How does the keurig/coffee maker make that amount of cold water so boiling hot in such a quick time?
In: Engineering
If your kettle was the size of a single cup of water. It would boil in a few seconds. Instead it has a lot of empty space that takes longer to heat up, and raise the temperature to boiling. Adding more water just fills that empty space with more water to boil, lengthening the process.
The Keurig uses a small reservoir, separate from the main water tank, that is more efficient due to being much smaller, and therefore faster to heat. Essentially a really tiny single-cup kettle, or drip straw, inside the machine, refilled from the large tank you see on the side.
For one, it uses a *lot* of power.
Another trick they do is heat water while it’s being drawn up through a thin tube. It’s a lot easier to heat the water in the section of the tube right before it hits the coffee grounds than simultaneously heating all the water contained in the machine.
One thing to consider: there is no device that can heat water disproportionately faster than any other device using just electricity. A typical small appliance like this is going to max out at about 1500 watts.
1500 watts for a minute (1500 watt-minutes) is about 90,000 joules.
To heat a gram of water from ~20 C to boiling (100 C) at standard conditions takes about 330 joules. There’s about 225 grams in a serving, so we need ~75,000 joules (225 * 330).
This means the theoretical maximum speed for a 1500 watt small appliance to bring an 8 ounce cup of water from room temperature to boiling is 50 seconds.
But it doesn’t have to bring the entire volume to boiling first. It can heat a small portion of water up and pass that through the cup while continuing to heat more water. That way the cycle is completely done by the 50 seconds. Further, I don’t think Keurig actually goes up to boiling (not sure).
It uses a trick: it heats only a little of the water at a time, putting that through the coffee grounds while it heats some more.
Also, I hear some models preheat some of the water while idle.
The water goes through a tube to a resistor (which is a piece of metal that becomes hot using electricity). What makes it fast is the small size of the tube : only a small amount of water is in contact with the resistor at a given time.
You can easily make a few drops of water boil in seconds if you drop them on a hot stove. That’s the same principle. What takes time is to boil a large amount of water, but an expression machine only uses a small amount of water every second, so it’s easy to boil it rapidly.
I hope this was clear, tell me if it wasn’t.
Latest Answers