氧气透平压缩机的轴封差压控制有哪些？
参考答案：
（1）混合气与进口氧气差压，正常情况下，混合气压力高于进口氧气管道压力。
（2）轴封处氧气与混合气差压，正常情况下，氧气腔的氧气压力高于混合气管道的混合气压力，以保证氧气腔的氧气流向混合气腔。
（3）轴封氮气与混合气差压，正常情况下，轴封氮气的压力高于混合气压力，以保证轴封氮气流向混合气管道。
| Lichens may grow on the bark of a tree in a steaming tropical rain forest, on the bricks of big city buildings, on rocks in hot springs, on wind-swept mountaintops, and in the driest desserts. In the arctic, they provide the principal food for caribou, and they are one of the few plants that grow in Antarctica. They are pioneers, appearing in barren rocky areas and starting the formation of soil in which mosses, then ferns, and then other plants can take root. Lichens are a partnership of two plants — fungi and algae. The lichen body is made up of a network of fungal strands. In the upper layers of these grow groups of algae. The two organisms live together to the benefit of both, a relationship known as symbiosis. The fungi provide support, absorb water, and shelter the tender algae from direct sunlight. The algae carry on photosynthesis and provide the fungi with food. The algae can live independently and are recognizable as a species that grows alone. The fungi, on the other hand, cannot live apart from their partners. They can be placed in known classes of fungi but are unlike any species that lives independently. So definite are the form, color, and characteristics of these double organisms that for hundreds of years, they were classified as one. More than 15,000 "species" were named. If these organisms are classified as separate species, it is difficult to fit them into the existing system of classification. But if they are classified separately, these species of fungi seem rather strange. Lichens are a splendid example of the difficulties faced by taxonomists in classifying species. |
Lichens may NOT grow ______ .
A．in the tropical woods
B．on the ceilings of city buildings
C．on rocks in hot springs
D．in dry desserts
