumped down the channel toward the sharp edge. Pressure dam bearings are for one direction of rotation. They can be used in conjunction with cylindrical bore bearings as shown in Figure 13-6. 5. Lemon bore or elliptical. This bearing is bored with shims at the split line which are removed before installation. The resulting bore shape approximates an ellipse with the major axis clearance approximately twice the minor axis clearance. Elliptical bearings are for both directions of rotation. 478 Gas Turbine Engineering Handbook 6. Three-lobe bearing. The three-lobe bearing is not commonly used in turbomachines. It has a moderate load-carrying capacity and can be operated in both directions. 7. Offset halves. In principle this bearing acts very similar to a pressure dam bearing. Its load-carrying capacity is good. It is restricted to one direction of rotation. 8. Tilting-pad bearings. This bearing is the most common bearing type in today s machines. It consists of several bearing pads posed around the circumference of the shaft. Each pad is able to tilt to assume the most effective working position. Its most important feature is self-alignment when spherical pivots are used. This bearing also offers the greatest increase in fatigue life because of the following advantages a. Self-aligning for optimum alignment and minimum limit. b. Thermal conductivity backing material to dissipate heat developed in oil film. c. A thin babbitt layer can