Team 17: Clean Coffee

Paul Bootsma, Kirk Brink, Chris Greaves, Erik Karlson

ENGR 339/340 Senior Design Project

May 10th, 2018

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© 2018, Team 17 and Calvin College

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1. Executive Summary

Senior Design Team 17: Clean Coffee, of Calvin College Engineering, examined the scaling effects for a

coffee roasting exhaust separating device. This device operates by combining cyclonic separation and water

jets to capture particulates and pollutants. A 450 CFM model of this product is currently produced and sold

by Vortx Kleanair Systems, however, the company is looking to scale this technology up for higher flow

rates. The team developed an analytical model of the system, using small scale testing and research. This

model was applied to the existing system dimensions to find an optimized system geometry with regards to

pressure loss, fabrication costs, practical concerns, and separation behavior. Based on the results of these

calculations and evaluations, the team recommends modifying the existing 450 CFM design to

accommodate 800 CFM by enlarging the vortex’s top exit pipe diameter by 40% while leaving the

remaining geometries unchanged.

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Table of Contents 1. Executive Summary……………………………………………………………………..…………….. 3

2. Table of Figures…………………………………………………………………………..…..…..…… 5

3. Table of Tables……………………………………………………………………………...…...……. 6

4. Narrative………………………………………………………………………………..……………....7

5. Background…………………………………………………………………………………..………....8

6. Problem Description………………………………………………………………………….……….10

7. The Team……………………………………………………………………………………….……..11

8. Budget…………………………………………………………………………………………….…...12

9. Methods ……………………………………………………………………………………………....13

9.1. Modeling Methods ……………………………………………........................................13

9.2. Optimization Methods…………………………………………………………………...16

10. Sensitivity Studies…………………………………………………………………………………….18

10.1. Optimization Variables…………………………………………………………………..18

10.2. Cut diameter……………………………………………………………………………...19

10.3. Pressure Loss…………………………………………...................……………………..19

10.4. Cost………………………………………………………………...…………………….20

11. Testing……………………………………………………………………………...…………………22

12. Results and Optimizations…………………………………………………………...………………..25

12.1. Optimization Bounds……………………………………………………...……………..25

12.2. Trade-Offs…………………………………………………………………...…………...25

12.3. Cost-…………………………………………………………………………...…………25

12.4. Cut diameter……………………………………………………………………...………26

12.5. Pressure Loss……………………………………………………………………..……...27

13. Final Proposal…………………………………………………………………………………...…….28

14. Project Impact……………………………………………………………………………...………….30

14.1. Sustainability Study………………………………………………………..………..…...30

14.2. Economic Viability Study………………………………………………….......………...30

15. Conclusion……………………………………………………..……………………………………...31

16. Acknowledgments……………………………………………………………………………..……...32

17. Appendices...………………………………………………………………………………….………33

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2. Table of Figures Figure 1: Cyclonic Separation…………………………………………………………………………..8

Figure 2: Block Diagram of Optimization Process…………………………………………………….17

Figure 3: Key Cyclone Geometries …………………………………………………………………...18

Figure 4: Cut Diameter Sensitivity Analysis……………………………………………………….….19

Figure 5: Pressure loss Sensitivity Analysis……………………………………………………….…..20

Figure 6: Cost Sensitivity Analysis…………………………………………………………………....21

Figure 7: Sonofresco 1 lb Roaster, and Cyclone Separator…………………………………………….22

Figure 8: Pressure Drop Test Setup………………………………………………………………..…..23

Figure 9: Pressure Drop Validation…………………………………………………………………....24

Figure 10: Roasting Test Setup………………………………………………………………………..24

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3. Table of Tables

Table 1: Itemized Budget……………………………………………………………………...………12

Table 2: Cyclone Geometry Variables with Description………………………………………...…….18

Table 3: Cost Values for Optimization………………………………………………………………..20

Table 4: Optimization Bounds…………………………………………………………...……………25

Table 5: Cost Optimization Dimensions………………………………………………………………26

Table 6: Cost Optimization Key Parameters…………………………………………..………………26

Table 7: Cut Diameter Optimization Dimensions………………………...…………………………...26

Table 8: Cut Diameter Optimization Key Parameters…………………………………………………27

Table 9: Pressure Loss Optimization Dimensions………………………………………….………….27

Table 10: Pressure Loss Optimization Key Parameters……………………………………….………27

Table 11: Balanced Optimization Dimensions……………………………………….….…………….28

Table 12: Balanced Optimization Key Parameters…………………………………………………….28

Table 13: Balanced Dimensions Compared to 450 CFM Model………………………………………29

Table 14: Balanced Optimization Compared to 450 CFM Model………………………………….…29

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4. Narrative It’s another beautiful sunny spring day in West Michigan. A local craft coffee roaster is starting up for the

day, preparing his roaster for business. He looks over his roaster, removing any loose chaff and wiping it

down to clear out any leftover oils from the previous roast. Out of habit he makes his way toward the

ventilation system to check for creosote build up. He turns and laughs to himself as he remembers that the

old afterburner is gone and has been replaced with a Vortx Kleanair filter. That conical filter removed any

worry of chimney fires that would occur due to buildup from using an afterburner. It also cut back his

expenses, due to the the amount of natural gas he saved from not having to keep a pilot light burning. With

the money he saved he was able to buy higher quality beans. Ready to begin, he fired up his roaster and and

started his meticulous work.

