A Novel and Cost Effective Radiant Heatflux Gauge. Samim Safaei. M.S. Candidate Worcester Polytechnic Institute, Worcester, MA

Transcription

1 A Novel and Cost Effective Radiant Heatflux Gauge Samim Safaei M.S. Candidate Worcester Polytechnic Institute, Worcester, MA

2 Outline Background Fundamentals Methodology Results Next Steps 2

3 Background: Research Context Objective: To develop a cost effective and practical tool for analysis and detection purposes. Background: B.Eng., University of British Columbia (UBC), Canada, 2012 Electrical and Mechanical Engineering Independently conceived technology during B.Eng. Currently validating technology for M.S. Thesis in Fire Protection Engineering at Worcester Polytechnic Institute (WPI) Patent-Pending Collaborators: Ali S. Rangwala, Associate Professor, Supervisor, WPI V. Raghavan & T. Muruganandam, Co-supervisors, Mech. & Aero. Eng., Indian Institute of Technology Madras, IITM L. Genovesi, CEO, Global Fire Products Inc. 3

4 Background: Current Technologies Radiant heatflux (light) communicates a wealth of information remotely and instantly. Radiative heatflux Geometries/dynamics Parameter Device Physics Spectra Unit Cost Requires Temperature Radiant Schmidt-Boelter Thermoelectric UV, Vis, Chemical characteristics Fire hazards heatflux / Gardon Gauge = OFD effect SWIR, MWIR, 5000 Fundamental sensor physics limit current tools: Resource intensive Data sparse Cost prohibitive Radiant heatflux + Temperature Radiant heatflux + Temperature + Soot fraction, speed Thermal Imaging Cameras Prototype Thermoelectric effect Photoelectric effect LWIR UV, Vis, SWIR, MWIR, LWIR SWIR N/A Figure 1. Technology Comparison Continuous cooling Cooling, Specialized operation 4

5 Fundamentals: Flame Radiation General Combustion Reaction: C n H 2n + Oxidizer Soot (Carbon Intermittents) H 2 O + CO 2 + Visible Chemiluminescene Thermal Radiation Photoluminescence (Small, Fuel Dependant) (Fuel Dependant) x10 [2] G.P. Smith, et al. Low pressure flame determinations of rate constants for OH(A) and CH(A) chemiluminescence, Combustion and Flame, Volume 131 (1 2), 2002, p >>>For all carbonaceous diffusion flames, soot radiation dominates. [1] Spectrum of Typical Hydrocarbon Flame, NFPA 72, Figure A

6 Emissive Power, E(T) [W/m 2 ] Fundamentals: Thermal Radiation All objects emit light-energy as a strong function of their Temperature; E=f(T 4 ). Function also influenced by: Surface properties (emissivity, reflectance, ) Geometries (emission area and orientation) Emissions distributed over a range of wavelengths; tending towards shorter wavelengths as Temperature increases UV V SWIR MWIR LWIR 1500K 1300K 1100K 900K 700K 500K Visible light makes up a minor portion of this range, only visible when emission source passes 900K (1200 F). F.P. Incropera, D.P. DeWitt, Fundamentals of Heat and Mass Transfer, Wiley, 1996, p Light Wavelength [μm] 6

7 Methodology: Validation Approach Prototype, G n Theoretical, G n Established Experimental Platform Measured Computed? G n is the Sensible Irradiance on a sensor 7

8 Methodology: Experimental Platform Soot & Temperature Data from published co-flow Ethylene-Air Partially-Premixed Laminar Flames [1] r i = 0.5 cm Equivalence Ratio Pure Diffusion ~Stoic. Premix [1] C.P. Arana, S. Sen, I.K. Puri, Field measurements of soot volume fractions in laminar partially premixed coflow ethylene/air flames Combustion and Flame (2004) 8

9 Methodology: Prototype Irradiance Lens Sensor n Circuit E(T) Sensor Signal Stabilize, ADC Total incoming radiative flux [W/m 2 ] ϴ Proprietary low cost lens focuses view to ϴ, filters excess heat Off-The-Shelf Sensor output proportional to sensible Irradiance; C n + - Digital Signal Amplify, R Recorded Data, X n DAQ Blackbody Calibrator: E(T) G n (T) Verify sensor constant C n G n = C n (R(ADC(X n ))) 9

10 Effective Emissivity, ϵ Methodology: Theoretical Model Radial Soot Distribution Abel Transform (Line of Sight Average) Integrated Soot Fraction Effective Emissivity: 1 D s Portion visible to Sensor; 1/tan 2 ϴ ϴ Sensible Emissions Wavelength Flame Thickness, Ds [meters] ε = 1 e C o C 2 f v T s D s v E n { ( E(λ) S n λ τ )dτ} dλ v [1] C. Tien, K. Lee, A. Stretton, Radiation Heat Transfer, SFPE HB, (2002) 0 10

11 Corrected Soot Temperature [K] Results: Flame Comparison Flame heights and thermocouple measurements were very comparable (<10% error) 1700 Axial Flame Temperature Lit. High Lit. [1] Lit. Low Measured Normalized Height Above Burner [z/h] [1] C.P. Arana, S. Sen, I.K. Puri, Field measurements of soot volume fractions in laminar partially premixed coflow ethylene/air flames Combustion and Flame (2004) Thermocouple Correction: T g T t t T h t 4 t [2] [2] D. Bradley, K.J. Matthews, Measurement of High Temperature Gas with Fine Gauge Thermocouples, Journal of Mechanical Engineering Science, 10 (4)

12 Sensible Irradiance, G n [W/m 2 ] Results: Radiation Comparison Measured and Computed Irradiance are comparable. = H Measured Computed Normalized Height Above Burner [z/h] G n = C(R(ADC(X n ))) G n ε E n F 16 tan 2 θ 12

13 Results: Sources of Error Hypothesized Source Description Estimated % Error Proposed Solution Sensor specification Soot temperature input Build limitations Soot fraction Input Variation in specification to actual performance Effective soot temperature at local regions is difficult to measure & error is amplified drastically Optical alignment & attenuation, electronic component accuracy Not directly measured; limited accuracy of literature interpolation <50 -Consult manufacturers -Change sensors -Rigorous calibration <30 -Move to larger flames -Use radiant heatflux gauge measurements to avoid thermocouple input <20 -Revise circuit for stability -Revise optics for accuracy -Self-contain for integrity <10 -Move to large flames to avoid input requirement 13

14 Next Steps: Application to Real Fires Large-Scale Liquid Pool Fires Crude oil fuel; Multi-component hydrocarbon Optically thick; Effective emissivity=1; Less inputs Turbulence; Time fluctuating micro-scale gradients [1] [1] Prateep Chatterjee, John L de Ris, Yi Wang, Niveditha Krishnamoorthy and Sergey B Dorofeev, Laminar Smoke Point Based Sub-grid Soot Radiation Modeling Applied to LES of Buoyant Turbulent Diffusion Flames, FM Global Research Division, 2012 J. Phys.: Conf. Ser

15 Thank you - Questions? 15