Why water heated with electric heater remains hot for long time than water heated by gas stove
Two main reasons.
1. The water tank is usually well insulated (lagged).
2. The quantity in a hot water tank is much larger than the quantity in a kettle. Because the surface area (for heat loss) is much less per litre in a big tank, temperature falls at a lower rate.
There is one way in which using a kettle / pot may be better value, though. When you 'run' the water for several seconds from a hot water tap, before it gets warm enough to use, the pipes need to get full of hot water (possibly several litres). This may well cool down before you need any more so you will have wasted the energy used to heat it. If you just heat up 2l of water in a kettle and use it all quickly, there is no such loss.
Because the heater element take longer to cool down, the pot have direct contact and it keep heating the water for a little while. For a gas burner, the moment you turn off the gas, no more direct contact with the pot and so it cool faster.
That's why when I cook noodles, I turn off the electric burner a minute before the noodle is ready and let the remaining heat keep cooking without using any power........I am cheap.
And how much longer does the electric element take to heat up. One needs to address the relevant factors.
Well, being stuck with the electric burner, you make the best out of it. I am a Chinese, when I really cook, I have my 60,000BTU giant propane burner to cook Chinese food. The frame has to wrap around the wok, food has to catch on fire to frame out to get the essence of Chinese saute cooking!!!:rofl:
But still, with the big burner, once you turn it off, it immediately stop cooking.
Steel (the wok) doesn't have a particularly high specific heat and the essence of chinese cooking seems to be to cook small quantities at a time. So there isn't a lot of thermal capacity there. Any water in the wok that is above 100C will boil off (without a lid) and that uses a lot of latent heat. These are all good reasons why the temperature drops fairly fast.
Contrast this with a good old European Stew in which there is a large quantity of liquid in a covered pot. It will stay cooking for quite some time once the heat is removed.
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