AC 2012-5134: INTRODUCING LAB-ON-A-CHIP-TYPE EXPERIMENTALACTIVITIES IN A THERMODYNAMICS AND HEAT TRANSFER LAB-ORATORY COURSE

Dr. Irina Nicoleta Ciobanescu Husanu, Drexel University

Irina Ciobanescu Husanu (Co-PI) is Assistant Professor in applied engineering at Drexel University. Shereceived her Ph.D. degree in mechanical engineering from Drexel University and also a M.S. degree inaeronautical engineering. Her research interest is in thermo-fluid sciences with applications in micro-combustion, fuel cells, green fuels, and plasma assisted combustion. Husanu has prior industrial experi-ence in aerospace engineering that encompasses both theoretical analysis and experimental investigationssuch as designing and testing of propulsion systems including design and development of pilot testing fa-cility, mechanical instrumentation, and industrial applications of aircraft engines. Also, in the past sevenyears, she gained experience in teaching ME and ET courses in thermal-fluid and energy conversion ar-eas from various levels of instruction and addressed to a broad spectrum of students, from freshmen toseniors, from high school graduates to adult learners. She also has extended experience in curriculumdevelopment.

Dr. Michael G. Mauk, Drexel UniversityPatrick lee Kirby, Drexel UniversityMiss Bailu Xu

c©American Society for Engineering Education, 2012

Introducing “Lab-on-a-Chip” Type Experimental Activities in “Thermodynamics and Heat Transfer Laboratory” Course

Abstract

In recent years, increasing industry demands for skilled graduates from universities has required a substantial refocus on engineering technology programs across the nation towards improving or even changing their traditional ways of imparting knowledge to students. One aim is to incorporate as much hands-on activities as possible in their curricula without having to curtail the theoretical foundation and yet to stay within the total number of existing credit hours. However, adding more laboratory activities implies a financial burden on the department and institution. In particular, for thermal-fluid educational areas, experimental equipment could be excessively costly, requiring dedicated laboratory space. Our thermal-fluid courses included up to now only laboratory activities based on traditional 'bench-scale' equipment. While these experiments have proven to be valuable educational tools for our courses, we continue to strive to improve and adapt our curricula to include more current and innovative experiments. To overcome both financial and space constraints that presently limit the laboratory, we developed sustainable improvements of “Thermodynamics and Heat Transfer Lab” course, including several “lab-on-a-chip” based activities to support our educational objectives in thermal sciences and process engineering.

Micro-fluidics (Lab-on-a-chip) approach has tremendous potential in scientific and emerging industrial applications from health care (clinical diagnostics) and medical research to micro-electromechanical systems and sensors. As a result of these experimental activities, students will gain both in-depth understanding of physical phenomena presented in the lectures and hands-on experience in developing and working with these miniaturized devices and systems1-7.

In this paper we report the development of laboratory activities introduced in the revised “Thermo and Heat Transfer Lab” course that has been offered during the winter term of AY2011-2012. The impact of the new activities has been assessed during this term and will continue to be evaluated and improved during subsequent terms when the course will be offered. Because this is mainly a junior to senior undergraduate course, this assessment will also focus on evaluating the level of critical thinking and creativity development that the course is promoting17.

The activities are based on development of microfluidic devices that will allow students to visualize streams and types of flows and also evaluate enthalpy of formation of a substance, and heat capacity of substances, heat production. The temperature variation is controlled by micro-heaters and local micro-temperature and pressure sensors embedded around the channels formed in plastic substrate ‘chips’. The micro-calorimeter device type is expected to give an excellent control of the thermal transfer, phenomenon that can be explored further by students extending the experiments into small team projects8-12. The fabrication of these micro-devices is fairly inexpensive and can be produced in our lab facility.

Introduction and Background

Engineering Technology programs, in contrast to traditional engineering programs, place greater emphasis on practical applications, hands-on learning, and engineering theory related to energy and energy conversion, manufacturability, maintainability, reliability, and quality assurance. Engineering Technology graduates often specialize in prototyping, instrumentation, statistical process control, and manufacturing operations. They develop the skills needed for deployment and implementation of sophisticated devices and systems in the field, and closely interact with end-users of technology.