Directly outside, an elderly couple sits on a park bench, watching their grandchildren playing - trying to

climb up the slide. They hear the coffee roasting process begin. Expecting to see a plume of smoke emerge

from the stack, they are surprised to see a thin wisp emerge and quickly dissipate into the blue sky. They

say to each other, “How great it is, that we don’t have to smell that awful smoke anymore”. The children

go on playing, oblivious to the previous alternative. This is life for them, free to play whenever they like

and free from pollutants due to coffee roasting.

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5. Background Coffee roasting produces exhaust containing chaff, smoke, and oil vapors. These need to be separated so

that they are not released into the air. The roasting industry commonly uses cyclone separators to remove

the chaff, and afterburners to burn off smoke and oils from the exhaust. These afterburners use

nonrenewable resources such as natural gas, increasing the carbon emissions associated with coffee

roasting. They also cause creosote buildup within the chimney, which can lead to chimney fires without

regular maintenance. The afterburners also produce an unpleasant odor that permeates the surrounding

neighborhood, resulting in complaints for the roaster.

Vortx Kleanair Systems, the team’s client, has begun to market a cyclone separator solution: the Vortx

Ecofilter, which separates both the coffee-bean chaff and oils without using an afterburner. They received

the production and distribution rights for the model from a foreign company who lost interest in developing

the product. Vortx’s marketing has been successful due to the economic and environmental benefits of

removing the gas afterburner from the process.

Cyclone Separators

Figure 1: Cyclonic Separation

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In essence cyclone separators are accelerated settling devices, or open flow centrifuges. Solid particulates

have higher density than air, and accordingly sink downward in air. However, because these particles are

so small they experience high drag forces relative to the downward pull of gravity. This is why dust takes

a long time to settle in a room, and will not settle in a room with air currents. Inside of a vortex separator,

the flow is forced to rapidly rotate. The rotational acceleration experienced by the flow is similar to the

field of gravity but stronger, and causes the denser fluid and particles to be moved outward to the walls.

From the walls these separated particles slide down and out of the separator unit, while the clean air

spirals up and out of the gas outlet tube.

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6. Problem Description The Vortx EcoFilter is a water assisted cyclone separator for treating coffee roasting exhaust. It is rated for

treating a 450 CFM exhaust flow. This makes it best suited for smaller commercial coffee roasters, who

typically use 8-10 kg drum roasters. Vortx Kleanair Systems is looking to produce and market larger

separators to sell to higher volume sections of the roasting industry. However, they do not have the ability

to redesign or rescale the product because they received their design from a source that is no longer active.

Therefore, Team 17 was given the task to determine how the EcoFilter works, and adapt the working design

to larger capacities. The scope of this problem involves investigating the behavior of the current design, as

well as determining what modifications or scaling are necessary in order to treat the 800 CFM exhaust

output of a 15 kg coffee roaster.

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7. The Team The team consisted of four senior mechanical engineering students. Additionally, the team was surrounded

by resources including a faculty advisor, the client, and a coffee roasting consultant to advise the team and

guide their project.

Paul Bootsma has a wide range of engineering experience from working on a factory floor to

performing vibrations research. He brought strong conflict resolution and communication skills to

the team which he gained as a Resident Assistant during the 2016/17 school year. His research

experience was valuable in the design of experiments and during the testing process.

Kirk Brink interned at Unist Inc. in the Summer of 2017 where he designed spray nozzle

components for metal cutting and forming lubrication systems. In the summer of 2016, he interned

at Blackmer Pump, where he worked in the research and development lab testing sliding vane

pumps and gas compressors. Kirk has the most SolidWorks and graphic design experience and

covered the modeling portion, including creating prints and rendering high quality 3D images.

Chris Greaves was the team sustainability expert and knows what questions to ask regarding

emissions. He also has the most experience with the coffee roasting process. Upon graduation he

was commissioned as a 2nd Lieutenant in the Army National Guard. While at Calvin he spent a

summer doing research on heating alternatives and solutions with the engineering department.

