Centrifuges: A Basic Introduction
From the Wikipedia page
on centrifuges, "a centrifuge is a piece of equipment... that puts an object in rotation around a fixed axis, applying a force perpendicular to the axis. The centrifuge works using the sedimentation principle, where the centripetal acceleration causes denser substances to separate out along the radial direction (the bottom of the tube). By the same token lighter objects will tend to move to the top (of the tube; in the rotating picture, move to the centre)."
Basically, a centrifuge is a device that spins a tube containing a liquid sample about a central axis. This rotation causes the sample to be subjected to a centripetal force. Since the tubes are oriented radially with the top of the tube towards the axis, the centripetal force simulates an extreme gravitational force on the tube. It is as if you stood the tube on end in a laboratory (or kitchen) on Jupiter (only the centrifuge actually exerts much, much more force than Jupiter's gravitational pull would). This increased force causes heavier parts of the sample, like suspended solids and fats to sink to the bottom of the tube, while lighter components, like liquids, float to the top.
Centrifuges are typically used in chemistry, biology, and biochemistry for isolating and separating suspensions. However, they have recently begun seeing use in molecular gastronomy, a field of food science that seeks to utilize scientific principles and techniques in the preparation of food. Little documentation exists as yet, however, of recipes for food prepared with centrifuges. It is the goal of this Instructable to begin changing that.
The overall goal of this project is to create a centrifuge capable of spinning up to eight 15mL samples at high enough speeds to achieve separation of the liquid, solid, and semi-solid portions of the sample. In addition to this function, the centrifuge must
be safe both during normal use and in the case of failure.
be easy to use.
be sanitary as it could be used in the preparation of food for human consumption.
be aesthetically pleasing and customizable in order to fit in with the decor of a kitchen.
Parts of the CentrifugeMore detail is given on the steps dedicated to each system.Drivetrain
(Step 5): The drivetrain is the portion of the centrifuge that interfaces with a drive motor and transfer's the motor's torque to the rotor. The drivetrain must be strong enough to withstand rotational speeds as high as the maximum of which the drive motor is capable, plus a generous margin of safety.Rotor
(Step 6): The rotor is the portion of the centrifuge that rotates and secures the sample-containing tubes during operation. The rotor will be capable of holding a maximum of eight 15mL tubes. Tubes are loaded into the rotor in pivoting brackets so that, when the centrifuge is at rest, the tubes hang vertically, and during operation, the tubes lie radially, parallel to the direction of the centripetal force exerted upon them. The rotor must be strong enough to hold the sample tubes under centripetal forces generated at the maximum rotational speed of the centrifuge, plus a generous margin of safety.Safety Enclosure
(Step 7): The safety enclosure contains all the moving parts of the centrifuge, save the drive motor. The enclosure is designed to do two things. First, the enclosure prevents any foreign object from entering the centrifuge during operation. Second, the enclosure is a shield designed to prevent any part of the centrifuge, or the sample tubes, from being ejected from the machine in the case of failure. The enclosure is designed to protect the centrifuge operator, and anything else that could suffer damage from a mechanical failure of the centrifuge.
Sources of Inspiration
As mentioned in the introduction to this Instructable, the primary source of inspiration for this project was an article in Popular Science by Paul Adams. Mr. Adams wrote a great demonstration piece showing how a centrifuge could be used in food preparation, specifically by making pea butter out of the fat separated from a pea puree. It was this article that piqued by interest in experimenting with food in a centrifuge. However, because centrifuges are quite expensive, I got to work designing my own.
Before I started the project, I had heard a story about how a 3D printer was used to produce a small centrifuge attachment for a Dremel rotary tool. The project, called the DremelFuge
, is a fantastic proof-of-concept that 3D printing can indeed by used to make a centrifuge, however, there are some serious oversights in the design, especially relating to safety. The DremelFuge has no safety enclosure whatsoever. If one of the sample tubes were to detach from the rotor during operation, it could cause serious, even life-threatening injuries to the operator, or others. Even operating at the minimum rotational speed discussed on the Thingiverse page, 3000 rpm, the tubes have a tangential speed over 70 mph, which, even though the sample tubes are small and light, is fast enough to cause bodily harm. The truly frightening bit though is the discussion of operating the DremelFuge at a much faster, 30,000 rpm. With this rotational speed, the sample tubes have a tangential velocity of approximately 715 mph! This speed is quite close to the speed of sound and the sample tubes traveling at this speed would have more than enough kinetic energy to cause severe damage to whatever they might hit, including a human body.
The last source of inspiration for the centrifuge design in this Instructable came from simply searching the web for other examples of homemade centrifuges. A simple image search on Google will return many examples of homemade centrifuges. Some are better than others, but they all offer ideas for the many different ways a centrifuge could be designed from scratch.