Coffee Maker Lab   

        Our Intro to Chemical Engineering class conducted an experiment to determine how a coffee maker works and what applications of chemical engineering apply to it. To determine how the coffee maker works each group of two students first ran the coffee maker and then tore it apart, literally in some cases.

What goes on inside of the coffee maker?

   After pouring cold water into the coffee maker it flows from the water reservoir through the hole in the bottom of the reservoir and into an orange tube. The water then flows through the one-way valve into an aluminum tube. The one way valve is there so steam will not go back into the water reservoir. The water the goes into the heating element, and then flows partially up through the other aluminum tube. This all happens naturally because of gravity.

    When the coffee maker is turned on, the heating element begins heating the aluminum tube until the water in the tube starts to boil. When the water boils, the bubbles rise up in the aluminum tube. The tube is small enough and the bubbles are big enough that a column of water can ride upward on top of the bubbles. The semi-vaporized water collects in a small area above the coffee grounds and begins to drip into the coffee grounds. The coffee grounds dissolve into the water and then the new coffee stream passes through the coffee filter, so the coffee grounds do not get into your coffee, and into the coffee pot.

    The coffee is kept hot by the hot plate that sits on top of the heating coil. The heating coil heats both the water and the hotplate at the same time. There is a thermostat that is connected to the heating coil. This thermostat acts as a circuit breaker. Inside the thermostat are two metal plates that expand when heated. If the coils get too hot the two metal pieces inside the thermostat expand and break the circuit, breaking the circuit and shutting off the heating coil. As the coil cools down, the tow metal pieces come back together and complete the circuit so more coffee can be made. There is also a thermal fuse that also will shut the coffee maker down if the coil gets too hot.

Applications of Chemical Engineering Principles

    You may be wondering how any principles of chemical engineering apply to making coffee. How does chemical engineering apply to dumping some water and coffee grounds in a machine and flipping a switch? Well it applies in more ways than you would think....

• Fluid Mechanics

• Heat transfer

• Mass transfer

• Process Control

• Materials and Corrosion

• Economics

   Fluid Mechanics - how fluids flow in a system

      In the coffee maker fluid mechanics is applied in the flow of the water from the water reservoir through the tube sitting on top of the heating coil and up the tube to the area above the filter.

Heat Transfer - how heat transfers from one material to the other

    Heat transfer is observed in several areas of the coffee maker. The first and most obvious is the transfer of heat from the heating coil, to the water in the tube sitting on top of the heating coil. The second is the transfer of heat from the heating coil to the hotplate that sits above the heating coil holding the coffee pot. The third area where heat transfer is applied is in the thermostat. When the thermostat reaches a certain temperature it breaks the circuit and automatically shuts off the coffee maker until it cools down again.

Mass Transfer - how molecules move relative to each other

    There are five subtopics of mass transfer: distillation, evaporation, drying, filtration, and liquid-liquid transfer. The topic that applies to the coffee maker is filtration. Filtration is when solid particles are separated from a liquid. When the water stream is introduced to the coffee grounds the grounds that aren't diluted into the water are filtered out of the coffee by a piece of filter paper.

Process Control - adjusting process variables to maximize product quality and       lower operating costs

    The variables in the coffee maker that need to be adjusted are the amount of water heated and the amount of heat used. The thermostat is used to control the amount of heat used and the amount of water heated.

Materials and Corrosion - how materials respond to mechanical stress and/or chemical attack

    When selecting materials to construct a coffee maker is is important to choose materials that will with stand the heat of the process and materials that will not rust from exposure to water. It is also important to select materials that will properly shield heat sensitive materials from the high temperatures in the coffee maker.

Economics - costs of various design and operating options

    When designing a coffee maker it would be wise to select a design that is energy efficient and cost efficient. It should be designed to minimize the amount of materials used and maximize the efficiency of the process. When choosing tubing and piping the selected materials should be cheap and strong.

Michael Fears

Brian Hopkins