Question 97 on Boiler Foundations, November 22: (A certain score will be given to the top 50)
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True or False: In a boiler drum, the greater the resistance of the orifice plate submerged in water, the better, as this allows the orifice plate to effectively reduce the kinetic energy of the steam-water mixture. ( ) Thank you for your support. Correct answer: additional wealth gain of +5–8 points; incorrect answer: additional wealth gain of +1 point
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The greater the resistance of the orifice plate under water in the drum, the better, as this allows the orifice plate to effectively reduce the kinetic energy of the steam-water mixture. Yes
The greater the resistance of the orifice plate under water in the drum, the better, as this allows the orifice plate to effectively reduce the kinetic energy of the steam-water mixture. (right)
The greater the resistance of the orifice plate under water in the drum, the better, as this allows the orifice plate to effectively reduce the kinetic energy of the steam-water mixture. (X)
The greater the resistance of the orifice plate under water in the drum, the better, as this allows the orifice plate to effectively reduce the kinetic energy of the steam-water mixture. (X)
The greater the resistance of the orifice plate under water in the drum, the better, as this allows the orifice plate to effectively reduce the kinetic energy of the steam-water mixture. ( Wrong )
The greater the resistance of the orifice plate under water in the drum, the better, as this allows the orifice plate to effectively reduce the kinetic energy of the steam-water mixture. Yes, the greater the resistance of the submersed orifice plate, the easier it is for a stable vapor cushion to form beneath the orifice plate, effectively reducing the kinetic energy of the vapor-water mixture. In this way, steam can pass through the orifice plate more evenly, and the water level in the boiler drum remains more stable, thereby reducing splashing droplets and mist. However, the flow rate of steam piercing should not be too high either; otherwise, the resistance will be excessive, and the formation of a too-thick vapor cushion can easily cause vapor to enter the downcomer. In addition to distributing steam evenly, the submersible orifice plate can also reduce the rise in water level, thereby minimizing the impact on the height of the steam space. Underwater orifice plates are usually made of steel plates with a thickness of 3–4 mm, and they are equipped with small holes distributed evenly across their surface, with a diameter of 8–10 mm. If the pore size is too small, it is prone to clogging; if it is too large, it will result in uneven distribution of steam flow. In heating boilers, the steam flow velocity through the orifice plate can range from 3.5 to 8.5 m/s, depending on the operating pressure ； Boilers with lower pressure use higher values. The underwater orifice plate should generally be installed horizontally at a depth of 80 mm below the lowest water level in the drum, to ensure that it can still provide a uniform evaporation surface load even at the lowest water level. The length of the submersed orifice plate should not be less than 2/3 of the straight section length of the boiler drum, and every bit of steam entering the water space should pass through the submersed orifice plate. At the same time, a gap of 150~200 mm should be left between the orifice plate and the cylinder wall to allow water to flow down smoothly. To prevent steam short-circuiting, a water seal baffle 100–150 mm high is installed at the edge of the orifice plate. Water is supplied evenly over the orifice plate, which helps to break up bubbles while also ensuring proper flushing of the steam.