Study of a micro-structured PHE for the thermal management of a fuel cell

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.In the constantly growing market of fuel cells, the heat management of the system is a crucial area of research, since it affects the efficiency, operability and lifetime of the fuel cell. The CFD simulations performed for a plate heat exchanger (PHE) with flat plates clearly demonstrate temperature non-uniformity across the membrane of the unit cell. The CFD code was successfully validated with experimental data acquired from a setup that reproduces the geometry and simulates the thermal behaviour of a typical unit PEMFC. Additionally, the performance of a novel PHE, with micro-structured corrugations on its plates, was studied with the previously validated CFD code. The results clearly show that the proposed plate modifications can increase temperature uniformity across the membrane more than 20% compared to that of the flat plate

Investigation of liquid phase characteristics in an inclined open microchannel

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.An important variable in the designing of gas-liquid reactors is the interfacial area available for the conduction of the two phases. Falling film microreactors (FFMR) are devices which can offer extended specific surfaces (up to 20,000m2/m3) and for this reason they are used in many multiphase processes. The aim of this work is to assess the effect of the microchannel width as well as the flow rate and the physical properties of the liquid phase on the geometrical characteristics (i.e. thickness and surface shape) of the liquid film, which were measured using Micro Particle Image Velocimetry (μ-PIV). The experiments were conducted in single microchannels with widths of 1200, 600 and 300μm and for Reynolds numbers between 0.9 and 39.7, while water and aqueous solutions of glycerol and butanol were used as working fluids. It was also verified that a common expression for predicting film thickness in macroscale is not applicable in microscale

Co-current horizontal flow of a Newtonian and a non-Newtonian fluid in a microchannel

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.In this work, the flow of two immiscible liquids in a glass microchannel, I.D.= 580μm, was exper-imentally investigated. Various aqueous glycerol solutions containing xanthan gum were the non-Newtonian fluids, while kerosene was the Newtonian one. The flow rate of the non-Newtonian fluids varied from 50 to 200μL/min, while the kerosene flow rate was kept constant. The two fluids were put in contact at a T-junction. Visual observations were made using a high speed CCD camera and data were collected by processing the corresponding video images. The flow pattern was slug flow irrespective of the fluid that initially filled the microchannel. The experimental results revealed that the length of the kerosene slugs decreases by increasing either the aqueous phase flow rate or its viscosity. Furthermore the non-Newtonian fluid results in smaller and more frequent slugs than the corresponding Newtonian one. Thus by rendering a fluid non-Newtonian the interfacial area increases and consequently the mass transport performance is enhanced. This observation is expected to aid to the optimal design of two-phase microreactors. More work is certainly needed to investigate the effect of all the design parameters on the characteristics of this kind of flow in microchannels

Prediction of the characteristics of the liquid film in open inclined micro-channels

Falling Film Microreactor (FFMR) is one of the most important microfluidic devices for gas-liquid applications. In these devices extended specific surfaces (up to 20,000m2/m3) can be obtained while the liquid film remains stable over a wide range of gas and liquid flow rates. In an effort to propose new design correlations for these devices, in a previous work we proposed correlations for the prediction of the gas-liquid interface and the thickness of the liquid film. In this study we aim to investigate the validity of these correlations when different channel materials are used, namely brass and silicon. Velocity profiles have been also obtained by a μ-PIV system, while the thickness of the liquid film and the shape of the interface were also determined using the μ-PIV system. It was proved that the shape of the interface can be predicted with reasonable accuracy by the previously proposed correlations. Also the film thickness can be predicted with acceptable accuracy provided that some of the constants are modified according to the material of the test section

Prediction of the liquid film characteristics in open inclined microchannels

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.Falling Film Microreactor (FFMR) is one of the most important microfluidic devices for gasliquid applications. In these devices extended specific surfaces (up to 20,000m2/m3) can be obtained while the liquid film remains stable over a wide range of gas and liquid flow rates. In an effort to propose new design correlations for these devices, in a previous work we proposed correlations for the prediction of the gasliquid interface and the thickness of the liquid film. In this study we aim to investigate the validity of these correlations when different channel materials are used, namely brass and silicon. Velocity profiles have been also obtained by a μ-PIV system, while the thickness of the liquid film and the shape of the interface were also determined using the μ-PIV system. It was proved that the shape of the interface can be predicted with reasonable accuracy by the previously proposed correlations. Also the film thickness can be predicted with acceptable accuracy provided that some of the constants are modified according to the material of the test section