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Home , Coffee filter, Engineering

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WAKE-UP TO ENGINEERING!

R OBERT P. HESKETH* The of Tulsa • Tulsa, OK 74104-3189

Robert Hesketh is an assistant professor at he an does is a mystery to many the University of Tulsa. He received his BS try (1982) at the University of Illinois-Urbana and people. will to explain their work to his PhD (1987) from the University of Dela­ T non-engineers by giving an example of a typical ware. His interests are in the areas of problem that they have solved, but the explanation frequently combustion, fluidization, and multiphase flows, and he teaches freshman engineering, mass includes a description of an engineering process and the transfer, and reactor . At the University equipment contained in the process. So, despite the engineer's of Cambridge, England, he conducted postdoctoral research in fluidization (and enthusiasm in giving his explanation, the non-engineer often cleaned many plugged !). leaves the conversation as puzzled as he was to begin with. , area, and general and organic chemis­ This presents a different approach by using a device try. Additional considerations such as strength of materials, that everyone is familiar with: a coffee . Just about engineering , , and circuits are involved. every home has one on the kitchen countertop. While other appliances or equipment could be used to demonstrate engi­ The department at the University of neering concepts, they are less accessible to the non-engi­ Tulsa uses a coffee machine demonstration to introduce high neer. For example, a home heating and cooling would school students to engineering concepts. Also, for the past be an excellent subject, but it is usually hidden away from four years, a coffee machine demonstration has been used at view and parts of it extend both under the floor and through university recruitment functions and at Engineering Week, the ceilings. Coffee machines, on the other hand, can easily and at an NSF Young Scholars summer it is used to be cut open for closer examination and are inexpensive (you introduce the Young Scholars to a series of engineering can pick one up at a yard sale for next to nothing). laboratory (described later in this article). It could be used in other summer programs, such as the Sum­ The coffee machine (see Figure 1) embodies principles mer Institute at the University of Nevada.1' 1 In recruitment from several engineering disciplines. Chemical and mechani­ activities, where a large number of students visit the depart­ cal engineers design the heaters, the condensers, and the ment, an abbreviated version (20-30 minutes) of the demon­ for multiphase of fluids, and they fabricate stration is given, and it is also used in engineering classes and glass components. Leaching organic compounds such as . Northwestern University uses a coffee from coffee beans uses principles from mass transfer, unique machine example for their freshman engineering classY1 to chemical engineering, while requires concepts from electrical, mechanical, and chemical engineering. Fi­ NOTE; In the following example I use technical terms for nally, engineering decisions are required to select the com­ the benefit of the readers on CEE. But in an actual demon­ ponents of a system and place them within an affordable, stration, I would eliminate the use of words such as leach­ compact unit that can be easily operated by the consumer. ing, condenser, thermocouple, etc. The coffee machine embodies examples of at least eight COFFEE MACHINE DEMONSTRATION unit operations, as can be seen in Figure 1: tank drainage For this demonstration, a coffee machine is altered to through a one-way valve; tubular heater; upward two-phase make all of the components visible to the students. The back flow in pipes; condenser; flow distribution and bypass; leach­ and top are cut out and replaced with clear plastic sheets. In ing and ; and particle size reduction. Underlying addition, the bottom plate is removed. The riser tube that these unit operations are fundamental principles of engineer­ connects the tubular heater to the condenser (see Figure 1) is ing and engineering such as fluid flow (both single replaced with clear plastic tubing. These alterations enable and two-phase), heat transfer, ("engineer­ the students to observe the two-phase flow and steam con­ ing science" and equilibrium), mass transfer, particle size densing as coffee is made. At the start of the demonstration, * Currently at Rowan College, Glassboro NJ 08028-1701 I set up a funnel stand with at least four funnels, which

© Copyright ChE Division ofABEE 1996 require and several receiving flasks . I also have

