> From: "David Roberson" <[email protected]> > Sent: Friday, August 16, 2013 4:33:03 PM
> Thanks for the good information. When the drop was calculated as .5 > bars, was that assuming dry steam at 165 C? I think the peak was 165C -- I may have used 14C in some of my calculations > Also, if the temperature measures 165 C at the output test point, does that > automatically > result in dry superheated steam? Depends on the pressure. Assuming 22kW, will be dry, superheated if it's below about 3.5 bar > I ask this question because there > most likely will exist an initial boiling point somewhere within the > device enclosure that should be a bit higher than 100 C. The initial > boiling vapor would transport some water drops along the pipe as it > moves toward the output. Extra heat would be gained as the wet vapor > travels outward which would vaporize additional water. At some point > in space all of the liquid is vaporized so that from that point > forward we have dry steam. Yes, you will have the various modes water, bubbles, voids, drops, dry steam at various points in the heater coil. The progression I described is what you see as the whole system heats up. Once it's stable, then you'll have these affects in the heater coil, but you wont see them at the outlet. Gravity will tend to hold the water at the bottom of the coils, so you might even hear it "percolating" in the earlier, inner coils. > I find it difficult to believe that the temperature measurement at > the output test meter would be able to read 165 C if water drops > could exist at that point. Of course, this assumption would only be > true if the pressure at the output test point were near atmospheric. > The .5 bar estimate is small enough for this to be true. How high is > your confidence level that the pressure remains this low? Not 100% -- I used a table similar to the metric one here : http://www.engineeringtoolbox.com/steam-pipe-pressure-drop-d_1129.html The flow rate was 0.5 l/min, total power 22kW (assuming no cheating and saturated steam) The pressure drop in a 20mm ID tube at 30 kg/hour in a 30m tube is about 0.2 But there's a scaling factor -- MUL * 5 for 0.5 bar, DIV 1/3 for a 10m tube Hmmm .. is the steam pressure standard (1 atm = 1bar) or gauge (1 atm = 0 bar ) 0.2 * 5 / 3 = 0.3 bar pressure drop It's sort of recursive ... but I'd guess in the range of 0.5 to 1.0 drop -- since the end of the tube is atmospheric, the temperature in the coil would be 0.5 gauge, 1.5 standard. > Could you direct us to a source that calculates the pressure drop in > copper pipes expected with steam flow? See above. The corrections for steam in a rough pipe isn't as great as the correction for water. Plugging those into my calculator gives : <a href="http://lenr.qumbu.com/ecatcalc.php?plot=Plot&ever=c&efzx0=0&efzy0=0&efzx9=9&efzy9=9&esl=1&epbr=1&enm=Defkalion+steam+0.5l%2Fmin+22kw+1.5+bars&edh=0&edm=1&eds=0&eif=0.5&eip=2&ecp=0&eop=22&eoxr=1&et0=25.62&ep0=1&et1=25.62&ep2=1.5&er2=2"; target="_blank">Defkalion steam 0.5l/min 22kw 1.5 bars</a> BUT : if the outlet pipe isn't insulated all the way then there'll be a temperature drop too, resulting in a different pressure gradient. You really need a skilled steam engineer here !
