Case Studies

Liquid Flow Through a Nozzle
Toronto, Ontario

Contributed by: Mohammad P. Fard, Ph.D. Chief Scientist Simulent Inc.

Tecplot is used to visualize liquid flowing through a 32 millimeter bore splash-plate nozzle. Flow simulations help improve nozzle design and predict flow characteristics before actual prototyping. Better nozzle designs improve the efficiency of spraying systems in fuel injectors, burners, printers, sprinklers, vehicles, and many other products.

The Engineer
Dr. Mohammad P. Fard, Ph.D., is chief scientist at Simulent Inc. in Toronto, Ontario. Simulent provides computational fluid dynamics (CFD) software and engineering consulting with a specialization in liquid spray nozzle design and testing.

Simulent develops a core software application for spray nozzle design, as well as several customized, industry-specific modules. Dr. Fard explains, "Tecplot and visualization are key in identifying nozzle design deficiencies. We closely inspect our nozzle results using Tecplot's extensive plotting and animation tools. The images and movies also greatly improve our presentations to customers."

The Animation
The Flash (SWF) animation shows a liquid jet of black liquor running into a splash-plate nozzle used in Kraft recovery boilers. Black liquor is a recycled by-product formed during wood pulping. Kraft recovery boilers burn black liquor for the dual purpose of energy production and the recovery of pulping chemicals. As an alternative to oil and gas, it represents the fifth largest source of energy in the U.S.

The energy and combustion performance of boilers is highly sensitive to the size and distribution of the black liquor spray in the furnace. New designs for splash-plate nozzles can improve the spray quality and lead to enhanced boiler efficiency, reduced sulfur emissions, and increased pulp production.

As seen in the animation, a pipe is attached to a flat surface plate at an angle. As black liquor strikes the plate's face it is turned and flattened into a liquid sheet. The sheet breaks up into ligaments and droplets as it leaves the plate.

Since the black liquor jet impacts the plate at an angle, a portion of it flows in the opposite direction of the spray. For this particular nozzle design, the backward flow is diverted towards the front of the nozzle by splash-plate edges known as side skirts. The diverted backward flow creates two liquid sheets with thick rims at the sides of the nozzle.

Film breakup and spray formation in another splash-plate atomizer design for a Kraft recovery boiler.

The Simulation
Results for this animation were generated with Simulent's Simulent-Spray software. The simulation took approximately two days on a 2.4 GHz, single-processor PC.

Simulent-Spray is a CFD code for simulating free-surface flows. In particular, it models the breakup of liquid jets into sprays by solving the liquid flow Navier-Stokes equations in combination with a volume fraction method which tracks the free surface — the boundary between liquid and air.

As Simulent-Spray runs it generates data files containing fluid information such as velocity, pressure, and volume fraction function for each computational cell. As this occurs a linked Tecplot macro automatically runs Tecplot in Batch mode. Tecplot takes each new file, manipulates the data, then saves the processed data (in this case solid and liquid volume fraction iso-surfaces) in Tecplot binary format.

To make the animation, a Tecplot macro imports each iso-surface data file and exports the next animation frame. This animation was done with Flash (SWF) export options.

Tecplot
Dr. Fard typically uses Tecplot to make plots and animations of 3-D iso-surfaces, slices, velocity vectors, pressure and temperature contours, as well as streamlines of particle movements in a flow.

He believes Tecplot's three greatest strengths are:

1. Animation options and capabilities like shading, lighting, and translucency.
2. Macros that automate all his data visualization processes.
3. Easy data manipulation, especially in Batch mode.

Simulated spray image of a splash-plate atomizer.

Film and spray analysis of simulation results for a typical splash plate nozzle: the distribution of film thickness, film velocity, mean drop size, and spray flow against angle from the splash-plate centerline.

Comparison between simulations and real life photos of impact and dripping of a water drop during its impact on a solid tube. This is a spray cooling application where a hot object is cooled by a spray of drops.

Product Reviews