210 Chemical Engineering Eduction available roasted coffee beans and a coffee grinder. At this point in the demonstration I have made a mess The demonstration begins by introducing the students to on the table and observe that "it would be nice to have the basic fundamentals related to the coffee machine's op­ this process contained in one unit." I tell the students eration. I explain that the engineer must have a working they are now engineers and that we will design a coffee knowledge of basic and engineering science just to begin machine, relating the principles of basic engineering sci­ designing the device. I introduce humor whenever possible ence to the design. and make a mess on the table. I begin with the water . The first questions are: I show the students a bag of gourmet coffee beans and ask What size? Where should it be located with respect to the them, "How do you make coffee?" The usual response is to other components? The next question involves how the wa­ "add water to the beans." So, in a humorous vein, I add cold ter should move from the reservoir to the heater. To help the water to the coffee beans and ask if anyone would like to students answer these questions, I show them a coffee ma­ share my "gourmet coffee." Continuing in this interactive chine on which the back wall of the water reservoir has been mode, I make "coffee" of widely ranging strengths and after replaced by a clear plastic sheet. Examples from around the each step I ask "Who would like to drink my gourmet cof­ , such as water towers and pumping stations, can fee?" The steps I use are listed in Table 1. be given to demonstrate fluid flow. Throughout this sequence, I add discussions of several The next step is the heat exchanger. Open-ended questions subjects of engineering science. such as what source For example, the thermodynam- should be used to heat the wa­ ics topic of phase equilibrium is ter (electric AC or DC, , Condenser and Distributor examined. I present it with the , solar energy, etc.) I.. ~ ypass are discussed. Based on avail­ question, "How hot can you heat .__~- - .. - .. - ,.--;--.. - .. .. ,,...,_._...b •• 0 • •• 0 •••••••••• °.,"8°g o:g .,0 ability, electricity is chosen as water?" Following their re­ 0 0 D O O o ···•~-..--.••._,., the energy source, and I show sponses I ask, "How could you .....--~, ...... get the water hotter than 100°C •• •• • t •.. •• . them the tubular heater at the or 212°F?" Usually there is no ••• bottom of the coffee machine. response to this question, and I Then there are questions on size, ask them to think about how a fluid flow rates, and the desired Coffee Beans pressure cooker works. I show •'••·· outlet temperature of the wa­ them a P-T phase of ' ter. I also show them the one­ •..• way valve at the inlet of the pure water and illustrate that at one-way valve higher pressures water boils at heater that prevents liquid and higher temperatures. Other sub­ gases from flowing back into tubular heater AC Power the reservoir. jects that can be introduced are with two-phase flow given in Table 2. Figure 1. of a coffee machine. I then ask, "How do we get

TABLE 1

St11de11t instr11cti011s Action-- Result-- I . Add water to the coffee Add cold water to the coffee beans. Clear liquid 2. Grind the coffee beans For dramatic/humorous effect, add ground coffee to a funnel without a filter paper present. Dispersed coffee grounds in water Pour cold water over the ground coffee and watch the grounds go into the receiving flask. 3. Use filter paper Separate the coffee grounds from the cold water using filter paper. Slightly colored water 4. Use hot water Make coffee. Brown colored liquid

TABLE2 Courses in the Basic Related to the Coffee Machine

Course Topic Comment -- - -- General Solubility ...... Effect of water temperature on solubility. Organic chemicals ...... The "brown stuff' and . The concept that everything is made of chemicals and the notion that chemicals are always bad as being ludicrous. Thermodynamics Boiling points ...... The effect of pressure on the boiling point. P-T phase diagram of water. Mass transfer Surface area and particle size reduction ...... The concept of increasing surface area on the leaching of chemicals from coffee beans.

