Effects of buoyancy on lean premixed v-flames, Part II. VelocityStatistics in Normal and Microgravity

The field effects of buoyancy on laminar and turbulent premixed v-flames have been studied by the use of laser Doppler velocimetry to measure the velocity statistics in +1g, -1g and {micro}g flames. The experimental conditions covered mean velocity, Uo, of 0.4 to 2 m/s, methane/air equivalence ratio, f, of 0.62 to 0.75. The Reynolds numbers, from 625 to 3130 and the Richardson number from 0.05 to 1.34. The results show that a change from favorable (+1g) to unfavorable (-1g) mean pressure gradient in the plume create stagnating flows in the far field whose influences on the mean and fluctuating velocities persist in the near field even at the highest Re we have investigated. The use of Richardson number < 0.1 as a criterion for momentum dominance is not sufficient to prescribe an upper limit for these buoyancy effects. In {micro}g, the flows within the plumes are non-accelerating and parallel. Therefore, velocity gradients and hence mean strain rates in the plumes of laboratory flames are direct consequences of buoyancy. Furthermore, the rms fluctuations in the plumes of {micro}g flames are lower and more isotropic than in the laboratory flames to show that the unstable plumes in laboratory flames also induce velocity fluctuations. The phenomena influenced by buoyancy i.e. degree of flame wrinkling, flow acceleration, flow distribution, and turbulence production, can be subtle due to their close coupling with other flame flow interaction processes. But they cannot be ignored in fundamental studies or else the conclusions and insights would be ambiguous and not very meaningful

Semi-empirical relationships to assess the seismic performance of slopes from an updated version of the Italian seismic database

Funder: Dipartimento della Protezione Civile, Presidenza del Consiglio dei Ministri; doi: http://dx.doi.org/10.13039/100012783; Grant(s): ReLUIS research project - Working Pachage 16: Geotechnical Engineering - Task Group 2: Slope stabilityAbstractSeismic performance of slopes can be assessed through displacement-based procedures where earthquake-induced displacements are usually computed following Newmark-type calculations. These can be adopted to perform a parametric integration of earthquake records to evaluate permanent displacements for different slope characteristics and seismic input properties. Several semi-empirical relationships can be obtained for different purposes: obtaining site-specific displacement hazard curves following a fully-probabilistic approach, to assess the seismic risk associated with the slope; providing semi-empirical models within a deterministic framework, where the seismic-induced permanent displacement is compared with threshold values related to different levels of seismic performance; calibrating the seismic coefficient to be used in pseudo-static calculations, where a safety factor against limit conditions is computed. In this paper, semi-empirical relationships are obtained as a result of a parametric integration of an updated version of the Italian strong-motion database, that, in turn, is described and compared to older versions of the database and to well-known ground motion prediction equations. Permanent displacement is expressed as a function of either ground motion parameters, for a given yield seismic coefficient of the slope, or of both ground motion parameters and the seismic coefficient. The first are meant to be used as a tool to develop site-specific displacement hazard curves, while the last can be used to evaluate earthquake-induced slope displacements, as well as to calibrate the seismic coefficient to be used in a pseudo-static analysis. Influence of the vertical component of seismic motion on these semi-empirical relationships is also assessed.</jats:p

Development of a Vane Swirler for Use in a Low NOx Weak Swirl Burner

This paper describes the continuing development of the Weak-Swirl Burner (WSB) for use in low NOx applications. Weak-swirl is a unique method for stabilizing lean-burning, premixed combustion as the flame is stabilized by flow divergence, not through recirculation as is commonly seen in nonpremixed industrial burners. Earlier versions of the WSB used a tangential airjet swirler that offers flexibility for determining the range of operation and evaluating the performance of the WSB. Though common in large applications, air swirler may not be amenable to small and medium-size appliances. To reduce manufacturing costs and burner complexity, we have developed a fixed vane swirler to replace the airjet swirler in the WSB. This paper describes the operating characteristics and key design parameters of the vane swirler. A new expression for determining swirl number intensity is developed. Testing of a laboratory water heater fitted with a WSB with the new vane-swirler shows 0 < NO < 20 ng/J, 10 < CO < 70 ppm, and thermal efficiencies ~ 78% over the lean burning range of 0.70 < $< 0.90. The continuous firing rate is robust for a 53 mm vane-swirled WSB, with initial tests ranging from 40,000 to 400,000 Btu/hr. for 0.60 <$ < 1.0. Successful development of the new vane swirler demonstrates that the low emission WSB is adaptable to a wide variety of industrial applications