Erik Karlson also completed minors in mathematics and business. He spent the summer of 2017

working at Robert Bosch Fuel Systems LLC as an intern with development engineering for large

engine fuel pumps. His mathematical background combined with his thermodynamics based

internship helped with the thermodynamic analysis of airflow through the vortex separator.

Prof. Renard Tubergen was the faculty advisor for this project. He is a mechanical engineering

professor at Calvin College and he also runs his own consulting firm, Gumbo Product

Development. He has previously consulted on cyclonic separation in coffee roasting and has a

positive relationship with the client. Having worked in industry and academic environments, he has

experience in transitioning from classroom knowledge to industry knowledge.

Ron Kleist was the team’s client and the co-founder of Vortx Kleanair Systems. He is a veteran of

the coffee roasting industry, having worked for previous coffee companies such as Loring Smart

Roast. His knowledge of the industry, and connections within the industry benefited the team on

this project. He has already provided the team with a 1 lb coffee roaster to use for testing.

Tyler Greenway is the coffee roasting advisor for the team. Tyler is a hobby roaster who is very

knowledgeable in the art of coffee roasting. He assisted the team in producing a variety of high

quality coffee roasts.

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8. Budget The allocated budget for this project was $600. The final budget of this project was $210, one third of the

allocated budget. Table 1 shows the final itemized budget.

Table 1. Itemized Budget

Item Cost

Cyclone separator $20.00

LPG Hose $35.00

Dryer Hose & Hardware $10.68

Water Spray Fittings $34.81

Cyclone Separator $19.99

Cyclone Separator $19.99

Shop Vac $69.00

Total $209.47

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9. Methods

9.1. Modeling Methods

The analytical model uses the Muschelknautz method of modeling. This empirical method of modeling

cyclone separators has been found to predict pressure loss with low residual errors. A walkthrough of the

Muschelknautz method in the textbook, “Gas Cyclones and Swirl Tubes,” provided a guide for modeling

as well as example problems to verify the analytical model.

In order to create a functional analytical model which could be used with the available knowns, certain

assumptions were necessary. The first and most crucial assumption involved the water droplets from the

spray nozzles. For this model it was assumed that the water droplets that were emitted by spray nozzles

would act the same as particles of similar density and size in the incoming exhaust flow. The primary driver

of particle separation utilizes the density difference between the fluid and the separated material. As the

density of the coffee particulates is very close to the density of water relative to the density of air, this

assumption can be reasonably explained.

The other major assumption in the model involves the contraction of the flow volume due to the exhaust

cooling from the water mist. In reality, as the exhaust flow cools it will contract in volume and drop in

pressure and velocity. However, modeling this transient and dynamic flow process would have been

impossible without detailed data from within the device. As there was neither the data, nor a device

available to perform these tests, it was not possible to account for this in the analytical model. However,

comparing the calculation results at different flow temperatures showed that a cooler flow temperature

would yield a smaller cut diameter, but higher pressure drop from frictional/irreversible losses. Since the

cut diameter is the most crucial element of system performance it was better to err on this side of results,

and use the conservative results for the cut diameter.

In order to predict the separation behavior of a given cyclone, the Muschelknautz method utilizes several

geometric relationships, key ratios between components of velocity, and multiple non-dimensionalized

numbers.

The first geometric relationship is the constriction coefficient 𝛼. This factor is used in calculating how the

flow velocity will change as it enters the cyclone body and begins to spin. It is defined as:

𝛼 =1

𝜉[1 − √1 + 4 [(

𝜉

2)

2−

𝜉

2] √1 −

(1−𝜉2)(2𝜉−𝜉2)

1+𝑐𝑜] [Equation 1]

Where

𝜉 =𝑏

𝑅 [Equation 2]

And Co is the solid loading rate(kg particles/kg air)

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This constriction factor can be used to find the velocity of the rotating flow at the outer wall. This is

performed by assuming that rotational speed at the inlet is related to the rotational speed of the flow at the

wall by the constriction factor. This yields the following equation:

𝑣𝜃𝑤 =𝑣𝑖𝑛𝑅𝑖𝑛

𝛼𝑅 [Equation 3]

The axial flow at the wall is calculated using an approximation of conservation of flow volume. This

requires dividing the exhaust flow rate by the cross sectional area perpendicular to the vertical axis.

However, the available area between the outer wall and the inner column of upward spiraling air is not

constant. As the outer radius decreases in the cone section of the body, so does the available flow area.

