双层壳体 meaning in English

double hull
double-shell

When the backing is a double - shell , the water layer causes obvious modulation phenomenon to the absorption coefficient curve
背衬为双层壳体时，水层对吸声覆盖层的吸声系数曲线有明显的调制现象。
Whether the backing is a single - shell or a double - shell , the absorption performance approaches more closely to that with a rigid backing
背衬为单层壳体或双层壳体时，从整体上讲，吸声系数更趋近于刚性背衬而非软背衬的情况。
This device has many advantage character with lower flow , higher delivery lift , small area for occupying and also has double cases structure , in which internal case is vertical and sectional type and external is simple sack type in order to guarantee safety arriving without any leaking absolutely
该型泵具有流量小、扬程高，占地面积小的优点，该泵为双层壳体结构，内壳为立式节段式，外壳为筒袋式，确保运行安全，达到绝对无泄漏。