Posts by BenWilson
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Hard News: Kitchen Hacks, in reply to Stephen Doyle,
:-) Cheers. I haven't even posted any recipes.
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Hard News: Kitchen Hacks, in reply to Ross Mason,
Sorry Ben, you are using the wrong tables and theory.
Yup, the fact that the system is not closed was causing me grief thinking about it. All my working there was intending to show was that the difference in the boiling point with the lid on is insignificant, since Ben Chapman kind of jokingly challenged that. And technically, yes, the boiling point probably is a tiny bit higher because the pressure is a tiny bit above the outside atmosphere. Unless you use a pressure cooker, which I wasn’t talking about.
I’m not sure that it can be worked out, which is why I haven’t used any tables at all. The saturated steam tables you give require you to know the pressure, as do the Clausis-Clapeyron equations Ben gave. We could only know the pressure by actually measuring it, but upper bounding it seemed straightforward to me. It’s tiny so it hardly matters what equations or tables you use.
But yes, ideal gas law is not working here. Thanks for the input, gentlemen. I feel I understand it better than yesterday.
Presumably no one is disputing the underlying point, that cooking on full bore doesn’t cook things any faster than cooking at a lower (but still boiling) rate? Given that the pressure doesn’t change, that we are talking about pots, not pressure cookers.. The temperature in the pot is going to be the same either way, and the power is simply being wasted creating hot water vapour in your kitchen, to no good effect at all (quite the opposite, you are making the house damp), unless it was your purpose to evaporate water.
I’m pointing it out because it’s strange and counter-intuitive, something many people may not realize, thinking that somehow they are speeding up the process by pouring 20 times as much power through their food. You can get almost the same effect putting pasta into a thermos flask and filling it with boiling water and leaving it to stand for 20 minutes as you can by putting it on the element, and cranking 2000 watts through it for 20 minutes.
Ironically, pressure cookers are highly effective for the same reason. The lid is on so energy is not leaving the system at a great rate – once the cooker has reached the right pressure, you turn it right down. Ideally it wouldn’t vent at all if you had the stove setting exactly right, so that the energy coming in perfectly balanced what was radiating out. If you could insulate it perfectly, then it could actually pressure cook without using any power at all, once the right pressure is reached.
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Hard News: Kitchen Hacks, in reply to Raymond A Francis,
This I have to try, does it work on all cans?
With the white can opener depicted, I have not encountered a can it won't open with ease. It was actually only today that I realized that the standard can opener can actually do the same thing. It's not perfectly designed to do it, but it still did a better job than it usually does. I tested it on the same can, on the bottom, which it would actually be difficult to cut off the other inefficient way since it's bevelled inwards, so getting a grip on the folded tin lip would be very difficult. Doing it the improved way it came off in 5 seconds. You can see the bevel in the close up - that's actually the bottom of the same can depicted.
The white one is designed specifically to be used this way - it actually can't do it the other way. The gripping cog and the blade are aligned parallel. It's also oriented more ergonomically - the handles of the device points directly into the center of the lid, rather than tangentially to the edge as you see in the picture with the green tick. But the way in the picture applied the same basic idea, so I'm showing that you don't even need to throw your old can opener away - just use it differently.
I'm using it right handed in the picture, because I always have. But you could leftie it, then you'd be able to see the mechanism at work. I'm just used to squeezing with left hand, turning with right. For the old way of doing it, that actually mattered, because both hands had to also apply other forces, which was what made opening a can so damned hard that way. The left had to not only squeeze but also twist, and apply downwards pressure. The right had to turn, and apply the lions share of the downwards. The results were unpredictable, from mangling the rim to breaking/bending the can opener, to having the can fly off half-opened. But this way of doing it, the squeeze hand only has to squeeze, the turning hand only has to turn.
We have one of those, and it’s great. Not least because everyone in the family can use the same damn tin opener.
Yes, it wasn't a job I relished, along with opening tight jars, to be handed a busted arse can and have to jimmy it for 5 minutes, often reverting to a pocket knife opener just to get through the part that just wouldn't cut.
That had never occurred to me. It looks like your method produces a much safer can edge, too.
The top edge is very neat, but it's also sharp, so there's a slight danger there. But the other way gives a sharp inner edge, which would often catch your fingers if you were trying to spoon out the last remnants. A small child could put their hand in the can and then get it stuck and severely lacerated pulling it out. So a slightly increased danger from the can lying around after use is more than counterbalanced by the decreased danger during the normal use. I usually rinse the lid whilst still holding it with the can opener (so I can use hot water), and then the can, and then put the lid in the can for disposal, all the while never putting my fingers within the can at any point.
Because the lip is entirely gone, getting all the stuff out of the can is easier too.
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On efficiency, also worth knowing – a bigger pot is usually more efficient than a smaller one. The bottom has a larger surface area so energy flows through it more easily. It heats up the contents faster, and/or uses less energy doing so.
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For my next hack, a picture is worth a thousand words. I can't believe I did it the hard way for so long.
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Hard News: Kitchen Hacks, in reply to Ben Chapman,
Am I right?
Don't know for sure, but my understanding is that they would be very close to the same temperature, the liquid and the gas, if they are close to thermal equilibrium, and all of the energy coming in from the element would be going into changing the phase of the water. There is some difference in the temperature throughout the space - the lid must be slightly cooler, otherwise the gas would not condense on it. Makes sense because the whole pot radiates heat in all directions and the lid is the farthest point from the source of heat. But the condensed water would be only fractionally below boiling point, since it is in constant contact with the steam. If it fell any further, the steam coming into contact with it would condense, the droplets would grow, and eventually they would fall. Looking at what is happening in the boiling pot, I notice that the droplets aren't growing and dropping back in at a high rate. Most of the energy leaving the system is doing so in the steam coming out the vent, which makes sense since convection transfers heat much faster than radiation.
