RE: Steam temperature (was meniscus mayhem)
Walt, I believe that your statement "the increasing vapor pressure keeps the water from shifting phase, requiring greater heat input per unit to increase the temp to make more steam" is correct. As the boiler continues to be fired the temperature and pressure both rise until the safety blows. Very early this morning I thought that I would be clever and consult Boyle's and Charles' laws in a physics text. I then calculated the steam temperature at 40 psig to be about 1100 degrees Celsius, which seemed a bit high, especially for an alcohol fired boiler. Then I remembered that those gas laws were for ideal gases that don't condense under high pressures like water. I realized that in our loco boilers, where we have both water and steam, there was another mechanism happening similar to all the discussions that have occurred on this list about liquid butane and vapor pressure. Luckily I remembered, and found, the Brooks catalog which sent me in the right direction. For a given pressure and temperature in the boiler, with no heat added or lost, I think there is an equilibrium condition between the water and steam. Turn up the fire and more water turns to steam than the other way around. Steve
Re: Steam temperature (was meniscus mayhem)
Steve, My fuzzy logic (Balvenie fortified) seems to think there is some sort of temperature gradient, otherwise all the water would flash to steam unless the increasing vapor pressure keeps the water from shifting phase, requiring greater heat input per unit to increase the temp to make more steam. Don't we have at least one Thermodynamics EXPERT on the list? As water increases in temperature, the molecules get more excited and occupy more space, thus becoming less dense, and rise to the top, being displaced by the less active (cooler) water molecules. Are some water molecules dull or dour, and thus take more heat input to excite them? Is this what allows 'flash boilers' to function? All those great old drawings of how a steam engine works have all those little arrows going around in circles inside the boiler, must mean something! Keep your steam up! and try some Balvenie. Wish I owned stock in that outfit! Walt
Steam temperature (was meniscus mayhem)
Walt and the List: According to "Properties of Saturated Steam" data from the 1991 Brooks Instruments catalog, saturated steam temperatures for various pressures (psig) will be: PSIGTemp (F) 0.0 212.00 20.3259.28 40.3287.07 60.3307.60 I will assume that in a boiler the water temperature will be the same as the steam temperature. Sort of the reverse effect of water boiling at lower temperatures at high elevations above sea level. Can anyone confirm this? Steve -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] Sent: Thursday, May 31, 2001 5:28 PM To: Multiple recipients of sslivesteam Subject: Re: meniscus mayhem Would not the portion of the tube that does not contain water have higher temp steam in it? I've never studied Thermodynamics, but there must be something like convection currents in the water portion, thus there would be some (maybe slight) temp differences. There should be some temp difference between steam and liquid, and since the system is pressurized, the temp should be higher than the 212 degree temp that water boils at in an open container at sea level. However, I could be as wet as the steam in a Ruby's cylinders! Keep it (your choice) up! Walt & Lunk
Re: meniscus mayhem
Du'h. Of course, you're correct about that. It's a function of pressure. royce [EMAIL PROTECTED] wrote: > In a message dated 5/31/01 8:30:03 AM Mountain Daylight Time, > [EMAIL PROTECTED] writes: > > << it can't be much over 200 > deg F that it would have to endure. >> > > It can be much higher than that depending on the steam pressure. > bill
Re: meniscus mayhem
Walt, The way these things are "supposed" to work is that the steam in the top leg is slowly condensing on the cooler metal and glass, and is supplying water which is slowly going down through the bottom fitting and back to the boiler. Peter Trounce. -- > From: [EMAIL PROTECTED] > To: Multiple recipients of sslivesteam <[EMAIL PROTECTED]> > Subject: Re: meniscus mayhem > Date: Thursday, May 31, 2001 8:27 PM > > Would not the portion of the tube that does not contain water have higher > temp steam in it? I've never studied Thermodynamics, but there must be > something like convection currents in the water portion, thus there would be > some (maybe slight) temp differences. There should be some temp difference > between steam and liquid, and since the system is pressurized, the temp > should be higher than the 212 degree temp that water boils at in an open > container at sea level. > However, I could be as wet as the steam in a Ruby's cylinders! > Keep it (your choice) up! > Walt & Lunk
Re: meniscus mayhem
>From what I can recall, not all plastics are "non-wetting". I believe High Density Polyethylene (HDPE) is non-wetting but it has many physical characteristics that would be undesirable for our application. Specifically, it is much more plastic (i.e. less rigid) and is milky as opposed to clear. Acrylic plastics such as those sold under the trade names of Plexiglas, Lucite, Acrylite, and Perspex (sp?) are naturally hygroscopic (have an affinity for water). While that fact alone is not a problem, it would seem to indicate they don't have the "non-wetting" characteristic we desire. Just some rambling recollections... Are there any polymer experts amongst us? Michael Martin [EMAIL PROTECTED]
Re: meniscus mayhem
Would not the portion of the tube that does not contain water have higher temp steam in it? I've never studied Thermodynamics, but there must be something like convection currents in the water portion, thus there would be some (maybe slight) temp differences. There should be some temp difference between steam and liquid, and since the system is pressurized, the temp should be higher than the 212 degree temp that water boils at in an open container at sea level. However, I could be as wet as the steam in a Ruby's cylinders! Keep it (your choice) up! Walt & Lunk
Re: meniscus mayhem
Hello Everyone, I had thought of plastic also. Not because of the capillary action being corrected (which I only learned after reading this post), but because my Mamod has an elongated plastic port hole style sight glass in the backhead. It's about 3/8" wide, 1.1/8" long, and .050" thick. What type of plastic? I don't know but I'm guessing probably polycarbonate. Just as Fritz has stated, the plastic might lose it's integrity at a higher temperature when subjected to the pressure of the steam in the boiler. If anyone finds a source for small diameter tubing, the company should be able to provide technical support/information for the product being sold. Later, Trent P.S.- Not meaning to open a can of worms here, but wouldn't the steam have a higher temperature than the water inside the boiler? Royce Woodbury wrote: > If there's water in the tube, it can't be much over 200 > deg F that it would have to endure. > > "Brohn, Fredrick" wrote: > > > Has anyone considered using plastic in lieu of glass? > such a plastic > > tube would have to be able to withstand the heat and pressure of steam. > > Here I can offer no information. Any "materials" experts out there should > > be able to provide the right info.
Re: meniscus mayhem
In a message dated 5/31/01 8:30:03 AM Mountain Daylight Time, [EMAIL PROTECTED] writes: << it can't be much over 200 deg F that it would have to endure. >> It can be much higher than that depending on the steam pressure. bill
meniscus mayhem
It appears that Fritz has the answer. Eliminate the meniscus ! Improve accuracy ! I'm for it. If there's water in the tube, it can't be much over 200 deg F that it would have to endure. "Brohn, Fredrick" wrote: > Has anyone considered using plastic in lieu of glass? In one of our biology > lab experiments we have our students measure water in a glass graduated > cylinder and then repeat the measurement in a plastic (Nalgene,TM) graduated > cylinder. With glass you need to read the "bottom" of the curve, called the > meniscus. With plastic this is not necessary as there is no "wetting" and > therefore no capillary action. Clearly (no pun intended) such a plastic > tube would have to be able to withstand the heat and pressure of steam. > Here I can offer no information. Any "materials" experts out there should > be able to provide the right info. May save a lot of headaches! > > Keep your steam and sap up! > > Fritz Brohn >