Summer 1996 211 water to flow uphill?" The students' usual response is a that allows water to flow through a bole located on the pump-this leads to a discussion of economics since the perimeter of the distributor plate. Water flowing through this addition of a pump would raise the price of the coffee ma­ passes between the filter paper and the plastic filter chine by about $100. In some instances, students suggest support. This device produces the same effect as diluting that if all of the water were converted to steam, a pump your coffee by adding hot water to your cup. would not be necessary-but I point out that this would The next aspect of the design is to determine the materials require larger heaters and condensers than are currently be­ of for the coffee machine. Several options for ing used, again involving additional expense. One creative each of the components are discussed, as well as the glass response has been to place the reservoir and heater above the coffee pot. We bring in aspects of strength of materials, coffee filter so that the water will drain by gravity. This leads temperature limitations, corrosion, and cost of materials. to a discussion of the limitations and the need for Finally, we discuss ways in which the process can be compact when a product. automated. This includes adding timing circuits and ends Upon starting the coffee machine, the students are able to with expensive options such as stereos and . Again, observe two-phase flow upward through the clear plastic basic aspects of marketing and economics are discussed. tube into the condenser. They see that the tubular heater has A summary of the courses and topics related to the coffee three functions: it warms the directly above machine are given in Table 3. Comparing Tables 2 and 3 the heater; it heats the water; and it provides the driving show that at least nine courses in the engineering curriculum force for fluid to flow uphill, similar to a thermosiphon unit. are introduced to the student through this demonstration. The demonstration shows the students that there are often many solutions to a single problem, but the best solution is RECRUITMENT ACTIVITIES often the cheapest. The coffee machine is excellent for recruitment activities. The condenser at the top is demonstrated by replacing the A typical recruiting session includes the coffee demonstra­ opaque plastic with a clear plastic sheet. The students dis­ tion, a tour of the undergraduate and unit opera­ cuss how much of the water must be boiled to move the tions laboratories, and research laboratory demonstrations. liquid to the top of the machine. This can be discovered by The tour of the research laboratory demonstrates the linkage performing experiments in which the amount of steam in the between , research, and as well as illus­ riser is varied and the total liquid flow rate is measured. trating undergraduate research opportunities. This, in tum, introduces the question of what fluid flow rate is needed for proper operation of the leaching unit. Would Typically, one of the best laboratories to demonstrate the maximum fluid flow rate flood the condenser or leaching chemical engineering principles is a flow visualization labo­ unit and cause dangerously hot water to flow out of the ratory. It contains many examples of familiar devices. For machine? The students can see that each unit within the example, everyone drives a car with a catalytic converter, coffee machine is interrelated; outputs from one unit are but they have not seen it. A brief review of how a catalytic inputs to another unit. In addition, aspects of safety in engi­ converter is made and how it works is given, followed by a neering design are considered. demonstration of how the small 1-mm square channels are coated with catalyst. Using a high-speed video camera, the The next observable unit operation is unique to the field of 13 41 students can observe the two-phase flow coating process. · chemical engineering: leaching. The need for a distributor is In another , the relationship of fluid to introduced by asking, "What happens if all the water flows the of a heat exchanger fin is demonstrated by down one side of the coffee grounds?" Again, questions of using advanced laser Doppler anemometry systems. filter size and shape are discussed since they determine both the amount of coffee grounds that can be loaded and the TABLE3 residence time of the water in the coffee grounds. Demon­ ChE Courses Related to the Coffee Machine strations of the effect of particle size and bed height on fluid flow rates can be given using and sand particles in Course Principle several of the funnels. ...... tank drainage, two-phase flow , flow through a bed of particles and filter paper Many coffee machines have a lever that adjusts the strength Heat Transfer ...... design of heaters and condensers of the coffee. How is this achieved? Typical student re­ Unit Operations ...... one-way valve; size-reduction equipment, filtration sponses suggest the examples of particle size, water tem­ perature, and contact time of the water with the coffee par­ Mass Transfer ...... leaching evaporation and fl ow distributors ticles, but none of those methods are used. Instead, the Properties of Materials ...... materials of construction strength of the coffee is altered by having a portion of the Circuits or Advanced ... timers and switches water bypass the coffee grounds and pass directly into the Economics ...... cost of engineering design and construction of a receiving vessel. This is achieved by using a lever and slide coffee machine

