Conceptual Design of a Thermoelectric Edu-Kitchen System

1. Conceptual Design of a Thermoelectric Edu-Kitchen System INTERNATIONAL CONFERENCE ON POWER, SIGNALS, CONTROL AND COMPUTATIONS Trissur, India, January 3-06, 2012 Akshaya Srivastava, Daryl Duran, Mark Pinder, Vrishank Raghav, Narayanan Komerath Daniel Guggenheim School of Aerospace Engineering Georgia Institute of Technology Atlanta, Georgia USA http://www.wfp.org/sites/default/files/imagecache/600x400/photos/600_0283_BAN_200807_WFP-She.jpg

2. Introduction Aim Issues & Objectives Improve air quality, fuel efficiency, steady lighting and clean drinking water supply to kitchens. • Multidisciplinary testbed for micro renewable energy technologies. • Demonstrate closure of conceptual design for an integrated solution. • Active Control Problem to optimize power, air quality, fuel use, storage. Approach • Thermoelectric (TE) generation. • Battery storage. • DC fan/blower to optimize fuel-air ratio,ventilation and TE cooling. • Ejector nozzle. • Thermocouple/ RTD for feedback. • LED floodlamp for lighting. • UV LED for water purification.

3. Requirements http://www.wfp.org/sites/default/files/imagecache/600x400/photos/600_0283_BAN_200807_WFP-She.jpg http://www.spraguephoto.com/stock-photos/3391-Girl-lighting-cooking-fire,-Nam-Ha-village,-Ky-Anh,-Vietnam.|7273.jpg • Add-on, modular solution to existing kitchens • Charge battery on fire used for cooking evening meal • Provide enough light for one child to do 3 hours of homework each day • Provide enough air flow range to optimize fuel-air ratio at cooking intensity • Safe, rugged, simple for use by residents • Inexpensive components (in mass production) • Adaptable to wide range of operating conditions

4. Concept & Question • Woodburning kitchen stoves provide a source of power to bring electric lighting, pollution control and water sterilization to communities. • A 13-watt thermoelectric converter module operating at 225 degrees Celsius recharges a battery using the heat from the fire. • Battery-powered DC fan drives air into the stove, cooling the TE module and optimizing the fuel-air ratio for high fuel efficiency and least pollution. • A temperature sensor provides feedback to adjust fan flow. • 5-watt LED floodlamp provides steady lighting so that a child may learn. • A milliwatt LED is used to sterilize drinking water. • Does the design close with the selected parameters? • Is enough air flow variation available from the fan to ensure optimal stoichiometry in the flame? • Can costs at wholesale level be brought down to reasonable levels for adoption by NGOs and community programs?

5. Components Identified

6. System Concept

7. 13-watt thermoelectric converter module Bismuth Telluride alloy 13 watts rating 225 Deg. C max temperature Still working to achieve anywhere near this power curve!!

8. DC Fan/Blower Performance • 12 volt DC Fan from discarded computer • Nozzle/casing from 12-oz aluminum beverage can TSI “Velocicalc” integrated hot-wire anemometer sensor traversed across nozzle exit to obtain mass flow rate by integrating velocity profiles.

9. Conceptual Design Estimation Process • 1kW heating rate assumed in stove. • Wood properties assumed as sample (Black Spruce) • Heat release rate per unit mass consumed • Mass of wood consumed per second • Mass of air needed for perfect reaction (stoichiometry) • Factor of 2 for imperfect mixing • Fan flow rate needed • Fan power needed, from experimental data • Range of stoichiometry/ excess air available • Power excess left at design conditions http://origin.arstechnica.com/journals/science.media/cookin.png

10. How much power does the fan need to provide twice the minimum air flow needed to ensure complete fuel consumption? Only about 2 watts.

11. Ultraviolet Germicidal Unit For Drinking Water • UV Waterworks system by Ashok Gadgil and Vikas Garud • at Lawrence Livermore national labs, sterilized drinking water and eliminating several harmful bacteria including e-coli. • Broadband content of 40- watt fluorescent black light sufficient for effective sterilization. • 254 nanometer far-UV radiation killed well over 99 percent of bacteria present in water, quickly enough to use the blacklight over slow-flowing water. • Luckiesh General Electric Corporation (1920s): dosage of over 200 microwatt-minutes per square centimeter was adequate for 100 percent destruction of e-coli in water even if strain had evolved through previous doses of same radiation. • 260 to 270 nm, centered probably at 264 nm, is much more effective, since this includes resonance wavelengths of the DNA of these bacteria. • LEDs with output over this narrow range can thus achieve the same results as the earlier fluorescents, at milliwatts.

12. Technical Design closes, Policy Case for Economics OK Power Budget: Fan: 3 watts LED lamp: 4 watts LED water purifier <1 watt Total < 8 watts Steady-state TE Module supply for DT > 170 C Charging of battery above this level during operation Single-Unit Costs TEM $100 DC fan $8 Coke can $0 LED light $25 270nm LED + power unit $200 Total: $333 Per unit, mass-production targets TEM $5 DC fan $2 Coke can $0 LED light $5 270nm LED + power unit $1 Total: < $13 (INR 650) Less than the cost of treating a child for one day’s hospitalization! Project funding must come from enlightened govt. health/education programs.

13. Challenges Leading-edge Research Capabilities In Several Areas • Computing the heating from a stove burning assorted scrap wood, • Enhancing mixing inside a cluster of wood pieces, • Modeling and improving entrainment by a low-Reynolds number fan nozzle, • Designing the EduKitchen insert, • Protecting the thermoelectric module and • Cooling TEM enough for optimal power generation and safety. Current work • TEM testing not successful yet: needs optimization of TEM system. • Detailed characterization of jet boundaries and flow entrainment. • TEM envelope cooling • Scrap wood combustion modeling • 264nm LED incorporation. • Possible application of Thermo PhotoVoltaics (TPV)

14. Conclusions First conceptual design of the EduKitchen, shown to close. Basic concept of integrating devices for thermoelectric generation, fuel efficiency improvement and air quality improvement, and basic lighting and drinking water sterilization, is technically viable. Power levels obtained with single TEM at very modest heating rates and temperatures from a domestic wood stove are sufficient to operate a DC fan, DC LED floodlamp generating the equivalent of a 40-watt incandescent lamp. Fan-driven air reaches a speed of several meters per second, adequate to greatly augment natural convection and ensure clean, efficient heat release. An estimation procedure is laid out to estimate stoichiometry and to generate design curves for various levels of heating needed from the stove. The paper is also intended to convey the multidisciplinary nature of this research project.

15. Acknowledgment This study was enabled by NASA Grant NNX09AF67G S01, the EXTROVERT initiative to develop resources for cross-disciplinary innovation. Mr. Tony Springer is the technical monitor.