Ampere A. Tseng Heat Transfer and Fluid Flow Laboratory Brno University of Technology

1. A Progress Report on Polymeric Hollow Fiber Heat Exchanger September 30, 2012 to November 16, 2012 Ampere A. Tseng Heat Transfer and Fluid Flow Laboratory Brno University of Technology Brno, Czech Republic Professor Emeritus Arizona State University Tempe, Arizona USA E-mail: ampere.tseng@asu.edu November, 9, 2012

2. My Roles in the Project of Polymeric Hollow Fiber Heat Exchanger (PHFHE) • Research and development on PHFHEs for applicability enhancement and for performance understanding & improvement. • Accountability: Numbers of EI (Engineering Index) and SCI (Science Citation Index) recognized journal papers, as well as EU and USA patents. • The purpose of this progress report: the short-term plan to conduct specific analyses and experiments related to PHFHE.

3. Polymeric Hollow Fibers (PHFs) • Polymeric hollow fibers (PHFs), also known as hollow fiber membranes, have been frequently used for making mass exchangers for many years. These PHFs normally possess a wide range of porosity with pore sizes between 0.1 and 10 µm. • The PHF is suitable for degassing and aeration of liquid; preventing liquid from passing through the pores of the PHF, allowing only gas to pass through. PHFs have been widely used as membrane filters for microfiltration applications, where pressure is the driving force (similar to the problem considered by Professor Tomas Sverak of Chemical Engineering, BUT). • Recently, PHFs have been applied for making heat exchangers, because their superior characters, including corrosion resistance, cost-effectiveness, light-weight, high ratio of surface-area to volume, dual transport ability, and less fouling ability. • Weakness: low thermal conductivities, mechanical strengths, and operating temperatures

4. Thermal Performance & Design Parameters

5. Thermal Performance & Design Parameters • The essence to increase thermal performance is to increase the heat flow, Q [J/s], where Q = T/ R, T is the overall temperature difference, and R is the total thermal resistance. For a single fiber, one has • In an efficient heat exchanger, T has to be large and R has to be small.

6. Heat Exchanger in Solar Thermal Collector • Solar energy striking the Earth's surface averages about 1,000 watts per square meter under clear skies with the surface directly perpendicular to the sun's rays. Solar thermal collectors are designed to collect heat by absorbing sunlight. They are ranged from simple solar hot water panels, to complex collectors used in solar power plants. Collectors can be used for either heat or electricity generation and have many different types,from the simple flat plate to the huge power tower. We are focusing design a flat plate thermal collector. Flat plate collector for heat generation

7. Flat Plate Solar Collector Flat plate thermal collectors consist of (1) a dark flat-plate absorber of solar energy, (2) a transparent cover that allows solar energy to pass through but reduces heat losses, (3) a heat-transport fluid (air, antifreeze or water) to remove heat from the absorber, and (4) a heat insulating backing. The absorber consists of a thin absorber sheet (of thermally stable polymers or metals, to which a matte black or selective coating is applied) often backed by a grid or coil of fluid tubing placed in an insulated casing with a glass or polycarbonate cover. In water heat panels, fluid is usually circulated through tubing to transfer heat from the absorber to an insulated water tank. This may be achieved directly or through a heat exchanger. Polymer collectors can suffer from overheating when insulated, as stagnation temperatures can exceed the melting point of the polymer. For example, the glass transition temperature (Tg) of polypropylene is -20 °C (C.E. Wilkes, PVC Handbook, Hanser Verlag, 2005). and the melting point is 130–171 °C (en.wikipedia.org/wiki/Polypropylene), while the stagnation temperature of insulated thermal collectors can exceed 180 °C, if control strategies are not used. For this reason polypropylene is not often used in glazed selectively coated solar collectors. Increasingly polymers such as high temperate silicones (which melt at over 250 °C) are being used. Conventional metal collectors are vulnerable to damage from freezing.Freezing cracking can be a problem for PHF.Polypropylene has high freeze-tolerance and should not expected to have this problem. Also, a mixture of water with antifreeze is also used as a heat exchange fluid to against freeze damage.