The Engineering Technology Program at Drexel University offers an attractive option for technically-inclined students whose interests and motivations center on practical applications, manufacturing, hands-on problem solving, and intuitive and visual thinking; and for whom the abstract theory and analysis emphasized in traditional engineering courses of study proves to be a disincentive. This type of student is a valuable asset to industry and such students may forego a career path in science and engineering unless options such as Engineering Technology are open to them. Due to its straightforward conceptual basis, amenability to visual demonstrations, accessibility of the prototyping technology to students, and its impressive applications in the biomedical area, microfluidics offers an excellent avenue for attracting students to science and engineering 1-7.

Microfluidics has become an important commercial technology and engineering discipline in its own right, with extensive applications in biotechnology, medicine, chemistry, materials science, nanotechnology, and energy conversion. Microfluidics also provides an outstanding vehicle to educate and expose students to engineering subjects that are hallmarks of Engineering Technology curricula. Further, the instructional materials and resources developed here will have widespread applicability and broad interest to engineering students in general, and will also serve the needs of students in engineering technology, applied sciences, biotechnology, biomedical engineering and healthcare technology programs. Microfluidics can be an effective ‘gateway’ to biotechnology and biomedical fields for students with otherwise little background in biology. Also, new applications of microfluidics have been developed related to energy storage and energy conversion fields, mostly in renewable energy areas6. Although micro-fluidic devices for energy conversion are still in the research and development stage, their basic operating principles provide effective educational tools in exploring and understanding physical concepts related to thermo-fluids and heat transfer areas.

Course Development and Improvement

Thermodynamics and Heat Transfer Laboratory is a three hour-credit junior to senior undergraduate core curriculum course designed for all Engineering Technology (ET) students. Our ET program majors range from mechanical engineering technology, electrical engineering

technology, industrial engineering technology and biomedical engineering technology. Also, this course is one of the main precursors of the capstone Senior Design course. The Senior Design encompasses a student-led team project that has as a main outcome demonstrating a working prototype of a new product or engineering system. The Thermodynamics and Heat Transfer Laboratory course is designed for students that have limited prior exposure to fluid mechanics such as gained through a Fluid Power laboratory course, and a formal prerequisite of the first of Thermodynamics. The unique character of this course consists in being the only opportunity to engage students in a heat and mass transfer laboratory based course. Laboratory activities account for two thirds of the course, while the classroom-lecture part, only for one third. The material is being conveyed primarily using hands-on approaches.

During this course students will experimentally explore basic thermodynamic relations; they will conduct experiments related to flow of compressible fluids and to energy conversion of a fuel into a working substance as well as related heat transfer mechanisms14, 15. The main course objectives (lectures and labs combined) are focused on using heat transfer principles to understand the behavior of thermal-fluid systems, on illustrating the development of the governing equations associated with thermal systems, on investigating the influences of various system parameters and conditions on the resulting steady or transient response of the system, on providing students with the basic tools used in thermal system design, and exposing students to heat transfer applications in industry. After the completion of this course, students should be able to apply their knowledge in analyzing thermal-fluid systems and to combine and apply analytical techniques and design principles to thermal systems. They also should be able to prepare high quality engineering reports including presentation of goals, background, results, analysis, and conclusions, as well as a working prototype of a thermal-fluid system. The topics covered in this course range from a review of basic thermodynamic concepts and principles (First and Second Law of thermodynamics, Energy Balance, Entropy), to heat and mass transfer concepts (basic modes of heat transfer, heat conduction, convection (natural and forced), and radiation), with applications for heat exchangers.

The existent laboratory experiments developed in the past for Thermodynamics and Heat Transfer Lab are simple and practical, aiming to illustrate basic concepts and the behavior of thermo-fluid systems and energy conversion and heat transfer. These activities included the practical demonstration of basic concepts such as Newton’s Law of Cooling or Vortex tube principle. However, these experiments require space to perform the activity as well as space to store the equipment. Due to these limitations, the number of existent experimental stations is limited (one or two stations for each setup), making it difficult to accommodate increased number of students requiring this course. Recently, due to increasing demand in developing lab-based courses that enables students to develop industry related skills, combined with tighter budgets allocated to the programs, the lab space and budget became less available. Therefore, the “lab-on-a-chip” approach seeks to overcome these difficulties, and yet to provide students with

meaningful experiential activities that support and enhance the topics lectured, that are based on emerging technologies and may be easily adapted to emulate real-industrial settings.

