Now the calculation and discussion of the scheme of adopting a set of 3 single hinged expansion joints to absorb the thermal compensation of the pipeline, that is, the two-dimensional plane L-shaped pipe system
Expansion joint deformation angle and inlet flange force:
(1) Calculation formula for the deformation angle of each expansion joint (considered by 50% of the pre-deformation of the expansion joint): a1 = arcsin22A, a2 = arcsin1 B2A2C, a3 = a1 a2
(2) The equivalent displacement of one peak of each expansion joint: Ei = Dm2ni180ai (i = 1, 2, 3).
(3) The bending distance of each expansion joint due to deformation: mai = KDm4Ei (i = 1, 2, 3).
(4) Deformation reaction force of each expansion joint: Fa1 = Ma2 Ma3C (horizontal direction), Fa2 = Ma1 Ma3A (vertical direction).
(5) Friction force of pendulum bracket: F1 = Gr / h.
(6) The impulse due to the change of airflow direction at the elbow of the horizontal pipe in front of the hood: F2 = 2SV2sin45 (the horizontal force is the same as the vertical force).
(7) Deflection force of vertical pipeline due to wave 1 deformation: F3 = G1tga1.
(8) The force of the inlet nozzle of the smoke machine: Fx = Fa1 F1 F2 F3 (horizontal direction), Fy = Fa2 F2 F pipe weight (vertical direction) Force calculation.
Since the pendulum bracket is used and the center of gravity of the entire pipe system is designed between the two pendulum brackets, each moment Mx = My = 0.
analysis:
(1) There are four kinds of forces on the inlet flange of the smoke machine: the reaction force of the expansion joint, the friction force of the pendulum bracket, the impulse force at the front elbow of the smoke machine due to the change of the airflow direction, and the deflection of the vertical pipe due to the wave deformation force. Among these four kinds of loads, the friction force of the pendulum support is a temporary load, which exists only when the machine is started and stopped and the working conditions change, and disappears during normal operation. While the other three types of loads are continuous loads, and during the whole process of starting and stopping the turbine and normal operation, the air flow impulse and the deflection force of the vertical pipe are changing continuous loads.
(2) According to the above deformation angle and deformation reaction force calculation formula of expansion joint, it can be seen that the distance between the hinge points of the expansion joint directly determines the deformation angle and deformation reaction force. The larger the value of A and C, the greater the deformation angle and deformation reaction. The smaller the force, the B value should be as small as possible.
(3) In the normal operation of the smoke machine, the deflection force generated by the vertical pipe is an important factor that affects the force of the inlet flange of the smoke machine. Practical calculations indicate that the larger the pipe diameter or the longer the length of the pipe, the greater the proportion of the generated deflection force in the force of the entire inlet flange of the smoke machine.
(4) Although the friction force of the pendulum bracket is small in the inlet flange force of the smoke machine, the friction force can be ignored when the working condition is stable, but because the domestic smoke machine generally has a short start-up period, the start-stop Frequently; at the same time, the flue gas temperature also fluctuates frequently, which will cause the existence of friction force, so reducing the friction force is an important means to improve the force of the inlet flange of the smoke machine. The main methods are: on the premise of satisfying the relevant conditions, shorten the length of the horizontal pipeline as much as possible to reduce the positive pressure of the pendulum bracket; set a reasonable spring hanger on the horizontal pipeline to make it bear part of the pipeline weight, thereby reducing Small positive pressure on the pendulum bracket; reduce the radius of the pendulum shaft and lengthen the length of the pendulum plate; try to reduce the rolling friction coefficient of the pendulum bracket.
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