2002 Progress Report: Flow Control and Design of Environmentally Benign Spray SystemsEPA Grant Number: R829587
Title: Flow Control and Design of Environmentally Benign Spray Systems
Investigators: Plesniak, Michael W. , Frankel, Steven H. , Sojka, Paul E.
Current Investigators: Plesniak, Michael W. , Frankel, Steven H. , Shu, Fangjun , Sojka, Paul E.
Institution: Purdue University
EPA Project Officer: Richards, April
Project Period: January 1, 2002 through December 31, 2004
Project Period Covered by this Report: January 1, 2002 through December 31, 2003
Project Amount: $350,000
RFA: Technology for a Sustainable Environment (2001) RFA Text | Recipients Lists
Research Category: Sustainability , Pollution Prevention/Sustainable Development
The main objective of this research project is to reduce air pollutant emissions by improving droplet transfer efficiency (i.e., reducing overspray and particulate and solvent effluents in spray coating processes).
Considerable progress was made in achieving the technical objectives for both the experimental and computational components of the investigation.
Experimental Program. To provide a physical understanding of flow control on a spray process and to facilitate computational model development and benchmarking of numerical results, a simple canonical model flow was investigated first. Several building blocks that capture many of the relevant physical processes in spray coating have been investigated. First, a large-scale water jet was constructed and probed extensively using flow visualization and Particle Image Velocimetry (PIV) to examine the effects of nozzle geometry on the jet structure and spreading. Solid particles will be introduced into the jet to simulate the action of the smallest spray droplets, which are important to control in order to achieve increases in transfer efficiency. The following specific accomplishments were achieved: (1) literature review of spray transfer efficiency, dynamics of impinging jets, indeterminate origin (IO) nozzle geometry and effects; (2) design and construction of water jet facility; (3) facility benchmarking and performance testing; (4) design and manufacture of various IO nozzle exits; (5) design and installation of impingement target; (6) Laser-Induced Fluorescence (LIF) flow visualization of various configurations, baseline plain nozzle (free jet), impinging jet plain nozzle, IO nozzle free jet (17 configurations) and IO nozzle impinging jet (3 configurations); (7) PIV measurements of velocity field, baseline plain nozzle (free jet), impinging jet plain nozzle, optimum IO nozzle free jet (modified 4-point crown nozzle) and optimum IO nozzle impinging jet; and (8) design of particulate supply and recovery system.
Computational Simulations. In the first year, the commercial computational fluid dynamics code, FLUENT 6.0, was used to study the effect of nozzle geometry on impinging jets with a focus on improving transfer efficiency. The initial modeling approach was based on the Reynolds Averaged Navier-Stokes (RANS) equations to predict the mean flow in conjunction with a number of different turbulence models. Both single-phase and two-phase (particulate) simulations were conducted to examine transfer efficiency issues. Current efforts are focused on the use of the Large Eddy Simulation (LES) technique to better understand nozzle geometry effects on instantaneous flow structure within the jet.
We performed a benchmarking study to assess the accuracy of standard turbulence models provided within FLUENT 6.0 for prediction of single-phase impinging jet flow. The Reynolds stress turbulence model using enhanced wall functions provided the best agreement with the data as compared to other standard two-equation models. The model underpredicted the mean velocity and was not consistent with the data for the Reynold stresses. We also performed three-dimensional RANS calculations for the conventional round nozzle and the four-point crown nozzle studied in the experimental part of this project. Increased entrainment rates were observed with the four-point crown nozzle as compared to the standard round nozzle, and more rapid mixing in the jet near field resulted in lower turbulence levels near the plate. Predictions generally were consistent with the experimental findings for the same. Two-phase flow simulations were conducted using an Eulerian-Lagrangian approach for both the conventional round and four-point crown nozzle. Averaged data for the number of particles hitting the wall were compared for both nozzles to assess transfer efficiency; there was slight improvement in transfer efficiency, but more study is required. Lastly, the initial and boundary conditions of an LES research code were modified for the impinging jet problem and preliminary simulations were run. Results are expected for the next report period.
We will take measurements and complete computations of two phase water-particle jets, and we will perform more LES simulations.