Broader objectives in microfluidics education, of which this course is an important component, stem from a two-year awarded NSF TUES project. The primary goal is to integrate microfluidics technology and applications into Engineering Technology (ET) curriculum, mainly for the “Thermodynamics and Heat Transfer Laboratory” course. The immediate objective will be achieved by a combination of experimental activities and demonstrations, with emphasis on aspects of microfluidic technology related to micro-scale fluidics, heat transfer and instrumentation and control with a brief introduction to design of experiments (DOE) 13, 16.

Laboratory Activities

The experiments will enable students to measure and observe the behavior several fluid flow parameters such as pressure, temperature, flow rates, as well as to gain a broad perspective on design and application of microfluidic devices for medical diagnostics; biosensors for process control, environmental monitoring; microfluidic systems for R&D automation, high-throughput screening and discovery; as well as biomedical devices and instrumentation for healthcare applications.

Microfluidics systems are miniaturized fluidic networks comprising channels, conduits, chambers, filters, valves, and actuators formed in a substrate ‘chip’ made from plastic, silicon, glass, or ceramic. Microfluidic devices have numerous uses such as analytical chemistry, clinical diagnostics, biomedical research, and as components in sensors and other microsystems. Microfluidics provides a versatile platform to study process dynamics and control. Process variables of interest include temperature, flow rate, pressure, fluid composition or degree of mixing, and flow velocity profiles. The microfluidic chip can be instrumented with various sensors and actuators. Microfluidic devices are also amenable to imaging techniques, i.e., image capture and analysis of flow fields in the microfluidic circuit, which can be enhanced with dyes and fluorophores. Temperature measurements are made with thermistors (RTDs) or various thermocouples. Thermal imaging of the chip to determine the spatial temperature profile and temperature uniformity (or lack thereof) is also feasible with an IR camera. Heating and cooling of the chip can be done with resistive heaters, Peltier (thermoelectric) elements, as well as hot or cold air streams for convective heating. Phase change materials (e.g., paraffin with various melting temperatures) in contact with or contained in the chip can help stabilize temperatures. Pressure measurements can be made by making a fluid-filled manometer fashioned out of tubing attached to a long ruler and filled with a colored liquid for viewing the height of the column. Controlled flow can be realized with programmable syringe pumps, small micro-pumps, or from liquid reservoirs maintained at variable pressure heads.

Experiment 1: Capillary Effects in Microfluidic Channels

Chips are fabricated with straight channels of varying width. They can be closed at one end or opened to the atmosphere at both ends. A drop of liquid dye added to the cup formed at the inlet chamber is wicked into the channel by capillary forces. A CCD camera follows the filling of the channel as a function of time. The fluid front x(t) moves according to:

𝑥(𝑡) = γ⋅ cos(θ)ℎ3µ

∙ 𝑡1/2 (1)

where γ is the surface tension of the liquid (against air), θ is the wetting angle of the liquid against the channel , h is the height of the channel, and µ is the viscosity of the liquid. A plot of x vs. √𝑡 should then show a straight line.

Students will add various detergents (surfactant agents) such as Tween, Triton-X, SDS (sodium dodecyl sulfate) laurate 1, 3 to the liquid to modify its surface tension. Alternatively, or in addition, the channel can be coated with surfactants to change the wetting of liquids 3. The effect of surface tension on capillary forces will be observed by the students.

