Atomization Process of Viscous Fluid in Three-Channel Air-Jet Nozzle

Literature Overview

This paper, published in Chemical Engineering (2005, Vol. 33, No. 5, pp. 26-29), investigates the atomization process of viscous fluids in a three-channel air-jet nozzle. The research team from East China University of Science and Technology combined experimental testing with numerical simulation to examine the influence of fluid viscosity, liquid flow rate, and gas flow distribution on atomization performance. The work is supported by the National Basic Research Program of China (Grant No. 2004CB217703) and the 863 Program (Grant No. 2003AA521021).

Core Technical Findings

The study establishes quantitative relationships between operating parameters and atomization droplet size:

The non-monotonic behavior of the gas flow ratio is particularly significant. As the ratio α increases from zero, the Sauter Mean Diameter (SMD) first increases, reaches a maximum at α ≈ 0.22, and then decreases. This indicates an optimal gas distribution configuration for achieving the finest atomization.

Technical Interpretation for Fitting Engineers

While this paper focuses on nozzle design rather than pipe fittings per se, the three-channel nozzle geometry is fundamentally a specialized tee-like configuration where fluid streams converge and interact. The principles governing flow interaction at junctions in this nozzle directly relate to tee fitting design:

• The three-channel geometry creates controlled flow impingement patterns, analogous to the branch-main interaction in a tee
• The optimal gas distribution ratio (α ≈ 0.22) represents a balance between competing flow regimes, similar to the convergence/divergence balance identified in tee erosion studies
• The viscous fluid behavior at the junction demonstrates how fluid properties interact with geometric features to determine performance

Process and Standards Analysis

From a manufacturing perspective, the three-channel nozzle requires precise geometric control:

1. Channel dimensional accuracy: The gas flow ratio is sensitive to channel cross-sectional area. Manufacturing tolerances on channel diameters must be tight enough to ensure the designed α ratio is achieved.
2. Surface finish: For viscous fluid applications, the internal surface roughness of the liquid channel directly affects flow rate and, consequently, atomization performance. Ra values below 0.4 μm are typically required for consistent performance.
3. Welding considerations: For nozzles fabricated by welding multiple channels together, the internal weld geometry must be carefully controlled. Any weld reinforcement or undercut creates flow disturbance that can alter the atomization characteristics.
4. Material compatibility: Viscous fluids in atomization applications may be chemically aggressive. Material selection must consider both mechanical requirements and chemical compatibility, potentially requiring stainless steel (316L, 904L) or specialty alloys.

Integration with Engineering Practice

In spray drying, combustion, and coating applications, nozzle performance directly determines product quality. The findings of this study provide design guidelines for nozzle manufacturers:

• Viscosity has a relatively weak influence on SMD (0.088 exponent), meaning that moderate viscosity changes do not dramatically affect atomization. This is favorable for process robustness.
• Liquid flow rate has a stronger influence (0.37 exponent), meaning that flow rate control is more critical than viscosity control for maintaining consistent droplet size.
• The optimal gas ratio of 0.22 provides a clear design target, but process engineers must recognize that deviations from this optimum in either direction degrade performance.

For quality control, the SMD measurement should be incorporated into nozzle acceptance testing. The quantitative relationships established in this study enable the development of acceptance criteria based on measured SMD values under standardized test conditions.

Key Questions and Reflections

Several aspects merit further consideration:

• The study examines steady-state conditions, but practical atomization processes often involve transient start-up and shutdown phases. How do these transients affect droplet size distribution?
• The relationship between nozzle geometry and atomization performance suggests that similar principles may apply to tee fittings used in spray applications within piping systems.
• The weak viscosity dependence (0.088 exponent) implies that the nozzle design is relatively robust to viscosity variations, which is advantageous for processing fluids with variable compositions.

The connection to fitting design is that any tee or junction used to deliver atomization fluid must maintain the precise flow characteristics assumed in the nozzle design. Flow rate fluctuations, pressure drops, or flow instabilities introduced by upstream fittings can compromise atomization performance.

Study Insights and Implications

This research demonstrates that precise geometric and flow control at multi-channel junctions enables optimization of fluid atomization performance. The quantitative power-law relationships between operating parameters and SMD provide a rational basis for nozzle design and process control. For engineers working with spray systems integrated into piping networks, the study reinforces the importance of maintaining precise flow conditions from the source to the nozzle outlet. The finding that gas flow distribution has a non-monotonic effect on performance underscores the need for careful design optimization rather than simple parameter maximization. This work exemplifies the principle that junction geometry—whether in a nozzle or a pipe fitting—fundamentally determines flow behavior and system performance.