principal cross-section

International E-Commerce contracts as the main form of e-commerce, Means in different countries and regions, Civil Principal entered into via the Internet or foreign law, international treaties concerning the effectiveness of cross-border sales contracts.

国际电子商务合同作为电子商务的主要形式，是指处于不同国家和地区的民事法律关系主体通过国际互联网所订立的涉及国际条约或外国法律效力的跨国交易。

Practice proved that the change in the overheater end connection from cross arrangement to parallel arrangement can increase the air preheater inlet fume temperature, principal steam temperature and reheated steam temperature, and reduce the thermal deviation of overheater, and improve the efficiency of boiler.

实践证明，通过调整对流受热面面积，将过热器末段间连接交叉布置改为平行布置，能够提高空气预热器入口烟温、主汽温和再热汽温，降低过热器热偏差，提高锅炉效率。

The part of tube prescribes the throttle character and the pressure regulation principal of the valve, and calculating press lose of straight tube, siphon and cross tube.

详细分析了阀门的节流特性与调压原理，以及直管、弯管、三通的压力损失计算方法；