Experiment 2: Microfluidic Mixing

Mixing at microscale is difficult due to the low Reynolds number; turbulence is hard to achieve and combined flow streams tend to stay laminar without much cross mixing between adjacent flow lines. Methods of mixing two convergent streams are useful. There are many concepts for microfluidic mixers. We constructed a circular mixing chamber fed by two streams of differently colored dyes (Figure 2). A rotating stirring ‘bar’ is included in the mixing chamber as shown in Figure 4. We find that an oval or D-shaped stirring ‘bar’ made of steel wire executes more effective stirring action than a short length of wire, and has less tendency to get pinned to a

Camera

Pipette tip Wicking direction

Figure 1: Experimental set-up to observe the effect of surface tension on capillary forces

sidewall or entrapped in a channel. A commercial magnetic stirring plate may be used to actuate the stirring bar, or a permanent magnet can be mounted on an electric motor (such as a cooling fan) to produce a rotating magnetic field in the vicinity of the chip.

The degree of mixing can be quantified by imaging the chamber during the mixing process. When the two distinctly-dyed inlet streams are fully mixed, the chamber will have a uniform color. An analysis of a plan view image of the chamber, captured by a CCD camera positioned over chamber during the mixing process, will yield a digitized image. A mixing index is defined based on the color levels of the pixels.

mixing index = 1𝑁∑ 𝑐𝑘−𝑐

𝑐2

𝑁𝑘=1 (2)

Complete mixing corresponds to a mixing index of zero.

Micro-devices were first designed using AutoCAD software and later fabricated using a laser cutting and etching equipment. The material used to cut the micro-devices is 1mm thickness clear plastic sheet. The channels size is approximately 200µm or less. Since the channels are cut through the plastic, the top and the bottom of the micro-device is covered with a very thin acrylic adhesive sheet, to prevent any leakages. The fluid is pumped into the channels using a

Figure 2 Experimental set-up for visualization of mixing phenomena

Syringe pump Chip

Mixing chamber

Outlet

Camera

Motor

Chip Mixing chamber

Magnet

programmable syringe pump, and the flow is observed using a digital microscope of 500x magnification combined with imaging software. The setup is illustrated in Figure 3.

Figure 3 Syringe pump, microscope and micro-device set-up

During this experiment students were encouraged to modify the design of the current chamber, redesign a new micro device and then test it. The main goal was the optimization of the design to achieve mixing without the usage of an external stirrer (mixer). Although these designs presented above have limitations and shortcomings, the main success was related to student interaction and involvement in the design and development of the experimental micro-devices and testing set-up.

Figure 4: Micro-mixer chip designs. (A) Includes a magnetic mixer applied to eliminate bubbles and induce mixing. (B) Alternate chamber mixer design with the more common v-type inlets.

In Figure 4A the rounded nature of the mixer should be noted. The inlets are positioned in a manner that allows the incoming fluid to follow the outer edge of the pattern and to circulate around the mixer in an attempt to better produce mixing. The design in Figure 4B incorporates a scored cover and in this particular instance lacks a magnetic stirrer. Figure 4A is a variation of a previous design similar to the basic configuration illustrated in Figure 4B with the addition of a metal stirrer but without the surface of one of the layers being scored.

A B

Besides the chambered channel with the magnetic stirrer, various other design ideas have been created and applied in our lab setting to allow students to better understand the intricacies and difficulties involved with mixing phenomena in microfluidic devices. Amongst the different chip designs, we also examined chips with and without mixing chambers. The inlet angles by which the fluids intersect one another were also varied as was the flow rates from the syringe pump; both of these parameters were more explored in the chip designs without mixing chambers. Amid the numerous possibilities of chamberless chip designs, two were chosen (Figure 5). The first chip incorporates two inlets, each at a 45° and the second one incorporates a design of two inlets positioned at 45° and 60° (measured in the flow direction).

Figure 5: Microfluidic Chip Designs incorporating different inlet angles (A) 45° and 45°; and (B) 45° and 60°.

As shown in Figure 6, by changing the design of the chips the students were given the opportunity to see the influence of bifurcation angle on the mixing behavior within a microfluidic device as well as the influence of flow velocity on mixing phenomenon, by varying the inlet flow rate from 0.1 ml/min to 19 ml/min. As illustrated in Figure 6B and Figure 6C the change in flowrate does change the overall flow behavior, yet does not produce mixing as illustrated in Figure 7 A and Figure 7 B. Instead due to an increase in resistance one inlet becomes more dominant over the other, meaning one dye color, in this case red, dominates throughout the channel. Overall these experiments are an excellent way for students to quickly and easily study fluid dynamic phenomena and see how these phenomena apply to real world applications, as well as to become aware of the problems associated with these phenomena.