Stability Characteristics and Emission Levels of a Laboratory Hot Water Heater Utilizing a Weak-Swirl Burner

This paper reports the test results of a collaboration between Lawrence Berkeley National Laboratory and Teledyne Laars to assess the viability of incorporating the Weak-Swirl Burner (WSB) into a 15 kW (50,000 Btu/hour) Telstar spa heater. By stabilizing premixed lean combustion down to equivalence ratios $~ 0.6, the WSB greatly reduces NOx levels by minimizing thermally generated NOx through the Zeldovich mechanism. The first set of experiments focus on establishing the WSB's minimum and maximum swirl requirement (corresponding to blowoff and flashback) for varying$, power levels, burner size, and enclosure. The second set of experiments evaluates the performance of a laboratory water heater where the WSB is incorporated into a Telstar heat exchanger. I t was found that the laboratory test station achieves "low" « 50 ppm) and "ultra-low" « 25 ppm) NOx emissions without compromising the thermal efficiency. The optimum operating condition is for $ = 0.8 at 18 kW (60,000 Btu/hr) where NOx < 25 ppm and CO < 50 ppm (both corrected to 30/0 02). The results will be used as design guideline for using the low emission WSB in a prototype. The stable operation we found for enclosed WSB demonstrates the potential for its use in other combustion applications as well

Scaling the Low Swirl Burner from 15 kW to 600 kW

The lean premixed low swirl burner (LSB) concept has been successful scaled to input powers of up to 600 kW. Using a constant velocity approach, the design of a large capacity LSB (10.16 cm ID) is a linear scaled-up version of a smaller LSB (5.28 cm ID) developed previously for smaller water heaters of up to 18 kW. The operating regimes of the large burner have been investigated and found to be stable over an input power range from 100 to 600 kW. These tests demonstrate the validity of using the constant velocity approach in scaling the LSB. The non-dimensional swirl number for the larger LSB is constant for the input power range we have investigated. However, it is higher than that of the smaller burner. This is attributed to the fact that the swirl rate does not scale with velocity, instead, it scales with the residence time of the swirl air within the burner's exit tube. The NOx, CO and UHC emissions of the large LSB were investigated in a furnace simulator and compared to those of a small LSB operating in a burner evaluation facility. The test matrix was limited to = 0.8 (25% excess air) at various input powers. The results showed that the NOx emissions of both the large and the small LSBs average about 14 ppm (3% O2) over the entire input power range of 15 to 600 kW. Therefore, NOx emissions from the LSB is independent of burner size and combustion chamber geometry. On the other hand, the CO and UHC emission showed a strong dependence on burner chamber coupling. Both sets of data showed that a minimum input power is needed in order to keep CO emission below 25 ppm (corrected to 3% O2) and UHC concentrations at the undetectable level. When operating above the minimum input power, the performance of the LSB is very encouraging. With NOx at 14 ppm, CO at 25 ppm, and UHC at an undetectable level, the LSB should be a prime candidate for use in natural-gas furnaces and boilers

