A lot of things to consider here... A lot of energy in the kitchen application is radiated. A fiberglass jacket would save a lot of energy loss. A six quart pressure cooker filled to 4 quarts takes about 10 minutes on "high" to come up to pressure, it takes half power to maintain pressure with a minimal "hiss". 15 pounds of pressure may not seem like much but when it is superheated water a sudden breach releases a lot of energy. A smaller pressure vesell would minimize the risk. I cannot recommend a pressure cooker for anything other than its intended use. It excels as a cooking tool. John Ferrell W8CCW "My Competition is not my enemy" http://DixieNC.US ----- Original Message ----- From: "Peter P." To: Sent: Thursday, November 23, 2006 7:15 PM Subject: Re: [OT]: Pressure cooker burst disk ? > John Ferrell earthlink.net> writes: > >> Our 23 qt Pressure cooker has a gauge that sits at 15 pounds during >> normal >> cooking. The rocker weight is pretty lively at 18 pounds. No info on the >> safety vent... > > Ok, thanks for that. From what I know until now the burst disk is probably > set > to go at 130-140 deg C, for a safety factor of at least 2x (pressure is > 45psi > abs = +2bar at 135 deg C). > > So I can say that an ordinary pressure cooker could be used to drive a > 'victorian' steam engine (a small one). Now we have a kettle. I happen to > know > that such a cooker whistles fine after about 30 minutes on a 2kW > electrical > heater plate, venting steam at high speed through 3 2mm orifices. That > would be > 2m^2 of sun at 100% absorbance (impossible to realise). More realistically > with > 0.8 mirrors and 0.8 absorbance about 3.2m^2 of mirror (a 2 meter/6 foot > dish). > > Anyway 2kW will boil only slightly less than 1 gram of water per second. > That is > not a lot to work with. Maybe it will drive a small impulse turbine and > generate > about 10-20 Watts or so. That is about 0.5-1% efficiency ! Yes, steam is > painfully inefficient at low pressures. Sorry about that. Anyway ~1 > gram/second > mass flow of steam at 300m/sec (speed of sound in air, wrong for steam but > I > have to start somewhere, assuming a de Laval nozzle that outputs at Vs) is > about > 45 Watts in the jet (less nozzle loss) ? (which corresponds to a > mind-boggling > 2% efficiency heat in to jet power out). > > I have experience with such single stage turbines, connected directly to a > generator, air driven (due to materials limitation - plastic formed > nozzle). A 2 > inch turbine will produce said 10 Watts at about 30,000 rpm (running very > inefficiently, at about 20% calculated very roughly - optimum speed for a > de > Laval nozzle and 300m/sec ejection speed is slightly less than 60,000 > rpm - on > something like 0.5l/sec of air at 2.2 bars with a 1.5 mm nozzle (the > narrow > part) - interestingly by running a lower pressure efficiency is higher). > > A simple turbine made from soft steel sheet like I used cannot be taken > much > beyond 30,000 rpm as it starts to bend out under its own weight. The high > rpm is > not a real problem as there is a variety of small motors that will spin > that > fast and can be used as generators here. E.g. up to 60,000 rpm it is > relatively > easy to find suitable motors (e.g. old Dremel, model aircraft/rc motor, > battery > operated vacuum cleaner etc). > >> I am probably the only guy around that is hoping for a couple more >> pressure >> cookers for Christmas... > > Does it connect to a distillation column ? ;-) > > Peter > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist