Experimental Apparatus for the Study of micro Heat Exchangers with Inlet Temperatures between -200 and 200 °C and Elevated Pressures

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.The current paper presents a test bench for micro-fabricated Recuperative Counter Flow Heat Exchanger (RCFHE). The bench is suitable for up to 200 K difference between inlets temperatures and operating pressures up to 32 MPa. The experimental setup allows controlling the physical state of the gas (i.e. temperature, pressure and flow rate) at the RCFHE inlets. The bench has 5 controlled parameters and 5 more that are monitored and enables studying each of the hot and cold channels separately. We demonstrate a steady supply of liquid nitrogen into the device for 10 minutes without thermal insulation of the specimen. Another run is a steady state experiment with a temperature difference of about 20-30 K between inlets. These show that the apparatus is capable of characterizing heat exchangers and serve as preliminary results

Microvalve-Based Tunability of Electrically Driven Ion Transport Through a Microfluidic System with Ion-Exchange Membrane

Microfluidic channels with embedded ion permselective medium under the application of electric current are commonly used for electrokinetic processes as on-chip ion concentration polarization (ICP) and bioparticle preconcentration to enhance biosensing. Herein, we demonstrate the ability to dynamically control the electrically driven ion transport by integrating individually addressable microvalves. The microvalves are located along a main microchannel that is uniformly coated with a thin layer of an ion-exchange membrane (IEM). The interplay of ionic transport between the solution within the microchannel and the thin IEM, under an applied electric current, can be locally tuned by the deformation of the microvalve. This tunability provides a robust and simple means of implementing new functionalities into lab-on-a-chip devices, e.g., dynamic control over multiple ICP layers and their associated preconcentrated molecule plugs, multiplex sensing, suppression of biofouling as well as plug dispersion, while maintaining the well-known application of microvalves as steric filtration