Laboratory Study of a Low NO{sub x} Hot Water Heater with a Weak Swirl Burner

Due to environmental concerns and increasing regulation, manufacturers are searching for methods to reduce combustion-generated emissions from their products. Lean-burning is one recognized method for reducing NO{sub x} emissions from gas appliances. This paper describes the performance of a laboratory, low NO{sub x} hot water heater consisting of the premixed, lean-burning Weak-Swirl Burner (WSB) and a heat exchanger from a commercial 15 kW (50,000 Btu/h) Telstar spa heater. In order to identify an optimum design for a WSB water heater, data was gathered on the overall thermal efficiency and emission levels of NO, CO, and O{sub 2}, while varying the equivalence ratio, water flow rates, and power inputs. Results of our testing show that the WSB/Telstar system achieved thermal efficiencies of 80% while producing ``ultra-low`` (<25 ppM) NO emissions for equivalence ratios below 0.85. Efficiency was essentially independent of equivalence ratio, as well as NO and CO emissions

Development of lean premixed low-swirl burner for low NO{sub x} practical application

Laboratory experiments have been performed to evaluate the performance of a premixed low-swirl burner (LSB) in configurations that simulate commercial heating appliances. Laser diagnostics were used to investigate changes in flame stabilization mechanism, flowfield, and flame stability when the LSB flame was confined within quartz cylinders of various diameters and end constrictions. The LSB adapted well to enclosures without generating flame oscillations and the stabilization mechanism remained unchanged. The feasibility of using the LSB as a low NO{sub x} commercial burner has also been verified in a laboratory test station that simulates the operation of a water heater. It was determined that the LSB can generate NO{sub x} emissions &lt; 10 ppm (at 3% O{sub 2}) without significant effect on the thermal efficiency of the conventional system. The study has demonstrated that the lean premixed LSB has commercial potential for use as a simple economical and versatile burner for many low emission gas appliances

Stability characteristics and emission levels of a laboratory hot water heater utilizing a weak-swirl burner

This paper reports the test results of a collaboration between Lawrence Berkeley National Laboratory and Teledyne Laars to assess the viability of incorporating the Weak-Swirl Burner (WSB) into a 15 kW Telstar spa heater. By stabilizing premixed lean combustion down to equivalence ratios {phi} {approx} 0.6, the WSB greatly reduces NO{sub x} levels by minimizing thermally generated NO{sub x} through the Zeldovich mechanism. The first set of experiments focus on establishing the WSB`s minimum and maximum swirl requirement) for varying {phi}, power levels, burner size, and enclosure. The second set of experiments evaluates the performance of a laboratory water heater where the WSB is incorporated into a Telstar heat exchanger. It was found that the laboratory test station achieves ``low`` and ``ultra-low`` NO{sub x} emissions without compromising the thermal efficiency. The optimum operating condition is for {phi} = 0.8 at 18 kW where NO{sub x} < 25 ppM and CO < 50 ppM. The results will be used as design guideline for using the low emission WSB in a prototype

Development of a vane-swirler for use in a low NO{sub x} weak-swirl burner

This paper describes the continuing development of the weak-swirl burner (WSB) for use in low NO{sub x} applications. Weak-swirl is a unique method for stabilizing lean-burning, premixed combustion as the flame is stabilized by flow divergence, not through recirculation as is commonly seen in nonpremixed industrial burners. Earlier versions of the WSB used a tangential air jet swirler that offers flexibility for determining the range of operation and evaluating the performance of the WSB. Though common in large applications, air swirler may not be amenable to small and medium-size appliances. To reduce manufacturing costs and burner complexity, the authors have developed a fixed vane swirler to replace the air jet swirler in the WSB. This paper describes the operating characteristics and key design parameters of the vane swirler. A new expression for determining swirl number intensity is developed. Testing of a laboratory water heater fitted with a WSB with the new vane-swirler shows 0 < NO < 20 ng/J, 10 < CO < 70 ppm, and thermal efficiencies {approx} 78% over the lean burning range of 0.70 < {phi} < 0.90. The continuous firing rate is robust for a 53 mm vane-swirled WSB, with initial tests ranging from 40,000 to 400,000 Btu/hr. for 0.60 < {phi} < 1.0. Successful development of the new vane swirler demonstrates that the low emission WSB is adaptable to a wide variety of industrial applications