Multiple Jet System Research Articles

Experimental study on solid circulation in a multiple jet fluidized bed

AbstractParticle image velocimetry was used to investigate the evolution of multiple inlet gas jets located at the distributor base of a two‐dimensional fluidized bed setup. Results were used to estimate the solid circulation rate of the fluidized bed as well as particle‐entrainment into the individual jets. The effects of fluidization velocity, orifice diameter, orifice pitch, particle diameter, and particle density were studied. It was determined from this study that the solid circulation rate linearly increased with an increase in the fluidization velocity until the multiple jet system transitioned from isolated to an interacting system. In the interacting system of jets, the solid circulation increased with fluidization velocity but at a much lower rate. For multiple jet systems, this phenomenon may indicate the presence of an optimum operating condition with high circulation rate and low air input in the bed. © 2011 American Institute of Chemical Engineers AIChE J, 58: 3003–3015, 2012

Convective Heat Transfer in Impinging- Gas- Jet Arrangements

The paper deals with heat transfer by convection between impinging gas jets and solid surfaces. It considers both single and multiple jet systems. It emphasizes the flow and geometrical parameters as well as the environment conditions at which the jet emerges. In particular, it points out the effect of the jet tilting, thermal entrainment and jet confinement. ASN and ARN schemes are illustrated through industrial and aeronautical applications. Design correlations are proposed. Experimental data obtained from infrared thermography are compared to CFD simulations.

Full-Field Flow Measurements and Heat Transfer of a Compact Jet Impingement Array With Local Extraction of Spent Fluid

Jet impingement cooling is widely used due to the very high heat transfer coefficients that are attainable. Both single and multiple jet systems can be used, however, multiple jet systems offer higher and more uniform heat transfer. A staggered array of 8.46 mm diameter impingement jets with jet-to-jet spacing of 2.34 D was examined where the spent fluid is extracted through one of six 7.36 mm diameter extraction holes regularly located around each jet. The array had an extraction area ratio (Ae/Ajet) of 2.23 locally and was tested with a jet-to-target spacing (H/D) of 1.18 jet diameters. Magnetic resonance velocimetry was used to both quantify and visualize the three dimensional flow field inside the cooling cavity at jet Reynolds numbers of 2600 and 5300. The spatially averaged velocity measurements showed a smooth transition is possible from the impingement jet to the extraction hole without the presence of large vortical structures. Mean Nusselt number measurements were made over a jet Reynolds number range of 2000–10,000. Nusselt numbers near 75 were measured at the highest Reynolds number with an estimated uncertainty of 7%. Large mass flow rate per unit heat transfer area ratios were required because of the small jet-to-jet spacing.

Operational characteristics of a parallel jet MILD combustion burner system

This study describes the performance and stability characteristics of a parallel jet MILD (Moderate or Intense Low-oxygen Dilution) combustion burner system in a laboratory-scale furnace, in which the reactants and exhaust ports are all mounted on the same wall. Thermal field measurements are presented for cases with and without combustion air preheat, in addition to global temperature and emission measurements for a range of equivalence ratio, heat extraction, air preheat and fuel dilution levels. The present furnace/burner configuration proved to operate without the need for external air preheating, and achieved a high degree of temperature uniformity. Based on an analysis of the temperature distribution and emissions, PSR model predictions, and equilibrium calculations, the CO formation was found to be related to the mixing patterns and furnace temperature rather than reaction quenching by the heat exchanger. The critical equivalence ratio, or excess air level, which maintains low CO emissions is reported for different heat exchanger positions, and an optimum operating condition is identified. Results of CO and NO x emissions, together with visual observations and a simplified two-dimensional analysis of the furnace aerodynamics, demonstrate that fuel jet momentum controls the stability of this multiple jet system. A stability diagram showing the threshold for stable operation is reported, which is not explained by previous stability criteria.

Confined multiple impinging slot jets without crossflow effects

Transport data for single impinging jets are frequently used in the design of equipment that involves multiple impinging jets. Geometric and flow conditions at which jets in a multiple impinging jet system no longer behave as independent single jets are not known. In the present study criteria are developed to make this distinction by comparing turbulence, mean flow, and heat transfer characteristics of a jet in an array of confined impinging slot jets with those of a single jet. Flow analysis showed that a flow cell, defined as volume contained by the impingement and confinement surfaces and the centerlines of adjacent inlet and exhaust ports, is characterized effectively with a single nondimensional ratio S/ H, the ratio of the lateral and axial length of flow cell. The second nondimensional ratio necessary for complete geometric similarity of flow cells affects the pressure profiles to some extent only in the wall jet region. The critical S/ H ratio where jet-to-jet interactions become important is somewhere between 1–0.75. Heat transfer analysis showed that for flow cell ratio S/ H > 1.5 a multiple jet system is effectively an assembly of single jets. For S/ H < 1.5 interaction between adjacent jets increases heat transfer under the exhaust ports. For S/ H < 0.7 this interaction causes a depression of stagnation heat transfer.

Investigations of Heat-Transfer Coefficients for Air Flow Through Round Jets Impinging Normal to a Heat-Transfer Surface

In this paper, empirical equations of local as well as average heat-transfer coefficients of single jet system were derived. Two aspects of multiple jet systems have been studied. One concerns mainly the uniform distribution of heat-transfer coefficients and economy of power consumption. The other concerns the high magnitude of heat-transfer coefficients and the interference among jets. The experiments were conducted at Reynolds number from 103 to 104 and hole size from 1/8 to 1/4 in. diameter. An attempt was made to correlate empirical data to render practical application possible.