Figure 6: A. Flow at the exit of dual inlet (45°) at 0.1 ml/min; B. Flow at the exit of dual inlet (45°/60º) at 0.1 ml/min; C. Flow at the exit of dual inlet (45°/60º) at 19 ml/min

A

A B C

B

Figure 6A illustrates the flow through the exit of the dual 45° inlet chip at 0.1 ml/min; a very similar profile is also seen in the instance when a 19ml/min flowrate is applied. Lack of mixing can also be observed in when the inlets are altered to a configuration including one inlet incoming at 60° and the other at 45° with an in flowrate of 0.1 ml/min Figure 6 B. With that said when the flowrate is increased to 19 ml/min in the same 60°/45° configuration we observe a single flow color potentially indicating either mixing or one dominant flow.

Figure 7: 30/60 inlet chip. (A) Flow visualization at bifurcation for a flowrate of 0.1 ml/min (B) Flowrate of 19 ml/min

In addition to exposing the students to the questions surrounding producing mixing within a microfluidic device, the students are also given the chance to acknowledge and attempt to solve hands-on some of the many issues involving flow through microfluidic devices. One such problem is the production and necessary removal of bubbles, typically observed in designs which include chambers (Figure 8). While the usage of a magnetic mixer will break down a sizable bubble, at times such venues of problem solution will not be available and hence the students were challenged to come up with their own creative designs relying upon chip design and geometry in an attempt to limit bubble formation. Various design ideas were created, many of which involve moving the location as well as the angle of attachment of the two inlets. Students then explored the influence of these design variations upon bubble formation and removal.

Figure 8: Illustration of chip with mixing chamber during mixing experiment.

A clear bubble is formed in the mixing channel (Figure 8) which adversely affects the mixing as well as the fluid flow through the channel. The reason why the bubble forms at one location

A B

versus another remains unknown and it shall be explored further in experiments yet to be developed.

Experiment 3: Flow Through a Porous Media

Filtration and solid-phase extraction require forced flow through a porous media that selectively entraps or binds components of a mixture. This can be implemented in microfluidics devices by embedding a porous material in a chamber formed into the chip that intercepts the flow path to form a packed bed. Flow through porous material can generate large pressure drops and unusual flow patterns that depend on the porosity of the media, the properties of the fluid, the geometry or shape of the porous material, and the flow rate. The flow dynamics at microscale can be characterized with a simple test chip, with the objective of determining the pressure drop across the membrane ∆𝑃 (measured by manometer and/or pressure sensor) as a function of flow rate Q (programmed with syringe pump) (Figure 9).

Membrane materials: glass fiber, porous silica, cellulose, Porex. These materials can be cut with a CO2 laser to fit snugly in the chamber.

Experiment 4: Monitoring Temperature-Actuated Expansion of Microbeads

We use Expancel microbeads to simulate a temperature-dependent volume phase change. Expancel beads are small, hollow polymer spheres, 10 to 15 microns in diameter, filled with a liquid hydrocarbon. Upon heating to a specific temperature (∼80 °C), the hydrocarbon contained in polymer shell vaporizes and the volume of the microsphere expands by an order of magnitude.

Syringe pump

_ _ _ _ _ _ _ _ _

Manometer

Pressure sensor Chamber packed with porous

media (membrane)

Chip

Outlet

Figure 9. Experimental set-up to study flow dynamics (relationship between pressure drop and flow rate)

In microfluidics, these microbeads can be pre-loaded into chambers and used for temperature-triggered displacement of liquids to make one-shot valves and pumps5.

