HIGH EFFICIENCY ENERGY CONVERSION FROM LIQUID JET FLOW Yanbo Xie, Lennart de Vreede, Trieu Nguyen, Hans L. de Boer, Ad Sprenkels, Albert van den Berg, Jan C.T. Eijkel BIOS lab on chip group, MESA+ Institution of Nanotechnology, University of Twente ABSTRACT We investigate the performance of a microfluidic energy conversion system using jetting flow. Preliminary results indicate that a voltage can be generated of several kilo-Volts and energy efficiencies can reach 15%. Such values are by far the highest obtained for electrokinetic conversion systems and open new perspectives for energy conversion. KEYWORDS liquid jet, energy conversion; streaming potential. INTRODUCTION The energy crisis is one of the most pressing topics due to the rapid increase of electrical power consumption and projected decreasing availability of traditional sources of energy such as fossil and fuels. Novel sources of electrical energy, such as fuel cells and solar cells are therefore developed to replace the traditional sources of energy. Such new energy sources should preferably cause less harm to our environment than traditional ones, for example by not producing carbon dioxide or toxic chemicals. A relative little know method of energy conversion is electrokinetic conversion of fluidic mechanical energy to electrical energy.[1] Electrokinetic energy conversion relies on the transport of the layer with net charges that is present close to most solid/liquid interfaces. When this charged layer is transported in a channel, an ionic current is generated (streaming current) as well as a potential difference between the channel ends (streaming potential).[2] In the past ten years, many investigators have tried to enhance electrokinetic energy conversion efficiency using micro- or nanochannels. The highest experimental efficiencies reached were about 5%[3-5] when nanopores were used in which double layers of opposing walls partially overlapped. Theoretical predictions using numerous assumptions predicted maximal efficiencies in such systems of 40%. [6] Recently, Duffin and Saykally reported on the use of a microjet for energy conversion. [7] Under high pressure water was forced through a membrane orifice, forming a jet which broke up into droplets. The droplets were charged due to the electrokinetic phenomenon described above, and the charged droplets were collected by a downstream electrode. These authors found an energy conversion efficiency of around 10% in this two phase system. In their analysis, Duffin and Saykally attribute the enhancement of efficiency in their two-phase system with respect to the values in traditional single phase systems to the occurrence of low resistance fluidic entrance flow in the pore due to its short length and high pressure applied, as well as to electrical isolation offered by the air which prevented back flow of current. In this paper, we however show that the energy conversion mechanism of this jetting flow is radically different from the traditional electrokinetic energy conversion mechanism. We show it relies on a direct conversion of the kinetic droplet energy conversion potential energy. This knowledge of the conversion mechanism allowed us to minimize the loss factors and obtain a conversion efficiency of 15%. Setup Figure 1: A liquid jet produced by pressure applied across a Si 3 N 4 membrane pore breaks into (charged) droplets which are collected in a stainless steel bowl. Streaming current I 1 flows through the pore and current I 2 flows through 16th International Conference on Miniaturized Systems for Chemistry and Life Sciences October 28 - November 1, 2012, Okinawa, Japan 978-0-9798064-5-2/μTAS 2012/$20©12CBMS-0001 198