Therefore, it is necessary to define a geometric mean radius:

𝑅𝑚 = √𝑅𝑥𝑅 [Equation 4]

The axial flow area can be approximated as the area of the ring defined by the outer radius and the geometric

mean radius. Accounting for a ten percent flow rate loss to “short circuiting” of the flow near the vortex

finder, and applying a flow volume balance, the definition becomes:

𝑣𝑧𝑤 =0.9𝑄

𝜋(𝑅2−𝑅𝑚2)

[Equation 5]

Having described the flow velocity, it is necessary to determine the friction encountered by the exhaust

flow. Before this can be accomplished, two non-dimensional parameters must be found to characterize the

flow regime. These parameters are the Reynolds number and the Froude number. The Reynolds number

describes the fluid behavior near the boundary layer, and is accordingly crucial in finding the friction

encountered by the gaseous portion of the exhaust. The Froude number describes the balance between the

flow momentum and the gravitational/buoyant forces acting on the suspended particles in the flow. It is

used to find the portion of the friction arising from particles interacting with the walls. These two values

are calculated as follows:

𝑅𝑒𝑅 =𝑅𝑖𝑛𝑅𝑚𝑣𝑧𝑤𝜌

𝐻𝜇 [Equation 6]

𝐹𝑟𝑥 =𝑣𝑥

√2𝑅𝑥𝑔 [Equation 7]

As mentioned above, the friction factor is composed of air and solids portions. The air portion of the friction

factor is composed of two sub-portions. There is a smooth wall contribution, and a portion that accounts

for the surface roughness of the walls.

𝑓𝑎𝑖𝑟 = 𝑓𝑠𝑚 + 𝑓𝑟 [Equation 8]

The equations used to find these air friction factors are based off of empirical correlations. There are

different friction factor equations for different types of cyclones. The Kleanair Vortx EcoFilter uses a hybrid

design incorporating both conical and cylindrical sections for the separator body. There exist different

correlations for these two section types.

For Conical Cyclones:

𝑓𝑠𝑚 = .323𝑅𝑒𝑅−.0623 [Equation 9]

𝑓𝑟 = (log (1.60

𝑘𝑠𝑟𝑎

−.000599)

2.38

)

−2

(1 +2.25×105

𝑅𝑒𝑅2(

𝑘𝑠𝑟𝑎

−.000599).213)

−1

[Equation 10]

And for Cylindrical Cyclones:

𝑓𝑠𝑚 = 1.51𝑅𝑒𝑅−1.0 [Equation 11]

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𝑓𝑟 = (log (1.29

𝑘𝑠𝑟𝑎

−.000599)

2.59

)

−2

(1 +2.14×105

𝑅𝑒𝑅1.64 )

−1

[Equation 12]

These two pairs of equations are averaged together based on the height of each respective section. For

example, if the two sections are of equal height, then it is a simple average of the two sets of results. The

relative surface roughness term in the denominator must be equal to at least .0006, or else this value must

be substituted for the calculations to be accurate. For smooth sheet steel cyclones of the size considered in

this study, this substitution is always required.

Now that the air portion of the friction factor has been found, it can be combined with the solids friction

factor to establish an overall friction factor:

𝑓 = 𝑓𝑎𝑖𝑟 + .25 (𝑅

𝑅𝑥)

−0.625

√𝜂𝑐𝑜𝐹𝑟𝑥𝜌

𝜌𝑠𝑡𝑟 [Equation 13]

However, 𝛼, the separation efficiency is still unknown. It must be determined using a system of equations

which simultaneously determine friction factor, cut diameter, central vortex rotational velocity, and

separation efficiency. These equations will be explored shortly. The area where the friction occurs is the

internal surfaces of the device across which the flow passes. The total internal surface area can be tabulated

using:

𝐴𝑅 = 𝐴𝑟𝑜𝑜𝑓 + 𝐴𝑏𝑎𝑟𝑟𝑒𝑙 + 𝐴𝑐𝑜𝑛𝑒 + 𝐴𝑣𝑜𝑟𝑡𝑒𝑥 𝑡𝑢𝑏𝑒 [Equation 14]

𝐴𝑅 = 𝜋 [𝑅2 − 𝑅𝑥2 + 2𝑅(𝐻 − 𝐻𝑐) + (𝑅 + 𝑅𝑑)√𝐻𝑐

2 + (𝑅 − 𝑅𝑑)2 + 2𝑅𝑥𝑆] [Equation 15]

Now, it is possible to determine how the small rapidly rotating column of air at the center of the device will

behave. The rotational speed of this central column will be as follows:

𝑣𝜃𝐶𝑆 = 𝑣𝜃𝑤𝑅 𝑅𝑥⁄

1+𝑓𝐴𝑅𝑣𝜃𝑤√𝑅 𝑅𝑥⁄

2𝑄

[Equation 16]

This equation appears very complex, but is easier to understand when broken down into individual

relationships. The rotational speed of the inner column will increase directly when the flow rate or rotational

speed of the flow by the wall increase, and will decrease when the relative size of the central column grows

or when more friction is encountered. The rapid rotation of this central column causes the individual units

of fluid and particulates to experience centrifugal buoyant forces relative to its surroundings. This is what

drives the separation. Combining the viscous drag forces and buoyant separating forces offers a force

balance on suspended particles. This balance determines which particles are likely to be separated by the

cyclone. The particle diameter at which at least half of particles that size or larger will be seperated is known

as the cut diameter. The cut diameter is an important metric in describing the separation performance of a

cyclone separator.

