This paper reports on an exemplary study of the performance of commercial computational fluid dynamic (CFD) software programs when applied as engineering tool for microfluidic applications. Four commercial finite volume codes (CFD-ACE+, CFX, Flow-3D and Fluent) have been evaluated by performing CFD-simulations of typical microfluidic engineering problems being relevant for a large variety of lab-on-a-chip (LOAC) applications. Following problems are considered as examples: multi lamination by a split and recombine mixer, flow patterning on a rotating platform (sometimes termed “lab-on-a-disk”), bubble dynamics in micro channels and the so called TopSpot® droplet generator for micro array printing. Hereby mainly the capability of the software programs to deal with free surface flows including surface tension and flow patterning of two fluids has been studied. In all investigated programs the free surfaces are treated by the volume-of-fluid (VOF) method and flow patterning is visualised with a scalar marker method. The study assesses the simulation results obtained by the different programs for the mentioned application cases in terms of consistency of results, computational speed and comparison with experimental data if available.

This paper reports on a novel 1/3 and 1-in thermal bubble jet printhead with integrated nozzle plate. The printheads are made by a combination of a standard printhead substrate with a new three-dimensional (3-D) structured polyimide nozzle plate avoiding a three-layer assembly known from other commercial printheads. The 50-mum- (respectively, 75-mum)-thick nozzle plate contains the fluidic channels and 208 (respectively, 312) nozzles with minimum lateral dimensions of 10 mum. The misalignment of the two laser structured layers has proved to be less than 1 mum. The nozzle plate is assembled with the substrate using a 3-mum-high adhesive layer with an alignment accuracy of 5 mum. The integrated nozzle plate leads to a better control of the printhead geometry and saves one processing step in production. A 1/3-in as well as a 1-in design were studied because it was not sure if the 1-in design survives the fabrication of the silicon substrate. The powder blasting of the ink feeding slot was considered as critical process step. To predict the effect of misalignments or variations in the adhesive layer during the assembling process on the characteristic inkjet parameters-like droplet volume, droplet velocity, droplet quality, or print frequency-computational fluid dynamic (CFD) simulations have been performed. For these purposes, a fully three-dimensional model was set up using the volume of fluid method. The presented CFD model in combination with the applied pressure boundary condition substituting the behavior of the exploding vapor bubble provides a valuable possibility to simulate media variations, actuation variations, as well as 3-D related geometrical variations. The differences in ejected droplet volume and droplet velocity between simulation and experiment are below 5%. Conclusively, the innovations presented in this paper are as follows. The presented printhead layout designed by Olivetti I-Jet provides an improved print frequency compared to commercially available printhead designs. The 1-in integrated nozzle plate and the required innovative fabrication technology offers a tripling of the printing speed compared to a conventional 1/3-in design only by means of an increased printing area. The new fabrication and packaging approach offers the reduction of processing and assembling steps leading to a better control of the printhead geometry. The CFD simulations provide a three-dimensional approach to estimate the influences of manufacturing and adjustment tolerances