11.03.2006
dead man pedaling
My secret life in the world of international culinary espionage takes a back seat to my career. I did collect data last night, and am getting ready to blow the lid off this story...as it were.
But work comes first.
Please, any guesses? Let's make this a guestimate game so that I get to have a little fun before I meet my grim fate.
"Forgotwhoiam" amended their 5 minutes-per-whistle estimate, and now has a guess in the 3-4 minute range. (Please, commit to a more specific estimate...for entertainment's sake.)
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5 comments:
I'm going to guess 2 min 50 sec
2 min 49 sec.
2 min. 40 sec.
If I was to make a solid guess... I'm thinking about 462 head bobs.
It is unfair to have to guess the time between whistles when we are not given the temperature being applied to the pot. However, we can deduce that to get to 15 atmospheres you need to raise the vapor pressure to 1.519875 MPa. That means the temperature of the steam must be about 257° C. So I'll take that as my starting point. I will assume you are applying a constant temperature and it the minimum amount of energy you need to apply because you are frugal and seeking to hold back the heat death of the universe.
Now we have to guess the safety margin for the device. This is tricky. The manufacturer wants the device to cook things quickly so they don't want to release too much pressure. However, they also don't want to kill a lot of people. Given that there are a lot of people in India and consumer protection law is immature let's say they only back off the pressure by about 10%. So we drop from 15 atmospheres to 13.5 or 1.3678875 MPa.
Now, how long does it take for the pressure in the vessel to go from 1.36 to 1.52 at a constant temperature of 257° C? Keep in mind that by releasing pressure we actually increased the boiling rate of the water.
With a pressure cooker we are looking at a non-flow or batch heating process. The mean rate of heat transfer would be q = m c dT / t (2). The formula assumes pure water (specific heat=4186 J/kg °C) and we obviously have food, spices, and salt in the water. At this point we need to know the mass of water. Based on these values and a guess on the amount of water I believe from start to finish it takes about 7 minutes for three whistles. So the time between whistles will average 2:20. The first whistle taking the longest.
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