It’s equation is:

𝑥50 = √18𝜇(0.9𝑄)

2𝜋(𝜌𝑝−𝜌)𝑣𝜃𝐶𝑆2 (𝐻−𝑆)

[Equation 17]

As mentioned previously, the buoyant forces (due to differences in density) are balanced against the viscous

drag forces. The term Q/(H - S) captures the time it takes for the flow to travel from the bottom of the device

to the opening of the vortex finder tube. This time for separation is known as the residence time and is

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crucial for determining what fraction of separable particles will be removed. The cut diameter can be

applied to a incoming particle distribution to find the separation efficiency. This is done using bins of

particle size and finding individual efficiencies for each particle size range, and then averaging these values

by the mass fraction each bin contains. The individual calculations, and the total summation are written as:

𝜂𝑖 =1

1+(𝑥50𝑥𝑖

)5 [Equation 18]

𝜂 = ∑ 𝜂𝑖 ×𝑁𝑖=1 Δ𝑀𝐹𝑖 [Equation 19]

These equations yield a curve with logistic growth that can be used to quantify the separation efficiency at

a given particle diameter, as well as giving a bulk description of separator performance under a given load.

The slope exponent of five is normally selected for use with smooth-walled cyclone, and is appropriate for

this design constructed of stainless steel.

Lastly, pressure drop across the system may be modeled. However, the pressure drop results are generally

more deviant from true experimental values than are cut-diameter results. Similar to the friction factor, the

pressure loss consists of two separate components. These two parts are the pressure loss resulting from

friction with the cyclone body, and the pressure losses that occur in the central upward vortex. The body

pressure loss is simply a calculation of the frictional work performed by the flow divided by volume:

Δ𝑝𝑏𝑜𝑑𝑦 =𝑓𝐴𝑅𝜌(𝑣𝜃𝑤𝑣𝜃𝐶𝑆)1.5

2×0.9𝑄 [Equation 20]

The pressure loss across the vortex finder/outlet results mostly from the loss of the energy that was used to

create the swirling of the central vortex, since this flow energy is not recoverable. However, the equation

itself for determining this pressure loss is mostly empirical, and uses the rotational velocity and outlet

velocity to estimate this loss.

Δ𝑝𝑥 = [2 + (𝑣𝜃𝐶𝑆

𝑣𝑥)

2+ 3 (

𝑣𝜃𝐶𝑆

𝑣𝑥)

4

3]

1

2𝜌𝑣𝑥

2 [Equation 21]

Finally, these two components can be summed to yield the final system performance descriptor, total

pressure drop.

Δ𝑝 = Δ𝑝𝑏𝑜𝑑𝑦 + Δ𝑝𝑥 [Equation 22]

9.2. Optimization method

Since Vortx currently has a working system which operates at 450 CFM, the dimensions and predicted

particle loading of the 450 CFM model were implemented in an analytical model of the Muschelknautz

Method. The analytical model was constructed in a numerical solver EES (Engineering Equation Solver.)

The separation behavior was drawn from the model and used as desired outcomes for the 800 CFM

optimization. The desired separation behavior could then be used as an input to the system and the new

geometric properties could become the output variables (Figure 2).

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Figure 2: Block Diagram of Optimization Process

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10. Sensitivity Studies Before running optimizations, each dimension was varied independently within its valid range to determine

the sensitivity with regards to cut diameter, cost, and pressure loss. These sensitivity studies give insight on

the critical dimensions for optimization.

10.1. Optimization Variables Only geometric variables were altered in the optimization process. These independent variables are listed

with descriptions in Table 2 below and can be seen in Figure 3.

Table 2: Cyclone Geometry Variables with Description

Variable Description

B Inlet Diameter

R Cone Radius

Rx Exit Radius

Rd Particle Drop Radius

S Exit Pipe Depth

H Cyclone Height

Hc Cone Height

Figure 3: Key Cyclone Geometries

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10.2. Cut Diameter

Cut diameter is the key parameter which represents separation efficiency. The smaller the cut diameter, the

better separation of small particles. Cut diameter is most sensitive to inlet diameter, exit diameter, and depth

of vortex finder tube (refer to Rx, S and b in Figure 4 below)

Figure 4: Cut Diameter Sensitivity Analysis

10.3. Pressure Loss

To control pressure drop, the size of the openings in and out of the system are particularly important (refer

to Rx and b in Figure 5 below). This is sensible, as pressure loss occurs due to the constriction of airflow.