8. Materials & Design Parameters • According to the US plumbing code, we may have problems since the hoop or effective stress can be higher than the long-term tensile strength of PP!!! • Thermal conductivity of PP is also needed to be found!!!

9. Thermal & Mechanical Properties of Polymers Used for PHFHE *The thermal conductivity (k) of PP with 15.0 wt % graphite modification reached 0.348 W/m-K, which is about twice higher than that of the pure PP fiber (k = 0.19 W/m-K), while the strength decreases about 10%, Qin, Li, Wang (2012) +The tensile strength of PVDF modified with 9.0 wt % graphite increases about 10% as well as the overall heat transfer coefficient, Li, Fan (2012). PEX = cross-linked polyethylene, Liu Davidson, Mantell, 2000; Engineering TooLBox, 2012 PSU = polysulfone, Freeman, Mantell, Davidson, 2005 PB = polybutylene, Freeman, Mantell, Davidson, 2005, Akoalit PB 4269 data sheet PA66 = polyamide 6/6, Freeman, Mantell, Davidson, 2005 PP = polypropylene, Sabic PP 525P data sheet PVDF = polyvinylidene, T’Joen, Park, Wang, Sommers, Han, Jacobi (2009) PEEK = poly-ether-ether-ketone, en.wikipedia.org/wiki/PEEK, 2012

10. Thermal & Mechanical Tests for Polypropylenewithout and with Graphite • To improve the long term thermal and mechanical performance, it is recommended to measure k, Tg, Tm, su, su,82 of single PP fiber with and without graphite!! A mini tensile tester and a thermal analyzer should be available., Freeman, Mantell, Davidson, 2005. • Creep data is also encouraged to be obtained, Wu, Mantell, Davidson, 2004. • The thermal conductivity (k) of PP with 15.0 wt % graphite modification reached 0.348 W/m-K, which is about twice higher than that of the pure PP fiber (k = 0.19 W/m-K), while the strength decreases about 10%, Qin, Li, Wang (2012). • The tensile strength of PVDF modified with 9.0 wt % graphite increases about 10% as well as the overall heat transfer coefficient, Li, Fan (2012).

11. Polypropylene Hollow-Fiber Bundle Micrograph of the head of polypropylene hollow-fiber bundle is made of polydiclopentadiene (PDCPD), which is molded by a 1000- to 1500-rpm centrifugal force (20 cm in radius) at room environment. Polypropylene hollow fiber (600 fibers, di = 0.46 mm) bundle for making portable & disposable solar collector

12. Polydiclopentadiene (PDCPD) Properties (by MatWeb) Ref: www.matweb.com/search/datasheettext.aspx?matid=78164

13. Current Brno Experimental Setup for Thermal Performance Evaluation • The fiber bundles currently made have about 20% of fibers been blocked or clogged by the PDCPD. Is this could be that the centrifuge is too high during molding?? • The current configuration can be used as an immersed heat exchanger for thermal performance evaluation, since the flow rate of the hot water is not large enough to cover most of the heat exchanger operating condition. • Can we put a motor to rotate the fiber bundle??? To increase the heat transfer coefficient!! • Can we have a higher hot water temperature, such as 90 °C?? Brno experimental setup for heat transfer measurements in PHFHEs,

14. Portable and Disposable Flat Plate Collector * Due to the high thermal expansion of polymer, the fibers should have less fouling problem; the repeated expansion and contraction of the fibers during operation can lead to scale or undesired accumulation detachment. It is expected that the fibers do not need for defouling or to be replaced for a long time, say one year??? * Since PHFs are very cost-effective and light-weight, they are ideal for making a portable and disposable solar collector. * Two portable and disposable flat plate solar collector. The outer container is attached to the absorber. As an illustration, two hollow fiber bundles were attached. *Patentable!!!!

