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强制循环锅炉有哪些特点？

答案

参考答案：

（1）由于装有强制循环泵，其循环推动力比自然循环大好几倍可达0.25－0.5MPa，因此可采用小直径的水冷壁管，使管壁减薄，节约金属。

（2）循环倍率降低，可以采用蒸汽负荷较高、旋转强度较大的涡轮式汽水分离装置，以减少分离装置的数量和尺寸，从而可采用较小直径的汽包。

（3）蒸发受热面中可保持足够高的质量流速，并且水冷壁管子进口处一般装有节流圈，而使循环安全；因此蒸发受热面可采用较好的布置方案。

（4）调节控制系统的要求比直流炉低。

（5）锅炉在点火前就可启动循环泵，保证了水循环的建立，锅炉能快速启停。

（6）缺点是由于循环泵的采用，增加了厂用电率及设备的制造费用，而且循环泵长期在高压高温的环境运行，需用特殊材料才能保证锅炉安全运行。

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梁的结构分为大梁（主梁）和（）。
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Part 1


·Read the article below and choose the best sentence from the list on the next page to fill each of the gaps.
·For each gap (1-8) mark one letter (A-H) on the Answer Sheet.
·Do not mark any letter twice.

Ways to Save


"But I can’t save any money." It’s an excuse I hear a lot. Sometimes it’s a whine. (1) . In the past few years, it has become increasingly frequent, as more and more of us Americans make less than we spend, eating up the equity in our homes, borrowing from banks. The national savings rate is declining. (2) .
The question is: Why Why don’t Americans make saving a priority We certainly know that saving money—like eating broccoli and strengthening our core muscles—is good for us. (3) . Yoga has never been hotter. And broccoli now comes as a baby vegetable, precut and bagged, and even in purple. (4) There are three reasons for this.
One: Saving today is harder. "We’ve had an income transfer away from the middle class," says Anthony Pratkanis, a psychology professor at the University of California Santa Cruz, who specializes in financial issues. The typical household income has held largely steady around the mid-S40,000 range for a good half decade, he points out, while prices have continued to rise. (5) .
Two: Credit became too accessible. (6) . While banks at one time would not let you spend more than 36 percent of your total income on debt (including mortgage) they stretched that number to 55 percent during the housing boom: Why save when yot could get that big flat-screen TV today—just like the one the neighbors installed—and pay for it with mortgage debt that was both cheap and deductible
Three—and most intriguing: Saving is, was, and always will be no fun. "Saving money," explains Jason Zweig, author of Your Money and Your Brain, "doesn’t feel good." Think about it this way: (7) . "You can buy a pair of shoes today," says Zweig, "or have a nice retirement 20 years from now." (8) . You’re going to buy the shoes or head to the restaurant because the pleasure of getting something good today is much greater than the pleasure of getting something good years in the future—even if the reward in the future is bigger.
  • A. You can go out to dinner now or put the money into an emergency fund in case the car’s transmission goes out—someday.
  • B. For years it was simply too easy to get your hands on money to spend.
  • C. In the latter cases, we listen.
  • D. Choosing to save almost always means opting for delayed gratification instead of immediate gratification.
  • E. Yet saving for tomorrow is still a largely ignored and unappreciated skill.
  • F. Other times I detect a note of defiance.
  • G. "If you’re having to spend a disproportionate amount of income on food and gas, it’s hard to save."
  • H. And the situation seems to be getting wors
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