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Coffee Maker

To engineer an object means to make choices. Bill illustrates how the choice of having a single heating element made an engineer find a creative way to pump water with no moving parts.

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To engineer an object means to make choices, and I'll show you with this coffee maker.

The key choice? To use a single heating element to keep the cost low - nine bucks in the case of this coffee maker. Now, the heater must be below the carafe to keep the coffee warm, yet it also needs to heat the water for brewing and since the grounds are at the top that presents a problem: How to get the water from here to here.

Now, of course a coffee maker doesn't need to look like this. An engineer could have built this: Here I've moved the water reservoir to the top, which lets gravity drain the water through the coffee grounds: No water transfer problem to be solved! But that's an expensive way out: You'd still need a costly heating element at the bottom and now one for the top - and that would double the cost.

This cost constraint made the engineer be very clever about how he or she moved the water from the bottom to the top: They made the heating element do double duty - both heat the water and move it!

Hidden in the tubing is a one-way valve - it's tiny! These two small pieces support the ball so water can flow through the reservoir into the heating element, but if water flows the other way the ball rises preventing it from returning to the

reservoir. This simple device creates a pump with almost no moving parts. Its called a bubble pump and to show you way I'll replace the plastic tubing inside with a glass tube.

Now what I've done is by-pass the plastic tube inside so we could see the bubble pump action and I have re-routed the water with this black hose back into the carafe and so let me go ahead and turn it on ... and let's see what happens. Oh! [notices it is unplugged]

Now it's on. I'm always amazed at how fast this happens. You can see the water rising already.

The water rises because the tubing and heating element create a "bubble pump." In the heating element the cool water becomes two phases - liquid and vapor - which is less dense than the cooler water and that makes the liquid/vapor mixture more buoyant that the cold water, which creates a slug or churn flow up the tube because the one-way valve stops any backward flow.

The beauty of it: no moving parts, just a one-way valve, some tubing and a heating element - very inexpensive, but effective. I'm Bill Hammack the engineer guy.