想請問板上的各位 Determination of specific surface involves the measurement of the solid surface area as well as that of solid volume and presents no problem for uniform geometric shapes. For irregular solid, especially for porous materials, however, surface area determination becomes involved. The surface of porous materials is necessarily full of holes and projections. Different surface areas are usually defined in connection with porous materials, viz., total surface area, external visible surface area, geometric surface area, etc. A simple rule of thumb is you should consider using a (PD) pump whenever you might be operating a centrifugal at other than at the BEP. Of course the further away from the BEP you get the more likely a PD pump will be a better choice. This can typically happen at low flow conditions, modest to high head conditions, or any type of elevated viscosity. As you can see from the efficiency curve it takes more horsepower to operate a centrifugal outside of its BEP. This horsepower has a cost, the initial cost of the larger motor plus a higher life cycle cost in energy consumed. Many times the PD pump will have a lower initial cost as well as a lower operating cost. 此兩篇文字敘述雖然能夠之後每個字的意思 但是卻難以把整段解釋的很好 (英文程度不夠 ORZ) 所以不知道有哪位可以幫忙的嗎? 另外問有沒有人 有單操的一些歷屆考題的解答?? PS 我不是故意要打"單"這個音的.... --

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