Microcapillary Films Research Articles

The application of plastic microcapillary films for fast transient micro-heat exchange

This paper reports an experimental investigation into the heat transfer response of plastic microcapillary films (MCFs). The first section presents experimental determination of temperature profiles and heat transfer coefficients for an MCF-based micro-heat exchanger. The next section presents two case studies: the first concerns cooling an electrical load, whereas the second examines heat transfer from an exothermic chemical reaction occurring within the MCF. The results demonstrate that heat transfer transients within MCF heat exchange devices are rapid. These systems provide an effective means of either heating or cooling fluids flowing within an MCF, or for removing heat from a hot surface.

The fluid flow and heat transfer performance of thermoplastic microcapillary films

This paper is concerned with the evaluation of microcapillary films (MCFs) for microfluidic applications. MCFs are a novel type of low cost plastic film containing continuous arrays of microcapillaries that are extruded from thermoplastics where the capillaries within these films can be round or elliptical with diameters between 30 and 500 µm. The hydrodynamic response of MCFs has been investigated in a series of experiments where the flow within each capillary was laminar with Reynolds numbers up to a maximum of 1800. Pressure drop measurements were consistent with standard laminar flow predictions. A set of experiments involving single- and two-flow systems were conducted to characterize the heat transfer performance of MCFs and the efficacy of heat transfer was found to rank close to that of metallic microfluidic devices. The experimental heat transfer measurements were compared to finite-element model predictions for the MCF geometry and the modelling results were in good agreement with experiment. The overall results demonstrate the viable performance of MCFs for low cost application to examples such as flow within capillaries where temperature profiling is required along the length of the capillaries.

The melt processing of polymer microcapillary film (MCF)

This paper reports experimental results and initial numerical modelling for a novel extrusion process developed to continuously manufacture thermoplastic microcapillary films (MCFs) that contain embedded hollow capillaries. Using a linear low-density polyethylene (LLDPE), initial polymer melt extrusion experiments were carried out within a slit die with a gas-entrainment assembly that had a single hollow needle. By suitable control of flow and downstream haul-off conditions, a stable regime was found in which hollow microcapillaries were formed within the extrudate. Two multiple injector assemblies were also tested, a prototype 10-injector assembly and a 17-injector assembly. The final external shape of the film produced from these injectors, together with the dimensions and sections of the internal capillaries was shown to depend on the injector geometry, the melt drawing length, and the draw ratio. Draw resonance was noted for high draw ratios where the melt drawing length was greater than two-third the width of the die exit. Both simple and more advanced numerical modelling using POLYFLOW ® provides insight into the factors controlling the stable production of the microcapillary film.