The fact that the relationship between Rx and pressure loss is opposite to that of the relationship between

Rx and cut diameter shows that these variables will have functional tradeoffs during optimization.

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Figure 5: Pressure loss Sensitivity Analysis

10.4. Cost

The production cost evaluation was based on a semi-incremental system. Only the components which would

be modified had their costs evaluated. This allowed for cost models to include only geometries that would

be altered. It also allowed for the less direct manufacturing costs to be ignored, as the same processes would

be used. The cost was modeled by associating square footage of 304 stainless sheet steel and inches of weld

seam each with a respective cost (Table 3). Then, the areas and lengths required were calculated within the

model so that the cost could be determined from material used. As seen in Figure 6, as the dimensions

decrease, the cost of production decreases as well due to less material use and shorter weld seams.

Table 3: Cost Values for Optimization

Item Cost Units

14 Gauge SS 0.07 $/in2

11 Gauge SS 0.12 $/in2

Welds 2.00 $/in

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Figure 6: Cost Sensitivity Analysis

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11. Testing Small scale testing was performed to validate the analytical model, and develop practical knowledge about

the coffee roasting process. Testing was primarily performed on a fluid bed roaster connected to a small

Cyclone separator. The roaster has a one pound roasting capacity and is manufactured by Sonofresco. The

cyclone separator was a commercially available separator primarily used for dust collection (see both in

Figure 7 below.)

Figure 7: Sonofresco 1 lb Roaster (Left), and Cyclone Separator (Right)

The pressure drop measurements across the cyclone were used to validate the analytical model. The

observed pressure drop across the cyclone could be compared to the pressure drop predicted by the

analytical model. The analytical model predictions required data for the cyclone geometry and air flow

through the system. The air flow was determined from measuring the centerline velocity of the exit stream

using a hot wire anemometer. The pressure drop was measured with a digital manometer. A picture of the

pressure drop test setup is shown in Figure 8 below.

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Figure 8: Pressure Drop Test Setup

The pressure drop measured through the cyclone ranged from 220 Pa to 230 Pa and the exit velocities

ranged from 8.7 m/s to 9.3 m/s. When compared to the analytical model, the experimental data fell within

20% of the predicted value. In fluid dynamics it is not uncommon for widely used models to diverge from

actual results by as much as 30%. By this measure, the use of the Muschelknautz Method in the context of

this project was validated (Figure 9).

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Figure 9: Pressure Drop Validation

The roasting setup consisted of the Sonofresco roaster connected to a cyclone with water spray jets. The

roasting setup is shown in Figure 10 below. Roasting coffee with the vortex separator attached did not

provide significant numerical data, but provided a visual confirmation of chaff and smoke separation with

air stream cooling.

Figure 10: Roasting Test Setup

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12. Results and Optimizations The system was optimized for cost, cut diameter and pressure drop, respectively, before determining a

balanced optimization. Each optimization was compared to the proposed design for the 800 CFM model as

this project is providing an alternative to that proposition. A visual representation of optimized geometries

by objective variable can be seen in Appendix A2

12.1. Optimization Bounds

In order to set bounds on optimizations, the allowable movement of the most crucial separation behavior

metric, cut diameter was established. By specifying a max allowable cut diameter of 6.5 microns, it was

ensured that the separation efficiency at the 450 model cut diameter of 5.5 microns would not fall below

30%. This bound rules out the client’s current proposed design for the 800 CFM exhaust flows. Through

studying both current predicted pressure for the 450 model and examining typical systems, a max allowable

pressure loss of 1400 Pa across the system was estimated. The individual geometric bounds were set by

studying the existing and proposed system geometries and considering what range of values were

reasonable and achievable.

Table 4: Optimization Bounds

H(m) Hc(m) R(m) Rd(m) Rx(m) S(m) x50(µm) ∆P(Pa)

Lower .75 .3 .15 .04 .04 .05 0 0

Upper 1.75 1.2 .4 .14 .16 1 6.5 1400

12.2. Trade-Offs

When performing optimizations for a final design solution, trade-offs had to be made between the three

performance objectives of the system: cut diameter, cost, and pressure drop. These trade-offs are visibly

apparent in the in the sensitivity studies. The conditions which allow for a better cut diameter are in conflict

with those that reduce the pressure drop of the system. The team decided that maintaining the separation

performance of the 450 CFM model was critical. Minimizing cost and pressure loss was desirable, but

marginal increases could be justified.

12.3. Cost

As predicted through the sensitivity studies, the cost optimization resulted in a system in which most

component dimensions were decreased until the upper limit of pressure was reached (Table 5). The height

of the cone was the only dimension that was increased. This was to keep the system within the specified

pressure bounds while keeping material usage to a minimum. When optimized for cost the system can be

produced for $360 less than the proposed 800 CFM model. However, through this decrease in cost, the

system behavior regarding cut diameter and pressure drop reaches the upper limits of the optimization

criteria (Table 6).

