Heat Transfer Enhancement By Elastic Turbulence in a Micro Curvilinear Channel

Abstract

With the increasing level of microelectronic techniques, such as MEMS, the effective heat transfer become crucial to their performance. Genernally, the flow in microscale behaves laminar because of the extremely low Reynolds number (Re), which results in very low heat transfer effeciceny. So far, an increasingly efforts have been paid to develop techiniques to improve the heat transfer therein. As is well known in the conventional scale, flow instabilities and turbulence could significantly promote the mixing and heat transfer. Therefore, a great deal of efforts have been paid to to perturb the low Reynolds number flows in order to increase the contact interfaces between fluids with different temperature in microchannel. For example, some efforts are paid to design and utilize specially designed microchannel to excite the unstable flow motion. Another alternative way is to adopt different kinds of working fluid such as nano-fluid, non-Newtonian fluid and so forth. The viscoelastic fluid, a kind of Non-Newtonian fluid, shows nontrivial flow phenomena such as die swell effect (Barus effect), rod climbing effect (Weissenberg effect), Kaye effect, tubeless siphon effect, etc. Moreover, it has been proven that purely elastic flow instabilities or elastic turbulence is possible to be induced under inertialess or creeping flow conditions. This provides another efficient way to realize heat transfer enhancement, which is also the focus of present paper. In this paper, we carried out experimental and numerical investigations on the heat transfer characteristics of viscoelastic fluid and Newtonian fluid in three dimensional (3D) curvilinear microchannel. For the experiments, microelectronics manufacturing technology was taken to fabricate microchips. Platinum films were embedded in a Polydimethyl-siloxane (PDMS) microchannel in order to measure micro heater and channel wall temperature. The polymer solutions (PAAM) were the chosen viscoelastic fluid and sucrose solutions (Newtonian fluid) were used for comparison. For the numerical simulation, the log-conformation algorithm were implemented into the open source software OpenFOAM in order to simulate the viscoelastic flow at high Weissenberg number. Before simulating the viscoelastic fluid flow passing through the target channel, the numerical solver was firstly validated by two benchmark problems i.e., flow around a cylinder and passing a cross-slot by comparing the obtained dimensionless drag coefficient and flow patterns with those in the existing literatures. Combing the experimental and numerical results, the present identified the heat transfer enhancement by the occurrence of elastic instability and turbulence in a curved microchannel.