Figure 10. Set-up for studying heat transfer related phenomena

The output of this experiment is the pressure sensor voltage reading 𝑉𝑝𝑟𝑒𝑠𝑠 𝑠𝑒𝑛𝑠(𝑠). The input is a voltage signal to the heat source 𝑉𝑖𝑛(𝑠). The system response function is denoted as 𝐺𝑠𝑦𝑠(𝑠). This is the product of the response of the heater 𝐺ℎ𝑒𝑎𝑡𝑒𝑟(𝑠) , the heat transfer between the heated material and the beads 𝐺𝑡ℎ𝑒𝑟𝑚𝑎𝑙(𝑠), the volumetric change of the beads with temperature 𝐺𝑒𝑥𝑝𝑎𝑛𝑐𝑒𝑙(𝑠) , and the response of the pressure sensor 𝐺𝑝𝑟𝑒𝑠𝑠 𝑠𝑒𝑛𝑠(𝑠)

𝐺𝑠𝑦𝑠(𝑠) ≡ 𝑉𝑝𝑟𝑒𝑠𝑠 𝑠𝑒𝑛𝑠(𝑠)𝑉𝑖𝑛(𝑠)

= 𝐺ℎ𝑒𝑎𝑡𝑒𝑟(𝑠) × 𝐺𝑡ℎ𝑒𝑟𝑚𝑎𝑙(𝑠) × 𝐺𝑒𝑥𝑝𝑎𝑛𝑐𝑒𝑙(𝑠) × 𝐺𝑝𝑟𝑒𝑠𝑠 𝑠𝑒𝑛𝑠(𝑠) (3)

In the above setup, several methods of heating can be utilized (thermoelectric, resistive, infrared light or hot air convection), or combinations thereof. The temperature can be measured by a thermocouple or RTD. The position of the temperature sensor with respect to the chamber and

Heater power

Controller

Thermoelectric or resistive heater

Chamber preloaded with liquid and Expancel beads

T/C or RTD

Piezoresistive pressure sensor

Chip

Vpress.sens

V

V

1 Ω

Infrared heating

Camera

Convective heating/ hot air

heat sources will affect its response. An infrared temperature detector is also an option. The heating can be applied as a step function, or a ramp, or some other more complicated waveform. Students are also provided with the opportunity to attempt to disentangle the relative contributions of the subsystem responses to the overall system response, as well as determine which method of heating provides the fastest response with the least overshoot.

The laboratory experimental set-up (Figure 11) includes several microchips loaded with Expancel microbeads suspended in a liquid at different concentrations, type K micro thermocouples and thermocouple adaptors (Fluke 80TK), temperature control modules, pressure sensors and data acquisition system.

Figure 11 Pressure –temperature experimental set-up to study heat transfer related phenomena; pressure sensors (right)

The FTC 100 Temperature control system used in this experiment is an innovative new thermal control platform for precision temperature applications and is designed specifically for thermoelectric temperature control. FTC100 controller incorporates features like PWM, bi-directional power, auto-tune PID, broad sensor support, and an RS232 interface for managing the controller using a computer. For configuration flexibility, the FTC100 was used with a matching Accuthermo FTX-series H-bridge amplifier. As pressure sensor we use a 1mbar 26PC pressure sensor from SENSORTECHNICS. This type of pressure sensors allows us to use lightly corrosive liquids and gases. The sensors are calibrated and temperature compensated, providing analog mV output signals. Different miniature SIL and DIP housings allows for space-saving PCB-mounting. Data are collected using a computerized data acquisition system (USB DAQ and LABView VI) presented in Figure 12 and Figure 13.

Data Acquisition Device (DAQ)

LabVIEW Visual Recording

Hearter Temperature

Chip Temperature

Chip Pressure

Chip

HearterFTC100 PID Temperature

Controller

Figure 12 Data Acquisition system diagram

Figure 13 LABView VI for data acquisition system

The VI contains both data display and file output. In order to get constant visualization, some initiations are set up before the DAQ recording. The DAQ Assistant enables selection of data reading mode. Considering the limitations of LabVIEW array storage, for a maximum of six minutes of data recording, we choose 20Hz continuous sampling mode. Signals below 2Hz frequency are filtered by an Elliptic low-pass filter. Data is stored in an array temporarily during the while loop, and will not be written to excel file until user push stops the recording.