Hence the overall point that the temperature of what's in the pot can't be more than the steam, which in turn can't be much more than the water. So there's no increased cooking value from a higher rate of phase change of the water molecules. The temperature is still virtually constant, at the boiling point, whatever it is.
But I don't know how the boiling point alters, mainly because I don't know what the pressure would be - I could only put an upper bound on it before in terms of the weight of the lid. It's somewhere between that and 1atm. But that range is really small, probably less than any consumer temperature gauge can distinguish.
Essentially, we have two unknowns, the pressure and the temperature. But we can say something about the bounds of the pressure, and thus the bounds of the temperature. I can only presume the boiling point is within those bounds. It must be since it's greater than at 1atm, and less than or equal to the temperature of the steam.
Even assuming that the ideal gas law applies to confined steam above boiling water
Well it's not an ideal gas, since H2O is not monatomic.It's not even diatomic. Which is why I said "some variant of PV=nRT". It will probably be multiplied by some fraction specific to the ability of the molecule to take on energy in other ways than just bouncing around. Like it might rotate, or vibrate, or something. But that fraction will be constant, I think.
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Legal Beagle: MPs' Pay, in reply to Matthew Poole,
It would be nice if salaries were indexed to the median income, but as a feedback measure it loses its power if it doesn't take effect until the following term. I like the idea of Key et al having their pay cut as a consequence of their presidency over a decline in the median income.
Word. Inflation adjustment isn't enough. They should be pegged to what the middle is earning, and if they want to also get inflation pegging, then they should achieve that by inflation pegging the median income, or taking steps for that to be what happens in practice, anyway. Then their interests are aligned with the people they represent. The median income should include people who earn nothing, so that they are further incentivized to reduce unemployment, as well, or perhaps to raise benefits.
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Hard News: Kitchen Hacks, in reply to BenWilson,
But n is not constant
Well, actually in this formula it will be constant, until the water is gone. Every gram of water leaving through the vent is replaced by a gram coming out of the water in gaseous form into the pot.
I'm still puzzling over whether the water will boil off quicker with the lid on or off (in the case that boiling it off is what you are trying to do). First guess is that it doesn't make much difference. I can quite clearly see through the lid (it's glass) that the water is boiling harder with the lid on. But it also collects inside the lid and drips back in, which doesn't happen with it off. Will test this.
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Hard News: Kitchen Hacks, in reply to Ben Chapman,
However, having a quick scan of your working
Ah, yes, thanks. That'll teach me to do the conversion in my head - out by 10-fold (but on the good side, so far as my argument is concerned :-))
I don’t think that %-age of pressure above atmospheric is going to convert directly into boiling point temperature
I don't know either, whether it's linear or something else. But I do know that the steam temperature will probably follow some variant of PV=nRT. So T=PV/nR. V is close to constant, the pot doesn't change size much. R is a constant by definition. If n is kept constant, then T of the steam will rise linearly as P rises (and vice versa). But n is not constant, the steam is escaping from the pot via the vent, and in fact it is P that is constant, and only a tiny bit more than one atmosphere. So T will actually remain constant, and very close to the T at one atmosphere, until all the n are gone.
Not quite sure where you get your 5× wattage figure.
That's just the difference between the wattage coming out of the element at the lowest and the highest setting. It was a very rough guess based on observation of the difference in the amount of time each one takes to boil water. But for fun, I've just now done an actual experiment on it, seeing how fast each setting can evaporate off 100ml of water. The results:
On setting 6 (highest) water at room temperature evaporated completely away in 6.5 minutes.
On setting 5 it took 25 minutes.
On setting 1 it hadn't reached boiling before I had to cook dinner 40 minutes later. Will have to come up with a different experiment for that setting.So I'll revise the above guess to say that the difference in power is considerably greater than 5-fold between the highest and lowest settings. It's at least 6-fold (and probably a lot more than that, blind guess now is that it's probably more like 20 to 30-fold), and I now believe that the scale is not linear.
Will do a better experiment later tonight to be sure :-) I will have to read the meter to find the actual electricity usages.
This refers to power delivered to the water, of course, not power used by the element, which will be a lot more. I expect that will also be more efficient at lower levels.
All of which goes way further to my point that you gain massive advantages from putting on the lid and almost no losses.
I was being facetious when I made my point about pressure and temperature.
I guessed as much but I'm studying thermodynamics right now for an exam on Tuesday so there's no harm in my getting expert feedback :-)
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Hard News: Kitchen Hacks, in reply to Hebe,
And you have a microwave in there too: well done!
Cheers. I agonized over how to fit it in when we designed the kitchen. It was a real pain in the arse in the original kitchen, took up huge amount of bench space.
here when the oven or dishwasher door is open, you are imprisoned at one end of the kitchen.
That sucks. Fortunately, our kitchen has exits at both ends, so you can get to the other end just by walking through the lounge. Handy during parties when the place is packed.
But from painful experience I can say that 15cm is not really a safe gap to be walking through either. So usually we have to close the dishwasher constantly. Its location is not that good, opposing the fridge and between the dining room and the sink (so rinsing involves closing the dishwasher to get past, then opening it again, then closing it to get some more dishes. In practice I end up piling them up instead). But if it was on the other side of the sink it would oppose the stove, which would be downright dangerous, you could open it behind someone working at the stove and they could fall over backwards into it. The solution is, of course, a bigger kitchen. Or the one I'm always trying to sell to my wife, a bigger house.
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