Proceedings of the 1st European Conference on Microfluidics - Microfluidics 2008 - Bologna, December 10-12, 2008 μFLU08-111 HEAT TRANSFER BETWEEN WALLS AND FLUIDS: MD SIMULATIONS WITH VIBRATING WALLS Pieter van den Akker 1 Eindhoven University of Technology, Department of Mechanical Engineering PO Box 513, 5600 MB Eindhoven E.A.T.v.d.Akker@TUE.nl A.J.H. Frijns, A.A. van Steenhoven Eindhoven University of Technology, Department of Mechanical Engineering PO Box 513, 5600 MB Eindhoven P.A.J. Hilbers Eindhoven University of Technology, Department of Biomedical Engineering PO Box 513, 5600 MB Eindhoven KEY WORDS Micro channel, evaporation, thermal boundary condition ABSTRACT In Molecular Dynamics simulations of micro channels, a lot of computation time is used to simulate the channel walls when the wall molecules are explicitly simulated. To save computation time, implicit boundary conditions such as the Maxwell conditions can be used. With these boundary conditions, heat transfer is still a problem. In this work, we derive a new boundary condition, based on a vibrating potential wall. The heat transfer properties of the new boundary condition are shown to be comparable to the explicit wall. The computation time needed for the implicit boundary condition is very small compared to the explicit simulation. 1. INTRODUCTION Last decades computer chips have become more powerful and smaller in size at the same time [1]. As a direct consequence of this technological improvement, the heat per area produced by a computer chip has increased, and is expected to increase further [2]. The conventional way to remove this heat is by air cooling, but the limits of air cooling are being reached. Micro channel cooling is a promising way to solve the cooling problem for computer chips. In micro channel cooling, a fluid is flowing through a micro channel in close contact with the computer chip. Due to the large area to volume ratio of the micro channel, the heat removal is larger than by conventional air cooling. Heat transfer by forced convection for gases is in the range 25 − 250 kW/m 2 [3], whereas experimental micro channels with water have shown a heat flux of 500 kW/m 2 [4]. The heat removal is optimal when evaporation takes place in the micro channel [5]. To optimize micro channel configurations, the heat and flow problems in the micro channel need to be understood, including the heat transfer between the channel wall and the fluid. Because the heat removal by evaporation is large, evaporation should be included in the model. 1 Corresponding author 1 c  SHF 2008