15. Experimental Setup for Thermal Performance Evaluation for PHFHE This setup can have two different flow configurations: hot flow inside hollow fibers and hot flow outside. The shell side flow can also across woven hollow-fiber bundles with both countercurrent and parallel flows Experimental setup for heat transfer measurements Zarkadas, Sirkar, 2004 It is believe that a heat transfer correlation can be developed for the overall heat transfer coefficient. Also, a similar correlation for mass transfer can also obtained.

16. Air Heat Collector This type of collectors heats air directly, almost always for space heating and falls into two categories: Glazed and Unglazed. Glazed systems have a transparent top sheet as well as insulated side and back panels to minimize heat loss to ambient air. The absorber plates in modern panels can have an absorptivity of more than 93%. Air typically passes along the front or back of the absorber plate while scrubbing heat directly from it. Heated air can then be distributed directly for applications such as space heating and drying or may be stored for later use. Unglazed systems, or transpired air systems, consist of an absorber plate which air passes across or through as it scrubs heat from the absorber. These systems are typically used for pre-heating make-up air in commercial buildings.

17. Parabolic Trough Collector It is constructed as a long parabolic mirror, which is usually coated silver or polished aluminum connected with an insulated tube (Dewar tube) or a heat pipe running its length at the focal point. Sunlight is reflected by the mirror and concentrated on the Dewar tube or heat pipe, which is containing coolant which transfers heat from the collectors to the boilers in the power station. The trough is usually aligned on a north-south axis, and rotated to track the sun as it moves across the sky each day. This tracking method works correctly at the spring and fall equinoxes with errors in the focusing of the light at other times during the year; the magnitude of this error varies throughout the day, taking a minimum value at solar noon. There is also an error introduced due to the daily motion of the sun across the sky, this error also reaches a minimum at solar noon. Parabolic trough concentrators have a simple geometry, but their concentration is about 1/3 of the theoretical maximum for the same acceptance angle. Heat transfer fluid, usually oil, runs through the tube to absorb the concentrated sunlight. This increases the temperature of the fluid to some 400°C. The heat transfer fluid is then used to heat steam in a standard turbine generator.

18. Carbon Hollow Fiber Application Carbon Dioxide (and/or H2S) is separated from natural gas (CH4) by selectively permeation through a hollow fiber membrane (see the figure below). The driving force is the partial pressure difference across the membrane for CO2 (and/or H2S) , CH4 and other gas components. CO2 (and/or H2S) is the “fast” gas whereas CH4 is the “slow” gas. This membrane technology is based on polymeric hollow fiber. The pressurized feed gas enters the bundle from the shell side, the methane stays under pressure, and the CO2 (and/or H2S) is collected at a lower pressure. High selectivity makes 95%+ methane recovery available.A typical membrane system consists of a pre-treatment skid and a series of membrane modules Air Liquide (MEDAL) Newport, DE USA

19. Technical Writing Improvement Technical writing essentially is the communication abilities with technical data and language. I do not have any shortcut for the improvement of these abilities, since, in most of time, I also have difficulties to write a technical paper with the quality I feel comfortable with. This should be a long term effort. I have few suggestions: • I should be able to have lunches with any of your graduate students, so that they have to talk to me one-to-one in English while I have a better understanding of your students as well as the Czech culture, as a whole. • To set-up a PC workstation with an English operating system with the software of Photoshop, MathLab, PDF professional version, and ...... (immersing in a globalized world!) • Encouraging students to have a gmail account to read its English news at least 20 mins everyday. To have n gmail account, you can have a face-to-face talk to anyone in the world FREE!

20. A Personal Note

21. Acknowledgements & Thank You!! The generous funding provided by Czech Ministry of Education, Youth and Sports through Project No. HEATEAM - CZ.1.07/2.3.00/20.0188and professorship by Brno University of Technology (BUT) for me to stay in Brno are acknowledged. I am thankful to my host, Professor MiroslavRaudenský, for providing the wonderful opportunity for me to work with his talented group. Special thanks are to MessrsOndrejKristof and TomášVeselý for their technical support in preparing this presentation. I also like to express my gratitude and appreciation to Miss HanaHladilova and MrsZuzanaVetešníková for their enormous patience and hospitality for making my stay in Brno a lovely experience.