Students studied the chip temperature and pressure behavior during the experiment and they analyzed the data collected (charts of T vs. time and P vs. time). Also they studied the effect of the concentration of micro-beads in chip’s chamber on the temporal behavior of the chip temperature and pressure. Some of their results are presented in Figure 14. Following the same heating pattern, temperature on chip surface increases gradually. There is a certain delay in response of plate temperature changing. Although the cover plastic is thin enough, however heat loses still exist, which results in the gap of top surface temperature and plate temperature that is controlled by the heater. Pressures vary obviously among different concentrations of temperature sensitive expander (Expencel). Based on the same heating pattern, chip chamber pressure follows a positive correlation of expander concentration.

Figure 14 Temperature and pressure behavior vs. time for different microbeads concentration in micro-devices

ASSESSMENT AND EVALUATION

Student learning assessment is based on their laboratory reports and final projects. One student-led team (2 students) undertook a project involving a microfluidic device. They successfully created a micro heat exchanger, overcoming the hurdles of leaking and mounting small thermocouples at the inlet and outlet of each flow (cold and hot).

At the end of the term, students were asked to complete a survey regarding the experiments involving microfluidic devices. The survey was divided in two parts: one based on Likert type scale and one with small essay answers type. The Likert scale is based on a 5 to 1 scoring system, where 5 is strongly agree and 1 is strongly disagree. The questions were focused on the assessing if microfluidics experiments enhanced students’ understanding of heat and mass transfer phenomena, if the experiments stimulated their interest in microfluidic devices areas, and if students understood the connection between heat and mass transfer and the presented experiential activities involving microfluidics. Another aspect assessed was the interdisciplinary character of the presented experiential activities. Largely, students’ scores average for all and each question was 4 out of 5 on the Likert scale.

The small essay type questions focused on inquiring if designing and prototyping their own micro devices for various experiential activities enhanced students’ understanding of engineering principles being studied during these laboratory activities, if students gained an appreciation that scaling down fluid and thermal processes may involve challenges and effects (such as surface

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T plate (C)

T chip (C)

P (Bar)

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pera

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Chip Pressure (Bar)Te

mpe

ratu

re (C

)

Chip Pressure (Bar)Chip Pressure (Bar) Te

mpe

ratu

re (C

)

A B

C

Figure: According to different concentrations of the Expencel, results are shown in three sub plots: (A) low concentration, (B) medium concentration and (C) high concentration.

tension and mixing) that might not be operative or significant at macro-scale, and also if students learned how to design and prototype small practical microfluidic devices that could serve for different applications.

Based on their responses we may conclude that students believed that the exercises provided an excellent opportunity to expand their understanding of the topics covered during the laboratory activities presented in this paper. Overall the students liked that the experiments were more hands-on. They became aware of the problems associated with fabricating an experimental apparatus involving microfluidic devices (miniaturized devices difficult to handle, fluid leaks, bubble formation etc.).

Overall the feedback received at the end of the term from the participating students was largely positive with regards to the experiments involving microfluidic devices. Many students appreciated the ease with which a prototype can be designed and tested in an attempt to deal with issues as they arise. Without a doubt all of the students were exposed to the variety of topics surrounding fabrication, testing, and measurements in microfluidic devices; all of which are problems that we seek to slowly phase out as more progress is made in understanding and development of these technologies. Some of the main drawbacks pointed out by the students include the fact that since the devices are extremely small it is difficult at times for all students to directly work hands-on with the experiment and hence it may be better suited for an individual or much smaller lab group than the 3-5 students pairing used this past term. Furthermore, majority of students (~80%) developed a special interest in the biomedical and power applications for this technology. Other applications such as electronic cooling could be further discussed and emphasized to broaden the impact of this experiment.

Conclusions and Future Work

These experiments allow students to not only gain experience with modern temperature, pressure and flow measurement techniques, but also to better understand the phenomena associated with various heat transfer and fluid dynamic systems. In addition, students are provided with another opportunity to familiarize themselves with the various microscale systems. Due to the digital nature of the sensors used in these experiments, quantization error is also discussed. Concepts as calibration will be also tested by students during laboratory.

As future work we will continue to develop more laboratory activities based on the “lab-on-a-chip” approach for this course as well as for other laboratory based courses such as the “Measurement and Instrumentation” lab.

This work was supported in part by NSF TUES Grant Award Number 1044708 “Lab on a Chip: Integrating Microfluidics into the Applied Engineering Curriculum”

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