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Research Papers: Flows in Complex Systems

In Situ PLIF and Particle Image Velocimetry Measurements of the Primary Entrainment Fuel Jet in a Naturally Aspirated Water Heater

[+] Author and Article Information
Jon D. Koch

e-mail: jondkoch@gmail.com
Department of Mechanical Engineering,
1515 West Wisconsin Avenue,
Marquette University,
Milwaukee, WI 53233

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received September 24, 2012; final manuscript received August 6, 2013; published online December 18, 2013. Assoc. Editor: Peter Vorobieff.

J. Fluids Eng 136(2), 021104 (Dec 18, 2013) (6 pages) Paper No: FE-12-1471; doi: 10.1115/1.4025865 History: Received September 24, 2012; Revised August 06, 2013

The time-averaged characteristics of a fuel jet have been measured via acetone planar laser-induced fluorescence (PLIF) and particle image velocimetry (PIV) in the primary mixing region of an operating gas-fired water heater. These measurements allow for experimental characterization of the cross-sectional scalar and velocity fields as well as the estimation of the mass entrainment as the flow enters the burner in a practical system. In these experiments, reasonable results were obtained when only the fuel jet was seeded with acetone or PIV particles rather than the entire flow, thus demonstrating the potential for simplified experimental configurations in some applications where controlling or seeding the entire flow may be difficult. The entrainment characteristics of the fuel jet are compared with benchmarks from literature. The commercial device exhibits a larger mass entrainment rate than is found in typical free jets that have been studied in the literature. This may be a result of the jet's low Reynolds number (9,600) in comparison with other literature studies, and a result of initial conditions.

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Figures

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Fig. 1

Photo of 40k Btu/h pancake burner in water heater. The burner is 120 mm diameter and 55 mm overall height. This study focuses on the turbulent jet created by the fuel nozzle that entrains primary air before the mixture enters the bottom of the pancake.

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Fig. 2

PLIF and PIV experimental configuration. Particle loading (0.01 cc/min) and acetone tracer concentration (5% by volume) is controlled via a branched methane flow with a total mass flow rate of 21.4 SLPM, corresponding to a 40,000 Btu/h (11.7 kW) firing rate.

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Fig. 3

Cross section of fuel nozzle. The nozzle is cost effective to manufacture, but it is not similar to common nozzles used in the study of free jets, namely straight pipe, sharp orifice, or smoothly contracting nozzles.

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Fig. 4

Relative Sum Squared Difference of scaled, average, radial concentration, and velocity profiles. The profile at each axial location is normalized by its centerline value and half-width. The SSD is calculated relative to the profiles at about 9 orifice diameters downstream (where SSD is zero). When the SSD for a property approaches a fairly constant, low value, that property of the jet has become self-similar. The data from the self-similar region can then be fit to Eqs. (2) and (3).

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Fig. 5

Measurement of entrainment by a turbulent jet with a straight pipe exit with comparison to the work of Han and Mungal [11], which had a similar configuration. Axial distance is normalized by the effective momentum diameter. The data reduction technique used in this work shows good agreement with work that used a seeded coflow.

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Fig. 6

Fuel and air flow rate along jet axis, normalized by orifice diameters. The metered line indicates the fuel flow rate as controlled by the mass flow controllers. The fuel flow deduced from the PLIF and PIV measurements agrees well with the metered rate, providing confidence in the accuracy of the technique.

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Fig. 7

Relative mass entrainment of the water heater jet and comparison with measurements of jets with other initial conditions

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