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Table 5: Cost Optimization Dimensions

Variable Base Case Optimized % Difference

R[m] 0.2794 0.15 -45%

Rx[m] 0.127 0.07 -47%

S[m] 0.3937 0.05 -87%

H[m] 1.314 1.03 -22%

Hc[m] 0.8128 1.03 27%

Rd[m] 0.0762 0.07 -7%

Table 6: Cost Optimization Key Parameters

Base Case Optimized +/-

Cost [$] 761.8 399.8 -48%

x-50 [µm] 7.5 6.5 -14%

dP [Pa] 482 1400 190%

12.4. Cut Diameter

The optimization for cut diameter had the effect of reducing the length of the vortex finder tube into the top

of the separator by 87% to hit the lower bound. At the same time, it pushed the pressure loss to the upper

bound. These characteristics indicated that this would not be an acceptable optimization, however the cut

diameter was also reduced by 55%, from 7.5 µm to 3.4 µm. While lowering cut diameter is beneficial, this

result exceeds the performance of the 450 CFM model to such an extent that the magnitude of the trade-off

makes it undesirable.

Table 7: Cut Diameter Optimization Dimensions

Variable Base Case Optimized % Difference

R[m] 0.2794 0.28 0%

Rx[m] 0.127 0.1194 -6%

S[m] 0.3937 0.05 -87%

H[m] 1.314 1.75 33%

Hc[m] 0.8128 0.84 3%

Rd[m] 0.0762 0.84 28%

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Table 8: Cut Diameter Optimization Key Parameters

Base Case Optimized +/-

Cost [$] 761.8 865.5 14%

x-50 [µm] 7.5 3.4 -55%

dP [Pa] 482 1400 190%

12.5. Pressure Loss Optimizing for reduced pressure loss was limited. The upper limit for cut diameter prevented any significant

change in dimensions, causing the optimization to settle near the base case. The pressure still increases

from the base case due to cut diameter constraints, but is the lowest observed through optimizations at only

41% increase.

Table 9: Pressure Loss Optimization Dimensions

Variable Base Case Optimized % Difference

R[m] 0.2794 0.2868 3%

Rx[m] 0.127 0.1125 -11%

S[m] 0.3937 0.3936 0%

H[m] 1.314 1.314 0%

Hc[m] 0.8128 0.8128 0%

Rd[m] 0.0762 0.07602 0%

Table 10: Pressure Loss Optimization Key Parameters

Base Case Optimized +/-

Cost [$] 761.8 765.9 1%

x-50 [µm] 7.5 6.5 -13%

dP [Pa] 482 679 41%

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13. Final Proposition The balanced optimization was aimed at maintaining variables within acceptable operational conditions

while minimizing cut diameter, pressure drop, and cost. A single objective function was not used, but

suitable results were recorded during optimizations of each of the other objectives. From these acceptable

results, a single optimization was chosen due to a well balanced cut diameter, pressure drop, and cost result.

Table 11: Balanced Optimization Dimensions

Variable Base Case Optimized % Difference

R[m] 0.2794 0.2485 -11%

Rx[m] 0.127 0.1429 12%

S[m] 0.3937 0.3302 -16%

H[m] 1.314 1.138 -13%

Hc[m] 0.8128 0.6998 -14%

Rd[m] 0.0762 0.0762 0%

Table 12: Balanced Optimization Key Parameters

Base Case Optimized +/-

Cost [$] 761.8 667.4 -12%

x-50 [µm] 7.5 5.5 -26%

dP [Pa] 482 912.6 89%

This optimization was also selected due to how it compared with the 450 CFM design. The 800 CFM design

provides similar cut diameter with an increase in size of 0.1 microns or 3% for a cost increase of around

$30. There is an increase in pressure loss of 57% which is within the limits of optimization and can be

countered with the use of a fan, either in the chimney or in the roaster. A major benefit of this design comes

in ease of manufacturing. Since the only difference between the designs is in the lid portion,the rest can be

manufactured identically. The lid and tube are bolted to the top ring of the assembly, a new lid and tube can

simply be swapped on an existing 450 CFM body.

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Table 13: Balanced Dimensions Compared to 450 CFM Model

Variable Base Case Optimized % Difference

R[m] 0.2485 0.2485 0%

Rx[m] 0.1016 0.1422 40%

S[m] 0.3302 0.3302 0%

H[m] 1.138 1.138 0%

Hc[m] 0.6994 0.6994 0%

Rd[m] 0.0762 0.0762 0%

Table 14: Balanced Optimization Compared to 450 CFM Model

450 CFM Optimized +/-

Cost [$] 640.3 667.4 4%

x-50 [µm] 5.4 5.542 3%

dP [Pa] 580.7 912.6 57%

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14. Project Impact

14.1. Sustainability Study

Team 17 performed an analysis of the potential environmental impact of the EcoFilter to develop a

quantitative understanding of the sustainability benefits of the system. It was important to execute this

analysis because the team has strong commitments to the stewardship of the planet and cares about the

overall environmental footprint of the coffee roasting industry.

