Integrated micropower generator
This presentation is the property of its rightful owner.
Sponsored Links
1 / 25

Integrated Micropower Generator PowerPoint PPT Presentation


  • 85 Views
  • Uploaded on
  • Presentation posted in: General

Integrated Micropower Generator. Combustion, heat transfer, fluid flow Lead: Paul Ronney Postdoc: Craig Eastwood Graduate student: Jeongmin Ahn (experiments) Graduate student: James Kuo (modeling) University of Southern California

Download Presentation

Integrated Micropower Generator

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Integrated micropower generator

Integrated Micropower Generator

Combustion, heat transfer, fluid flow

Lead: Paul Ronney

Postdoc: Craig Eastwood

Graduate student: Jeongmin Ahn (experiments)

Graduate student: James Kuo (modeling)

University of Southern California

Collaborator: Prof. Kaoru Maruta (Tohoku Univ., Sendai, Japan) (catalytic combustion modeling)


Integrated micropower generator1

Integrated Micropower Generator

Objectives

  • Thermal / chemical management for SCFC

    • Deliver proper temperature, composition, residence time to SCFC

    • Oxidize SCFC products

      Task progress

  • “Swiss roll” heat exchanger / combustor development

  • Catalytic afterburner

  • Micro-aspirator


Combustor development

Combustor development

  • Prior results in Swiss-roll burners show surprising effects of

    • Flow velocity or Reynolds number (dual limits)

    • Catalyst vs. non-catalyst (reversal of limits)

    • Lean limits richer than stoichiometric (!) (catalytic only)

    • Wall material


Combustor development1

Combustor development

  • Limit temperatures much lower with catalyst


Combustor development2

Combustor development

  • Temperature measurements confirm that catalyst can inhibit gas-phase reaction


Mesoscale experiments

Mesoscale experiments

  • Steady combustion obtained even at < 100˚C with Pt catalyst

  • Sharp transition to lower T at low or high fuel conc., low or high flow velocity - transition from gas-phase to surface reaction?

  • Can’t reach as low Re as macroscale burner!

  • Wall thick and has high thermal conductivity - loss mechanism?


Mesoscale experiments1

Mesoscale experiments

  • Next generation mesoscale burner - ceramic rapid prototyping using colloidal inks (Prof. Jennifer Lewis, UIUC)

    1.5 cm tall 2-turn alumina Swiss-roll combustor


Combustor development3

Combustor development

  • 4-step chemical model (Hauptmann et al.) integrated into FLUENT

    (1) C3H8(3/2)C2H4 + H2

    (2) C2H4 + O2 2CO + 2H2

    (3) CO + (1/2)O2 CO2

    (4) H2 + (1/2)O2 H2O

  • Typical results (V = 20 cm/s, Re = 70, lean propane-air)

Temperature

Heat release rate


Combustor development4

Combustor development

  • Model predicts intermediates H2 and CO used in electrochemical cell

H2

CO


Combustor development5

Combustor development

  • Individual reactions occur at different locations within Swiss roll - possibility for in-situ reforming of C3H8 and O2 to CO and H2without a catalyst

1

2

3

4


Heat exchanger combustor modeling

Heat exchanger / combustor modeling

  • Simple quasi-1D analytical model of counterflow heat-recirculating burners developed including: (1) heat transfer; (2) chemical reaction in WSR; (3) heat loss to ambient; (4) streamwise thermal conduction along wall


Heat exchanger combustor modeling1

Heat exchanger / combustor modeling

  • Results show low-velocity limit requires heat loss (H > 0) and wall heat conduction (B < ∞)

  • Very different from burners without heat recirculation!

H = dimensionless heat loss

B-1 = dimensionless wall conduction effect

Da = dimensionless reaction rate


Heat exchanger combustor modeling2

Heat exchanger / combustor modeling

  • High-velocity limit almost unaffected by wall heat conduction, but low-velocity limit dominated by wall conduction

  • Thin wall, low thermal conductivity material (ceramic vs. steel) will maximize performance


Heat exchanger combustor modeling3

Heat exchanger / combustor modeling

  • Much worse performance found with conductive-tube burner


Catalytic combustion modeling

Catalytic combustion modeling

  • Detailed catalytic combustion model integrated into FLUENT computational fluid dynamics package

  • Interactions of chemical reaction, heat loss, fluid flow modeled in simple geometry at microscales

    • Cylindrical tube reactor, 1 mm dia. x 10 mm length

    • Platinum catalyst, CH4-air and CH4-O2-N2 mixtures

  • Effects studied

    • Heat loss coefficient (H)

    • Flow velocity or Reynolds number (2.4 - 60)

    • Fuel/air AND fuel/O2 ratio


Catalytic combustion modeling1

Catalytic combustion modeling

  • “Dual-limit” behavior similar to experiments observed when heat loss is present


Catalytic combustion modeling2

Catalytic combustion modeling

  • Surface temperature profiles show effects of heat loss at low flow velocities


Catalytic combustion modeling3

Catalytic combustion modeling

  • Heat release inhibited by high O(s) coverage (slow O(s) desorption) at low temperatures - need Pt(s) sites for fuel adsorption / oxidation

a

b

Heat release rates and gas-phase CH4 mole fraction

Surface coverage


Catalytic combustion modeling4

Catalytic combustion modeling

  • Computations with fuel:O2 fixed, N2 (not air) dilution

  • Minimum fuel concentration and flame temperatures needed to sustain combustion much lower for even slightly rich mixtures!

  • Typical strategy to reduce flame temperature: dilute with excess air, but slightly rich mixtures with exhaust gas dilution is a much better operating strategy! (and consistent with SCFC operation)


Catalytic combustion modeling5

Catalytic combustion modeling

  • Behavior due to transition from O(s) coverage for lean mixtures (excess O2) to CO(s) coverage for rich mixtures (excess fuel)

Lean

Rich


Catalytic combustion modeling6

Catalytic combustion modeling

  • Predictions consistent with experiments (C3H8-O2-N2) in 2D Swiss roll at similar Re

  • Opposite (conventional) fuel:O2 ratio effect seen in gas-phase combustion


Catalytic combustion modeling7

Catalytic combustion modeling

  • Similar behavior at other Re


Catalytic combustion modeling8

Catalytic combustion modeling

  • Also seen with methane - surprisingly low T


Micro aspirator

Micro-aspirator

  • FLUENT modeling being used to design propane/butane micro-aspirator

  • Goal: maximize exit pressure for given fuel/air ratio

  • Unlike macroscale devices, design dominated by viscous losses

Propane mass fraction fields for varying inner nozzle diameters (outside dia. 2 mm)


Future plans

Future plans

  • Build/test macroscale titanium “Swiss Roll” burner (2x lower conductivity & thermal expansion coefficient)

  • Test macroscale Ti Swiss Roll IMG

    • H2, CO, H2/CO mixtures

    • Hydrocarbons

  • Meso/microscale "Swiss Roll”

    • Optimized for SCFC use using FLUENT - determine the conditions required for stable 2D combustor at target operating temperature & composition

      • Number of turns

      • Wall thickness

      • Catalyst type & surface area

      • Reactant flow velocity and composition (fuel, air, exhaust gas, bypass ratio)

    • Build/test stand-alone Swiss roll, verify design

    • Build/test IMG

  • Design micro-aspirator


  • Login