On Fri, Jul 15, 2011 at 12:50 AM, Joshua Cude <joshua.c...@gmail.com> wrote:
> > > On Thu, Jul 14, 2011 at 10:19 PM, Abd ul-Rahman Lomax <a...@lomaxdesign.com > > wrote: > >> >> Semantics. Yes, steam can be much wetter than 20%, particularly after >> condenstation, under marginal conditions it could approach 100%. This, >> however, wouldn't be called "steam." It would be called "hot water." > > > Yes, 100% liquid would be called hot water. But 99% liquid by mass is 94% > gas by volume, and if the liquid is in the form of a fine mist, then that is > called steam -- very wet steam. > It occurs to me, looking again at the two-phase flow literature, that the relationship I have been using between mass and volume ratio only applies if the two phases are travelling at the same speed (or are both stationary); i.e. if the liquid is entrained as a mist in the flow of gas. In this case, the volume fraction vf is given by vf = 1700*mf/(1+1700*mf) where mf is the mass fraction, and 1700 is taken as the ratio of densities. However, if the liquid is flowing more slowly along the walls or something, then the ratio of the volume occupied by the gas at any instant (the "void fraction" in the literature) can be much less, and is not simply determined by the mass fraction. For example, if the gas flows 1700 times faster than the liquid (equal to the density ratio), then the mass ratio is in fact equal to the void ratio. Of course, the volume *flow rate* ratio still follows the above formula, and the transport of power in a given phase depends on the volume flow rate, and it still means that if 1% of the water by mass is steam, then 94% of what comes out of the hose by volume is gas. I don't think this changes my picture of things drastically, because I still think the rapidly moving steam will cause turbulence and produce droplets, many of which will be entrained, and even the water which is not entrained will likely move faster, and the steam probably doesn't move 1700 times faster than the liquid, and so on. But it does make it less obvious that the chimney is occupied by mostly gas. Even so, it's hard to imagine steam bubbles rising through a chimney filled with water at a rate hundreds of times faster than the water flow without producing a kind of mist or spray. But this is probably a case of over-analysis. The simple facts remain that no credible evidence has been presented in the public demos that the output from the hose is dry steam, and the quantitative data presented (temperatures and flow rates) and the visual evidence from the videos are consistent with a mixture of water and steam, the ratio of which can affect the output power by a factor of 7 or so.