The primary focus of the study was on the energy-associated emissions produced in processing the coffee

roasting exhaust. The Vortx EcoFilter was compared to the afterburner method. With an the EcoFilter

system there is no natural gas use, but there is additional electricity use for the water pump and fan. The

afterburner combusts natural gas and uses electricity. Through market research it was determined that the

afterburner gas use rating needed for the exhaust of 15 kg batch roasters is 50 kW (~3500 BTU/hr). Data

and conversion metrics from the U.S. Energy Information Administration were used to calculate emissions

from natural gas and electricity use. The resulting emissions reduction is 0.15 kg of carbon dioxide per kg

of roasted coffee, or 2.3 kg of carbon dioxide per batch.

14.2. Economic Viability Study Installed Vortx EcoFilters have experienced payback periods of 10 months. These savings come from

reducing operation costs in two main areas: natural gas costs and chimney stack cleaning costs. Through

analysis using national average prices for commercial use in 2017, it was determined that the EcoFilter

would save $0.32 per batch through reducing natural gas usage. There is significant variability in this

number depending on the individual roaster. The larger potential for savings comes from minimizing the

frequency of chimney cleaning and reducing maintenance costs.

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15. Conclusion The final balanced result yielded a system that can handle 800 CFM with comparable performance to the

450 CFM size. There are minimal modifications needed to change from the current 450 CFM model to the

designed 800 CFM model. It requires only an increase of the vortex finder tube diameter and lid inner

diameter. This allows for the client to easily modify a current system for validation at a low cost. Then

minimal production changes will be needed to produce the 800 CFM system.

The success of this design will be significant for the environmental footprint of the coffee roasting industry.

It will provide a larger percentage of the industry with the ability to cut carbon emissions from their

production of roasted coffee beans. Environmental sustainability is not only an essential aspect of this

product, but also a driving value of Vortx Kleanair Systems and Team 17.

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16. Acknowledgements 1. Professor Renard Tubergen - As the faculty advisor for the team, Dr. Tubergen was critical to the

completion of this project. He provided consistent feedback for the team through which he gave

valuable insight and support.

2. Ron Kleist and Vortx Kleanair Systems - Mr. Kleist was a valuable connection to the coffee

roasting industry. He supplied the group with product information for the Vortx EcoFilter and

provided them with a one-pound coffee roaster for the project.

3. Tyler Greenway - Tyler was a great help in introducing the team to the basics of coffee roasting.

The volunteering of his time to give the team hands on coffee roasting experience was invaluable.

4. Skyler Rich - Team photographer.

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17. Appendices A1: References

A2: Optimization Iterations Diagrams

34

A1. References

Hoffman, A. C., and L. E. Stein. Gas Cyclones and Swirl Tubes: Principles, Design and Operation. Second

ed., Springer, 2010.

Elsayed, Khairy, and Chris Lacor. "Analysis and optimisation of cyclone separators geometry using RANS

and LES methodologies." Turbulence and Interactions. Springer, Berlin, Heidelberg, 2014.

Taiwo, Muhammad I., Mohammed A. Namadi, and B. Mokwa James. "Design and analysis of cyclone dust

separator." American Journal of Engineering Research (AJER) e-ISSN: 2320-0847.

Schwartzberg, Henry. "Batch coffee roasting; roasting energy use; reducing that use." Advances in Food

Process Engineering Research and Applications. Springer, Boston, MA, 2013. 173-195.

Kim, J. C., and K. W. Lee. "Experimental study of particle collection by small cyclones." Aerosol Science

and Technology 12.4 (1990): 1003-1015.

Farah, Adriana. "Coffee constituents." Coffee: Emerging health effects and disease prevention 1 (2012):

22-58.

Calligaris, Sonia, et al. "Insights into the physicochemical properties of coffee oil." European journal of

lipid science and technology 111.12 (2009): 1270-1277.

Heumann, Bill. “Basic Cyclone Design”. October 2017. PowerPoint presentation.

“T304 Stainless Steel Sheet.” MetalsDepot®, www.metalsdepot.com/stainless-steel-products/stainless-

steel-sheet-plate.

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A2. Optimization Iterations Diagrams

Table A1 show the cross-section geometries of the optimization results for different inlet sizes for each

objective function to scale.

Table A1: Optimized Iterations

Inlet

Size Base Case Cost Pressure Drop Cut Diameter Balanced

6”

8”