Original article Analysis of the Effects of Joule Heating and Viscous Dissipation on Combined Pressure-Driven and Electrokinetic Flows in a Two-Parallel Plate Channel with Unequal Constant Temperatures Harshad Sanjay Gaikwad 1 , Pranab Kumar Mondal 1 , Dipankar Narayan Basu 1 , Nares Chimres 2 and Somchai Wongwises 2 Abstract In this article, we perform an entropy generation analysis for the micro channel heat sink applications where the flow of fluid is actuated by combined influences of applied pressure gradient and electric field under electrical double layer phenomenon. The upper and lower walls of the channels are kept at different constant temperatures. The temperature- dependent viscosity of the fluid is considered and hence the momentum equation and energy equations are coupled in this study. Also, a hydrodynamic slip condition is employed on the viscous dissipation. For complete analysis of the entropy generation, we use a perturbation approach with lubrication approximation. In this study, we discuss the results depicting variations in the velocity and temperature distributions and their effect on local entropy generation rate and Bejan number in the system. It can be summarized from this analysis that the enhanced velocity gradients in the flow field due to combined effect of temperature-dependent viscosity and Joule heating and viscous dissipative effects, leads to an enhancement in the local entropy generation rate in the system. Keywords Entropy generation, microchannel heat sinks, Joule heating, lubrication approximation, electroosmotic flow, viscous dissipation Date received: 8 September 2017; accepted: 30 September 2018 Introduction A high surface-to-volume ratio in microfluidic chan- nels leads to a better heat transfer characteristics. Owing to this advantageous feature, the microchan- nels are widely used in different applications namely, thermal management systems like microchannel heat sinks (MCHS) in electronic devices, microelec- tromechanical systems (MEMS), and micro heat exchangers. 1 Recently, in such applications, the incorporation of electrokinetics have caught much attention of several researchers. 2,3 In electrokinetics, the applied electric field under the influence of elec- trical double layers (EDLs) at the walls generates a convection current and conduction current in the channel of which, the convection current leads to an electroosmotic flow while the conduction current leads to a volumetric Joule heating effect. Such Joule heating effect alters the temperature distribution of the flow field and hence the physical properties of the fluid such as dynamic viscosity. 4,5 Accounting such phenomenon, several studies have been carried out following numerical simulations and analytical models, to understand the relation between simultan- eous increment in the Joule heating and fluid velocity in the channel for electroosmotic flows (EOFs). 5–11 In aforementioned applications, there could be a situation where microchannels are required to sustain Proc IMechE Part E: J Process Mechanical Engineering 0(0) 1–9 ! IMechE 2018 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/0954408918809612 journals.sagepub.com/home/pie 1 Department of Mechanical Engineering, Indian Institute of Technology Guwahati, Guwahati, India 2 Fluid Mechanics, Thermal Engineering and Multiphase Flow Research Lab (FUTURE), Department of Mechanical Engineering, Faculty of Engineering, King Mongkut’s University of Technology Thonburi, Bangmod, Bangkok, Thailand Corresponding author: Pranab Kumar Mondal, Department of Mechanical Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, India. Email: mail2pranab@gmail.com