Dispensing nozzle
CJ Ackley | CFD | Project brief

STATUS
Flow study brief; operating range to define. Detailed design and analysis pending.

THE PROBLEM
A viscous liquid is dispensed through a restrictive nozzle. The outlet and mounting envelope cannot change freely, so the internal geometry needs a closer look. This study compares bore size, transition shape, and outlet length.

DESIGN QUESTION
How much pressure can be saved without losing the required delivery rate or increasing retained liquid too far?

SCOPE
- Use a specified Newtonian liquid with known viscosity at a fixed temperature.
- Model steady, slow, rotationally symmetric flow through candidate nozzles.
- Compare required pressure, internal velocity, and retained liquid volume.

CONSTRAINTS
Fluid: Known, essentially constant viscosity
Flow regime: Steady, slow, single-phase flow
Geometry: Axisymmetric bore within a fixed mounting envelope
Acceptance: Required flow within a defined pump-pressure budget

ENGINEERING DECISIONS (PROPOSED)
Pressure drop and retained volume
Compare a pressure-drop versus retained-volume curve for each bore. Keep the fluid properties, outlet condition, and required flow identical across candidates.

ALTERNATIVE
A larger passage reduces resistance, but can retain more liquid and exceed the mounting or cleaning envelope.

TRADEOFF
There may be no single best geometry. Select from candidates that meet the pump budget, then explain the retained-volume and machining compromise.

PROPOSED TOOLS AND METHODS
Axisymmetric CFD, Pipe-flow reference, Parametric geometry

VERIFICATION SCENARIO (NOT YET RUN)
Viscosity rises at the edge of the operating range
Repeat the flow sweep at the upper agreed viscosity and check whether the assumed flow regime and fluid model still apply.

PASS CONDITION
Identify which candidates deliver the required flow within the pressure budget. Reject a comparison if its physical assumptions are no longer appropriate.

EVIDENCE TO RETAIN
A straight-pipe reference calculation, mesh study, mass balance, and pressure/volume comparison using consistent pressure sampling locations.

MEASUREMENT AND LIMITS
State whether the pressure difference uses static or total pressure and which losses the modeled domain includes. Extend the domain if boundaries materially affect the result.

COMPLETION CRITERIA (PLANNED)
- The reference flow solution is reproduced.
- The candidate ranking is stable under mesh refinement and the specified viscosity range.
- The recommendation includes the dimensions and pump conditions it depends on.

VERIFICATION PLAN
Known flow solution
Check the solver against a straight-pipe case with an analytical pressure-drop solution.

Mass balance and mesh
Check inlet/outlet flow balance and refine the mesh around transitions and narrow passages.

Operating range
Repeat the comparison across the required flow range and a realistic viscosity range.

PLANNED DELIVERABLES
- Baseline and candidate nozzle CAD models
- Pressure-versus-flow comparisons and reproducible simulation inputs
- Selected nozzle drawing and a pump-pressure test procedure

SCOPE NOTE
This scope covers internal flow. Droplet formation, shutoff behavior, and physical dispensing accuracy need separate investigation.

NEXT STEP
Specify the liquid, temperature, required flow range, and available pump pressure.
