Components Arrive for Airflow Testing

2011 November 1
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The next major test for the prototype is the addition of airflow. We are using hot, moving air to heat the coffee beans via convective heat transfer. This coupled with a small amount of heat transfer from conduction and radiation is the best way to roast coffee for full bean development and flavor complexity.

The device that generates the airflow is a blower. Our test blower has arrives in pieces, which is handy for showing each component by itself. The heart of the blower is the impeller, which is essentially a centrifugal fan. As it spins, air is forced out radially from the blades and air is sucked into the center of the impeller. This impeller has straight blades and is made of cast aluminum. Impellers also are made with blades that curve in the direction of rotation and also in the opposite direction. We will determine which blade shape is best for our use.

The impeller is powered by an industrial motor. For testing purposes we are using a 3/4 horsepower motor that uses standard household 110V power. In the final design, we will likely use a higher voltage motor.

The impeller is contained within a housing to channel the air. In this case, the housing is made of sheet metal, but others we will consider are made of cast metal. The air enters though the center hole and then is collected and sent out the rectangular duct on the side.

We are designing ductwork to match up with the rectangular duct on the blower. It will have the capability of throttling the airflow and we will attach various probes to measure pressure and airflow volume.

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