On Thursday 25 September 2008 17:11:24 Martin Vlietstra wrote: > Hi Pierre, > > As I said, I am not a hydraulic engineer. However, you stated that there > are many different types of "head". Can you add these types of head up > (either as scalars or as vectors)? If so, they must all be in the same > units - pascals. If not, then there has been some messy overloading of > names.
You can add them as scalars, and they are all in the same unit. When using pounds, head is in feet, and the author of the hydro book states that head is measured in meters in the metric system. The author, however, is not a native metric speaker (e.g. he gives the specific weight, not density, of water at various temperatures and the one at 4 °C is wrong). So I'd like to know whether hydraulic engineers who work in metric use head, or what do they use instead. Once the prof worked an example on the board involving oil, getting the head, then converted it to "feet of water", stating that that is the standard. That made no sense. Head is used because, where a still container has an open top, it is visible as the elevation of the top. A head of oil is not a head of water, and if you're going to compute one from the other, you need to compute the pressure at the oil-water interface. Pierre