212 Chemical Engineering Eduction In both of the above experiments, the students can relate ene chloride and supercritical fluids. We have taken scan­ the principles of two-phase flow and heat transfer of the ning electron micrographs of coffee beans and filter paper at coffee machine to that affect their daily various stages of brewing. lives. This tour usually ends by capturing the image of a student volunteer on video, and then the image is digitized SUMMARY and patterns are enhanced with a dazzling display of colors. We have used the coffee machine for undergraduate re­ This laboratory is usually a highlight of the tour! cruitment and for our engineering summer camp, and I have also used it as part of a demonstration day in the mass NSFYOUNGSCHOLARSSUMMERPROGRAM transfer class. Using dynamic simulators (such as HY SYS), The Young Scholars program is a hands-on summer camp the coffee-making process could also be modeled as a to introduce engineering to students entering the 9th and short design project in a senior class. The coffee ma­ 10th grades. The experiments in this camp are designed to chine, familiar to everyone, is an effective tool for moti­ stimulate the students' interest in the fields of science and vating students in engineering. engineering by involving a device that is familiar to them: ACKNOWLEDGMENT the coffee machine. Each of these experiments is designed to I would like to thank Martin Abraham, John Henshaw, be challenging, but not overwhelming, to the student. In Ramon Cerro, Christi Patton, and Brenda McLaury for summary, these activities their helpful suggestions. Funding for the Engineering • Demonstrate the role of laboratory experiments in the Summer Camp is through the NSF Young Scholars Pro­ engineering decision-making process gram ESI-9255956. • Show the interrelationship of engineering and science required for the design and fabrication of a si ngle product REFERENCES • Give stimulating and challenging experiments that relate the 1. Bayles, T.M., and F.J. Aguirre, "Introducing High School laboratory experiments to a consumer product with which Students and Science Teachers to Chemical Engineering," Chem. Eng. Ed., 26(1), 24 (1992) most students are familiar. 2. Miller, W.M., and M.A. Petrich, "A Novel Freshman Class to Introduce ChE Concepts and Opportunities," Chem. Eng. In these experiments, we use equipment from the Ed., 25(3), 134 (1991) undergradute and graduate laboratories. A selection of ex­ 3. Kolb, W.B., A.A. Papadimitriou, R.L. Cerro, D.D. Leavitt, periments that have been used in previous Engineering Sum­ and J .C. Summers, "The Ins and Outs of Coating Monolithic mer Camps is given in Table 4. Structures," Chem. Eng. Prag., February, p. 61 (1993) 4. Thulasidas, T.C., M.A. Abraham, and R.L. Cerro, "Bubble­ We also discuss the chemical composition of a coffee Train Flow in Capillaries of Circular and Square Cross bean, the roasting process, and using methyl- Section," Chem. Eng. Sci., 50(2), 183 (1995) 0

TABLE4 Engineering Laboratory Experiments

Principle Experimental Goals E11gi11eeri11g Equipment Particle Size Establish the relationship of gri nding time and grinder type to the size Optical , sieves, coffee grinders, stopwatch, of coffee grounds produced while exploring techniques for analyzing and funnels particle size. Examine relationship between particle size, pressure drop, and fluid flowrate Extraction of Coffee Determine the effect of water temperature, particle size, and filter type UV spectrophotometer, electronic balance, grinder, stop­ on the strength of coffee produced watch, coffee machines, filter paper Heat Transfer Examine conduction, convection, and radiation. Determine the effect Thermocouples, insulation, rods, heaters, and mixers of insulation on heat loss Fluid Flow Determine effect of tube length, tube diameter, and liquid height on tank Tanks, tubes, measuring tape, compressed gas, rotameter, drainage time and the length of a free jet. Simulate the riser in the graduated cylinders, stopwatch coffee machine using gas phase introduced at bottom of vertical tube. Timer construction a timing device to turn a circuit on and off Electrical circuit components: , potentiometer, re­ sistors, LED, capacitors, peizoelectric disk, circuit board Digital & Robotics Examine digital control and automation Oscilloscope, robotic cars with paper card reader Fracture of Materials Examine and compare the strength of glass, metal and Mechanical testing equipment Polymer Chemistry Examine the production of polymers used in making plastics Molds, polymers Organic Chemistry Measure the concentration of caffeine as a function of time in a HPLC, percolator, and stopwatch percolator coffee machine Computer-Aided Process Control Investigate liquid control using a computer Tanks, valve, , pressure transducer and computer

Summer 1996 213